G4ALG's QRP Radio Pages

[ Previously GW4ALG (QRT in February 2007) ]

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IC-R71E Receiver

My IC-R71E was a gift from my good friend Robert Davies, M1FFY who gave it to me in 2021.  Robert no longer had a use for the receiver which, following re-alignment, is providing excellent service at G4ALG as the main station receiver.

As many people have found, the voltage controlled oscillators (VCOs) in the R71E become unreliable, with the VCOs going out of lock.  This was the case with the receiver as received from Robert.  The cause is almost always due to the plastic trimmer capacitor in the VCO where their internal contacts go high resistance.  Repairers often replace the plastic trimmers with ceramic trimmers, and this resolves the problem.  But I found that simply turning the trimmers back and forth many times also resolved the problem.  By this means, I was able to get the trimmers into a stable state such that I could proceed to re-align the receiver without further issues.

I have modified the receiver by fitting a sidetone oscillator which can be keyed from an external source.  The oscillator is based on an analogue phase shift oscillator and the output signal is connected to the internal audio amplifier.

I have also added an Icom FL-32A (CW Narrow Filter, 500Hz) and replaced  the original Icom ROM module in the R71E with the module produced by Roberto, IK2RND.



Here is the circuit of the sidetone oscillator that I built into the R71E: