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Re: [Amps] Measuring IMD in a home workshop

To: Amps Reflector <>
Subject: Re: [Amps] Measuring IMD in a home workshop
From: "Bob Wilson, N6TV" <>
Date: Mon, 27 May 2019 18:23:28 -0700
List-post: <>
The new Elecraft K4 XCVR announced at Dayton will support the
pre-distortion concept when connecting the KPA1500 "TX SAMPLE" output to
the K4 TX SMPL IN connectors.

Bob, N6TV

On Mon, May 27, 2019, 6:10 PM Jim Thomson <> wrote:

> Date: Wed, 22 May 2019 14:23:12 -0700
> From: "Bob Wilson, N6TV" <>
> To: Amps Reflector <>
> Subject: Re: [Amps] Measuring IMD in a home workshop
> <The Elecraft K3 also has a built-in 2 TONE generator.
> <Switch to SSB mode
> <Exit the menu and tap the *XMIT* button.  You can vary the amplitude of
> one
> <of the tones using the MIC knob; the other is fixed.
> <73,
> <Bob, N6TV
> ##  Nice wont  work !    The  IMD  from a K3  is an abysmal –24
> db  below one tone....
> which is on a par with  sweep  tubes from the  70s.   All  that the  2
> tone generator thats  built into the
> K3  will  achieve... is an easy method to measure the  K3s  IMD, thats
> it.
> ##  IE:  to test the IMD  from a 1.5 kw linear, the driving source has to
> be a LOT cleaner than the amp under test.
> You cant use the  2 tone  /  100  w pep out from a K3,  to test  IMD on a
> L4B amp with its  2 x 3-500Zs.
> ##  something like an  ANAN  7000 / 8000, using pure signal will  work.
> They are typ  -70 for  IMD3 +
> ##  So will a yaesu  running Class  A.    Class  A  is very clean. –70  to
> –85  for  IMD3+
> ##  another method is  to use  two xcvrs,  each outputting a CW  cxr....
> then combine the  2 x signals
> with a hybrid combiner.   2  tone spacing would be equal to the
> difference between the  2 x VFOs.
> ##  My problem with the  2 tone method is  everything is In a steady
> state.... like  B+, bias, drive,  ALC, etc, etc.
> IE:  all loads are static, and not normal  ssb.
> ###  Having said all that,  I have  two  FT-1000-MK-V’s.     I TX  on one
> of them.... while listening a bit off freq  on the
> 2nd xcvr.   I then  toggle the  TX  between Class  AB.... and the
> cleaner  class  A..... and the  difference in imd / splatter
> while listening on a 2nd  xcvr is blatantly obvious.   I tune  2nd xcvr
> just off freq enough, so no splatter is heard.... while using
> Class  A  on  tx.    Then swap to  class  AB... and yoza.... splatter
> galore.
> ##  Unless the xcvr is something like the  ANAN, using  Pure  signal,,,,
> or Class  A  with the yaesu,  its all a moot point really.
> Any decent linear  TUBE  amp  will have far better  IMD  vs the  typ
> xcvr... like the K3..and  every other  xcvr out there.
> ##  Most  SS  xcvrs  will have cleaner  IMD  when the PO  is reduced a
> bit, and depending on drive required for  the linear amp
> under test, that could easily affect results.   Big difference between
> 100w drive to a 2 x 3-500Z  amp... and  40-50  watts  into
> a  8877
> ##  SS  1.5 kw amps  are a whole  different ballgame.   IMD is typ not
> good, on older models..when run at max rated power.
> ##  still another method is to monitor the Tx  ssb  signal on a spectrum
> analyzer...or sdr rx.   Assuming a semi clean xcvr,
> you can then see how wide the  ssb  signal is...when barefoot..or with
> external linear amp on.
> ##  yaesu, kenwood,  icom,  elecraft, all need to get with the program,
> and implement some form of  either analog or digital
> pre-distortion techniques in future  xcvrs.   Then the sample can be taken
> from the  1.5 kw  amp itself... fed back to the xcvr,
> the the  pre-distortion  concept  will correct for non linearity  in the
> external amp as well.   Folks using  ANAN  xcvrs   driving
> external  linear amps  are all having good success.  IMD on the external
> amp is much improved.
> ##  Big difference between an  ANAN   7000 / 8000  with its  -80 db  imd
> vs  -24 db  imd  from a K3.   Apples +  Oranges.
> Jim   VE7RF
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