[Elecraft] re: ARRL K3 review for Apr QST posted [TX IMD]

[David Wilburn]

Thanks for the explanation Wayne.


Dave Wilburn
K4DGW
K2/100 - S/N 5982


wayne burdick wrote:
> AB2TC - Knut wrote:
> 
>> Receiver results as expected, great. Disappointed with the transmitter 
>> IM,
>> even at reduced power.
> 
> A couple of comments on this, Knut.
> 
> The league measured around -30 dBc worst-case when using the K3's highly 
> accurate internal 2-tone generator (as did we). 12-V class radios are 
> rarely better than -30 dBc on their worst-case band, and some are in the 
> -23 dBc range, based on a survey of QST reviews from the past 5 years 
> (more on this below).
> 
> QST's published -27 dBc figure was measured with an external 2-tone 
> generator via audio injection (this is the ARRL's reference method). 
> This was disappointing for us, since we were expecting -30 dBc. The fact 
> that they did see -30 with our internal 2-tone generator suggests that 
> the SSB setup procedure in the K3 manual, and/or our SSB ALC algorithm, 
> could be improved. We're looking into this already. Any improvement we 
> make in firmware (or hardware, for that matter) will immediately be made 
> available to all K3 owners.
> 
> Transceivers that are very heavy (including some that probably have 
> their own zip code) can incorporate a large internal or external power 
> supply that provides greater than 12 V (typically 24 to 50 V) for 
> improved PA-stage overhead. Some can even be operated class A, which I 
> applaud. But neither greater weight nor class A operation near 100 W is 
> possible in the K3's form-factor. At just over 8 pounds, it's portable. 
> This *was* a design goal  :)
> 
> QST always publishes the worst-case per-band IMD number, in our case on 
> 12 meters. On most bands, IMD is much better than this by any 
> measurement method, exceeding -40 dBc in some cases. The worst-case IMD 
> is also much better if you're running less than 100 W. So, anyone 
> driving an amplifier that requires less than 100 W to reach full power 
> will see even better numbers.
> 
> 
>> My question to Elecraft is: If this had been a
>> factory assembled unit, would it have passed QC at Elecraft?
> 
> There is no difference in measurement method or performance between kit 
> and assembled. The 10-W and 100-W modules are all pre-tested before they 
> go into either the radio or the parts kit. The RF boards are also 100% 
> pre-tested, and any problem with IMD would show up immediately. But IMD 
> is generally a non-issue for the RF board, which at the 0-dBm transmit 
> drive point shows worst-case 3rd-order IMD of -45 to -55 dBc.
> 
> I'm sure this unit passed our QC tests, given that the League found -30 
> dBc worst-case with the internal 2-tone generator.
> 
> 73,
> Wayne
> N6KR
> 
> 
> ---
> 
> http://www.elecraft.com
> 
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft   
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>