[Elecraft] KX3 AM-breakthrough

Klaus Dittrich kladit at arcor.de
Tue Jul 30 05:20:50 EDT 2013


Again, thank you all for taking the time to contribute to
the issue.

Ken, there was a relay of Radio China in Albania but
I don't know if it is actually active.

Ralf, this morning I "measured"  the vfo leakage with my
second receiver a NRD-535 connected to a R&S active antenna
positioned at about two meters distance from the feedpoint
of my dipole.

At 15m the received vfo signal was about S3, dropping down
to just noticeable if I switched on the isolation
amplifier.

I wonder why this isolation amplifier is off by default,
but assume the reason is to save battery power which
does not matter in case of use as home station.

So I would like to know if there are any degradations
in IP3 or more probable in opposite sideband suppression
if this amplifier is permanent in the signal path because
of additional phase shifts.
As far as I remember this case is not included
in the OSB adjustment procedure.

I was astonished to see during OSB adjustment how
sensitve the procedure is to frequeny dependend phase
shifts which I never thought they could be of importance.

Every 10th mm on the circuit board and every ns in software
seems to matter.

Wayne, could you please drop a few words about this?

I assume such small rf-levels are not able to cross-modulating
the local oscillator's "carrier" in the AC mains.
In general I agree with your technical analysis and hope we met
us on the bands some day for a longer talk.

"If the AM breakthrough is a real (direct rectification) one, the 90 
degree phaseshift between the two quadrature "channels" would probably 
not occur (in contrast to "true" signals). This could probably be used 
for suppressing it by software (?)"

I such a direction my hopes went.

Wayne, thank you very much for answer, technical statements, 
clarification and your offer.

Now the reason of this AM-breakthrough is determined by the relevant 
authority.

Good to hear as well that the dynamic range at 2 kHz drops not as far as 
I assumed because of the data measured by Sherweng.

To your offer, which is much appreciated, I have several technical
questions but these we will handle in separate e-mails as desired.


Igor, I agree the problem is not a permanent one, as I already
wrote and in no way my intention was to cast a bad light on the KX3.

I already had a lot of fun and fine dx qso's with it.
But if your are in a cw-qso at 15m and suddenly because of this
AM-breakthrough you can't complete it, that's annoying.

"Did you send message to elecraft technical support? Or do you expect 
them to answer your concerns here on the reflector? They sure are not 
obliged to do the latter."

Shure they are not, but in practice they do. :-)

I contacted qrp-project (main Elecraft distributor in Germany) before.
They told me the problem is already known but the reason unclear.

Now, now it is clear. :-)

"BTW, later you may discover couple of other issues  with KX3 which are 
not that obvious and which I have already discovered. Or you may just 
search this reflector and find out."

I will look at your contributions to find out or contact you direct. OK?
I am always interested in problems. :-)

-- 
73 es mny tnx
Klaus DF1TL




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