OK, before reading the rest of this post, read the following link from Heil Sound on removing RFI from your mic input:
http://www.heilsound.com/amateur/harmonics.htm#RFI
Now the funny part:
My girlfriend bought me a belated Christmas gift today: a Heil GM-5 mic for my Icom 746 Pro. I hooked it up and proceeded to adjust all the settings on the rig as recommended to get the good audio. The problem was that I had a horrible hum. After paying closer attention, I found it was coming from the power supply for the rig. It was especially noticeable when the power supply "fired up" as it does to supply more juice to the radio. I swapped back the stock mic and the hum was gone.
I tried a few toroids on the mic cable and it didn't make any difference. I stopped to think, knowing about this issue that Heil talks about and said to myself, "hmm...I wonder if this Heil cable has a loose ground". After opening up the mic cable, I found the braid pigtail was indeed making good contact with the mic plug.
Out of curiosity, I attached the plug back to the radio with the pigtail not grounded, and the RFI from the power supply was gone! I tried a few tests back and forth, and the test was conclusive. So needless to say, the pigtail got cut off and all is well now. It's kind've funny that Heil's own documentation on how to fix this problem was actually causing it in my case...LOL!
http://www.heilsound.com/amateur/harmonics.htm#RFI
Now the funny part:
My girlfriend bought me a belated Christmas gift today: a Heil GM-5 mic for my Icom 746 Pro. I hooked it up and proceeded to adjust all the settings on the rig as recommended to get the good audio. The problem was that I had a horrible hum. After paying closer attention, I found it was coming from the power supply for the rig. It was especially noticeable when the power supply "fired up" as it does to supply more juice to the radio. I swapped back the stock mic and the hum was gone.
I tried a few toroids on the mic cable and it didn't make any difference. I stopped to think, knowing about this issue that Heil talks about and said to myself, "hmm...I wonder if this Heil cable has a loose ground". After opening up the mic cable, I found the braid pigtail was indeed making good contact with the mic plug.
Out of curiosity, I attached the plug back to the radio with the pigtail not grounded, and the RFI from the power supply was gone! I tried a few tests back and forth, and the test was conclusive. So needless to say, the pigtail got cut off and all is well now. It's kind've funny that Heil's own documentation on how to fix this problem was actually causing it in my case...LOL!
