SIMPLE EASY SOMETHING FOR EVERYONE 80 METER REC
by Paul Daulton - K5WMS

 

My latest project: SESE80 -
Simple, Easy, Something for Everyone 80m rec.

SES080 article from QRP Quarterly Winter 2011
provided by Paul Daulton

This is a superhet using two singly balanced mixers, constructed of discrete components. A total of 8 2n3904 transistors, a LM386 audio ic, and five microprocessor xtals are used. Three 10.7 if transformers form the bandpass filter and vfo coil. Cost of the board mounted components exclusive of the PC board is about $12.00 Tuning is accomplished by four 1n4001 diodes used as varactors. It tunes 3500khz to 4000 mhz with a little overlap. Either a 10turn pot or two pots(50k and 5k in series) for course and fine tuning can be used. Pending the response from a couple of beta test builders I plan to submit it for publication. Performance equals similar designs using the ne602 or other IC chips.

Sensitivity and selectivity are good. Stability is fair, I have copied PSK31 from a cold start, for cw it works quite well. Properly aligned it is immune to BC feed through. Only test equipment required is a freq counter or gen coverage receiver to set vfo and VOM for preliminary tests. Frontend band pass is aligned for max noise, not critical at all.

Idea for this came from a qrp tranceiver designed by VK3agj, google BC547 qrp ssb and you will find it. I also used bias scheme from a direct conversion rec described in the first chapter of EMRFD by Wes Hayward.

I think this might be a good companion for the Tuna Tin Two's and other simple transmitters.
I have four prototypes on the bench all with different configurations. The picture is of the one I like best. I will send pics of others later. A couple of guys in the 4sqrp group have the parts to build copies, with boards made by Farcircuts.

Not anything new or cutting edge but I think there might be some interest. First two prototypes were built dead bug style with good results. Not much has been written about the single balanced mixers but properly used gives remarkable performance for minimum cost.


updated June 2013

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