Couple favorite toys for field use around the house are a Motorola URC-200 and just acquired GRC-215 (RT-1511) transceiver. Although the Motorola  has a microscopic internal speaker the 215 was intended to be handset only. Long story short decided I need an external amplified speaker. Have  a black external military speaker with the connector on it and the like to connect to the radios and it works just fine but discovered that when I transmit using antenna on the radios RF gets back into the speaker and it howls! Connect the radios to a load or external antenna away from the radio and speaker its fine, just that plastic case for this speaker sucks in terms of keeping RF out. The microphone cable is shielded but not the box the amplifier lives in.

Long story short, thinking something like a MRC-67 or maybe the older AM-4979 may be the trick if they are in meatal cases and relatively RFI proofed? Imagine if I had to can line the inside of the box for the speaker I have with foil or copper plate but just not digging the plastic nature of the box anyway. Anyone have experience using a MRC-67 in high RF environment?

Ray F/KA3EKH