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Hum while TX #bitx20

Werner de Vos
 

I have the V5 uBITX. All seems to be okay but in TX I get a big hum. The issue is even worse when keying. I disconnected the mic so that can't be an issue. Replaced the powersuppy also, that doesn't help. When I touch the heatsinks of the irf510 it get worse.

It looks like a ground loop issue but even with nothing connected the hum is there.
RX is perfect.

Any ideas?

Thanks, Werner pa3gyv

Werner de Vos
 

Forgot to say, I check my signal with my other rig.

Evan Hand
 

You might be getting RF back into the radio.  Does it happen into a dummy load?

73
Evan
AC9TU

Werner de Vos
 

Evan, I am testing with a dummy. It sounds like there is a lose ground somewhere but I just can’t figure out where.

The issue started when finnishing the enclosure. I did test the board on arrival and can’t recall this issue. 

73 Werner 

Jonas Sanamon
 

Hi Werner,

It sounds to me like the problem could be the opposite, a ground loop where there shouldn't be one; maybe caused by the enclosure or standoffs touching something it shouldn't. Try to remove the screws holding the main board down and place a magazine or similar under it and test.

Best Regards,
Jonas

Den sön 8 sep. 2019 kl 21:47 skrev Werner de Vos <wernerdevos@...>:

The issue started when finnishing the enclosure. I did test the board on arrival and can’t recall this issue. 

Evan Hand
 

Werner,

I reread your post.  Since the RX audio is perfect, the hum could be coming from either the mic input or the power supply due to higher current draw on transmit.

Do you get the hum with the mic input shorted?

I would also check the ground/shield connections of the mic connector and wiring to the audio connector on the main board.

FWIW
73
Evan
AC9TU

Werner de Vos
 

Thanks all for help! The biggest problem was RF getting back into the radio. The dummy was to close to the radio. 

Have to sort out one more thing, the input for my souncard for digital radio is parallel to the mic. So when the radio is transmitting both pc line out and mic are open. Easiest way is to disconnect the mic but I’m not born easy lol.

73