[Elecraft] K3 Hum on transmit

Mon Jan 23 11:28:53 EST 2012

Cary,

I battled a hum/buzz problem just two weeks ago.  After almost a full day spent hunting, experimenting, searching, and doing everything under the sun plus some very helpful dialog from others here on Elecraft forum, the hum/buzz was finally fixed.

I did not fix it, it just disappeared.  So, here are some things I did...

(1)  I did all my tests with the monitor on and TX in TEST mode since that in itself showed the hum/buzz.

(2)  With the help of Jim Brown (K9YC) I used the TX EQualization feature of the K3 to crimp down to minimum
      the low frequencies of the hum/buzz.  Doing this, it appeared that this was indeed a buzz and not a 60-cycle
      hum because the buzz did not start to be attenuated until after the 400 Hz TXEQ was set to zero and I started
      working on the next higher frequency band.

(3)  I was confused as to whether this was front mic and back end mic inputs or just front.  I finally determined that
      this was on the front mic only with 98 percent confidence.  It is not 100 percent confidence because all of my
      experiments to prove one way or the other were a bit scrambled but I think this was front panel mic only.

(4)  I then focused on the mic itself, an Elecraft MH2 hand mic.  Unfortunately it was the only mic I had for the front
      panel but if you have more then one then I definitely suggest you test them all to see if the hum/buzz is 
      independent of mic.

(5)  I jiggled and bumped this front panel mic and connector to see if there was some loose connection.  Someone
      suggested florescent lighting as a noise generated and I tested with all lights turned off (see next point).

(6)  I also had a nice 13.8 Li-nanoPhosphate battery so I disconnected EVERYTHING from the K3.  The only two
      things connected were the 13.8 volt battery on the power and the mic on the front panel.  No Antenna, no
      ground, no other connector to the K3.  Hum/Buzz was still there and in that test I also turned off the circuit
      breaker for all AC in my shack.  Did not help.

(7)  After some tests, and other things, the hum just seemed to disappear and never came back since.  My best
      guess is that it was one of the following: (1)  either an external noise source that eventually turned off and
      my front panel mic was just more susceptible to picking it up; or, (2) the front panel mic itself had some kind
      of loose connection that just seemed to finally correct itself.  I favor cause (1) though.  I am kind of hoping it
      comes back so I can test some more.

73, phil, K7PEH

On Jan 23, 2012, at 7:37 AM, Hunsdon Cary III wrote:

> Don:
> 	You know it's hard to tell the difference between a buzz and a 60 hertz hum, at least to my 66 year old ears.  HOWEVER, when I disconnected the mic front the front panel connector and used the XMIT button on the front panel, there is no buzz or hum!  I'll start troubleshooting the mic cable now!
> 	Tnx for your help.
> 	73,
> 	Cary, K4TM
> 
> On Jan 23, 2012, at 10:23 AM, Don Wilhelm wrote:
> 
>> Cary,
>> 
>> Is it hum or is it actually "buzz"?  Hum is 60 Hz AC, but buzz will be of various frequencies, and it is difficult to tell them apart with just your ears as detectors.
>> 
>> Does it disappear if the microphone is not connected?  Use XMIT to put the K3 in transmit while you are listening.  If it is only when the microphone is connected, you may have a broken wire in the mic cable.
>> 
>> 73,
>> Don W3FPR
>> 
>> On 1/23/2012 10:10 AM, Hunsdon Cary III wrote:
>>> K3 Experts:  My K3-100 has been flawless in its performance until yesterday.  I had a schedule with W5ZNN who told me I had a hum on my signal; I put my headphones on and sure enough there it was on transmit.  I tried plugging the Astron 35M directly into the AC outlet instead of the outlet strip - no luck, hum was still there.  I connected the K3 to my SEC 1223 switching power supply and, you guessed it, the hum is still there.  I hate to think there's something amiss with the K3 but it looks that way.  Any ideas?
>>> 73,
>>> Cary, K4TM
>>> Lynchburg VAh
>>> h3cary at gmail.com
>>> 
>>> 
>>> 
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> 
> H. Cary III
> h3cary at gmail.com
> 
> 
> 
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