Post by byensradio on Feb 12, 2014 11:24:49 GMT -6
Hello fellow pirates!
We run a local pirate radio in the heart of Copenhagen, Denmark. Now when it comes to getting a license (which we're not going to do), I've been told that one of the things you pay for is that (the danish equivalent of) FCC comes out measures your transmitter to make sure that it's not faulty and broadcasting on other frequencies than the allowed FM (87,5 - 108 MHz).
Now we don't want them to come out and check this for us since we don't want a license, however we'd like to make sure that we don't broadcast on ANY OTHER frequency than the one we use, and especially not on any that are used by hospitals or air traffic.
Now, I've tried googling this, but it doesn't return much usable information. Is there a device that enables me to measure all the output frequencies. What I'm looking for is probably an oscilloscope. Could any of you point me towards some information regarding the use of such a device, and perhaps a list of frequencies used by hospitals and air traffic?
If you can't help, then thanks for trying, and have a good day. If nothing turns out, we might just call the danish FCC and ask them how they do it
Spectrum analyzer is what you would use to measure any harmonics or spurious emissions. Problem is they are very expensive so if you could borrow one that would be your best bet. Alternatively you could simply use an old VHF/UHF radio and tune around to ensure you are not on any other frequencies but of course that will not be very accurate. Harmonics will always be multiples of your main frequency so those would be the first to check. Spurs are usually found near your transmit frequency so you can check on a regular FM radio to make sure you aren't putting out garbage near your transmit frequency.
Post by byensradio on Feb 20, 2014 17:12:59 GMT -6
Thank you very much this is exactly the kind of information that I'm looking for. This is not our main priority at the moment since we only broadcast at low power. Again, thanks for the information!
Getting a spectrum analyzer doesn't really seem like an option since they are really expensive. I have been looking at a homemade spectrum analyzer made from a DVB-T TV usb dongle, but it is only able to reach down to 22MHz, do you think this would be sufficient?
Getting a spectrum analyzer doesn't really seem like an option since they are really expensive. I have been looking at a homemade spectrum analyzer made from a DVB-T TV usb dongle, but it is only able to reach down to 22MHz, do you think this would be sufficient?
Though not a true spectrum analyzer using one of those SDR radios (TV usb dongles) will be much better than using any other method as long as you use a shielded USB extension cable to it to block out interference from the computer itself.
I actually use one myself and have occasionally used it for that very purpose. Being able to see any noise you put out next to your frequency like spurs and seeing harmonic content at multiples of your frequency is very important to ensure all is working well. I even made a thread here for my little SDR setup, including an upconverter I made for it for listening into mediumwave and shortwave.
By itself covering down to 24MHz is plenty good enough. It is the high harmonic content you have to worry about most, everything above your frequency of broadcast, since most important services like police and airband reside there.
One tip: Be careful about using the SDR dongle so close to the transmitter since the dongles easily overload with high RF next to them. You may need to put the software gain all the way down to zero. I found even with a dummy load on my transmitter that when a few feet away from the dongle it still overloaded causing false readings to show up on the SDR software.
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