[Elecraft] SSB IMD

[Joe Subich, W4TV]

> Is there something critical in the radio that
> gives this outcome? Critical adjustment perhaps?
> Is it very sensitive what PS we use (ala W4ZV)?

Yes, it is very sensitive to power supply voltage. 
Look at any of the application notes - the one 
Craig mentions for the P-P RD100HHF FETs is a 
good example.  Decreasing Vcc (or Vdd) by just 
one Volt will increase the IMD at 100 Watts by 
10 dB and decrease the maximum output power by 
almost 20 Watts.  

Running the power supply at 14.0 - 14.5 Volts and 
using a power supply with good dynamic regulation 
will go a long way to keeping the K3 "clean." 

73, 

   ... Joe, W4TV 
 

> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jan Erik Holm
> Sent: Tuesday, January 27, 2009 1:54 AM
> Cc: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] SSB IMD
> 
> 
> Yes I´ve seen those figures, there are are lot of
> data from component manufactures however by the
> time we see the finished product data doesn´t
> even come close.
> 
> I tried to look for the data on the FT-990 that
> K6LL informed about but couldn´t find it. I was
> thinking what reference level they used, I think
> I remember ARRL changed their procedure, the -38
> prity well could be -32 in real life.
> 
> However, something struck me, why is it we see
> this big variation in data on the IMD3? We have
> a spread between -38 to -24 dB. A number of
> people has measured below -30 dB and as far as
> I know "only" one around -38 dB. Who is right
> and who is wrong?
> Is there something critical in the radio that
> gives this outcome? Critical adjustment perhaps?
> Is it very sensitive what PS we use (ala W4ZV)?
> 
> As I said before, here I am first time on 20m
> SSB and people report trash around my signal,
> i e bad IMD. However at that time I had K3 at
> 120W, aftter I´ve made measurements and it
> looks like something slowly starts to happen
> at 80W.
> Also I have myself heard K3´s on SSB with "trash"
> around the signal "however" I have also heard
> K3´s that did NOT have that.
> So what´s going on here, I´m getting reel puzzled
> and frankly quite tired of this.
> 
> I wish there would be a "service manual" available,
> like there is for any Japanese rice box. I mean
> a manual that contains all data for all adjustments.
> Why not??
> 
> / Jim SM2EKM
> ---------------------------
> Joe Subich, W4TV wrote:
> > 
> >> Jan Erik Holm wrote:
> >>> Bill and others, hold on and think about these
> >>> figures. -35 to -38 dB IM3 !! We are dealing
> >>> with 2SC2782 transistors operating at around
> >>> 12V DC. I say no more, the knowledge and intelligent
> >>> individual will understand.
> > 
> > I would be careful here ... the Toshiba 2SC2879 data sheet
> > clearly does -38dB IMD at 60 watts with VCC=12.5V.  There
> > are certainly devices capable of that level of performance  
> > means that there are devices capable of that level just as 
> > there are devices capable of similar levels of performance 
> > at 120-140 watts per device with Vcc=28V. 
> > 
> > I would expect the 2SC2879 to also be capable of this level
> > of performance ... if not, I would have expected the design 
> > of the KPA3 to have been based on another device. 
> > 
> > 73,
> > 
> >    ... Joe, W4TV
> >