Re: Sideband Suppression (receive) #ubitx #ubitx-help

Tim Gorman

I've never been able to get over 25db of carrier rejection according to
my Rigol DSA815. Not unless I move the BFO so far that signals are
unintelligible. If you adjust by 6db to allow for PEP equivalence this
is still only 31db of rejection.

In looking at the modulator circuit I don't see much of a way to
increase carrier rejection without major butchery, i.e. totally
replacing the modulator with a ring mixer which would allow providing
for a carrier balance adjustment.

tim ab0wr

On Fri, 27 Apr 2018 18:22:21 -0700
"ajparent1/KB1GMX" <kb1gmx@...> wrote:

Two things result in carrier...

One is the BFO too close to or in the filter passband, it should be
6-10 db down the edge of the filter. Blaming the filter will not fix
that, unless its seriously broken.    NOTE: Each unit will vary some
on the best BFO setting this happens with commercial filters too.  

The other is imbalance in the modulator circuit.  Solution is fix it.

There is a remote possibility of a tone at higher than you can here
present in the tx due to a circuit or wiring issue. 

Its not rocket science to measure the power out and the residual
carrier.  a 50 ohm load, a diode detector is all that is needed plus
a voltmeter.  Compare power out at full power and with no audio at
all the ratio in DB should be better than 40DB (10,000:1) or for 10W
out less than 1mW.


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