you experienced intermittent interference?
Do you have a communications
mast near to your site?
If so, the following is
probably the reason:
Some of these communication
systems emit short bursts of radiation at regular intervals between similar masts or aerials and it is just unfortunate if
a model happens to be in a particular spot when it occurs.
The effect of this interference
is to generally cause a receiver to drive one or more servos out of position for a period whilst the model is passing through
a segment of airspace. This is a particular hazard if the model is fitted with a PCM receiver since the 'glitch' can cause
the receiver to go into 'failsafe' lockout with disastrous results.
This interference is caused by dishes mounted
on the mast 'talking' to similar dishes mounted on other masts.
The radiation from these masts, although so far removed
from our frequencies as to have apparently no possible effect on the 35 MHz band, does somehow directly effect the microprocessor
in modern receivers. For the technically minded, the transmissions are in the order of 2 - 3 GHz in frequency, and consequently
cannot and will not be detected by any of our available 35 MHz band frequency monitors. The transmission strength is in the
order of 25 watts so it can easily swamp our receivers which are operating on a maximum of 100 mwatts transmitted power.
So how is it that at certain times no interference is detected?
The theory put forward is
that, although the microwave frequencies are so high that there should be no possibility of them interfering with the 35MHZ
band there is the possibility that perhaps two or more frequencies are 'beating' together and the resulting harmonic is the
one that is causing the interference. This certainly could explain why sometimes we do not have any trouble as these particular
frequency transmissions are not all active at the same time.
We think this is the
problem we had at our last flying site (Beaumont Leys), with the mast on top of the Police Station.