Rfi caused by AC units in dome
In oct05 it was found that the ac units in the gregorian
receiver room produce rfi. It was seen at 327 Mhz and 430Mhz. The rfi consists
There is a 1 Mhz comb. The individual spikes are not resolved in a 95 hz
The comb can drift by up to 30 Khz/hour.
At 327 Mhz it got up to 8 times the noise power in a 95 hz channel.
The birdie does not go away if you turn off the ac with the remote
unit. This will cause it to jump in frequency.
The birdie will go away if you turn off the breaker to the ac units. This
shows that the birdie is coming from the digital control units of the AC.
There are two combs that drift at different rates. Each ac unit (there
are two in stalled) produces its own comb.
Attempts at fixing the problem:
There is a switch to turn off the power to the old AC unit. This will make
the birdie go away. It also causes the room to heat up.
We tried putting capacitors in the line that went down to the compressor
on the service platform. This made little difference.
We will eventually replace the digital portion of the AC unit with an analog
one. The units will also be moved up on top of the dome.
Pages that deal with the comb: