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This is a spectroscopic picture of the RF
activity close to the 2m repeater frequencies. It shows a frequency window on the horizontal axis and RF power on the vertical. We have 3 things happening here, 2 of which are problematic to the repeaters operation. So... what's happening: 1- The big blob at around -40 dBm is the repeater's output being keyed by the input 600 kHz lower. 2- The noise floor is very polluted and is shown about -80 dBm. This is too high and the source was a defective power pole, fixed by TXU. Normally around -100 to -90 dBm in the area. 3- The "main culprit" of the interference was the noise spikes (all over the place), with the highest spike centered very close to the repeater's input. It's actually the noise keying up the repeater!!! |
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Here the noise floor problem was already
corrected by TXU, you can see that it's back
to around -90 dBm average. The "messy" spikes is what was creating the background noise on the repeater for several days during early April 2004. As you can see on the picture, the most offending noise was located right at 146.277 MHz, which is basically the exact frequency of our repeater input (146.280 MHz). It was strong enough to key up the repeater and also mix with the FM signals from people talking into the machine, garbling their transmissions. |
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Here is Jim, W5JBP opening the "noise
box". It's an old TV distribution
system
located in an apartment complex near the repeater site. The FCC officers contacted the apartment management and informed them that the unit got turned off and that they can't turn it on again before a full service and maintenance check is performed. Thank you Jim, TXU, FCC and all hams involved in finding this little critter. |
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Another look at the "noise box". |