TS-520S transmit hum

[ko4kl]

Stations receiving my SSB signal detect hum. Removing the microphone from the radio did not fix it. I went to the CW mode and transmitted CW and no hum was heard by the receiving station. Since the hum is not there on CW I don't suspect the 800 volt (PA) or 300 volt (driver) supply filter capacitors. That leaves the 14 volt supply filter capacitors (2200 @ 16v) that supply the solid state devices. But if they are the cause of the hum why do I not hear hum in my receive audio since they use the same 14 volt power as the transmit audio? Any help pinning this down would be appreciated.

 

[EDUK8TR]

The audio is probably what is picking up the hum where the CW won't. If you have a spare ferrite core and enough slack in the power leads coming off the PS try wrapping a couple of turns of the leads around it and see if this takes out the hum.

 

[Beetle]

Bad/broken grounding of the mike audio wiring in the mike or connector?

 

[Sonwatcher]

An old post in another forum:

I have hum on my SSB signal. Several stations have complained about it, should I send my rig to you?
Before you send it off for repair, a simple check might solve your problem. Kenwood used separate grounds on the MIC connector for the PTT switch, and the microphone signal and ground leads. If your microphone is mis-wired, and I have seen a number that are, you will get hum on your signal. Kenwood stresses in their owner's manuals, "KEEP THE GROUNDS SEPARATE" but some people have to learn the hard way. If pins 3 and 4 on your microphone connector (on the microphone cord itself) are connected, you will have hum.

http://www.k4eaa.com/faq.htm

 

[Moleculo]

I'd bet money on a ground hum caused by a ground loop. Start there before assuming you have a problem with a piece of equipment.

 

[ko4kl]

KO4KL (originator)

Sonwatcher and Beetle:
When mic connector is removed from the radio in SSB mode receiving station still hears the hum so not in mic. The radio mic connector ground checked and OK.

EDUK8TR:
This radio has an internal power supply.

Molecilo:
I don't understand having a ground loop affecting only one mode. I will check though.

 

[Sonwatcher]

Stations receiving my SSB signal detect hum. Removing the microphone from the radio did not fix it

I am curious as to how you sent a signal on ssb without the mic and they still received a hum ? Did you just hit MOX ?

 

[Moleculo]

I am curious as to how you sent a signal on ssb without the mic and they still received a hum ? Did you just hit MOX ?

I can create ground hum intentionally on my station by disconnecting the audio cable that goes from the PC speaker out to the audio in on my rig. (yes, everything uses a common ground). Since there is still an audio out cable from the rig going to line in on the computer connected, an extra ground path is now created. All I have to do to hear a slight hum it is put on some headphones, hit the transmit button on the rig and even with the mic disconnected, I can hear it. Needless to say, I don't leave it this way on purpose!

I don't understand having a ground loop affecting only one mode. I will check though.

It might be there all the time. It's possible that it's level is low enough that modes with a carrier (CW, AM, etc.) just cover it up. Plus with the tone level of CW, that's probably covering it up, for sure. Or, perhaps the ground hum is coming from the mic, which is not active in CW mode? I had this problem once also and had to re-do the ground braid in the mic connector.

 

[Sonwatcher]

How did you make out ?