I broadcast on 1620 AM and am quite happy with that, and I have no intention of adding an FM for mass consumption. However ....
I am now providing audio for the public access cable channel in my town. This costs me nothing except equipment to make it work, and I'm on in every household with cable TV which is pretty much everyone as there's no OTA TV around here. So I set up an AM receiver and some switching, cabling, etc to interface it to the TV system over at City Hall (the only thing they broadcast on public access is city council meetings twice a month). The trouble is AM reception in the room where the equipment is located is marginal at best. The Dayton Am monitor I set up originally was so sensitive it picked up noise from every piece of equipment in the room. After playing around with varying radios, getting a long cable to move the radio far away from any equipment, it's passable, but not what I consider good. This room has a rack full of TV equipment, TV set, several computers, ancient flourescent lights, etc so the interference is horrible. Reception is fine in other parts of the building, but since it's a 100+ year old historic building, messing around in it too much is frowned upon. If I could put the receiver in another room and run 100+ feet of cable, I'd be good but that physically wont' work out. I do know that the interference is getting in through the radio reception, not in the audio cables/switching from the radio to the gear.
I'm considering FM. I've done no research at all on FM Part 15 transmitters. All I know is range is quite limited and the rules are for field strength not input power. City Hall is about 450 feet from the attic window where I have my AM transmitter set up. It would be easy to set up an FM transmitter in this same window. It's line of sight from my attic window to city hall, although by site a straight line would hit just above the office where I would set up the receiver, but it'd be mighty darn close. Could I expect a Part 15 FM transmitter that doesn't cost a fortune to hit City Hall 450 feet away? The receiver would be located up out of harms reach from bystanders and I could set up an indoor antenna if necessary. I don't need stereo, but I need a solid signal and I think FM would easily get me out of the interference from stuff in the room zone.
Is this a realistic expectation for an FM transmitter? And what would anyone recommend? this would basically be an FM studio to city hall audio link that I would not advertise the frequency, etc.
I have a solid as heck AM signal there -- sounds fantastic once I get out of the room full of gear, but all that equipment is just too much interference competition for my signal.
Tim in Bovey
Iron Range Country
make a tuned magnetic loop and place it outside of the building along with a preamp and bandpass filter. you'll pull in that flea power am like a big boomer and null out all the interference. the other thing is a wireless data link and a couple barix boxes or a nix pc running streaming software.
http://www.radiolabs.com/products/wireless/point-to-point-bridge-circular.php
An FM transmitter at USA allowed field strength with line of sight with no obstructions would make it 450ft with a car radio for sure,with no other station interfering. Maybe a hi-fi separate component tuner where FM sensitivity would be around 3uV for at least 30dB quieting would get it, not with a typical portable or other radio like a boombox. Transmitters?...CCrane, Wholehouse, Decade CM-10,etc. all are FCC compliant for the max allowed in the USA and don't cost a whole lot. The Decade is probably the best of them.
Mark
Send an internet stream... or use a part15 5.8ghz wifi system to stream direct. They are pretty affordable. If you use a video sender system (ebay for like $50) with a directional antenna, you should get a clean signal feeding the audio portion only.. just an idea.
Tim in Bovey's situation sounds like a very lucky one, given the line of sight.
Neil has posted in the past about infra-red or L.E.D. point-to-point links for line-of-sight solutions.
I would think AM would be a last choice for making a link.
Probably the Decade FM Transmitter would be excellent, but also to mention the Ramsey 25B FM which has an RF output adjustment that goes above typical levels to overcome obstacles like walls and windows. It's a good kit.
One guy I know uses 49MHz for S.T.L. work.
Hey, and maybe the cable company could enable an upstream solution so you could feed an "out-of-band" signal into your cable for demodulation over at their location.
here is a NLOS link that runs 900 mhz
http://3gstore.com/product/4601_long_range_ethernet_bridge_kit.html
and here...
cheap too as far as these types of links go.
Maybe someone could lend you
an FM broadcast band DX tuner and
a part 15 certified FM transmitter.
You could then just give it a try.
I say this because sometimes radio
enthusiasts have this kind of stuff
just sitting around not in use. I guess
it depends on how many radio people you know
locally. (I lent out a C Crane FM transmitter a
couple of years ago to a friend and he is still using it.)
If this could be done you could then try the FM BCB
link and see if it worked.
An old 1980s analog FM tuner would be good. I used
a Technics ST-9030 as an indoor program link. I believe
Carl uses the same tuner for KDX's radio link.
You would have to watch for band openings, though.
An E-skip or tropo cochannel signal could cover up
your link transmission. It's a little tricky - sometimes
it doesn't work. My Technics 9030 was feeding an
SS-Tran AMT-3000. There was some kind of interaction
and the FM tuner was overloaded somehow. It seems
unlikely that it would happen from an AM transmitter
but it did. I had to have the FM receiving antenna about 10
feet away from the tuner for it to work. But I guess no two situations
would be the same.
In any case, please let us know what happens.
Bruce, DOGRADIO 1020 kHz Carrier Curren
P.S. By the way -your set-up is very impressive!
Great job!!!
When using an FM transmitter/receiver combination with the stereo generator turned on, and with some of them you can't turn it off,
the 19kHz pilot frequency will modulate your AM carrier out too far on both sides and put whistles two spaces on either side of main.
It's happening now with my C.Crane being used as a STL.
The Technics tuner mentioned by MICRO1700 has a filtered output for recording which attenuates the pilot tone so it will not interfere with tape bias, and this is also good for AM radio feed.
I printed out the schematic for the C.Crane and was going to figure out a way to kill the stereo pilot, but the way it is drawn it is hard to figure out which overlapping lines connect and which are just crossing each other, because the teensy dots signifying a connection are smeared and hard to verify.
The Ramsey 25B allows turning off the stereo, as does the Wholehouse 2.0.
Decade makes a mono only unit.
The problem is that an FM Part 15 transmitter is not going to have 450 feet range reliably. I'd go with an Internet wireless link - you can use directional antennas and can have up to 1 watt power with a 6db antenna. Plus there's plenty of hardware options. An alternative would be some sort of proprietary intranet link, such as Trango (they claim 10-20 mile ranges with the appropriate antennas, and depending on the frequency being used - you can even go non line of site with 900 Mhz equipment).