[Elecraft] Simple spectrum analyser for SSB TX testing

[Don Wilhelm]

Dave,

Yes, such a 'block converter' (mixer) to convert the transmitted output 
to baseband is a great tool.
If I may, let me add some alternatives.  Some Elecraft builders already 
have some of the pieces required for this Spectrum Analyzer and may not 
realize it.

The spectral display can be most any of the audio spectrum analyzers 
that are available.  Many Elecraft builders already are familiar with 
Spectrogram which will also do the task nicely.   The dynamic range is 
limited by the soundcard, but even with only 60 dB of dynamic range, 
useful information can be obtained.

The Elecraft mini-modules can be used for several of the pieces.

In place of the 40 dB tap - a CP1 can provide either a 20 or 30 dB 
(depending on how it was constructed) coupling at its forward port (be 
certain to terminate the reverse port).  The Elecraft attenuator can be 
used between the coupler forward port to provide additional attenuation 
and prevent overdriving the mixer.  Also the 2T-GEN can be used to 
provide the 2 tone output if your computer soundcard does not do full 
duplex.

The signal generator should provide a +7 dBm to the mixer LO port for 
optimum performance (any attenuation built into the mixer will require a 
greater level).  The Elecraft XG1 or XG2 generators do not have enough 
output (50 uV is only -73 dBm) - but a QRP transmitter can be pressed 
into service for that purpose - only about 5 or 6 mW is required (do not 
overdrive the mixer), so the power from most transmitters must be 
reduced - a 2nd Elecraft attenuator mini-module will do that job.  Yes, 
you can test the SSB spectrum while tuned to the CW bands since 
everything is running into a dummy load - just don' try it with an 
antenna if you value your license!

Bottom line, most everything to do this task except the mixer and signal 
generator is available in the Elecraft mini-module line.

You did not publish a schematic of the mixer, although you described it 
well in the text.
There is a similar mixer module shown in Experimental Methods in RF 
Design page 7.35 for those who have that publication.

73,
Don W3FPR
 

Dave G4AON wrote:
> For those who are eager to build something while waiting for the 
> courier to bring your K3, you might like to try a simple spectrum 
> analyser. In the best traditions of amateur radio this can be built in 
> a few minutes using parts from your junk box. All that is required is 
> a computer with sound card and a signal generator or at least a 
> oscillator of sufficient level to feed a diode ring mixer. Details at 
> http://www.astromag.co.uk/ssa/
>
> Now you can check out your K2 with a two tone test!
>
> What do you think?
>
> 73 Dave G4AON
> K1 #1154, K2 #1892, K3... waiting...
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