[Elecraft] K3S QST Article

[Wes Stewart]

Without too much elaboration let's just say that I discovered this problem long 
before ARRL did.  (S/N 10020)

I can tell you that my measurements show that IMD varies with Vcc (Vdd), drive 
level, power output and frequency.  This latter parameter is, as best as I can 
determine, inexplicable by anyone, including the manufacturers of the 
transistors.  Initially, I compared my shiny new K3S to my tired old, unmodified 
K3.  At the original test frequency, 3.8 MHz the K3 had much lower IMD that the 
K3S under otherwise the same test conditions.  Moving up to 14 MHz the situation 
reversed.  Each of these radios had a different "sweet spot," neither of which 
was representative of the general case.  If a testing entity happens to test at 
only one frequency and reports the results as typical then you get a false sense 
of the general performance.

Wes, N7WS

On 10/14/2016 8:03 PM, Dave Hachadorian wrote:
> Yaesu FT-990, 12V finals
> 3rd order TX IMD  -38dB
> ARRL Review 11/91
>
> ARRL heaped glowing praise upon this rig way back in 1991 for its
> Tx IMD performance.  So, what was Yaesu's secret, and why haven't 
> manufacturers figured it out and capitalized on it ever since?
>
> Dave Hachadorian, K6LL
> Yuma, Arizona
>
>
> -----Original Message----- From: Kevin
> Sent: Friday, October 14, 2016 5:14 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3S QST Article
>
> The cause for this is the use of 12V finals. It would be much
> improved
> by moving to 24 or 50V finals.
>
> Move the /K3s II/ to 50V finals, say a pair of MRF 150's, limited
> to 150
> or 200W max output. Design/Sell an outboard 50V switching supply
> capable
> of 15-20A continuous current, with a 10A 12V switcher built in
> for the
> rest of the radio.
>
>
> On 10/14/2016 1:33 PM, Bill Leonard N0CU wrote:
>> I would not expect the synthesizer (old or new) to be a
>> contributor the IMD
>> issue. Hopefully someone will correct me if that is a bad
>> assumption. To me,
>> the primary issue appears to be the linearity of the two RF
>> power
>> amplifiers.
>>
>>
>