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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