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 signals....on VHF in our case, the transmitter case and your body act as the counterpoise of the ground plane....the earth is too far away and is de-coupled from the antenna....yes 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 antenna....FM receivers in this case will lock on to the strongest signal......also....raising the antenna straight up will sometimes fix a problem because the side lobes of the radiation pattern are the strongest....always remember that the worst radiation off of a verticle is directly off the end of the antenna....Don't point the end of the antenna at the airplane.. Kevin O'Dell RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
