Re: Re: LF: Simple image-cancelling exciter for digimodes

[dl4yhf@freenet.de]

Hi Stewart,

Thanks for the suggestion - sounds too good to be true !
(to build an image-cancelling "TX"-mixer without the need for a phase-split audio if I understand you correctly).

I must admit I blindly followed the ARRL handbook which seemed to imply
"you cannot build an image-cancelling mixer without some phase shifting
on the low-frequency side" (unless you use the "weaver" method with
pilot tones).

I have some old CMOS 4052 somewhere (not 74HC...) so may try these.
When using std CMOS in my "conventional" prototype, the
sideband-suppression was worse than with the 74HCxxx because they were
too slow, and the L.O. outputs were not symmetrically enough.


Will let you know about any progress with this. 
At the moment  I'm quite happy with my old design which still
waits to be connected to an amplifier for an on-air test (but that
won't be before next weekend).


Best regards,
Wolf DL4YHF .




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Hi,

You may wish to consider a dual 4-input analog mux such as
the '4052.  For instance, see
http://www.semiconductors.philips.com/pip/74HC4052.html

You can connect the quadrature LO outputs directly
to the S1 and S0 inputs.  Then, because there are two
muxes, you can create a differential output without
needing to phase-split the incoming audio.

For example, assuming address sequence is 0-1-3-2-0-1-3-2 
(S1 lags S0) connect:

1Y0=Left ch.
1Y1=Right ch.
1Y2=GND
1Y3=GND

2Y0=GND
2Y1=GND
2Y2=Right ch.
2Y3=Left ch.

Then, the voltage between 1Z and 2Z is the SSB output.

Perhaps, you can use a transformer-coupled output.
Put a cap across the primary to resonate at the
approximate output frequency, and connect it from 1Z to 2Z
through a suitable resistor.  No op-amps or precise
resistors needed, and it provides the first stage of
filtering.

Disclaimer: I have not tried this, and there may be
a stupid reason why it won't work.  Please don't
laugh too hard.

73,

Stewart KK7KA





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