On 24/01/2020 20:34, Bill Wright wrote:
On Friday, 24 January 2020 02:37:09 UTC, The Natural Philosopher wrote:
I fly model planes. The barbed wire fence glitch is well known

I haven't heard of this and I'm very interested. Please tell us more.

back in the days of 35MHz NBFM it was well known that flying at
reasonable range over rusty fences would cause momentary loss of or
corruption of signal. Generally seen as a massive twitch on all flight
surfaces and a loss of throttle.

35MHz was never the best of mediums anyway but club fliers got to know
that certain places were prone to this effect.

Whether it was multipath, or diodic mixing causing intermodulation I
cannot say - or both.

For more information, the signal modulation on FM RC is/was a series of
frequency excursions marking the edges of a series of channel frames
about 1ms long with the lengh of a frame being the position of the
associated servo - in the range of 0.5ms to 1.5ms. A very long frame -
10ms or so - was used as a synchronisation frame.,

This form of modulation has only one benefit. A simple CMOS shift
regsiter could decode the pulse train to the servos.

But as an interference rejecting schema it was pants. Loss of a frame
edge meant one channel got two channels worth of info and the subsequent
channels got te wrong info.

Hence the massive glitch/twitch.


Bill



--
"It is an established fact to 97% confidence limits that left wing
conspirators see right wing conspiracies everywhere"