UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Midland 77-805 Portapak transmit issue

SiriusHardware · 4th Oct 2019, 1:04 am

Well, I'm starting to run out of ideas now.

Your observations about things which make the problem go away are, I suspect, all instances in which the power radiated is being reduced, either by absorption (ie, your body in close proximity) or by detuning the aerial (adding a length of wire to the end of the aerial) or a combination of both (touching the aerial). The core of the issue seems to be that when the unit is radiating maximum power from its integral antenna, that's when you get the problem.

If you have a spare microphone plug with the right number of pins you could try strapping PTT (mic socket pin 1) to 0V (mic socket pin 4) and just plugging the plug in instead of the speaker / mic- if you get the same noises on TX even then, that will rule out anything to do with pickup in the microphone / microphone cable.

4th Oct 2019, 1:04 am	#12
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,556	Re: Midland 77-805 Portapak transmit issue Well, I'm starting to run out of ideas now. Your observations about things which make the problem go away are, I suspect, all instances in which the power radiated is being reduced, either by absorption (ie, your body in close proximity) or by detuning the aerial (adding a length of wire to the end of the aerial) or a combination of both (touching the aerial). The core of the issue seems to be that when the unit is radiating maximum power from its integral antenna, that's when you get the problem. If you have a spare microphone plug with the right number of pins you could try strapping PTT (mic socket pin 1) to 0V (mic socket pin 4) and just plugging the plug in instead of the speaker / mic- if you get the same noises on TX even then, that will rule out anything to do with pickup in the microphone / microphone cable.