Audio problem when using an antenna multicoupler, how to solve?
 

I'm using a Stridsberg antenna multicoupler to connect three scanners
to the same beam antenna. The audio of each of the three scanners is
fed to the line input of three separate computers.

After I connected the scanners to the multicoupler I noticed that in
the audio of each of the scanners you can hear the audio of the other
two scanners (but at a much lower volume). If I disconnect the
scanners from the multicoupler and switch to separate antennas the
problem goes away.

Is there something I can do to prevent the audio from each scanner
completely separate from the other two scanners?

Thanks for any suggestions,
Gordon

--
Listen to Gwinnett County, Georgia Police, Fire, and EMS radio
at http://www.ScanGwinnett.com

On 9 Jul 2004 08:11:40 -0700, (ScanGwinnett)
wrote:

I'm using a Stridsberg antenna multicoupler to connect three scanners
to the same beam antenna. The audio of each of the three scanners is
fed to the line input of three separate computers.

You say three scanners.

As far as I know, John S, makes a 4 input multicoupler. If you have a
4 input unit and are using only three, make sure you terminate the
unused input.

Use a formal terminator (cheap) for best results, or solder a 50 ohm
resistor across a make BNC if nothing else. Don't use a 75 ohm
terminator such as is used in CCTV systems.

Unused and unterminated inputs in a multicoupler can cause
unpredictable results.

Also call John Stridsberg and ask him. He knows his product. I expect
the first thing he'll tell you to do is terminate any unused input and
get back to him.

After I connected the scanners to the multicoupler I noticed that in
the audio of each of the scanners you can hear the audio of the other
two scanners (but at a much lower volume). If I disconnect the
scanners from the multicoupler and switch to separate antennas the
problem goes away.

Make sure you don't have ground loops. Look for bad coax shields on
all RF coaxes. If signals can't find the path they expect for the
return line, they'll force their way through the equipment.

Swap stuff around and try to narrow the problem down to one component.

Is there something I can do to prevent the audio from each scanner
completely separate from the other two scanners?

I've used many of John S' couplers and not had this problem.

I suspect you have a ground loop (open ground) in the RF or audio
wiring. Find and fix that and your problem will clear up.

Steve


************************************************** *******************
Steve Uhrig, SWS Security, Maryland (USA)
Mfrs of electronic surveillance equip
website http://www.swssec.com
tel +1+410-879-4035, fax +1+410-836-1190
"In God we trust, all others we monitor"
************************************************** *******************

My intuition is that it's a ground loop in the audio path. Try
unplugging audio from the other computers and see what happens.

If the crosstalk goes away, I'd try a radio shack audio isolation
transformer ($15) in the audio lines to the computers.

Ground Loop Isolator 270-054
--
Ron Hardin


On the internet, nobody knows you're a jerk.

I've had the same problem, but was only using two computers. It was a
ground loop. Simple take a heavy gauge wire (12 in my case) and ground
each computer chassie to eachother then ground that to the Stridsberg
multicoupler. In my case I didn't need to physically ground the cases
of the scanners as that was already taken care of my the outer sheld of
the coax between the scanner & stridsberg.

Someone mentioned terminating the unused Stridsberg output. I have 2 of
the amplified 4 port multicouplers and 1 of the 8 port amplified
couplers and never terminated unused ports so in my case that wasn't an
issue.

George - Daytona Beach, FL - KI4FIA
Look Me Up On IRPL Node 4053 or Echo Link 50666
http://www.MilAirComms.com

On Fri, 09 Jul 2004 15:42:27 GMT, Ron Hardin
wrote:

My intuition is that it's a ground loop in the audio path. Try
unplugging audio from the other computers and see what happens.

If the crosstalk goes away, I'd try a radio shack audio isolation
transformer ($15) in the audio lines to the computers.

Ground Loop Isolator 270-054

Ground loops produce hum, not usually cross-talk audio.

Try the cheap radio shack isolator first. If that doesn't work try
the Royal PAD.

Royal DB-25 attenuation boxes with ground lift solve most of the audio
problems I've had.

www.guitarcenter.com

On Fri, 09 Jul 2004 15:42:27 GMT, Ron Hardin
wrote:

My intuition is that it's a ground loop in the audio path. Try
unplugging audio from the other computers and see what happens.

If the crosstalk goes away, I'd try a radio shack audio isolation
transformer ($15) in the audio lines to the computers.

Ground Loop Isolator 270-054

Thanks all, the problem was a ground loop. Radio Shack's ground loop
isolators did the trick, all of the crosstalk is gone!

Thanks,
Gordon