Please help-Antenna questions

[Eric R Snow]

Greeting Radio Folks,
I have looked all over usenet and our local library but can't seem to
find the answers... I work in an all metal building, sort of like a
Quonset hut. I wear hearing protection all day that has a radio built
in. With the big roll-up door closed FM radio reception is terrible.
Is there some kind antenna I can use to gather signals outside the
shop and re-radiate them inside? Something passive would be best but
active would also be acceptable. And since I listen to several
different stations it also needs to broadcast all stations at once
because I need to stay at whatever machine I'm running and can't run
back and forth to change channels constantly. Hope I'm not asking too
much...
Thank You,
Eric R Snow,
E T Precision Machine

 

[Anthony Fremont]

Eric R Snow wrote:

Greeting Radio Folks,
I have looked all over usenet and our local library but can't seem to
find the answers... I work in an all metal building, sort of like a
Quonset hut. I wear hearing protection all day that has a radio built
in. With the big roll-up door closed FM radio reception is terrible.
Is there some kind antenna I can use to gather signals outside the
shop and re-radiate them inside? Something passive would be best but
active would also be acceptable. And since I listen to several
different stations it also needs to broadcast all stations at once
because I need to stay at whatever machine I'm running and can't run
back and forth to change channels constantly. Hope I'm not asking too
much...

If you search Google for "Faraday shield", it may help you better
understand what's happening. You need to get signal from the outside to
the inside of the building. The easiest way to do this is with an
external antenna. Since you probably don't want to drag a wire around
with you all day, you may have success with using two FM antennas
connected together, one outside and one inside. The outside antenna
will pick up signals and pass them thru the cable to the inside antenna
which will then re-radiate the signal. This is a passive system and
will result in some signal loss, but that can be overcome to an extent
by using a good outside antenna with some gain and perhaps an inline
20-30dB booster amp. I doubt you'll need the amp if you use something
resembling resonant antennas. Since you're in a shielded room your
receiver will be quite sensitive since the only signals present are the
ones generated inside the building, therefore it should work fine IMO.
Depending upon the strength of the stations you are trying to hear, you
may have success by simply passing some coax outside and exposing a
couple of feet of the center conductor at each end.

michael

 

[dB]

Eric R Snow <etpm@whidbey.com> wrote in message

I have looked all over usenet and our local library but can't seem to
find the answers... I work in an all metal building, sort of like a
Quonset hut. I wear hearing protection all day that has a radio built
in. With the big roll-up door closed FM radio reception is terrible.
Is there some kind antenna I can use to gather signals outside the
shop and re-radiate them inside?

Yes. You need two ordinary f.m. broadcast band antennas. Mount one
outside the building and one inside. Join them with whatever cable
they were designed to be usd with. The signals received on the
outside one will be re-radiated by the inside one.

 

[John Fortier]

"Anthony Fremont" <spam-me@houston.rr.com> wrote in message
news:jQckb.73177$7_1.35613@twister.austin.rr.com...

Eric R Snow wrote:
Greeting Radio Folks,
I have looked all over usenet and our local library but can't seem to
find the answers... I work in an all metal building, sort of like a
Quonset hut. I wear hearing protection all day that has a radio built
in. With the big roll-up door closed FM radio reception is terrible.
Is there some kind antenna I can use to gather signals outside the
shop and re-radiate them inside? Something passive would be best but
active would also be acceptable. And since I listen to several
different stations it also needs to broadcast all stations at once
because I need to stay at whatever machine I'm running and can't run
back and forth to change channels constantly. Hope I'm not asking too
much...

If you search Google for "Faraday shield", it may help you better
understand what's happening. You need to get signal from the outside to
the inside of the building. The easiest way to do this is with an
external antenna. Since you probably don't want to drag a wire around
with you all day, you may have success with using two FM antennas
connected together, one outside and one inside. The outside antenna
will pick up signals and pass them thru the cable to the inside antenna
which will then re-radiate the signal. This is a passive system and
will result in some signal loss, but that can be overcome to an extent
by using a good outside antenna with some gain and perhaps an inline
20-30dB booster amp. I doubt you'll need the amp if you use something
resembling resonant antennas. Since you're in a shielded room your
receiver will be quite sensitive since the only signals present are the
ones generated inside the building, therefore it should work fine IMO.
Depending upon the strength of the stations you are trying to hear, you
may have success by simply passing some coax outside and exposing a
couple of feet of the center conductor at each end.

michael

I've actually used the two antenna method of getting a wanted signal inside
an electronically sealed space, in my case a steel module on an offshore oil
production platform where UHF communications ere required but where the
intrusions of volatiles would have been disasterous..

There is another method of diseminatin the internal siganal and that is
leaky feeder. Connect the external antenna to the internal space, with or
without the booster amplifier, using a length of deliberately poor co-axial
cable, leavingthe end of the cable unterminated. This has the advantage of
allowing you to string the cable into all the areas of the internal space
you will be occupying, without th intrusion of a VHF antennal into the
internal space.

It's important to stand the leaky feeder off from the conductive
construction of the building hanging the cable from the ceiling using tie
wraps is quite effective. About 6" of separation should be sufficient.

You will need to experiment a bit, since the internal reflections inside the
building will affect the impedance of the cable. A leaky feeder system may
actually work better with the feeder cable terminated in its intrinsic
impedance, although this is not common.

Also, you can expect nodes and antinodes to form inside the building where
reflections add to each other or cancel each other. Your reception may vary
as you move around.

John

 

[Fred Abse]

On Sat, 18 Oct 2003 07:19:53 -0700, Eric R Snow wrote:

Greeting Radio Folks,
I have looked all over usenet and our local library but can't seem to find
the answers... I work in an all metal building, sort of like a Quonset
hut. I wear hearing protection all day that has a radio built in. With the
big roll-up door closed FM radio reception is terrible. Is there some kind
antenna I can use to gather signals outside the shop and re-radiate them
inside? Something passive would be best but active would also be
acceptable. And since I listen to several different stations it also needs
to broadcast all stations at once because I need to stay at whatever
machine I'm running and can't run back and forth to change channels
constantly. Hope I'm not asking too much...
Thank You,
Eric R Snow,
E T Precision Machine

Google for "passive deflector". may not be quite what you want, but will
point you the right way.

--
Then there's duct tape ...
(Garrison Keillor)
nofr@sbhevre.pbzchyvax.pb.hx