Discussion in 'VHF/UHF - 50Mhz and Beyond' started by K7IHI, Sep 1, 2014.
Are you sure one or more repeater users aren't using one of these:
Are you sure you're not just hearing the "PL" (CTCSS) being transmitted by the repeater? With a small communications speaker that's usually very soft, but if you use headphones or a large speaker, it can be rather disconcerting even while intentional.
Nope, this is a constant 60 cycle type hum that is there anytime someone keys up and stays there until they un-key. It sounds like they have a grounding problem at the one repeater although at one of the others I heard this at I heard them talking about a damaged antenna they had to replace and the club was saving up money to order one (evidently this was a repeater antenna and not your regular vertical that most of us use). It's unfortunate that the 146.980 repeater has the hum because it's probably one of the busiest repeaters in the Portland area and is used by a lot of nets as well as individuals.
I haven't heard it, but if it's really 60 Hz it's likely a ground loop issue and has nothing to do with the antenna and everything to do with an undesired ground path in the transmitter's modulation system. This is the kind of thing that can usually be discovered and fixed in an hour, if someone who knows the equipment simply visits the site and has ears.
I wouldn't think anything in the immediate Portland area should be very inaccessible.
A 60 HZ signal that you hear on your radio may be a problem with your station.
Your radios low pass PL audio filter should filter out all PL tone frequencies, Including 60 cycle.
If you are picky for me using the term "PL", Join the Old Farts Club.
Most amateur FM gear will pass 60 Hz and all the CTCSS tones pretty well if you use hi-fi headphones or a big speaker (not the one in the radio).
Or of course some hear a hum and think it's 60 Hz when it's really 120 Hz (power supply ripple problem). Easy to mistake one for the other, they're both really low frequencies.
If you do really hear a tone on the repeater, It is most likely the PL Tone Deviation on the repeater is to wide, or the Hum is coming from the Incoming station, Because the PL level is to high and the repeater passes instead of filtering it. Or Your station has problems.
PL on the output of a repeater is really not needed. I like to hear every transmitter that is transmitting.
If in doubt get the frequency counter and O-scope out.
I may not be describing it very well, but It's not a tone, it's a audible hum that only comes on when someone is keyed up through the repeater. They don't even have to be talking. I know what a tone sounds like and know what the CTCSS tones sound like. And though it may not be an actual 60 hz tone, I used that as an example since most people reading this should know what a 60 hz hum sounds like. The problem may be in the antenna, which I believe is up on one of the Sylvan Hill radio broadcast towers, which means it's pretty high up and not just anyone has access to it. The transmitter site itself may also have restricted access although for as long as I've heard this one repeater with this noise, I would think that they would have been able to get in and take a look at it.
I've not talked on the repeater myself (I very rarely talk on a repeater) but I do listen to a lot of them in the area. It is also possible that some of the other repeaters with noise are linked to a repeater with a problem since so many of the Portland repeaters seem to be linked together and when someone is talking on one it is also being relayed to the others. If I get a chance when I hear someone talking on it that seems to know the repeater I'll ask them, but usually it's nets or regular users chatting on the frequency. Mostly though I just jump past it when someone is talking since it's so annoying to my ears.
Are you very sure? CTCSS tones range from 67 Hz (which sounds exactly like an "AC hum") to 250.3 Hz (which doesn't, it's a much higher pitch). The lower-pitched tones like PL XZ, which is 67.0 Hz, sounds just like a hum -- I don't see how anyone could really tell the difference by just listening to it.
And many repeaters generate CTCSS, they do not "re-transmit" it, so as long as the repeater is transmitting -- whether it's actually repeating anyone's signal or not -- the tone should be there.
What is the CTCSS frequency used by the repeater you're discussing?
Addendum: I just looked up 146.980 in Portland, and that repeater is listed as having a PL frequency of 123 MHz both in and out, which means it generates its own CTCSS tone at 123.0 Hz any time the repeater is transmitting.
123 Hz sounds very much like a standard "power supply hum," which is 120 Hz. If the CTCSS deviation is a bit higher than normal, it could very much sound like a hum.