dave wrote:

The Phone Company doesn't use shielded cable for baseband audio.


No, but they use twisted pair and they can still pick up a lot of RF.
I've seen over 5 volts of RF on phone lines at AM radio stations that
were wired with 'station wire' instead of twisted pair. The radio
station audio was louder than either party on the line could talk. The
fix was to rip out everything, run 25 pair twisted cable to localized
terminals and use short runs to the phones. There was still some common
mode RF, but at least the lines were usable since it no longer caused
the volume limiter to go into continuous conduction.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

On Thu, 13 Mar 2014, Michael A. Terrell wrote:


dave wrote:

The Phone Company doesn't use shielded cable for baseband audio.


No, but they use twisted pair and they can still pick up a lot of RF.
I've seen over 5 volts of RF on phone lines at AM radio stations that
were wired with 'station wire' instead of twisted pair. The radio
station audio was louder than either party on the line could talk. The
fix was to rip out everything, run 25 pair twisted cable to localized
terminals and use short runs to the phones. There was still some common
mode RF, but at least the lines were usable since it no longer caused
the volume limiter to go into continuous conduction.

Yes, and even in the days of the no real electronics in the phones, there
were tips in the books about keeping RF out of the phones.

The issue becomes more significant when all the phones are made of
electronics, and there's a lot more that can act ad diodes to detect the
signals.

Michael

The Lady from Philadelphia suggests...

Have you tried using an inexpensive cable //simply to see what happens//,
rather than assuming you //need// a highly shielded cable?

If it doesn't work, you could encase the cable in braiding, grounding the
braiding at the reception end?

On Sun, 9 Mar 2014, Ralph D. wrote:

Hi,

I need a cable (ideally about 20ft), stereo 3.5mm male/male, highly
shielded to connect my audio source to a transmitter across a room. This
cable passes many sources of interference, so the shielding is critical.

Just use coax. Even something small like RG174 likely has better
shielding than many audio cables.

Of course, if there is a real issue here, little stereo plugs end up
leaving an unshielded area for the RF to get in. Changing to something
else would complete the shield. I know I'd use BNC connectors for audio
connectors if that pile of 200 male connectors I found on the sidewalk
had included 200 female BNC connectors as well.

Make sure the output feeding the coax is low impedance, that's not for
feeding the coax, but a high impedance would make it easier for the RF to
be picked up. And terminate at the transmitter end, so that point sees
relatively low impedance.

Make sure the usual low value bypass capacitors are at the input to that
transmitter, so even if there is RF pickup, it is bypassed to ground and
won't be rectified by the input stage. Get some ferrite beads (the tiny
ones, and put them on the lead between the input jack of the trnasmitter
and the first stage, or the traditional method would be an RF choke of
suitable value.

Look in any radio handbook and there should be a section on RF
interference, which would describe how to keep RF out of the first stage
of an audio amplifier.

Michael






I would prefer to get it from Amazon so as to get it quick with Prime
(incredibly narrow window of free-time during a currently very busy
schedule) but would be OK with ordering from one of the Ham sites if
turnaround time is very good. I could not get a good search parameter on
Amazon that didn't turn up thousands of hits that I just don't have time to
sift through right now.

Any good cable with known good isolation would be good. I have ferrite
chokes I can use, but would prefer a cable of suitable quality that did not
need them (current cable is getting interference even with them as this is
not just run-of-the-mill 60cycle stuff).

Any good suggestions would be appreciated.


Thanks!

Ralph D. udtrykte præcist:
Hi,

I need a cable (ideally about 20ft), stereo 3.5mm male/male, highly shielded
to connect my audio source to a transmitter across a room. This cable passes
many sources of interference, so the shielding is critical.

I would prefer to get it from Amazon so as to get it quick with Prime
(incredibly narrow window of free-time during a currently very busy schedule)
but would be OK with ordering from one of the Ham sites if turnaround time is
very good. I could not get a good search parameter on Amazon that didn't turn
up thousands of hits that I just don't have time to sift through right now.

Any good cable with known good isolation would be good. I have ferrite chokes
I can use, but would prefer a cable of suitable quality that did not need
them (current cable is getting interference even with them as this is not
just run-of-the-mill 60cycle stuff).

Any good suggestions would be appreciated.


You could go digital/optical with a analog-toslink-analog combo.

There is a combination at the bottom of the ad he
http://amzn.com/B005F20756

It claims only 18 feet, that could be close enough to your approx 20ft,
when there are analog cables in either end.

But I haven't seen an 18ft toslink cable...

There must transmitters which are more powerful, if you need a longer
range.

Leif

--
Husk kørelys bagpå, hvis din bilfabrikant har taget den idiotiske
beslutning at undlade det.

"Leif Neland" wrote in message ...

But I haven't seen an 18ft TosLink cable...

There are couplers.

On 3/13/2014 8:26 AM, William Sommerwerck wrote:
"Leif Neland" wrote in message
...
But I haven't seen an 18ft TosLink cable...

There are couplers.

Monoprice offers this 25 foot Toslink cable for under $5, as well as
longer ones out to 50 foot length.

They work beautifully for the applications I have tried, including the
connection of an AppleTV audio output to a distant A/V receiver in
another room.

http://www.monoprice.com/Product?c_i...seq=1&format=2

"Ralph D." wrote in message
...
Hi,

I need a cable (ideally about 20ft), stereo 3.5mm male/male, highly
shielded to connect my audio source to a transmitter across a room. This
cable passes many sources of interference, so the shielding is critical.

I would prefer to get it from Amazon so as to get it quick with Prime
(incredibly narrow window of free-time during a currently very busy
schedule) but would be OK with ordering from one of the Ham sites if
turnaround time is very good. I could not get a good search parameter on
Amazon that didn't turn up thousands of hits that I just don't have time
to sift through right now.

Any good cable with known good isolation would be good. I have ferrite
chokes I can use, but would prefer a cable of suitable quality that did
not need them (current cable is getting interference even with them as
this is not just run-of-the-mill 60cycle stuff).

Any good suggestions would be appreciated.


Thanks!


Thanks to everyone for their input. I guess the discussion has about worn
itself out.

After reading what was posted in both groups, I have decided to try this
option first, as I have cable on hand and it would be great if it resolved
for cheap :-)


http://www.amazon.com/Headphone-Jack...5mm+Balun+Cat5



Hopefully I'll have a positive follow-up.


Thanks again.