Home › Forums › temp › Part15 FM, another approach to attempting to “verify” compliance. › OK on FM only
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It definitely would have some effect on FM measurements as well if one used a larger reciever antenna, Neil. Not sure how to precisely determine how much it would, but I’d bet on it.
As I understand the spec for FM, it is 250 microvolts with a 1 meter long antenna located 3 meters from the transmitting antenna, basically. They also have other field strengths they can use at other ranges. I’d assume for the purpose of keeping people from being able to just put an FM xmitter antenna too high up to be measured by that method.
Now, the device they’re using has to be a reciever of some sort, since I believe it’s tuned to your frequency. If it wasn’t, it’d also be picking up whatever else was on the air nearby which might include regular broadcast stations, cell phone towers, tons of stuff.
I have to admit, I’m a little shakey on what s-meters *really* measure anyway. Microvolts at the detector stage? I just don’t know. Others here know much more about that matter than I do.
Now, so far as I understand the matter, AM is not required to comply in the same fashion as FM. But I’m purely a layman, not an engineer and certainly not an expert on FCC matters.
AM has it’s own restrictions, as you mentioned.
For the measuring idea I mentioned (using a reciever s-meter) to actually be near accurate, yes, one would pretty much have to have someone with a calibrated s-meter like they talk about in that spec, and compare the readings. Even then I’m sure it wouldn’t stand up in court or anything. My idea was strictly for a quick rough and ready check to try and see if they were drastically going over the limits for FM part15.
The readings I mentioned would not have much bearing on a compliant AM station so far as I know.
Not to say an s-meter reading off a nearby reciever doesn’t have any uses, though. As a quick relative check of if your station is “getting out” normally, it’s handy. Like if you noticed the s-meter reading was lower than normal, and you haven’t changed the reciever antenna, then something could be wrong at your xmitter antenna and it’d be a good idea to check everything. I think having some sort of reciever on to hear how your signal actually sounds is always good anyway. It can sound great on the headphones off your mixing board, but what’s going out can still be messed up for any of a number of reasons.