OT a sign of the times

[Baron]

default Inscribed thus:

On Wed, 01 Dec 2010 17:39:28 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

On Wed, 01 Dec 2010 16:12:40 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

Here's one for an RF guru though: I made this reflector out of a
wood
frame and "hardware cloth" (1/2" mesh). Doesn't work at all
well. Whilst experimenting I tried an unused BBQ grill as a
reflector - worked pretty well as long as the wires were aligned
with the bow ties (same plane, parallel wires with ~10" between
them - grounded is better than floating).

Grounded or not shouldn't make too much difference. Are you feeding
with co-ax and a balun ?

I'm not sure as to what hardware cloth is, but you can run into
strange behavior if the distance between two conductors in the
reflector is a half or quarter wave length apart at the operating
frequency. Ideally the conductors in the reflector should be 1/10th
or less, of a wave length apart. The closer to approximating a solid
sheet the better.

I'll drag it out and try again with a much closer spacing.

Hardware cloth is just wires in a cross pattern forming 1/2"
squares, that is hot dipped in zinc to rustproof and bond them.

Ahh ! "Chicken Mesh" Comes in 25ft rolls 3ft wide. Thanks.

I got the reflector I made out of the shed. I was mistaken it is 1/4"
(fine) mesh.

Same game, it doesn't work. At ~18+" it has little effect then it
steadily attenuates the signal as it gets closer to the dipoles.

That could just be the matching that is deteriorating as you get close
to the dipole.

I tried rotating it 180 degrees putting the reflector on the other
side and that is even worse.

The rotational angle of the mesh should have little effect. It seems
that your saying that the mesh size has a fairly large effect on signal
strength.

I looked at some ads for that type antenna and they also seem to use
horizontal parallel reflector wires not a cross hatch. If they have
vertical wires on the reflector it is in the center and edges only -
more for structural strength.

You could try a sheet of aluminum cooking foil. That would certainly
behave as a reflector.

Seems to me a "reflector" is intended to reflect so wouldn't you want
to observe some multiple of 1/4 wave? Ideally shouldn't the reflected
signal get back to the dipoles in phase with the primary wave?

Yes it should, but thats a function of distance behind the dipole. So
the reflection should be in phase with the signal on the dipole. Hence
the reflector being placed a 1/4 wave behind the dipole. The distance
also affects the feed point impedance. So there is a trade off between
matching, gain and directivity.

--
Best Regards:
Baron.

 

On Wed, 01 Dec 2010 23:10:16 +0000, Baron
<baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

On Wed, 01 Dec 2010 17:39:28 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

On Wed, 01 Dec 2010 16:12:40 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

Here's one for an RF guru though: I made this reflector out of a
wood
frame and "hardware cloth" (1/2" mesh). Doesn't work at all
well. Whilst experimenting I tried an unused BBQ grill as a
reflector - worked pretty well as long as the wires were aligned
with the bow ties (same plane, parallel wires with ~10" between
them - grounded is better than floating).

Grounded or not shouldn't make too much difference. Are you feeding
with co-ax and a balun ?

yes 75 ohm coax to 300 ohm balun

I'm not sure as to what hardware cloth is, but you can run into
strange behavior if the distance between two conductors in the
reflector is a half or quarter wave length apart at the operating
frequency. Ideally the conductors in the reflector should be 1/10th
or less, of a wave length apart. The closer to approximating a solid
sheet the better.

I'll drag it out and try again with a much closer spacing.

Hardware cloth is just wires in a cross pattern forming 1/2"
squares, that is hot dipped in zinc to rustproof and bond them.

Ahh ! "Chicken Mesh" Comes in 25ft rolls 3ft wide. Thanks.

I got the reflector I made out of the shed. I was mistaken it is 1/4"
(fine) mesh.

Same game, it doesn't work. At ~18+" it has little effect then it
steadily attenuates the signal as it gets closer to the dipoles.

That could just be the matching that is deteriorating as you get close
to the dipole.

I tried rotating it 180 degrees putting the reflector on the other
side and that is even worse.

The rotational angle of the mesh should have little effect. It seems
that your saying that the mesh size has a fairly large effect on signal
strength.

I wouldn't say mesh size - the best signal is with no mesh but

horizontal parallel wires support on the outside edges with vertical
wires is OK and a vertical wire in the center is OK too - but no mesh,
no solid reflector works.

I looked at some ads for that type antenna and they also seem to use
horizontal parallel reflector wires not a cross hatch. If they have
vertical wires on the reflector it is in the center and edges only -
more for structural strength.

You could try a sheet of aluminum cooking foil. That would certainly
behave as a reflector.

I have a large sheet size aluminum baking pan. It doesn't improve the
signal but attenuates the signal

Seems to me a "reflector" is intended to reflect so wouldn't you want
to observe some multiple of 1/4 wave? Ideally shouldn't the reflected
signal get back to the dipoles in phase with the primary wave?

Yes it should, but thats a function of distance behind the dipole. So
the reflection should be in phase with the signal on the dipole. Hence
the reflector being placed a 1/4 wave behind the dipole. The distance
also affects the feed point impedance. So there is a trade off between
matching, gain and directivity.

Well I've tried the solid pan at all distances . It is considerably
larger than the dipoles and it has to be further away for any signal
to get through but is not augmenting the signal strength at any
distance.

I'm coming to the conclusion that this reflector is not a reflector at
all but a director like a yagi antenna. This is also borne up by my
geographical understanding - on the driven element side there should
be an ocean out there somewhere not a TV station. I'm ~6 miles from
the ocean and from looking at a map with my street orientation and
house and antenna with respect to the street... Unless there's some
large object out there like a water tower that is reflecting a signal
from the wrong direction. There is a light tower ~30 miles offshore
in the general direction, large aluminum square on stilts 50 from the
surface.

 

On Wed, 01 Dec 2010 13:10:02 -0800, Rich Grise
<richg@example.net.invalid> wrote:

Tom Biasi wrote:
"Rich Grise" wrote in message
stratus46@yahoo.com wrote:
On Nov 30, 5:41 pm, Tim Wescott <t...@seemywebsite.com> wrote:
On 11/30/2010 01:53 PM, default wrote:

I was futzing around building a uhf bowtie antenna and needed some
fender washers. The hardware store is 6 miles away in a truck that
gets 12 mpg when cold. Figure the 8 washers for ~3 cents each and 45
minutes wasted, and I'm about ready to drop the project .

An Edison moment... pick up the metal punch, fish 8 cents out of my
pocket and instant fender washers! Cost 8 cents versus~$4, and only
took about two minutes.

I needed a larger one when repairing my truck today - a nickel and
electric drill...

But the ones you get from the store are made with steel, not zinc.

I suspect he's trying to hold pieces of coat hanger wire so zinc vs
steel won't be an issue. It may be better as pennies don't rust - or
do they?

Maybe one from 1943. ;-)

I have several 1943 U.S. one cent pieces and they are made of copper.
Someone told me that was unusual, are they worthless?
They are so few and so valuable that plenty of copper plated ones were

designed to fool people into paying big bucks for them - I had one of
those at one time.

http://www.usmint.gov/about_the_mint/fun_facts/index.cfm?action=fun_facts2a
A 1943 copper cent was first offered for sale in 1958, bringing more
than $40,000. A subsequent piece sold for $10,000 at an ANA
convention in 1981. The highest amount paid for a 1943 copper cent
was $82,500 in 1996.

Because of its collector value, the 1943 copper cent has been
counterfeited by coating steel cents with copper or by altering the
dates of 1945, 1948, and 1949 pennies.

The easiest way to determine if a 1943 cent is made of steel, and not
copper, is to use a magnet. If it sticks to the magnet, it is not
copper. If it does not stick, the coin might be of copper and should
be authenticated by an expert.

To find out about coin experts in your area, you may call the American
Numismatic Association at (719) 632-2646.

I can't swear to the date, but I do seem to recall that during some year
in WWII, they made pennies out of steel because copper was needed for the
war effort. I learned this about 40 years ago, when everybody was on a
coin-collecting jag, and I do remember seeing some description of steel
pennies.

Steel, grain of wheat style, pennies were in circulation when I was a
kid from the war years. Silver nickels too.

Or, I might have dreamed it. I'd say the best route would be to check with
a "real" coin person - if you have copper (or, actually bronze) pennies from
1943, they could be worth a fortune, or maybe you could get a couple of
bucks for the value of the copper.

Good Luck!
Rich

 

[Tom Biasi]

"Rich Grise" wrote in message
news:id6dlf$5eg$3@news.eternal-september.org...

Tom Biasi wrote:

"Rich Grise" wrote in message
stratus46@yahoo.com wrote:
On Nov 30, 5:41 pm, Tim Wescott <t...@seemywebsite.com> wrote:
On 11/30/2010 01:53 PM, default wrote:

I was futzing around building a uhf bowtie antenna and needed some
fender washers. The hardware store is 6 miles away in a truck that
gets 12 mpg when cold. Figure the 8 washers for ~3 cents each and 45
minutes wasted, and I'm about ready to drop the project .

An Edison moment... pick up the metal punch, fish 8 cents out of my
pocket and instant fender washers! Cost 8 cents versus~$4, and only
took about two minutes.

I needed a larger one when repairing my truck today - a nickel and
electric drill...

But the ones you get from the store are made with steel, not zinc.

I suspect he's trying to hold pieces of coat hanger wire so zinc vs
steel won't be an issue. It may be better as pennies don't rust - or
do they?

Maybe one from 1943. ;-)

I have several 1943 U.S. one cent pieces and they are made of copper.
Someone told me that was unusual, are they worthless?

I can't swear to the date, but I do seem to recall that during some year

in WWII, they made pennies out of steel because copper was needed for the
war effort. I learned this about 40 years ago, when everybody was on a
coin-collecting jag, and I do remember seeing some description of steel
pennies.

Or, I might have dreamed it. I'd say the best route would be to check with
a "real" coin person - if you have copper (or, actually bronze) pennies from
1943, they could be worth a fortune, or maybe you could get a couple of
bucks for the value of the copper.

Good Luck!
Rich

My comment was in jest. I really wish I had 1943 copper pennies

 

[Michael A. Terrell]

Tom Biasi wrote:

"Rich Grise" wrote in message
news:id6dlf$5eg$3@news.eternal-september.org...

Tom Biasi wrote:
"Rich Grise" wrote in message
stratus46@yahoo.com wrote:
On Nov 30, 5:41 pm, Tim Wescott <t...@seemywebsite.com> wrote:
On 11/30/2010 01:53 PM, default wrote:

I was futzing around building a uhf bowtie antenna and needed some
fender washers. The hardware store is 6 miles away in a truck that
gets 12 mpg when cold. Figure the 8 washers for ~3 cents each and 45
minutes wasted, and I'm about ready to drop the project .

An Edison moment... pick up the metal punch, fish 8 cents out of my
pocket and instant fender washers! Cost 8 cents versus~$4, and only
took about two minutes.

I needed a larger one when repairing my truck today - a nickel and
electric drill...

But the ones you get from the store are made with steel, not zinc.

I suspect he's trying to hold pieces of coat hanger wire so zinc vs
steel won't be an issue. It may be better as pennies don't rust - or
do they?

Maybe one from 1943. ;-)

I have several 1943 U.S. one cent pieces and they are made of copper.
Someone told me that was unusual, are they worthless?

I can't swear to the date, but I do seem to recall that during some year
in WWII, they made pennies out of steel because copper was needed for the
war effort. I learned this about 40 years ago, when everybody was on a
coin-collecting jag, and I do remember seeing some description of steel
pennies.

Or, I might have dreamed it. I'd say the best route would be to check with
a "real" coin person - if you have copper (or, actually bronze) pennies from
1943, they could be worth a fortune, or maybe you could get a couple of
bucks for the value of the copper.

Good Luck!
Rich

My comment was in jest. I really wish I had 1943 copper pennies

http://en.wikipedia.org/wiki/1943_steel_cent
--
For the last time: I am not a mad scientist, I'm just a very ticked off
scientist!!!

 

[Baron]

default Inscribed thus:

On Wed, 01 Dec 2010 23:10:16 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

On Wed, 01 Dec 2010 17:39:28 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

On Wed, 01 Dec 2010 16:12:40 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

Here's one for an RF guru though: I made this reflector out of
a wood
frame and "hardware cloth" (1/2" mesh). Doesn't work at all
well. Whilst experimenting I tried an unused BBQ grill as a
reflector - worked pretty well as long as the wires were aligned
with the bow ties (same plane, parallel wires with ~10" between
them - grounded is better than floating).

Grounded or not shouldn't make too much difference. Are you feeding
with co-ax and a balun ?

yes 75 ohm coax to 300 ohm balun

Mmm I would have thought that the (bowtie) dipole would have been a low
impedance feed ! Do you have any source of pictures ?

I'm not sure as to what hardware cloth is, but you can run into
strange behavior if the distance between two conductors in the
reflector is a half or quarter wave length apart at the operating
frequency. Ideally the conductors in the reflector should be
1/10th or less, of a wave length apart. The closer to
approximating a solid sheet the better.

I'll drag it out and try again with a much closer spacing.

Hardware cloth is just wires in a cross pattern forming 1/2"
squares, that is hot dipped in zinc to rustproof and bond them.

Ahh ! "Chicken Mesh" Comes in 25ft rolls 3ft wide. Thanks.

I got the reflector I made out of the shed. I was mistaken it is
1/4" (fine) mesh.

Same game, it doesn't work. At ~18+" it has little effect then it
steadily attenuates the signal as it gets closer to the dipoles.

That could just be the matching that is deteriorating as you get close
to the dipole.

I tried rotating it 180 degrees putting the reflector on the other
side and that is even worse.

The rotational angle of the mesh should have little effect. It seems
that your saying that the mesh size has a fairly large effect on
signal strength.

I wouldn't say mesh size - the best signal is with no mesh but
horizontal parallel wires support on the outside edges with vertical
wires is OK and a vertical wire in the center is OK too - but no mesh,
no solid reflector works.

I looked at some ads for that type antenna and they also seem to use
horizontal parallel reflector wires not a cross hatch. If they have
vertical wires on the reflector it is in the center and edges only -
more for structural strength.

You could try a sheet of aluminum cooking foil. That would certainly
behave as a reflector.

I have a large sheet size aluminum baking pan. It doesn't improve the
signal but attenuates the signal

Seems to me a "reflector" is intended to reflect so wouldn't you
want
to observe some multiple of 1/4 wave? Ideally shouldn't the
reflected signal get back to the dipoles in phase with the primary
wave?

Yes it should, but thats a function of distance behind the dipole. So
the reflection should be in phase with the signal on the dipole.
Hence
the reflector being placed a 1/4 wave behind the dipole. The distance
also affects the feed point impedance. So there is a trade off between
matching, gain and directivity.

Well I've tried the solid pan at all distances . It is considerably
larger than the dipoles and it has to be further away for any signal
to get through but is not augmenting the signal strength at any
distance.

I'm coming to the conclusion that this reflector is not a reflector at
all but a director like a yagi antenna. This is also borne up by my
geographical understanding - on the driven element side there should
be an ocean out there somewhere not a TV station. I'm ~6 miles from
the ocean and from looking at a map with my street orientation and
house and antenna with respect to the street... Unless there's some
large object out there like a water tower that is reflecting a signal
from the wrong direction. There is a light tower ~30 miles offshore
in the general direction, large aluminum square on stilts 50 from the
surface.

Good morning from a cold, damp, snow covered UK !

Lets see if we can make some sense out of this. I assume that we are
talking about an antenna like this <http://www.blake-uk.com/jbb.aspx>
which is a typical billboard type antenna. The signal is expected to
come from the dipole side. This antenna offers a nominal 75 ohm match
to 75 ohm co-ax. There is no balun on this antenna. 300 ohm ribbon is
used between the elements as phasing lines. Termination is in the box
in the centre. The reflector has a plastic molding supporting the ends
of the reflector rods. The spacing between the rods making up the
reflector are arbitrarily spaced at about 1/10 wavelength. In fact
this antenna is almost a perfect scaling from the two meter antenna in
the ARRL handbook, and very similar to the "144/148Mhz Cushcraft one"
except that its much smaller.

Oddly enough I have a UK made version of the two meter billboard antenna
somewhere stored in the garage. I bought it 15 or 20 years ago and
never assembled it. I'll have to see if I can find it

--
Best Regards:
Baron.

 

On Thu, 02 Dec 2010 10:54:36 +0000, Baron
<baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

On Wed, 01 Dec 2010 23:10:16 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

On Wed, 01 Dec 2010 17:39:28 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

On Wed, 01 Dec 2010 16:12:40 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

Here's one for an RF guru though: I made this reflector out of
a wood
frame and "hardware cloth" (1/2" mesh). Doesn't work at all
well. Whilst experimenting I tried an unused BBQ grill as a
reflector - worked pretty well as long as the wires were aligned
with the bow ties (same plane, parallel wires with ~10" between
them - grounded is better than floating).

Grounded or not shouldn't make too much difference. Are you feeding
with co-ax and a balun ?

yes 75 ohm coax to 300 ohm balun

Mmm I would have thought that the (bowtie) dipole would have been a low
impedance feed ! Do you have any source of pictures ?

I'm not sure as to what hardware cloth is, but you can run into
strange behavior if the distance between two conductors in the
reflector is a half or quarter wave length apart at the operating
frequency. Ideally the conductors in the reflector should be
1/10th or less, of a wave length apart. The closer to
approximating a solid sheet the better.

I'll drag it out and try again with a much closer spacing.

Hardware cloth is just wires in a cross pattern forming 1/2"
squares, that is hot dipped in zinc to rustproof and bond them.

Ahh ! "Chicken Mesh" Comes in 25ft rolls 3ft wide. Thanks.

I got the reflector I made out of the shed. I was mistaken it is
1/4" (fine) mesh.

Same game, it doesn't work. At ~18+" it has little effect then it
steadily attenuates the signal as it gets closer to the dipoles.

That could just be the matching that is deteriorating as you get close
to the dipole.

I tried rotating it 180 degrees putting the reflector on the other
side and that is even worse.

The rotational angle of the mesh should have little effect. It seems
that your saying that the mesh size has a fairly large effect on
signal strength.

I wouldn't say mesh size - the best signal is with no mesh but
horizontal parallel wires support on the outside edges with vertical
wires is OK and a vertical wire in the center is OK too - but no mesh,
no solid reflector works.

I looked at some ads for that type antenna and they also seem to use
horizontal parallel reflector wires not a cross hatch. If they have
vertical wires on the reflector it is in the center and edges only -
more for structural strength.

You could try a sheet of aluminum cooking foil. That would certainly
behave as a reflector.

I have a large sheet size aluminum baking pan. It doesn't improve the
signal but attenuates the signal

Seems to me a "reflector" is intended to reflect so wouldn't you
want
to observe some multiple of 1/4 wave? Ideally shouldn't the
reflected signal get back to the dipoles in phase with the primary
wave?

Yes it should, but thats a function of distance behind the dipole. So
the reflection should be in phase with the signal on the dipole.
Hence
the reflector being placed a 1/4 wave behind the dipole. The distance
also affects the feed point impedance. So there is a trade off between
matching, gain and directivity.

Well I've tried the solid pan at all distances . It is considerably
larger than the dipoles and it has to be further away for any signal
to get through but is not augmenting the signal strength at any
distance.

I'm coming to the conclusion that this reflector is not a reflector at
all but a director like a yagi antenna. This is also borne up by my
geographical understanding - on the driven element side there should
be an ocean out there somewhere not a TV station. I'm ~6 miles from
the ocean and from looking at a map with my street orientation and
house and antenna with respect to the street... Unless there's some
large object out there like a water tower that is reflecting a signal
from the wrong direction. There is a light tower ~30 miles offshore
in the general direction, large aluminum square on stilts 50 from the
surface.

Good morning from a cold, damp, snow covered UK !

Good morning. First freeze of the season here - somehow my basil

plants haven't keeled over yet.

Lets see if we can make some sense out of this. I assume that we are
talking about an antenna like this <http://www.blake-uk.com/jbb.aspx
which is a typical billboard type antenna. The signal is expected to
come from the dipole side. This antenna offers a nominal 75 ohm match
to 75 ohm co-ax. There is no balun on this antenna. 300 ohm ribbon is
used between the elements as phasing lines. Termination is in the box
in the centre. The reflector has a plastic molding supporting the ends
of the reflector rods. The spacing between the rods making up the
reflector are arbitrarily spaced at about 1/10 wavelength. In fact
this antenna is almost a perfect scaling from the two meter antenna in
the ARRL handbook, and very similar to the "144/148Mhz Cushcraft one"
except that its much smaller.

I can't post a picture of my antenna (my telecom"dropped Usenet

binaries" because "people just used them for porn." Ironically, they
do have binaries but only porn ones from what I can see - and their
support people have no idea that they even have a news server.)

BUT Damned if there isn't already almost the exact antenna I have
(looks like coins and everything - including balun)!
http://i302.photobucket.com/albums/nn88/EscapeVelo/IMG_0087.jpg

close up of balun connection (just like mine)
http://i302.photobucket.com/albums/nn88/EscapeVelo/IMG_0236.jpg
I used heavy aluminum wire for the elements and thin aluminum wire for
the connections, his is copper. (still sort of looks like coins too)

and the sketch I built it from:
http://i302.photobucket.com/albums/nn88/EscapeVelo/TATdiagram1.jpg

The page I gleaned it from has lots of antennas:
http://s302.photobucket.com/albums/nn88/EscapeVelo/?start=all&mediafilter=images

I got out my musty old 1990 ARRL manual (only one I own). Closest
match is on page 17-21 called a 16 element collinear array. They say
the reflector should be spaced 0.2 wavelengths away.

I also researched locations etc. and I am indeed aiming my antenna
into the ocean so it is picking up signals from the reflector side -
the compass directions even match the stations pretty well

Oddly enough I have a UK made version of the two meter billboard antenna
somewhere stored in the garage. I bought it 15 or 20 years ago and
never assembled it. I'll have to see if I can find it

Ditch my director (not calling it a reflector any more) and rotate the
antenna around with a sheet reflector spaced close in.

Try to build a proper director (since that may be what is working)

From the same page showing a balun on that style of antenna
http://i302.photobucket.com/albums/nn88/EscapeVelo/IMG_1288.jpg

One that is easy to build and looks interesting:
http://i302.photobucket.com/albums/nn88/EscapeVelo/G1483Hoverman.jpg

I have a 1" square, 8 foot length of aluminum extrusion for a mast
clamped to my rack mount stereo (only 30" off the floor). My "rotor"
is a piece of 1-1/2" plastic pipe on the mast. With a U-bolt holding
the wooden spar or boom the antenna mounts to. I raise and lower it
via a C-clamp. It's a kludge job.

 

[Baron]

default Inscribed thus:

Unimportant stuff snipped.

Here's one for an RF guru though: I made this reflector out
of a wood frame and "hardware cloth" (1/2" mesh). Doesn't
work at all well. Whilst experimenting I tried an unused BBQ
grill as a reflector - worked pretty well as long as the wires
were aligned with the bow ties (same plane, parallel wires
with ~10" between them - grounded is better than floating).

Grounded or not shouldn't make too much difference. Are you feeding
with co-ax and a balun ?

yes 75 ohm coax to 300 ohm balun

Mmm I would have thought that the (bowtie) dipole would have been a
low impedance feed ! Do you have any source of pictures ?

Snipped.

Ideally the conductors in the reflector should be
1/10th or less, of a wave length apart. The closer to
approximating a solid sheet the better.

I'll drag it out and try again with a much closer spacing.

Same game, it doesn't work. At ~18+" it has little effect then it
steadily attenuates the signal as it gets closer to the dipoles.

That could just be the matching that is deteriorating as you get
close to the dipole.

I'm coming to the conclusion that this reflector is not a reflector
at all but a director like a yagi antenna. This is also borne up by
my geographical understanding - on the driven element side there
should be an ocean out there.

That makes sense if you have it pointed the wrong way.

Good morning from a cold, damp, snow covered UK !

Good morning. First freeze of the season here - somehow my basil
plants haven't keeled over yet.

Don't know about your basil, but everything is under 3ft of snow here !

Lets see if we can make some sense out of this. I assume that we are
talking about an antenna like this <http://www.blake-uk.com/jbb.aspx
which is a typical billboard type antenna. The signal is expected to
come from the dipole side. This antenna offers a nominal 75 ohm match
to 75 ohm co-ax. There is no balun on this antenna. 300 ohm ribbon is
used between the elements as phasing lines. Termination is in the box
in the centre. The reflector has a plastic molding supporting the
ends of the reflector rods. The spacing between the rods making up the
reflector are arbitrarily spaced at about 1/10 wavelength. In fact
this antenna is almost a perfect scaling from the two meter antenna in
the ARRL handbook, and very similar to the "144/148Mhz Cushcraft one"
except that its much smaller.

I can't post a picture of my antenna (my telecom"dropped Usenet
binaries" because "people just used them for porn." Ironically, they
do have binaries but only porn ones from what I can see - and their
support people have no idea that they even have a news server.)

I don't think any of the ISP's offer news server access any more !

BUT Damned if there isn't already almost the exact antenna I have
(looks like coins and everything - including balun)!
http://i302.photobucket.com/albums/nn88/EscapeVelo/IMG_0087.jpg

Yep ! we're on the same page. If you got chance to look at the picture
in the link that I provided you will see almost the same antenna.

close up of balun connection (just like mine)
http://i302.photobucket.com/albums/nn88/EscapeVelo/IMG_0236.jpg
I used heavy aluminum wire for the elements and thin aluminum wire for
the connections, his is copper. (still sort of looks like coins too)

I would check, I think that balun is 1:1 ie 75 ohms balanced to 75 ohms
unbalanced. Either way the co-ax needs to run horisontally away
through the reflector and down behind it.

and the sketch I built it from:
http://i302.photobucket.com/albums/nn88/EscapeVelo/TATdiagram1.jpg

Should be fine ! The dimensions are quite critical though and the angle
of the dipoles will change the impedances at the feed points.

The page I gleaned it from has lots of antennas:

http://s302.photobucket.com/albums/nn88/EscapeVelo/?start=all&mediafilter=images

It certainly has. There seems to be a lot of stuff there...

I got out my musty old 1990 ARRL manual (only one I own). Closest
match is on page 17-21 called a 16 element collinear array. They say
the reflector should be spaced 0.2 wavelengths away.

That is probably the one that I have in storage. I really will have to
dig it out at some point and have a play with it.

I also researched locations etc. and I am indeed aiming my antenna
into the ocean so it is picking up signals from the reflector side -
the compass directions even match the stations pretty well

The front to back ratio is supposed to be very good on that antenna.
Better than 15db if I recall.

Ditch my director (not calling it a reflector any more) and rotate the
antenna around with a sheet reflector spaced close in.

Now that you have it the right way round, you can play with the
reflector/dipole spacing to get the maximum gain from it. I noted that
you mentioned 0.2 wavelength spacing. That would tend to push the feed
point impedance down a little.

Try to build a proper director (since that may be what is working)

Directors will be in front of the dipole and the reflector behind.

From the same page showing a balun on that style of antenna
http://i302.photobucket.com/albums/nn88/EscapeVelo/IMG_1288.jpg

One that is easy to build and looks interesting:
http://i302.photobucket.com/albums/nn88/EscapeVelo/G1483Hoverman.jpg

I have a 1" square, 8 foot length of aluminum extrusion for a mast
clamped to my rack mount stereo (only 30" off the floor). My "rotor"
is a piece of 1-1/2" plastic pipe on the mast. With a U-bolt holding
the wooden spar or boom the antenna mounts to. I raise and lower it
via a C-clamp. It's a kludge job.

If it works for you, I ain't knocking it. I've used all sorts of weird
and wonderful contraptions in the past. Good luck with your
experiments. One tip I will pass on to you, is make notes ! I've
pages and pages of them going back to around 1972/3 all in storage.
One of these days... ;-)

--
Best Regards:
Baron.

 

On Thu, 02 Dec 2010 17:35:41 +0000, Baron
<baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

Unimportant stuff snipped.

Here's one for an RF guru though: I made this reflector out
of a wood frame and "hardware cloth" (1/2" mesh). Doesn't
work at all well. Whilst experimenting I tried an unused BBQ
grill as a reflector - worked pretty well as long as the wires
were aligned with the bow ties (same plane, parallel wires
with ~10" between them - grounded is better than floating).

Grounded or not shouldn't make too much difference. Are you feeding
with co-ax and a balun ?

yes 75 ohm coax to 300 ohm balun

Mmm I would have thought that the (bowtie) dipole would have been a
low impedance feed ! Do you have any source of pictures ?

Snipped.

Ideally the conductors in the reflector should be
1/10th or less, of a wave length apart. The closer to
approximating a solid sheet the better.

I'll drag it out and try again with a much closer spacing.

Same game, it doesn't work. At ~18+" it has little effect then it
steadily attenuates the signal as it gets closer to the dipoles.

That could just be the matching that is deteriorating as you get
close to the dipole.

I'm coming to the conclusion that this reflector is not a reflector
at all but a director like a yagi antenna. This is also borne up by
my geographical understanding - on the driven element side there
should be an ocean out there.

That makes sense if you have it pointed the wrong way.

That is eggsackly the problem. I rotated it 180, removed the
directors, and put my screen behind it and at ~8" got a good signal
reading.

The on-screen "reading" is near useless- takes ten seconds to change
and I don't trust it, but it's all I have to work with.

Anyhow now the stations are more or less in the directions they should
be, and, while the station I was having the most trouble getting, is
reading very low. the audio and video seems good - leading me to
believe there is/was some multipath going on there.

Figure the response time very slow, add something like multi path
where the signal voltage can increase, throw a little wind and rain
into the mix and signal strength numbers don't mean much.

Good morning from a cold, damp, snow covered UK !

Good morning. First freeze of the season here - somehow my basil
plants haven't keeled over yet.

Don't know about your basil, but everything is under 3ft of snow here !

Fresh Basil is like, necessary IMO. I've thought about building a

basil grower.

Lets see if we can make some sense out of this. I assume that we are
talking about an antenna like this <http://www.blake-uk.com/jbb.aspx
which is a typical billboard type antenna. The signal is expected to
come from the dipole side. This antenna offers a nominal 75 ohm match
to 75 ohm co-ax. There is no balun on this antenna. 300 ohm ribbon is
used between the elements as phasing lines. Termination is in the box
in the centre. The reflector has a plastic molding supporting the
ends of the reflector rods. The spacing between the rods making up the
reflector are arbitrarily spaced at about 1/10 wavelength. In fact
this antenna is almost a perfect scaling from the two meter antenna in
the ARRL handbook, and very similar to the "144/148Mhz Cushcraft one"
except that its much smaller.

I can't post a picture of my antenna (my telecom"dropped Usenet
binaries" because "people just used them for porn." Ironically, they
do have binaries but only porn ones from what I can see - and their
support people have no idea that they even have a news server.)

I don't think any of the ISP's offer news server access any more !

Sure they do. My last ISP still has one Even though I left them, I

still use the news server... I can't post but can read or download.

I suspect they keep them for people that find them a deal breaker. If
I had to rely on what my current ISP says I'd believe that I had no
Usenet service.

But keeping out alt.binaries.schematics and allowing all the porno you
can imagine makes no sense at all - unless... the CEO or someone at
the teleco wants that stuff, and the IT dummies can't figure out how
to configure it.

BUT Damned if there isn't already almost the exact antenna I have
(looks like coins and everything - including balun)!
http://i302.photobucket.com/albums/nn88/EscapeVelo/IMG_0087.jpg

Yep ! we're on the same page. If you got chance to look at the picture
in the link that I provided you will see almost the same antenna.

Sure. First thing I did.

close up of balun connection (just like mine)
http://i302.photobucket.com/albums/nn88/EscapeVelo/IMG_0236.jpg
I used heavy aluminum wire for the elements and thin aluminum wire for
the connections, his is copper. (still sort of looks like coins too)

I would check, I think that balun is 1:1 ie 75 ohms balanced to 75 ohms
unbalanced. Either way the co-ax needs to run horisontally away
through the reflector and down behind it.

I should be able to rewind a commercial balun. All my junk box
ferrites are low frequency.

and the sketch I built it from:
http://i302.photobucket.com/albums/nn88/EscapeVelo/TATdiagram1.jpg

Should be fine ! The dimensions are quite critical though and the angle
of the dipoles will change the impedances at the feed points.

The page I gleaned it from has lots of antennas:

http://s302.photobucket.com/albums/nn88/EscapeVelo/?start=all&mediafilter=images

It certainly has. There seems to be a lot of stuff there...

I didn't try to find out why all that TV antenna stuff is there. I
searched for the file name of the drawing I had stored in my PC.

I got out my musty old 1990 ARRL manual (only one I own). Closest
match is on page 17-21 called a 16 element collinear array. They say
the reflector should be spaced 0.2 wavelengths away.

That is probably the one that I have in storage. I really will have to
dig it out at some point and have a play with it.

I also researched locations etc. and I am indeed aiming my antenna
into the ocean so it is picking up signals from the reflector side -
the compass directions even match the stations pretty well

The front to back ratio is supposed to be very good on that antenna.
Better than 15db if I recall.

Might be at that...

Ditch my director (not calling it a reflector any more) and rotate the
antenna around with a sheet reflector spaced close in.

Now that you have it the right way round, you can play with the
reflector/dipole spacing to get the maximum gain from it. I noted that
you mentioned 0.2 wavelength spacing. That would tend to push the feed
point impedance down a little.

Try to build a proper director (since that may be what is working)

Directors will be in front of the dipole and the reflector behind.

From the same page showing a balun on that style of antenna
http://i302.photobucket.com/albums/nn88/EscapeVelo/IMG_1288.jpg

One that is easy to build and looks interesting:
http://i302.photobucket.com/albums/nn88/EscapeVelo/G1483Hoverman.jpg

I have a 1" square, 8 foot length of aluminum extrusion for a mast
clamped to my rack mount stereo (only 30" off the floor). My "rotor"
is a piece of 1-1/2" plastic pipe on the mast. With a U-bolt holding
the wooden spar or boom the antenna mounts to. I raise and lower it
via a C-clamp. It's a kludge job.

If it works for you, I ain't knocking it. I've used all sorts of weird
and wonderful contraptions in the past. Good luck with your
experiments. One tip I will pass on to you, is make notes ! I've
pages and pages of them going back to around 1972/3 all in storage.
One of these days... ;-)

Well so far it is going great. Signal is lower on the weak station
but the sound and audio is staying in there (so far). I had to cut my
boom down couple of inches to put the reflector at 8" which seems to
be optimum. Now if I stand in "front" of it (180 from where it used
to be) the signal drops out. The whole antenna needs to be lower to
work (about 2 feet - which aligns, roughly, to window openings).

I do keep notebooks, getting too old to depend on memory and there's
just too many projects and interests. One for electronics and
another for the picaxe controllers (if you don't/can't use
programmable controllers check them out - easy as pie programming and
the "development system" set me back <$20, I love these things).

Anyway, right now its looking good. I need some wind and rain to see
if it hangs in there. Thanks for your help.

 

[Baron]

default Inscribed thus:

On Thu, 02 Dec 2010 17:35:41 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

default Inscribed thus:

Unimportant stuff snipped.

That makes sense if you have it pointed the wrong way.

That is eggsackly the problem. I rotated it 180, removed the
directors, and put my screen behind it and at ~8" got a good signal
reading.

The on-screen "reading" is near useless- takes ten seconds to change
and I don't trust it, but it's all I have to work with.

Yes its the same here ! It seems to take an age to change.

Anyhow now the stations are more or less in the directions they should
be, and, while the station I was having the most trouble getting, is
reading very low. the audio and video seems good - leading me to
believe there is/was some multipath going on there.

One thing you can do if the beam width is a bit wide (about 130/140
degrees with a flat reflector) is to make the reflector twice as wide
and then fold the extra outside edges towards the dipoles at about 45
degrees. Looking down on it should look like a flat pan... Excuse the
art !


\ --- /
\__|__/

I hope that it looks right.

Figure the response time very slow, add something like multi path
where the signal voltage can increase, throw a little wind and rain
into the mix and signal strength numbers don't mean much.

You will get much better results if you can get the antenna outside. At
the frequencies that you are playing with, you will get reflections
from walls, doors siding etc. Even your own body will cause things to
change.

Fresh Basil is like, necessary IMO. I've thought about building a
basil grower.

I'll not let the XYL see that last line. ;-)

I don't think any of the ISP's offer news server access any more !

I should have qualified that by adding UK ISP's...

I would check, I think that balun is 1:1 ie 75 ohms balanced to 75
ohms unbalanced. Either way the co-ax needs to run horisontally away
through the reflector and down behind it.

I should be able to rewind a commercial balun. All my junk box
ferrites are low frequency.

At the frequency you are using a quarter wave length of 50ohm co-ax,
corrected for velocity factor is all you need. Check out your ARRL
handbook.

I also researched locations etc. and I am indeed aiming my antenna
into the ocean so it is picking up signals from the reflector side -
the compass directions even match the stations pretty well

A compass and map can be an eye opener at times, particularly if you
have a big obstruction in the general direction of the transmitter.

The front to back ratio is supposed to be very good on that antenna.
Better than 15db if I recall.

Might be at that...

Try to build a proper director (since that may be what is working)

Directors will be in front of the dipole and the reflector behind.

Well so far it is going great. Signal is lower on the weak station
but the sound and audio is staying in there (so far). I had to cut my
boom down couple of inches to put the reflector at 8" which seems to
be optimum. Now if I stand in "front" of it (180 from where it used
to be) the signal drops out. The whole antenna needs to be lower to
work (about 2 feet - which aligns, roughly, to window openings).

I do keep notebooks, getting too old to depend on memory and there's
just too many projects and interests. One for electronics and
another for the picaxe controllers (if you don't/can't use
programmable controllers check them out - easy as pie programming and
the "development system" set me back <$20, I love these things).

I'm "having" to learn something about PIC's at the moment. I project
that I've been working on isn't playing nice. Finding out that some
junkbox bits decide to fail after you have soldered them in is a pain.

I grabbed a salvaged DPCO push switch (I tested it first) decided to go
OC on one of its poles. It took a while before I convinced myself that
it was actually faulty.

Anyway, right now its looking good. I need some wind and rain to see
if it hangs in there. Thanks for your help.

We've got our own wind at the moment thank you very much.. -16C here
plus wind chill ! Brrrr

--
Best Regards:
Baron.

 

On Fri, 03 Dec 2010 12:37:58 +0000, Baron
<baron.nospam@linuxmaniac.nospam.net> wrote:

Thanks Baron.

Thought I'd report back.

The thing is working beautifully. Reducing the space between the
reflector and the elements from 10" to 8" made all the difference in
the world.

I don't know that bending the reflector in on the sides would be
advantageous. Right now I get all the stations the converter was able
to find with excellent stability - and according to my research (and
borne out by experimentation) the stations are positioned in a 45
degree arc.

I also conclude that it is more indicative of good signal quality if
the on screen "meter" is stable and not changing much, rather than
showing a high, but variable signal strength.

My wooden antenna supports wouldn't survive the elements so it has to
stay indoors. BUT, I'm kinda fired up to experiment further.

I want to try this idea using PVC for the support and cross fittings
by Brian Mileshosky, N5ZGT

http://www.urfmsi.org/documents/yagi_presentation_abbreviated.pdf

Unfortunately my Adobe Acrobat won't let me see the whole thing, but I
like the construction technique Easy, cheap, "uptown" design, and
weather proof/resistant.

From what I can see: The boom is PVC with cross fittings (not usual
plumbing stuff but a large hardware store should have them) and slots
cut in the fittings with hose clamps holding the pipe sections.

Do you think using 1/2" galvanized steel tubing (called EMT
Electricians Metal Tubing here - thin conduit tubing) would be bad? I
could always spring for aluminum if it makes a difference. I figure
zinc isn't a great conductor - but then anodize is an insulator and
anodized aluminum is a material of choice.

Using thick tube should make the antenna more broadband, right?

That, mast and maybe a small JEFET or MMIC amplifier. . .

Anyhow, thanks for your help.

Take care
bob

 

[Baron]

Hi Bob,

default Inscribed thus:

Thanks Baron.

Thought I'd report back.

I did wonder if you might Its nice to know how you are getting on !
Anyway I have an interest in antennas myself.

The thing is working beautifully. Reducing the space between the
reflector and the elements from 10" to 8" made all the difference in
the world.

Good ! I'm glad that its improved signal strength for you.

I don't know that bending the reflector in on the sides would be
advantageous. Right now I get all the stations the converter was able
to find with excellent stability - and according to my research (and
borne out by experimentation) the stations are positioned in a 45
degree arc.

Yes ! What happens is that it reduces the strength of signals coming in
from the sides. You can take this to extremes and wrap the reflector
around much further so that the edges are further forward, in front of
the line of the dipole. Think parabolic dish but only in the vertical
plane. If done well, it can double and triple the antenna gain by
narrowing the width of the beam in the horizontal plane.

I also conclude that it is more indicative of good signal quality if
the on screen "meter" is stable and not changing much, rather than
showing a high, but variable signal strength.

If you have the skills you could make an active field strength meter and
get an almost instant indication of signal strength.

My wooden antenna supports wouldn't survive the elements so it has to
stay indoors. BUT, I'm kinda fired up to experiment further.

You would be surprised just how robust it can be.
I once made a two meter (144/146Mhz) transmitting antenna from two
bamboo canes, a brush stale, copper wire and fishing line. The brush
stale broke after a very large bird crashed into it whilst chasing a
pigeon !

I want to try this idea using PVC for the support and cross fittings
by Brian Mileshosky, N5ZGT

http://www.urfmsi.org/documents/yagi_presentation_abbreviated.pdf

I'll get back to you after I've had a look at that.

Unfortunately my Adobe Acrobat won't let me see the whole thing, but I
like the construction technique Easy, cheap, "uptown" design, and
weather proof/resistant.

I can turn PDF's into Jpegs/Giffs if I need to...

From what I can see: The boom is PVC with cross fittings (not usual
plumbing stuff but a large hardware store should have them) and slots
cut in the fittings with hose clamps holding the pipe sections.

PVC drain pipe is a useful material for antenna. As is 6mm PVC rod.

Do you think using 1/2" galvanized steel tubing (called EMT
Electricians Metal Tubing here - thin conduit tubing) would be bad? I
could always spring for aluminum if it makes a difference. I figure
zinc isn't a great conductor - but then anodize is an insulator and
anodized aluminum is a material of choice.

Avoid steel if at all possible ! Aluminum is the material of choice.
Anodised is fine if you don't need to make an electrically sound joint,
otherwise you will have to grind or sand the anodising away where the
connection is to be made.

Using thick tube should make the antenna more broadband, right?

Not so much that you would notice ! The diameter can become important
as the frequency rises.

That, mast and maybe a small JEFET or MMIC amplifier. . .

For the time being don't worry about amplification of the signal. Get
the antenna right first. You might find that you don't need it.
Anyway it can give rise to other problems. But thats another story.

Anyhow, thanks for your help.

No problem. You're welcome.

Take care
bob

--
Best Regards:
Baron.

 

[Baron]

Hi Bob,

http://www.urfmsi.org/documents/yagi_presentation_abbreviated.pdf

I had a look at that PDF. There is some good info there. Particularly
if you look at the radiation patterns. In particular the ones for just
a dipole and the one with a dipole and reflector. Essentially they
show you the radiation pattern for the antenna that you have just
built.

I have a suspicion that the antenna that you are thinking of building is
the three element yagi. If it is, please don't waste your time on it.
You will be disappointed by its performance in comparison to the one
you have just built !

--
Best Regards:
Baron.

 

On Sat, 04 Dec 2010 22:38:54 +0000, Baron
<baron.nospam@linuxmaniac.nospam.net> wrote:

Hi Bob,

http://www.urfmsi.org/documents/yagi_presentation_abbreviated.pdf

I had a look at that PDF. There is some good info there. Particularly
if you look at the radiation patterns. In particular the ones for just
a dipole and the one with a dipole and reflector. Essentially they
show you the radiation pattern for the antenna that you have just
built.

I have a suspicion that the antenna that you are thinking of building is
the three element yagi. If it is, please don't waste your time on it.
You will be disappointed by its performance in comparison to the one
you have just built !

You guessed it. Lots easier to build, make weatherproof, less
expensive, less awkward (neat, compact, lower wind loading) etc..

AND I could easily raise it almost 30 feet higher, where the trees are
a bit thinner. The downside is 30+ feet of coaxial losses.

In contrast, it would be more expensive to come up with a bow tie that
is rugged enough and long lived. I can count on high winds, and the
occasional falling tree limb, pine cones not to mention long leaf pine
needles (they seem to have a real penchant for affixing themselves to
any kind of screen wires suspended in air)

In total would it still be a net loss?

Regards
bob

 

[Baron]

default Inscribed thus:
Hi Bob,

http://www.urfmsi.org/documents/yagi_presentation_abbreviated.pdf

I had a look at that PDF. There is some good info there.
Particularly if you look at the radiation patterns. In particular the
ones for just a dipole and the one with a dipole and reflector.
Essentially they show you the radiation pattern for the antenna that
you have just built.

I have a suspicion that the antenna that you are thinking of building
is the three element yagi. If it is, please don't waste your time on
it. You will be disappointed by its performance in comparison to the
one you have just built !

You guessed it. Lots easier to build, make weatherproof, less
expensive, less awkward (neat, compact, lower wind loading) etc..

Whilst I see where you are going, I promise, a three element yagi will
not provide the performance that the four element billboard will give
you.

AND I could easily raise it almost 30 feet higher, where the trees are
a bit thinner. The downside is 30+ feet of coaxial losses.

You are right, you have to subtract the co-ax losses from the antenna
gain figure.

In contrast, it would be more expensive to come up with a bow tie that
is rugged enough and long lived. I can count on high winds, and the
occasional falling tree limb, pine cones not to mention long leaf pine
needles (they seem to have a real penchant for affixing themselves to
any kind of screen wires suspended in air)

The only real hazard that I see there is the falling tree limb. I doubt
that any antenna construction could survive that.

In total would it still be a net loss?

Regretfully "Yes" !

Regards
bob

You could put a director in front of each of the four dipoles of your
billboard array and have effectively the same gain as four of the three
element yagi added together. ie 6db more gain. As a rule of thumb
each 3db is a doubling or halving of gain depending which way you are
going.

As an example, if a single antenna has a gain of "one" then two antenna
will have a gain of two. The two antenna has a combined gain of 3db
over a single one. Four antenna will be 3db over two antenna or 6db
over a single one.

So a single three element yagi will be approximately -6db compared to
your billboard array. Notice the "-" sign. In practice the difference
is only about -4db.

If you look at the radiation patterns I mentioned, you should see that
antenna gain is created by confining the signal pattern in some
directions to the advantage of others.

The horizontal pattern of your billboard array is a very much reduced
signal from the rear, as you have already discovered, and a narrowing
of the pattern at the front.

--
Best Regards:
Baron.

 

[Jasen Betts]

On 2010-12-05, default <default> wrote:

On Sat, 04 Dec 2010 22:38:54 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

I have a suspicion that the antenna that you are thinking of building is
the three element yagi. If it is, please don't waste your time on it.
You will be disappointed by its performance in comparison to the one
you have just built !

You guessed it. Lots easier to build, make weatherproof, less
expensive, less awkward (neat, compact, lower wind loading) etc..

AND I could easily raise it almost 30 feet higher, where the trees are
a bit thinner. The downside is 30+ feet of coaxial losses.

For 10m at UHF frequencies and good coax, loss will be 1db or less
not a big deal.

In contrast, it would be more expensive to come up with a bow tie that
is rugged enough and long lived. I can count on high winds, and the
occasional falling tree limb, pine cones not to mention long leaf pine
needles (they seem to have a real penchant for affixing themselves to
any kind of screen wires suspended in air)

In total would it still be a net loss?

The 4 element bow-tie phase array gets its gain mostly by having a larger
aperature, the Yagi-Uda, or the similar log-periodic is a directional
antenna. IIRC your desired stations are spread over a 45 degree angle.

the bowtie is probably the better one for this application unless you
are troubled by multipath reception.

OTOH a 3 element yagi is probably not very directional.

--
⚂⚃ 100% natural

 

On 8 Dec 2010 11:08:19 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

On 2010-12-05, default <default> wrote:
On Sat, 04 Dec 2010 22:38:54 +0000, Baron
baron.nospam@linuxmaniac.nospam.net> wrote:

I have a suspicion that the antenna that you are thinking of building is
the three element yagi. If it is, please don't waste your time on it.
You will be disappointed by its performance in comparison to the one
you have just built !

You guessed it. Lots easier to build, make weatherproof, less
expensive, less awkward (neat, compact, lower wind loading) etc..

AND I could easily raise it almost 30 feet higher, where the trees are
a bit thinner. The downside is 30+ feet of coaxial losses.

For 10m at UHF frequencies and good coax, loss will be 1db or less
not a big deal.

Empirically that seems true enough. I connected a long piece and
carried a dipole around looking for hot locations and never really saw
any problem with losses in the line.

In contrast, it would be more expensive to come up with a bow tie that
is rugged enough and long lived. I can count on high winds, and the
occasional falling tree limb, pine cones not to mention long leaf pine
needles (they seem to have a real penchant for affixing themselves to
any kind of screen wires suspended in air)

In total would it still be a net loss?

The 4 element bow-tie phase array gets its gain mostly by having a larger
aperature, the Yagi-Uda, or the similar log-periodic is a directional
antenna. IIRC your desired stations are spread over a 45 degree angle.

the bowtie is probably the better one for this application unless you
are troubled by multipath reception.

OTOH a 3 element yagi is probably not very directional.
I miss the good old days of analog TV. You could look at the screen

and see multipath, or ignition noise, or a noisy power line connection
or arcing, or some idiot who bought one of the $69 vacuum toob linear
amplifiers and connected it to his CB rig.