[Elecraft] K3 Ground Loop Issues using Ameritron ARB-704

Clark L. Stewart w8tn at ntelos.net
Thu Jun 4 12:50:49 EDT 2009


At 09:55 PM 6/2/2009 -0400, Alfred Frugoli wrote:
>I've just gotten my K3 built and integrated into the shack about a week
>ago.  Operated WPX CW this weekend with GREAT success.  Was very happy.
>
>Tonight in setting up FSK, I was getting a lot of "AGN?" after my cq's.
>Listening to my signal on a 2nd receiver, I realized that my signal had a
>hum on it - basically sounded terrible. Tested in CW mode as well, and the
>hum was also there (haven't dug out the mic yet for the dreaded SSB mode to
>know if the hum was there as well, but I would suspect it would have been).
>Tried changing a bunch of menu settings to no avail.  Then I disconnected
>everything from the back of the K3 except for the antenna, power and FSK
>input.  Beautiful clean signal.  The hum reappeared when I connected the amp
>keying line.
>
><<<< SNIP >>>>>
>
>Thanks.
>
>73 de Al, KE1FO


Elecrafters,

      My friend, KC8UHE, just received his brand-new K-3 and in helping him 
set it up, we encountered a similar problem.  But, we are not using the 
ARB-704.  This K-3 is connected to a microHAM microKEYER II using the 
microHAM DB37-EL-K3R cable set.

      When the headset microphone is connected to the microKEYER and the 
Amplifier is connected to the microKEYER, a serious amount of hum is 
present on the mike audio.  This is evident both in TX TEST mode and in 
on-the-air reports.

      If the microphone is connected directly to the rear MIKE input on the 
K-3, there is no hum even with the amplifier connected.  If the microphone 
is run through the microKEYER and NO amplifier is connected to the 
microKEYER relay output, there is no hum.

      This hum is present when connecting the microKEYER relay output 
directly to either the Ameritron AL-82 or the Heathkit SB-200 which has 
been converted to 6-M.  (Only one amp is connected at a time.)  Both amps 
are connected to 220 VAC.

      The microKEYER has been modified with the RFI "fix" on the USB 
cable.  And, we swapped out KC8UHE's microKEYER with my own microKEYER and 
the hum is present with either microKEYER in line.

      Mike level on the K-3 was 20, CMP was Ø, and the internal pots of the 
microKEYER as well as the Router software were adjusted as per the 
manual.  The headset is a Heil Pro Set Plus using the HC-4 element.

      Does anyone have a suggestion to cure this as it is not possible for 
KC8UHE to operate his K-3 with either amp on SSB while this hum is 
present.  Thanks.


Clark, W8TN



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