Talkative Antennas

R

Ron Hubbard

Guest
With the glut of sci-fi shows on at the same time, I've set up
two VCRs and two antennas in a single room. I found that the
two antennas affect each other: by changing the settings on one
antenna it will change the picture quality on the other VCR and
TV.

I always thought antennas were passive devices and didn't
radiate any signals. Does anyone know of a way to reduce the
interference between the two antennas?

Thanks.
 
However, if you place one antennae in direct line between another and the
signal source they will affect the quality of the received signal at the
second antennae. Also, if the antennae are mounted on the same mast the
answer is that you are relocating both antennae. BTW you do not state if
these are roof mounted, inside antennae, or what. I presume they are roof
mounted and separate antennae having absolutely separate transmission leads.
"Ron Hubbard" <hubbard-ron@hotmail.com> wrote in message
news:bocq4c$1bp8rr$1@ID-43450.news.uni-berlin.de...
With the glut of sci-fi shows on at the same time, I've set up
two VCRs and two antennas in a single room. I found that the
two antennas affect each other: by changing the settings on one
antenna it will change the picture quality on the other VCR and
TV.

I always thought antennas were passive devices and didn't
radiate any signals. Does anyone know of a way to reduce the
interference between the two antennas?

Thanks.
Click to expand...
 
In article <bocq4c$1bp8rr$1@ID-43450.news.uni-berlin.de>, Ron Hubbard
<hubbard-ron@hotmail.com> writes
With the glut of sci-fi shows on at the same time, I've set up
two VCRs and two antennas in a single room. I found that the
two antennas affect each other: by changing the settings on one
antenna it will change the picture quality on the other VCR and
TV.

I always thought antennas were passive devices and didn't
radiate any signals. Does anyone know of a way to reduce the
interference between the two antennas?

Well you're sucking the TV signal out of the air with the antenna aren't
Click to expand...
you. Once one antenna has taken its signal, there isn't as much left in
the air for the other antenna.

--
Tim Mitchell
 
There are two factors here. If they are sharing the same feed, the effect
and match of the antennas will either sum or go differential, depending on a
lot of complex factors with phase delays. Infact the absolute figures would
be hard to calculate. When antennas are stacked or worked in an array, there
is a lot of careful matching that must be done to make sure that their
impedance is matched, and that the phase track through the spectrum that
they are to be used.

If you put two antennas in approximation to each other, they can certainly
effect each other. This has to do with mutual inductance to some degree.
Each antenna is resonant and is a tuned circuit. One will have an effect on
the other, as they may act as a reflector or diverter to each other. In
most cases they would have to be placed more than four times the wavelength
from each other in order to not have a measurable effect on each other. In
practice, this can also be indecisive. If the signal band to be received is
coming in at 3 meters wavelength, they should be placed at about 12 meters
from each other.

There is also the effect of the local oscillator in the receiver radiating
to some extent back up the antenna. Most of the receiver's local oscillator
works at about 10 to 20 mw power level. It is supposed to be isolated and
shielded. But, in many receivers this is not always perfect. In this case
the local oscillators between two receivers may induce some interference to
each other depending on the channels being watched, or stations listened to.
There are many aspects concerning radiated harmonic frequency generation to
also be considered.

What I would do for two receivers in the same location, is work out a way to
share the same antenna. This can be a bit complicated at times, if it is a
radio, but there will be less problems, than having two antennas in the same
area, and there will be a space savings.

--

I have heard some TV servicemen saying "One antenna is sucking from the
other". There is an essence of truth here...


--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"Ron Hubbard" <hubbard-ron@hotmail.com> wrote in message
news:bocq4c$1bp8rr$1@ID-43450.news.uni-berlin.de...
With the glut of sci-fi shows on at the same time, I've set up
two VCRs and two antennas in a single room. I found that the
two antennas affect each other: by changing the settings on one
antenna it will change the picture quality on the other VCR and
TV.

I always thought antennas were passive devices and didn't
radiate any signals. Does anyone know of a way to reduce the
interference between the two antennas?

Thanks.
 
"Tim Mitchell" <Tim@sabretechnology.co.uk> wrote in message
Well you're sucking the TV signal out of the air with the antenna aren't
you. Once one antenna has taken its signal, there isn't as much left in
the air for the other antenna.
Tim Mitchell
-----------------------------
Click to expand...

You are joking..... right?
 
In article <vqliqj2jikg204@corp.supernews.com>, Sofie <sofie@olypen.com>
writes
"Tim Mitchell" <Tim@sabretechnology.co.uk> wrote in message
Well you're sucking the TV signal out of the air with the antenna aren't
you. Once one antenna has taken its signal, there isn't as much left in
the air for the other antenna.
Tim Mitchell
-----------------------------

You are joking..... right?


yes, I was joking.
Click to expand...

I shouldn't do things like that, it will go into Google and people will
be quoting it in their physics essays.
--
Tim Mitchell
 
"Ron Hubbard" bravely wrote to "All" (05 Nov 03 22:34:53)
--- on the heady topic of "Talkative Antennas"

In order for an antenna to receive it must also transmit. You can't have
one without the other!


RH> From: "Ron Hubbard" <hubbard-ron@hotmail.com>

RH> With the glut of sci-fi shows on at the same time, I've set up
RH> two VCRs and two antennas in a single room. I found that the
RH> two antennas affect each other: by changing the settings on one
RH> antenna it will change the picture quality on the other VCR and
RH> TV.

RH> I always thought antennas were passive devices and didn't
RH> radiate any signals. Does anyone know of a way to reduce the
RH> interference between the two antennas?

RH> Thanks.

.... No electrons were harmed in the posting of this message.
 
"Sofie" bravely wrote to "All" (06 Nov 03 14:30:10)
--- on the heady topic of "Re: Talkative Antennas"

So> From: "Sofie" <sofie@olypen.com>

So> "Tim Mitchell" <Tim@sabretechnology.co.uk> wrote in message
Well you're sucking the TV signal out of the air with the antenna aren't
you. Once one antenna has taken its signal, there isn't as much left in
the air for the other antenna.
Tim Mitchell
So> -----------------------------
Click to expand...

So> You are joking..... right?

It's really funny too!

.... Well I defragged my TV and went all the way back to basic cable!
 
In order for an antenna to receive it must also transmit. You can't have
one without the other!
Click to expand...
The only thing it is fed to transmit is leakage of the local oscillator in the
tuner of the reciever, this should be quite low in the near 100% of recievers
using at least one TRF stage and even lower when any kind of signal amp is used
(towards the reciever that is) (I don't know if I was joking)

JURB
 
"JURB6006" bravely wrote to "All" (08 Nov 03 01:55:51)
--- on the heady topic of "Re: Talkative Antennas"

JU> From: jurb6006@aol.com (JURB6006)

In order for an antenna to receive it must also transmit. You can't have
one without the other!
Click to expand...
JU> The only thing it is fed to transmit is leakage of the local
JU> oscillator in the tuner of the reciever, this should be quite low in
JU> the near 100% of recievers using at least one TRF stage and even lower
JU> when any kind of signal amp is used (towards the reciever that is) (I
JU> don't know if I was joking)

The EM wavefront induces a current along the length of the antenna which
is converted to an EMF at the feedpoint and on down the transmission
line. However, that same induced current also sets up an EM wavefront
that interacts with the original but only delayed in time.

We don't need to talk leakage as note that the 2 local oscillators may
naturally interact when brought into proximity. I forget what this
effect is called but the closer they are brought together the stronger
the tendency to become synchronized if they are nearly the same
frequency. You can easily observe this effect with a couple toy
walkie-talkies both set to receive. The noise signal quality changes as
they are brought closer together.

Asimov
******

.... Which sparks some mnemonic circuitry.
 
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