external speaker feedback

[spiderman]

Hi All,
Whenever I have my talkback on , I get some squeal from my external speaker no matter where I place it in my car.I am running a DX95T/wilson 5K Mag mount on trunk and a 636L mic
with mic gain all the way up (as manual advises). I also have a
Turner 56RK mic, which mic is better ? should I switch them.
Any advice ?? Thanks , Spiderman

 

[paws264]

I know that this is a stupid question, does it still squeal when you turn the Microphone gain down, try that, turn all mic gain adjustments to 1/4 of max and start from there to see if it gets better.

.

 

[DXman]

I would agree also with Paws...mic gain probably to high.
About which mic is better, you will have to get reports from other people to find that out.
-----------------
DXman

 

[freecell]

#1 check to make sure the amc hasn't been disabled.
#2 get rid of the mag mount.
#3 use a shielded external speaker with shielded audio cable. (rg174 or equivalent)
#4 add .01 - .2 uf between pin 4 of the audio ic to ground.
#5 if the amc was disabled, get rid of the A636L and replace it with a CDL56KDX1. by comparison the 636 does not produce sufficient output (measured in millivolts) to properly drive the transmitter speech stages to produce maximum transmitter output. many cannot resist disabling the amc to compensate for this when the problem is the microphone itself.

to determine whether or not the external speaker, most of which are housed in plastic and manufactured with unshielded zip cord is contributing to the problem, unplug it from the ext spkr jack and see if the problem is lessened when using the internal speaker.

you may be experiencing both audio AND rf feedback. i would use the notes above to eliminate any possibility of audio feedback and see what's left before turning your attention to the antenna mounting situation. even the antenna itself could be adding to the problem if the loading coil is visible through the rear window. the bulk of the radiating energy emanates from the base of the loading coil and may be saturating the interior of the vehicle with higher-than-normal rf levels. an unshielded external speaker will react to these fields and the talkback levels will increase in the presence of a strong rf field.