How do I get the signal to the antenna?

BrentSpomer · #1 09-06-2007, 06:32 PM

In my application I need to have the input device to my FM25B located about 1/4 mile from the antenna. As I see it, two of my options include stringing 1/4 mile of wire between the input device and the transmitter and have a short piece of coax or put a linear amplifier on the output of the FM25B, run 1/4 mile of coax and adjust the output such that the antenna's field strength meets the 250uV @ 3 meter FCC requirement.

I know it sounds crazy but it is the problem I'm faced with. Any ideas or thoughts?

kb3cs · #2 09-06-2007, 07:40 PM

sure there isn't a way to redo things so the 1/4 mile separation
of the source and transmitter is not necessary?

otherwise, the first thought is the telephone company has been
moving audio signals around over long distances for many years.

radio8z · #3 09-06-2007, 10:23 PM

I have something in mind but it would depend on your program content. Two questions:

Does it have to be stereo?

Can the program be interrupted for a few seconds every three minutes?

Neil

kb3cs · #4 09-07-2007, 07:56 AM

8-track or Cart .. hadn't thought of that.

how about this: a removable hard drive can store quite a bit
of audio.

and this: there now exists devices which store lots and lots
of audio and can play it in a big loop. MP3 anyone?

BrentSpomer · #5 09-07-2007, 11:58 AM

It doesn't have to be in stereo but it would be nice if it was. I was thinking of a wireless feed on the CB frequencies that would input to the FM transmitter and maybe that is your thought as well, Neil. But phone lines run some distance but they are at a pretty high voltage relatively speaking. I was thinking I could feed from the mixer to some step up, run the 1/4 mile and step it back down again to meet the requirements of the FM25B. BTW: thanks for not laughing - at least in your responses.

radio8z · #6 09-07-2007, 01:33 PM

Brent,

I was thinking of putting the transmitter where you want and using FRS radios for the audio link from your source. They are cheap ($50 per pair range), have decent range (2 miles or so unlicensed line of sight), have tone squelch, but it would be bandwidth (3kHz or so) limited. Also, the are required to automatically shut down after about three minutes which would mean unkeying periodically to prevent timeout.

You are in a position to judge whether this is workable or not and you might want to do a search on "FRS radio" for more info. Just a suggestion.

Otherwise, running a 1/4 mile of coax to the antenna should work but you would have to deal with physically protecting the wire.

Neil

radioc · #7 09-07-2007, 08:31 PM

Here are a few thoughts, but not (yet) a specific solution.

You might try a "wireless music system" type of consumer audio or PC accessory.

I think that companies like Logitech and others make wireless accessories that take an audio output from either a hi-fi (via RCA plugs) or PC (via USB) and transmit it over either 900 MHz or 2.4 GHz to a receiver that has an audio output. I have an old Logitech unit, although it's advertised range is only 330 feet. I am sure that here are others out there.

I also recall seeing units by Linksys and DLink and Slim Devices in places like Best Buy or online that use Wi-Fi to link a PC to a stereo.

There may also be some sort of Wi-Fi solution. I have seen articles on the internet of people building inexpensive yagi antennas for Wi-Fi to achieve amazing ranges that are much longer than your application. Someone published a how-to article of building one inside a Pringles can.

If you want to go with a wired or cabled approach, you could use cheap Cat 5 cable and a pair of baluns that take stereo audio for a pair of RCA plugs and convert it to a single RJ-45 plug. The same balun at the other end converts back to RCA output. I recall seeing that for about $100 and I recall the range was at least a couple of thousand feet. Here's a link for one that I just googled:

http://sewelldirect.com/Intelix-Audio-Balun-2-RCA.asp

I have no idea whether it is any good or whether the dealer is reputable or not, but it illustrates the concept.

Here's a long range Bluetooth device:

http://www.aircable.net/host-xr.html

Again, I can't vouch for these, it's just something I googled or heard about.

Good luck.

Voltz · #8 09-07-2007, 11:55 PM

1/4 mile isn't that far. I played around with some of those wireless speakers. They work in the 900 mhz. region. The speakers have the rcvrs (L & R) and put out near line level to the amps in the speakers..

As long as you have a good, clear "Line of Sight" path between you and the xmtr, this could work for you..

I used a couple of these..

One for the xmtr and one for the two rcvrs at the FM xmtr. I built a "Y" cable to connect the rcvrs to the antenna. The output of the rcvrs are high impedence so it matched the xmtr input really nice. Set the levels with the pots on the board. (L-R)

The xmtr and rcvrs operate on 12 volts D.C. I figure that you'll have power at the FM xmtr end. The studio end would need a 12 volt D.C. supply of some sort also..

Something like these..

kc8gpd · #9 09-10-2007, 09:22 AM

you could always modify a 900mhz wireless speaker setup. you can't mess with the Tx section, but you can with the Rx section. putting a high gain yagi on the receive end will increase the range. you can also sit the Tx in front of something reflective to give you a little more gain in the desired direction.