need advice on hum from amp

[1iwilly]

looking for help on hum from solid-state 200 base amp even though it has a 3 prong power wire and also a ground strap going to a ground rod the hum is a tad noticeable when keying the radio without audio and monitoring on another radio

 

[Slowmover]

1). True three-wire home service?

2). Tried without additional ground mentioned?

 

[1iwilly]

1 yes my garage has the 3 wire service actually the whole house does
2 yes i disconnected the bare ground wire from the ground rod no changes

i was thinking it might be coming from the big round transformer

1). True three-wire home service?

2). Tried without additional ground mentioned?

 

[nomadradio]

You need an antenna for the monitor radio. A radio in the same room may hear more RF leaking out of the AC power cords than what comes out the antenna jack. This is especially true when using a dummy load. If it's shielded properly, the loudest RF in the room will be what leaks out of the radio cabinet by way of the AC power cord, or the power supply's power cord.

Just one problem with RF that came upstream leaking out of the power supply.

THAT signal has a hum modulated on it. It is radiating from the 60-Hz power wire, after all. Passing your RF signal through a power supply, and back out the power cord nearly always modulates a hum onto the signal.

And that's what radiates off the power cord into the room.

If you can instead listen to what's coming out the radio's antenna jack, you'll find the hum goes away.

73

 

[1iwilly]

makes sense one thing i did notice there is no ceramic disc cap on power wire to ground like you find on other units ???

You need an antenna for the monitor radio. A radio in the same room may hear more RF leaking out of the AC power cords than what comes out the antenna jack. This is especially true when using a dummy load. If it's shielded properly, the loudest RF in the room will be what leaks out of the radio cabinet by way of the AC power cord, or the power supply's power cord.

Just one problem with RF that came upstream leaking out of the power supply.

THAT signal has a hum modulated on it. It is radiating from the 60-Hz power wire, after all. Passing your RF signal through a power supply, and back out the power cord nearly always modulates a hum onto the signal.

And that's what radiates off the power cord into the room.

If you can instead listen to what's coming out the radio's antenna jack, you'll find the hum goes away.

73

 

[nomadradio]

Simply plugging a coax jumper into the monitor radio, and laying the plug at the other end on top of your wattmeter may do the trick all by itself.

73