Dual Comms problem

[SOT-Aj KIA 4th July 2010]

Gentlemen, running dual 148's in Afghanistan and am having occasional bleedover between nets during transmissions. I've changed out headsets and opened up the key button enclosure. Our JTACS have the same issue at times. Using the "good" Peltors, not the crappy MSAs. Any ideas?

Also when it heats up during the day sometimes the noise floor raises above the squelch lvl of the 148's. It doesn't effect tx/rx but you do get a rather annoying static sound "keying" frequently. Any home brew ideas to "raise" the 148's squelch?

[tyrsnbdr]

re 1st question: Are your antenna's to close together? Do your wires intertwine? Check sheilding on cables.

You may fing the info your looking for at https://s6.army.mil. You need AKO/CAC to log onto the site.

[SF_BHT]

tyrsnbdr is probally spot on.

Today just as in the past people started adding multiple radios in the vehicles and not spacing them out due to ease of use (Stacking) and spreading the antennas out and separating the cables. Space matters when you are mixing more than one radio.

Our military is outfitting our vehicles with so many RF emitting devices we are running out of room and they are stepping on top of others.....

I will bet if you separate the antennas and shield the cables better your problem will clear up.

Just my 2 cents......

[Zorro]

Be careful transmitting team internal when standing close to your JTAC/CCT.... what you say can bleed over his net to A/C that are recording. I hate having my words captured on tape. Just my .02 cents from experience.

[SOT-Aj KIA 4th July 2010]

Well, couldn't fix that, THey are already run completely on the opposite sides of my body. I'll see what I can do for shielding.

No ideas about other question then?

[shortbrownguy]

Are you running any type of amp? How close is the range between the frequencies you are using? All can contribute to the issue you are having.

[glebo]

As stated by previous posters, you're most likely running into an "intermodulation" problem.

Can be caused by to close proximity with various systems, cables intertwined (Coax doesn't shield totally) especially if there's an amp involved. Can also be caused by freq's being to close together and developing harmonics.

Also as stated, antenna placement could also be involved.

Try re-routing cables, and a little separation if possible, that should reduce and maybe stop some of the problems.

I guess ya just gotta fiddle with it for results.

Good luck

[albeham]

Originally Posted by glebo

As stated by previous posters, you're most likely running into an "intermodulation" problem.

Can be caused by to close proximity with various systems, cables intertwined (Coax doesn't shield totally) especially if there's an amp involved. Can also be caused by freq's being to close together and developing harmonics.

Also as stated, antenna placement could also be involved.

Try re-routing cables, and a little separation if possible, that should reduce and maybe stop some of the problems.

I guess ya just gotta fiddle with it for results.

Good luck

I agree with glebo.

In a high RF environment, there is going to be some direct pickup, or as us RF Spectrum guys would say. Brut force pickup.

Shielding of the systems cables can help a lot. EMI is a fun thing. Keep connectors clean, and watch you power out on all of the radio systems you are using. Use the lowest setting to talk in your net.

AL F.



PS get this passed up the chain to the JSC, Joint Spectrum Center. document it all with a JSIR report.

[SOT-Aj KIA 4th July 2010]

Great idea with the JSIR report. Didn't think of that one. We've actually had icom repeater harmonics bleed over onto our net. Thing's that make you go "hmmm?"

We've tried most of these suggestions already to no avail. Main issue is the noise level raising and causing the static. Annoying pain in the ass, but still 5x5 on rx/tx so it can be dealt with.

[SOT-Aj KIA 4th July 2010]

In reply to your previous questions, not running an amp. Just straight Mbitrs on opposite sides of my back (one on each kidney area). On has a "Blade" longwhip antenna, the other antenna is the 32-512Mhz shortwhip multi-band antenna. My first thought was connections so I redid all my cabling.