[Elecraft] K3 Transmit IMD (Mic adj for alc)

[Eric Swartz - WA6HHQ, Elecraft]

Yes - That firmware fix improved 3rd order TX IMD by 3-5 dB on the worst 
case band (12M) and it is better than that on all other bands. We also 
made other firmware changes in the gain of various stages to improve TX 
IMD. Those changes have been in every firmware release for many months.

One note: Rob's presentation of that slide was meant to comment on and 
was representative of ALL solid state 100W push-pull AB amplifiers. He 
was not intending to focus on the K3. Just about every solid state ham 
rig made in the past 20 years runs class AB and has a similar (or much 
worse) 3rd order IMD output. We absolutely are -not- a bad neighbor :-)

73, Eric   WA6HHQ

wrmoore wrote:
> In light of the Sherwood presentation referenced in the thread about K3
> audio, I haven't seen much comment on the spectrum analyzer plot of the K3
> transmit IMD.  Is this still an artifact of the (now fixed) firmware error
> mentioned by Eric earlier in this thread?
>
>   
>> The K3 firmware used for the original QST review did
>> not turn off the
>> K3's RF speech compressor clipper even when the
>> compressor was set to
>> zero for their TX IMD two tone test. This resulted
>> in a significant
>> increase in measured TX IMD when using an external 2
>> tone source. We
>> corrected this in a firmware update last month.
>>     
>
> Or is this a currently existing situation with the K3?  I'm so from an
> expert on these things that I hesitate to even ask, but it sounds like
> Sherwood is saying the K3 is a "bad neighbor" in transmit IMD, and it looks
> like it from the plots he provides.  
>
> 73,
> Randy, KS4L
> K2 #337
> K3 on order :-)
>