Twisted shielded pair and audio phoolery

[W1RKW]

For the few radio stations I worked at I used Belden 9451D dual twisted shielded pair for stereo audio interconnects and mic cables and never noticed any audio issues with it. So I use it here at the QTH. Out of curiousity, I was looking at some of the specs and noticed that this cable has a rather high capacitance, 67pF per foot compared to other shielded twisted pair which is less in uf or pf/Ft and what is deemed mic cable. I use this stuff and my audio cable runs are about 20 or so feet between the transmitter and mixer. The mic cable is only 5 feet between it and the mixer.  The EQ and processor have about 3 feet between them before heading out to the transmitter.  Am I EQing the high end more than need be? I'm thinking not but what do you think? I only used this because it was inexpensive and easy to work with.

[WA1GFZ]

Bob,
I wouldn't worry about it if you are passing highs ok. If you are really concerned take a length of cable and terminate one end and drive the other end with a signal generator Then look at the frequency response / phase shift with a scope

[flintstone mop]

Great stuff. I have seen it everywhere. 100% shield and usually balanced line level or higher audio levels. For Ham use no one would notice any roll off. It wouldn't be very flexible for constant movement..

[K1ZJH]

I may be all wet, and I usually am    but I'd suspect the capacitance per foot
would be directly affected by the impedance of the audio circuit. At 600 ohms, I'd
think it would be negligable.

Pete

[WBear2GCR]

right-o, IF the impedance down the receiving end is low and the driving Z is also low, then the capacitance of the cable is much less important. For ham use where >10khz is a bad idea, that might be a positive feature.

If ur driving a high Z input, I'd run a freq sweep and see empirically where things are.

Where you might get into trouble is if there is some sort of reactive resonance or dip driving into or out of a transformer... but that is not likely, and most folks don't use those old iron thingies in their line level stuff.

                    _-_-bear

[W7TFO]

driving into or out of a transformer... but that is not likely, and most folks don't use those old iron thingies in their line level stuff.

                    _-_-bear

True, but there would be a lot less whining about RF in the microphone circuit if they did!

73DG

[flintstone mop]

I may be all wet, and I usually am    but I'd suspect the capacitance per foot
would be directly affected by the impedance of the audio circuit. At 600 ohms, I'd
think it would be negligable.

Pete

Pete you're right on. It was used a lot in Bcast and 600 ohms was the impedance used and the levels were usually +10dBm
Balanced line , 100% shield