Icom IC-F43TR howling at high volume

[kf4aon]

I manage a number of Icom IC-F43TR portables on a LTR trunk for a university. Many of these are 5-7 years old. Since switching to narrow-band channels earlier this month, many of our users have needed to place their volume controls at a higher level than they did previously with wideband channels. Many of my radios are now exhibiting a problem where they emit a low-frequency oscillation or howl through the speaker, around maybe 400hz or so, when they are receiving signal and the volume knob is turned past about 75%. I am currently working with Icom to find a solution to this problem, but I was curious if anyone else has experienced this.

Thank you for your responses,
Ian

 

[ramal121]

Microphonics around the VCO section. Not limited to your model, many radios will do this.
A good internal cleaning and hardware tightening may help. Some manufacturers will have mods
to add ground straps, etc. See what Icom says.

 

[maxkelley]

A bit of foam rubber wedged in there against the VCO or even the ceramic filters may help. On some Vertex mobiles, we've found that the ceramic filters have gone sort of microphonic.. Perhaps since you've never used the NB filters in the past, a switch to them now revealed the issue?