MD-380 motorboat sound

When I transmit with a MD-380 and a rubber-duck antenna, there is a "motorboat" sound on my transmit audio when using a Retelvis speaker mic.  I opened the mic and observed that they are not using a shielded mic cable.  When I transmit into a dummy load or an outside antenna the "motorboat" sound is gone.

Has anyone been able to fix this RF into audio problem and what speaker microphones do not have this problem?

The problem goes away when you use the proper mic for it... such as the following unit.

1 comment:

DG2IAQ said...

Yes, I found a fix.

Just solder a 47pF capacitor in parallel to the electret capsule and motorboat/helicopter effect has gone.

It's needed to Keep the capacitor in this low capacitance, so please do not try any larger values. 47pF/100pF are perfect, not higher.

If there are any other parts on the mic line (e.g. 2k2 to ground or other capacitors), just desolder all of them. Only the 47pF or 100pF Need to be in parallel to the electret capsule.

I modified several external microphones from different companies and the mod works on all of them.

The mod is published on www.mods.dk in the meanwhile.

vy 73 + good luck on modding :-)
Jochen, DG2IAQ

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