- February 9, 2007 at 8:13 pm #6826hjk8393Participant
Total posts : 1
From a hardware standpoint, what kind of equipment do I need in order to broadcast on an FM signal?February 10, 2007 at 5:23 am #14762SaGRGuest
Total posts : 45366
What do you want to do?
You could get away with a cd Walkman and a transmiter…February 10, 2007 at 4:35 pm #14767scwisGuest
Total posts : 45366February 11, 2007 at 12:11 am #14771RattanGuest
Total posts : 45366
It’s not hard to get an FM signal up and running. The challenge is having listeners with the extremely limited range. That boils down to.. Location. If you have neighbors close or maybe live in an apartment complex, it’s possible to have some listeners.
The actual hardware can be done with fairly little, depending on what you want to broadcast. Antenna can be very simple, I cobbled mine together from some wire and some wooden dowelling and a few pvc plumbing parts. Coax.. well, with the limitations, a bit of swr mismatch and some leakage aren’t really much of a problem, so anything including “leftover” cable from an old VCR can work. There *is* some possibility of even the tiny legal signal causing some interference in the aircraft bands above 108 mhz or TVI, so I felt a lowpass filter was a good idea. Again, it will be a bit of loss, but since almost any transmitter can put well over the amount of signal to exceed the legal limit, loss can be good if it improves your signal quality or reduces the chance of interference.
The transmitter itself, you can go really inexpensive like I did with a little mono kit that tunes with a screwdriver.. But the stability isn’t great and it can be hard to pick up with digital radios, so I’d suggest going at least for one with crystal controlled digital oscillator, PLL, or whatever.
And before the transmitter, I’d suggest an audio limiter to act as a “brick wall” so you don’t overmodulate. Other than sounding like crap, overdriving your transmitter with to high a level of audio can cause it to go way beyond the proper bandwidth and you can get “spurs” where parts of your signal are spattering far from the frequency you think you’re on. That can cause interference with other services, and as such get trouble.
But after that, it’s basically down to whatever audio gear it takes to put together the kind of show you want and get it out. That could be as simple as a cd player (as has already been mentioned), or you could put together a whole studio including automation.
So far as a listener audience, it’s less a matter of the transmitter/antenna hardware than location and how many possible listeners you have very nearby, if you want to be on the air and keeping it legal, though. If that’s what you’re going for, you need either a fairly dense and friendly neighborhood around you or maybe an apartment complex to make a go of it on FM.
To be honest, for legal operation on FM, and getting it up and running fast and easy, you’d probably be best to buy something like the “Whole House FM transmitter” and place it high in or on your house and run your audio up to it. The manufacturer says it’s part 15 compliant for FM, and it’s factory built and tested. They claim it has a minimum range of about 150 ft, and that’d cover at least close neighbors which is about what you can do with FM part15 legally. Placed high to get it above trees and obstructions, you’d probably get a bit better range, but not all that much. If you’re looking for ranges like 1/4 mile to a mile, then AM will be a better bet.
Going with a commercial unit would save you a lot of work, unless you really like the tinkering (like I do). The commercial option would be a lot simpler than what I explained above, and would probably give you at least as much legal range.
DanielFebruary 11, 2007 at 2:18 am #14773radio8zGuest
Total posts : 45366
Daniel gives good advice and I can’t add much except to perhaps tell you specifically what I have here.
I use a Ramsey FM-25 with a Alesis Nanocompressor (from ebay for $35) between my PC sound card and the transmitter. The FM-25 that I use is an older model and I built it from a kit. It easily covers my house with just a 4 inch antenna and sounds pretty good.
As Daniel mentioned, some sort of audio limiter/compressor is a good idea. With the Nanocompressor I get good audio and don’t have to constantly fiddle with the volume to get good performance. It is pretty much set and forget.
The range to expect from a legally operating part 15 FM transmitter is quite limited, around 200 feet or so. Even with this you want to produce the cleanest signal you can. Start for quality of your signal before you go for distance.
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