feed back HELP!!!!!!!!!

[w5tmg]

i just got my am limiter back from the shop and it works great with my 250m bc tx.  but when i flip over to my 1r tx it sounds bad. no wire changes,,, cant get much audio out of it cause of feed back in the tx., but when i put the limter in bypass it staightens up... any suggestions??? im obviously missing something...thnxs... w5tmg0@gmail.com

[N8ETQ]

Probably a long shot, Phase?


/Dan

[W2ZE]

RF getting in the audio cables or limiter itself.

[W3RSW]

A good possibility:
"Somebody's got an open ground " whereby one rig properly grounds a cable and the other doesn't, expecting that the ground should be on the other end.  Perhaps the shop left off a ground or deliberately decided tha a cable ought to be grounded on other end a la somebody's idea of modern progress.
Interesting and I'd check out all the grounding. Any pix of limiter internals before it went to shop?

[w5tmg]

Probably a long shot, Phase?
my neg and pos peaks are correct, thats was the 1st thing i check, but thnxs

/Dan

[w5tmg]

A good possibility:
"Somebody's got an open ground " whereby one rig properly grounds a cable and the other doesn't, expecting that the ground should be on the other end.  Perhaps the shop left off a ground or deliberately decided tha a cable ought to be grounded on other end a la somebody's idea of modern progress.
Interesting and I'd check out all the grounding. Any pix of limiter internals before it went to shop?

  but why would it sound so good with my other tx??? its all wired the same...

[w5tmg]

RF getting in the audio cables or limiter itself.

why wouldnt it do it in bypass???

[W2ZE]

A whole whirl of changes happen when you go from 250 watts to 1000 watts. Huge difference. Something inside (limiter) is not properly grounded, and bypassing just connects the audio cables together essentially. Also, there maybe RF getting through the power cable from an improper connection on the TX or on the ground of the limiter. RF gremlins are not easy to fix and take time. I would disconnect the in and out cables from the limiter and connect them together and see if this eliminates the feedback. If so, then you have narrowed it down to the limiter itself. Another thing to try is to place radial RF chokes on each lead of the audio cable to the TX.

[KM1H]

Sounds like the typical Pin 1 problem or similar plus some ferrite chokes may be needed on cables.

Google K9YC and follow th links.

Carl

[flintstone mop]

Usually a B'cast quality limiter will be very hard to break with RFI. So, the shop musta messed something up.
That is a huge change in RF power.
Typical Amateur station will have many ways to get RF into the goodies. Grounding is usually not the problem.
Antenna system is usually the culprit, especially when it is near the shack. 100 feet distance is the beginning of happiness.

Fred

[Gito]

hy

sometimes there are RF feed back coming into the audio system,this can be positive feed back or negative feed back depending on the polarity connection of the Modulation Transformer,

The RF feedback is rectified as audio ,coming back at the input of the modulator input/limiter input,
So depending on audio phase,if it is positive it can cause oscillation ,
and if it is negative it causes lower gain ..

just a though

Gito

Gito