Re: [RCSE] Profi's with Rubber Duck's-another cause!

[Kevin O'Dell]

on 2/27/02 3:35 PM, Tony J. O'Hara at [EMAIL PROTECTED] wrote:

> Hi Kevin
> Thanks for your post!
> Regarding the FM "capture effect". I wondered abt that, so I asked an old
> friend and an RF design expert about a6 weeks ago. He told me that the FM
> capture effect property is higher with a larger modulation index a la
> broadcast FM stations. As he reasons that RC tx's probably use an index of
> abt half that, the capture effect wouldn't be as pronounced! That might
> also explain some of the interference (from other park flyers etc TX
> nearby) that were reported over the last few months! If there was a strong
> RC receiver capture effect wouldn't they be rejected!
> Do you have any knowledge of that?
> 
> Thanks & regards
> Tony
> Colorado
> 

Remember that part of the problem here is the distance from the offending to
the receiver vs. your transmitter to the receiverall these transmitters
operate at about 500 milliwattsdepending on the condition  of your
batteriesso, if in the process of flying you happen to fly the receiver
a bit closer to the offending transmitter than yoursyou will probably
get some hits...

Kevin O'Dell

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Re: [RCSE] Profi's with Rubber Duck's-another cause!

[Kevin O'Dell]

On 2/27/02 1:47 PM, "Tony J. O'Hara" <[EMAIL PROTECTED]> wrote:

> In doing some research on basic antenna propagation etc, I came across a
> section in the ARRL Antenna Handbook concerning ground effects on radiating
> antennas!
> Basically, they remind us that radiating RF waves that go downward towards
> the earth can be reflected and "interfere" with the direct radiated waves
> at certain vertical angles (and I think primarily at close distances!)  The
> amount of this refection is very dependent on the frequency, the antenna
> height and the "ground characteristics" However, it is possible that at
> certain vertical angles from the transmitter's antenna these waves subtract
> thus reducing the signal levels at the receiver, hence possibly causing the
> servo "jitter" and loss of control reported.
> I can also believe that a Rubber Ducky antenna could behave differently in
> this respect than the standard 1/4 wavelength whip, due to its different
> radiation characteristics.
> 
This effect is more associated with HF signalson VHF in our case, the
transmitter case and your body act as the counterpoise of the ground
planethe earth is too far away and is de-coupled from the antennayes
there can be some reflection of the signal that arrives at the rcvr at a
slightly different time...but the earth also absorbs part of that energy and
the RF that reaches the receiver is of slightly lower power than the signal
that came directly from the antennaFM receivers in this case will lock
on to the strongest signal..alsoraising the antenna straight up will
sometimes fix a problem because the side lobes of the radiation pattern are
the strongestalways remember that the worst radiation off of a verticle
is directly off the end of the antennaDon't point the end of the antenna
at the airplane..

Kevin O'Dell

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