magnetic field

Winfield Hill · Jan 13, 2005

Ross Mac wrote...

That's an interesting statement (soviet national anthem) since the "blue
states" believe in a political philosophy that boarders on socialism????

Totally false, and a gratuitous smear on half the country.

Just an observation not a personal attack....

Right.

--
Thanks,
- Win

Sal M. Onella · Jan 10, 2005

<nooneinparticular314159@yahoo.com> wrote in message
news:1104787856.310883.276250@z14g2000cwz.googlegroups.com...

Ok. I should probably point out some design constraints to go with my
original question :

I live in a high rise apt building. I can not mount anything on the
exterior of my building, nor do I have line of sight to a satellite
(especially since the 15 story building was put up in front of me).
This includes roof antennae

I can not modify the building in front of me. That building is still
under construction, and I do not own it, nor do I have access to it.

I am not looking to subscribe to any sort of pay service, such as cable
or satellite. It's too expensive. Likewise, I am not looking for a
replacement for my TV right now.

In other words, anything I do needs to be inside my own apt, and should
not be very expensive.

Considering all that went before ...

I don't think I got where you live. If you are in the US, you may
get what you want by going digital. I'll assume that.

Most areas of the US have begun the digital cutover and a few
areas are complete, meaning all stations are available on both
digital as well as traditional analog. A digital tuner (set-top-box --
STB for short) costs $200 and up. It will usually work, even
with blockage, if you don't mind fiddling with the antenna a little
bit. With digital, if the STB can make out most of the 1's and 0's,
the picture will immediately be perfect. I have had pretty good
luck with an antenna indoors (experimentally only, since
I usually use a roof-top antenna; yes, I know you said
your antenna must be indoors).

Wal-Mart sells a digital STB. If your Wal-Mart stocks it, then
there are digital signals in your area. If you find it doesn't
work, you will probably be able to return it if you unpack it
carefully. Others will likely have recommendations for an
STB. Not all STB's are created equal; I recommend you
check that the INPUT required for your TV is one of the
OUTPUTS of the STB you want to buy.

The Internet has info about digital TV & STB's. Please
return here or subscribe to the "alt.video.digital-tv" group
if you have more questions, which is kinda likely ;-)

Good luck.

Tony Williams · Jan 10, 2005

In article <10u06sd6nig276e@corp.supernews.com>,
"Watson A.Name - \"Watt Sun wrote:

"The Phantom" <phantom@aol.com> wrote in message

......You will have gotten rid of a big capacitor and possible
source of long time constant behavior, and have an easily
adjustable, low impedance bias supply.

I could just use the 9V supply and a resistor and zener to do
that, instead. Same diff and it saves batteries.

That capacitor *has* to be got rid of. There are other
problems as well though. The low voltage across S-D
is running the jfet in a place where it has a low output
impedance, and lots of distortion. The even-harmonic
components in the distortion is probably accumulating on
the capacitor and shifting the bias point, away from
oscillation.... a sort of leisurely squegging.

If you have to stay with a 9v supply, then a folded cascode
circuit could take away a lot of the fundamental problems.
As below, LTSpice says it works ok.

+--------------------------------------+9V
| |
\ \
/2k /1k5
\ \
_|_ 0.15mA approx, |
\_/ +--<-----------------------------+<--7V
| |/e so Rin= 180 ohms approx. |
+---|pnp | Id= 1.2mA
| |\ | Rd= 5k.
| | R2 R R |--+
| +--/\/\--+--/\/\--+--/\/\--+-->|J1,2N3819
| | 135k | 150k | 150k | |--+
| | +| +| +| |<--4.7V
\ \R1 ===C ===C ===C |
/1k6 /15k | | | +----+
\ \ | | | \_|_ |
| | | | | ZD1/_\ |
| | | | | 4v7 | |
| +--------+--------+--------+------+0V |
| R1=15k, and R1+R2 = R always. |
+-------------------------------------------+

The effective Drain load is R1, but the folded cascode
allows a high jfet current (high gm) and yet at the same
time have a high value of load resistance. The 180 ohm
input resistance at the pnp emitter means that about 90%
of the AC current from the jfet goes down the transistor
and it means that the AC Vd-s voltage is almost zero
(which keeps the distortion low).

The lagging phase-shifter allows a dc-coupled negative
feedback type of self-biassing. The dc voltage across R1
will always be 4.7V minus whatever Vg-s the jfet needs for
an Id of 1.2mA. The gm of the jfet has to be about 2.2mA/V
for the circuit to oscillate.

With the generic 2N3819, LTSpice gives a dc-operating point
of about 2.6V across R1, and an AC oscillation voltage of
4.8V pk-pk. The sinewave looks reasonable, just flat bottoms
at about 0.4V, as the transistor runs out of current.

For the lagging phase shifter, F= root-6/2.pi.R.C and with
1uF caps the simulated frequency is 2.59Hz.

It takes a few hundred seconds for the oscillation to come
up and finally stabilise.

--
Tony Williams.

Jim Thompson · Jan 10, 2005

On Mon, 10 Jan 2005 16:22:56 +0000 (GMT), Tony Williams
<tonyw@ledelec.demon.co.uk> wrote:

In article <bj65u0prck12kkb1i4dliaf4a1knnh0r5p@4ax.com>,
Jim Thompson <thegreatone@example.com> wrote:

Come on, Tony, you done gone and ruined this whole thread by
introducing some actual engineering thought into the process ;-)

Sorry Jim.......

The folded cascode (with dc feedback bias) was my favorite
circuit when using a single jfet, it evades all sorts of
problems. By ratio'ing the currents it is even possible
to do the self-bias for constant gm, as per the Siliconix
app note TA70-2.

In this case, getting 29x off a 9Vdc rail is possible,
but still a little too marginal for comfort.

"but for Wales", uh, LED flashing ?

480)460-2350 | |
| E-mail Address at Website Fax

Jan 15, 2005

do the Transformers from the lin above a high voltage diode

Don Pearce · Jan 15, 2005

On 15 Jan 2005 11:08:49 -0800, ngdbud@hotmail.com wrote:

do the Transformers from the lin above a high voltage diode

well, if they do

d

Pearce Consulting
http://www.pearce.uk.com

Jan 15, 2005

i mean the flybacks from the link in William j. beaty's posting.

Guy Macon · Jan 15, 2005

ngdbud@hotmail.com wrote:

Don Pearce wrote:

ngdbud@hotmail.com wrote:

do the Transformers from the lin above a high voltage diode

well, if they do

d

i mean the flybacks from the link in William j. beaty's posting.

ghilred frok at wifx. Dnighth? Ngfipht yk ur! Uvq the hhvd or hnnngh.
Blorgk? Blorgk! Blorgkity-blorgk!!!!

J. Yazel · Jan 15, 2005

On 15 Jan 2005 01:41:37 -0800, andreas.manoli@gmail.com wrote:

Hi,
I live in Europe where the electricity is 240V and 50HZ

I just bought a (WAHL) hair trimmer from the USA. The battery charger
for the hair trimmer is made for USA (input 120VAC, 60HZ, 5W) and has
output 2.0V DC and 1100mA.

Obviously I cannot use this charger here. I think that there are two
ways to charge my trimmer:

a) Buy a variable transformer and replace it (Local shops sell
variable transformers with output 1.5 or 3V and 1000mA ). I called a
shop and they said that with less mA it will just take longer to charge
and it does not matter if the voltage is 1.5 or 3 .He said that the
trimmer's original transformer output shouldn't be exactly 2V anyway.

b) Buy a transformer for the transformer! (transform 240V AC to 120V
AC) . The issue here is bulk, overheating and different frequencies.

Thanx
=======================

Have you contacted the manufacturer to see if they have a 240v
charger?

Jack

Pig Bladder · Jan 15, 2005

On Sat, 15 Jan 2005 11:08:49 -0800, ngdbud wrote:

do the Transformers from the lin above a high voltage diode

What in the fuck are you talking about?

Do you even have any idea?

Don't post to this NG from google groups.
--
The Pig Bladder From Uranus, Still Waiting for
Some Hot Babe to Ask What My Favorite Planet Is.

Bob · Jan 15, 2005

"Don Pearce" <donald@pearce.uk.com> wrote in message
news:41eb6b91.10490046@news.individual.net...

On 15 Jan 2005 11:08:49 -0800, ngdbud@hotmail.com wrote:

do the Transformers from the lin above a high voltage diode

well, if they do

d

Pearce Consulting
http://www.pearce.uk.com

The most crumulent usage of the word "do" I have ever encountered. I think
you've answered the poster's question. Are you a teacher?

Bob

Don Pearce · Jan 15, 2005

On Sat, 15 Jan 2005 21:47:12 GMT, "Bob"
<nimby1_notspamm_@earthlink.net> wrote:

"Don Pearce" <donald@pearce.uk.com> wrote in message
news:41eb6b91.10490046@news.individual.net...
On 15 Jan 2005 11:08:49 -0800, ngdbud@hotmail.com wrote:

do the Transformers from the lin above a high voltage diode

well, if they do

d

Pearce Consulting
http://www.pearce.uk.com

The most crumulent usage of the word "do" I have ever encountered. I think
you've answered the poster's question. Are you a teacher?

Bob

The higher, the fewer.

d

Pearce Consulting
http://www.pearce.uk.com

JeffM · Jan 15, 2005

Posting 101 Lesson
for those who post at the New, Improved Google Groups

Most people do not read the group at Google
and do not see what you see.

Mark and Copy a little of the post to which you are responding
and Paste it into your post,
so that people who do not read the group at Google
have some bloody idea what you're talking about.
Spell checking is also good.

Watson A.Name - \"Watt Su · Jan 16, 2005

"Rich Grise" <richgrise@example.net> wrote in message
news

an.2005.01.16.01.57.31.687726@example.net...

On Fri, 07 Jan 2005 00:29:02 -0800, Watson A.Name - "Watt Sun, the
Dark
Remover" wrote:

I'm still having problems with maintaining oscillation. But every
change I make takes the better part of an hour to find out. :-(

Chuck Harris said something like, "get it oscillating at a normal
frequency first, then fine-tune it" - at first, I thought, "Well,
yeah, if
you divide all the caps by, say, 100 - but would that mess with the
impedances?" And the part with the brains said, "No, the impedances
will
be the same, but at the higher frequency".

At least you'd be able to see it go through a cycle or two before the
coffee gets cold. ;-)

Good Luck!
Rich

Well, I don't drink coffee. But I took their advice and put a fixed
2.5V voltage source with a 200 ohm pot across it, and then connected the
JFET's source to the wiper. This allowed me to adjust the gate bias to
a fixed and somewhat exact voltage. Now I can set it to about 1.58VDC,
and it will sustain oscillations, and has been doing so all week long.

But it's kind og a waste to have to go to all that trouble to get the
FET to the right bias point. I'll have to again try to get it to
oscillate with the three diodes and resistor in series with the source.
Now that I know where the right bias point is. I'll have to play around
some more.

Hey, Rich. You live in Whittier? Have the rains filled up Whittier
Narrows and turned it and the recreation area into a giant mudflat?

Gizmofiddler · Jan 16, 2005

NOT free - you have to buy other crap you don't need and fulfill those
requirements first...

Art · Jan 16, 2005

Also: Vulgar responses normally indicate the intelligence level of the
respondant.
"JeffM" <jeffm_@email.com> wrote in message
news:1105832875.632325.269490@c13g2000cwb.googlegroups.com...

Posting 101 Lesson
for those who post at the New, Improved Google Groups

Most people do not read the group at Google
and do not see what you see.

Mark and Copy a little of the post to which you are responding
and Paste it into your post,
so that people who do not read the group at Google
have some bloody idea what you're talking about.
Spell checking is also good.

Clarence_A · Jan 16, 2005

"Art" <plotsligt@comcast.net> wrote in message
news:2sWdnYKP8v_eCnfcRVn-1g@comcast.com...

Also: Vulgar responses normally indicate the intelligence level
of the
respondant.
"JeffM" <jeffm_@email.com> wrote in message
news:1105832875.632325.269490@c13g2000cwb.googlegroups.com...
Posting 101 Lesson
for those who post at the New, Improved Google Groups

Most people do not read the group at Google
and do not see what you see.

Mark and Copy a little of the post to which you are responding
and Paste it into your post,
so that people who do not read the group at Google
have some bloody idea what you're talking about.
Spell checking is also good.

Top posters are totally ignored as well.

Mark Fergerson · Jan 16, 2005

ngdbud@hotmail.com wrote:

do the Transformers from the lin above a high voltage diode

Tesla coils are not the eldritch, occult devices they once were;
there are large groups of coilers that share data online.

To avoid a lot of disappointing thrashing around in the dark, I
suggest you go to www.pupman.com and go through the archives, then join
the mailing list and lurk a while before asking questions. Yes, there's
lots of advanced stuff in the archives, both theory and practice, but
also lots of "entry-level" data for your sort of project. The list
members range from total amateurs to degreed electrical engineers; they
are always ready to help anyone bitten by the Tesla bug.

Mark L. Fergerson

Mark Fergerson · Jan 16, 2005

Gizmofiddler wrote:

NOT free - you have to buy other crap you don't need and fulfill those
requirements first...

Not to mention installing their "helpful" toolbar...

Mark L. Fergerson

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