[Elecraft] KPA500 makes birdies on 6 meters

[Eric Swartz - WA6HHQ, Elecraft]

Hi Ed,

Dale from our customer support group will be contacting you today to see 
if he can help you determine what is going on. I believe Bob Wolbert, 
our KPA500 engineering product manager, has also emailed you for more info.

We do not see this noise on any of our KPA500s tested in production. 
Since we use a linear supply in the KPA500, there is nothing inside that 
should generate 140 kHz harmionics. This sounds suspiciously like a 
swithcing power supply, router wall wart etc. in the shack that is 
feeding into the rx system via a leaky coax or a coax with an open 
shield at one end. I've also run into this when the dummy load was 
coupling to the source of the noise. (Many dummy loads are not as well 
shielded as you may expect.)

Try moving the dummy load (and coax cables) while watching the noise. If 
it varies, its an external source. You might also try swapping out the 
coax between the amp and dummy load, and between the K3 and the amp. 
Also, try disconnecting the coax from the amp output and see if the 
noise changes. (Lastly, if you are using a switching power supply, try 
substituting a linear supply or battery.

Feel free to email dale and Bob any results you get from the above 
tests. I've copied their email addresses on the cc: part of this email.

73, Eric   WA6HHQ
--- www.elecraft.com
On 11/14/2011 6:48 PM, K7WIA wrote:
> I just did a calibration check on the P3 and it was right on using the XG3 at
> -107 DBM
>
> with the K3 connected to a dummy load my measured noise floor is -133 DBM (
> hard to get close as it is fuzzy)         the strength of the birdies is at
> - 125 DBM.
>
> they seem to have peaks every 140 KHZ  up and down the band,
>
>   my lowest noise floor in the city  is right at -125 at the best.
> so in the city this is not a big thing as you can just detect them if you
> know where to look for them.
>
> but I was planing to use the K3 + KPA500 for contesting in rare Grid squares
> in remote location out in the boonies, which would be away from city noise,
> and I am sure the noise floor would be at least -130 dbm
> then this would be a problem...
>
> maybe they can come up with a fix for it?
>
> Ed K7WIA
>