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.
73,
Bob, N6TV
On Mon, May 27, 2019, 6:10 PM Jim Thomson <jim.thom@telus.net> wrote:
> Date: Wed, 22 May 2019 14:23:12 -0700
> From: "Bob Wilson, N6TV" <n6tv@arrl.net>
> To: Amps Reflector <amps@contesting.com>
> Subject: Re: [Amps] Measuring IMD in a home workshop
>
> <The Elecraft K3 also has a built-in 2 TONE generator.
>
> <Switch to SSB mode
> <Set *CONFIG:TECH MD ON*
> <Set *CONFIG:2 TONE ON*
> <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 try...it 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 dynamic...like 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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