DIYbanter - View Single Post - What Shielded wire to use for RF Test Leads

Ralph Mowery

In article ,
says...

Looking on the web, I have found numerous suggestions and no definite
answer.

To make a shielded test lead for use on a RF device, such as a Signal
generator, Oscilloscope, or other, I have seen recommendations for TV
coax (RG59), CB/Ham antenna wire (RG58) and microphone cable. Which is
best?

I know that the TV cable is stiff, with that solid wire in the center,
so that would not be the ideal cable to use. It's been years since I
used the CB/Ham cable. I know that stuff is stoffer too, but maybe not
as bad. As far as handling and softness, I know the Mic cable is
probably the best, but I read that it's probably the least desireable
because of impedance issues.

So what is normally used?

BTW:
* I might be wrong on those RG numbers. I'm just going on my failing
memory.

All depends on the type of testing. For RF I usually use some rg-400.
It is slightly less than 1/4 of an inch in diameter ( same size as the
rg-58) That is double shielded silver plated and a stranded center wire.
But that is because I am often doing duplex work and need the isolation
of the double shielding. RG 58 is fine if you do not need the extra
shielding. Just get the kind with the stranded center conductor.

Usualy rg 174 for light weight leads. It is about 1/8 of an inch in
diameter. I am not sure of the number but there is a teflon and silver
cable made in the same size.

All that is for a 50 ohm system or audio work.

Most scopes will use a probe with a 10/1 on it. You can get them from
the China places off ebay for about 15 to 20 dollars per pair. I bought
a set and compaired them to some HP probes rated at 100 MHz and they
seem to be about the same. Not sure how long they will last, but at
that price should be good for a while if not mistreated. Without the
10/1 probe you will often load down a circuit with the scope leads. The
cable will have about 30 pf of capacitance per foot. I am thinking the
scope only has about a 1 meg ohm of impedance without the 10/1 probe.