Thursday, 21 August 2014

Wispy receiver - really as bad as I think?

A thought occurred to me a while ago - is my Wispy receiver really as bad as I think, or is there something else ive forgotten to take account of?

Well, using my Marconi 2955, I get no noticeable reception until -50dBm, ish. BUT - Im using the test sets own 'scope and audio system, or my Hitachi 212 oscilloscope, what if the audio level from the receive chain is too low for these? Might it be that the level from the AF stages is not sufficient to drive either of them until this input level?

Somewhere, I read about how Roger determined his sensitivity figures, which were done much like mine by ear, but I think Roger listened directly to the output of the AF strip. Now, did he use headphones, or perhaps a Hi-Z crystal earpiece? Is this my problem - I dont have enough audio output to actually listen to to determine the sensitivity?

Im going to rebuild the audio strip as a self contained module on Veroboard. I can then test it to see how it works, and either feed an earpiece, or use it to drive another amp capable of giving enough level for a small loudspeaker.

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