The AM Forum

After building the new shack I decided to re-cable the audio chain. These days, finding balanced audio cable is not as easy (nor as cheap) as it once was. I decided to make my own. Cut a length of RG-58 or RG-59 to the desired length of the cable you need and strip back about 1” on each end. Next, cut a length of CAT 5 network cable about 6” longer than the coax. Extract one twisted pair from the network cable, and securely attach both conductors to the center conductor of the coax. I found that a neat parallel soldered connection to join both cables works best. From the opposite end of the coax, grasp the coax and use the center conductor of the coax as a snake to pull the twisted pair through the coax jacket. That’s it – you’re done!

In one extreme case I created a double shielded cable by following this procedure again, pulling the completed RG-58 cable through a length of RG-8X. If the splice is neat, you can probably do this with RG-174U as well.

Keep in mind the spec of that cable, in that it can be used for even more things that could similarly benefit from the shielding tip described. Control and LV power leads come to mind.

pair: 100 Ohms
100MHz/100Mbit
twists vary between the 4 pairs
'FTP' or 'STP' CAT5 is already shielded but also harder to find surplus or free because of its expense.

Don't forget the other types of twisted pair stock that could benefit from adding the shield and may be very cheap.
CAT3 - like CAT5 but lower bandwidth of 10MHz.
If CAT2 is available for almost free as in surplus, it is also 8 conductor 4 pair, rated 4MHz/4Mbits and should be as good at analog audio frequencies.
CAT1 is just a single twisted pair sometimes used for indoor telephone type wiring.

Some data cable has the twisted pairs transposed or twisted with each other in a seemingly random manner, except that it is not random and is designed to reduce crosstalk. The only problem with this, is that over a substantial length the individual twisted pairs are not easy to just pull out of the jacket because they are entangled with the other pairs.

All understood, but for simple audio applications it works great.

I used about 35 ft of RG-58 that was originally aimed for the trash. You can find the balanced cable on line, but when you add the shipping and the wait, this was so much easier. I've been able to make lengths of up to 10 ft. You can "shimmy" your hand down the length and gradually separate the inner conductor out of the coax while pulling the twisted pair through.

There is also shielded Cat5/6 cable too.

I think I'll try it as the 65 year old 600 Ohm shielded twisted pair from the speech amp to the transmitter is old and rotten. I need more like 20FT due to routing. It might be a challenge to get that much out.

Start from the end that is secured and keep sliding back. Initially it will start slow, but the more you pull, the faster it advances. Just make sure you have the twisted pair connected to the inner conductor, so you will be pulling it through. I neatly solder the two wires together without twisting them, to avoid any edges that can get hung up on the inner braid.