Im still in the process of putting the station together. I was looking for some wire to connect from my audio source to the transmitter outside. All I need now is a waterproof box, run the wires and connect and run some counterpoise and tune the antenna.
Im still in the process of putting the station together. I was looking for some wire to connect from my audio source to the transmitter outside. All I need now is a waterproof box, run the wires and connect and run some counterpoise and tune the antenna.
I found at Home Depot "Sprinkler wire" made by Carol. It is 18 gauge and 5 conductor and 100 ft of it goes for about $21. It is suitable for direct burial, sunlight resistant and can handle up to 30 volts.
The Catalog # for the sprinkler wire is #23825.60.01 if anyone needs that info.
The best way to feed audio to a remote transmitter is to use what is called a differential balanced line. This is what the phone company uses for analog service drops and they run many miles with no problems. This would involve an audio transformer on each end of the audio line and you could use about any pair of wires on any type of cable.
Some will recommend shielded wire for "single ended" circuits and this might work but ground loops can cause hum problems even with the shielding.
It really comes down to trying it. Even with a single ended feed with unshielded wire, the low output impedance of a typical source (PC audio card, etc.) may allow for success. Keep in mind that since the the impedance of speaker output from a sound card is lower than the line ouput, it will probably work better than the line output. Try both and let us know what happens.
Neil
There are also Cat 5 Network cable audio baluns available that do the trick quite nicely.
Ours is made by Gefen but here's another brand - http://sewelldirect.com/Intelix-Audio-Balun-2-RCA.asp
I agree that Cat 5 (short for Category 5) network wire is a good way to go. It has extremely low capacitance per foot and is some of the least expensive wire you can buy for this type of application. If you are concerned about using it for audio, consider that professional radio stations are now being wired for audio with Cat 5, as it is much cheaper than conventional audio cable and does a good job.
If you don't want to spend a lot on baluns, I offer the results of my experimentation. I bought two 600 Ohm isolation transformers from Radio Shack. I attached one transformer to one end of several hundred feet of Cat 5 and the other transformer to the far end. I then fed various audio tones into the cable, while comparing the input and output on my o'scope.
What I found out is that I got the best results with only one isolation transformer on the input side of the Cat 5 (at the audio feed itself). For some reason, using a transformer at both ends was somewhat worse (contrary to what you would think). This may be due to the impedance of the isolation transformers or the impedance of the Cat 5 (100 Ohm). If you use commercial baluns, I would expect that you would need one at each end.
Another benefit of using Cat 5 is that there are eight pairs of wire in the cable, so you can also carry the power to the transmitter. If you do this, use two pairs in parallel, to minimize the voltage drop. Note that the "Power Over Ethernet" standard uses two pairs for this reason.
To simplify connections to everything, I build a simple adapter box that lets me use a single Cat5 cable for both audio and power.
The box is from an old 2400 Baud modem. The front panel has binding posts for power (I'm using a DC supply to minimize hum), a power LED and an audio jack. The Cat 5 is attached to the terminal block at the back. The isolation transformer is the green, rectangular thing. The whole circuit was built on perfboard, using point-to-point wiring. It isn't pretty, but it was built mostly with parts on hand and it does the job.
Note that there are enough pairs in the Cat 5 to feed both L/R audio channels to the transmitter. I didn't do this, since the SSTRAN transmitter can only transmit in mono. I used two resistors to combine the stereo signal to mono (just like the SSTRAN does internally). At the transmitter, I only have one audio plug. I saved one pair of wire and one isolation transformer. The reason I did this is that I wanted to have a spare pair to use for a temperature probe that will be mounted inside the box, with the transmitter. If you do feed stereo audio, you will need a transformer on each channel. I see that the baluns SaGR mentions are made for stereo use, so only a pair of them would be needed.
BTW, you don't have to use plugs for the front panel connections, like I did. It is overkill, but I had the plugs and decided to use them.
I realized that I should probably show the other end of things. I made the following from another piece of perf board. The circuit board from the SSTRAN mounts to the standoffs. You can see the audio and power plugs. The perf board will be mounted onto standoffs inside a weatherproof box (when I find a suitable box).
You don't have to remove the SSTRAN from its case, but it made things easier to mount securely and takes less room in the box.
The blue thing is a piece from an IC socket. I wired the spare pair of Cat 5 to it, for use with a possible temperature sensor.
That's along the lines of how I was thinking of mounting my SSTRAN. =)