[ARDF] More 80m Testing with RGE RX-4

[Dale Hunt, WB6BYU]

Matthew Robbins wrote:
> 
> ...At about 900m, I had the gain at max, and I was
> wondering if that was normal.


    It didn't take very many times having to adjust the sense
    antenna to motivate me to find a better way!  It is a royal
    pain otherwise.  (I sent the instructions directly to Matthew,
    since most of you don't have RX-4s, but they should be on 
    Ron Graham's site under "user comments".)

    Yes, the RX-4 is pretty deaf.  I used mine in Hungary, and I
    could hear all the transmitters, but not with much margin to
    spare.  Fortunately, the furthest one was the one I skipped.



> 
>     One thing I thought about was the weird layout of the RX4....


     I hold it in my hand with my thumb over the ferrite rod.  The
     controls certainly aren't ergonomic.  The toggle switch for
     the sense antenna can be a problem when (not "if") a branch
     bumps it to the unexpected position.

> ...Would there be any problems from the additional wire between the
> antenna and the PC Board?...

> generally, are there any recommended mods for the RX4?


     Regarding other mods, there is no reason you couldn't move
     the ferrite rod, or change it for an air core loop.  I haven't
     yet decided if the sensitivity problem is the wrong grade of
     ferrite rod, the shield channel spaced too close to the coil,
     or if it needs some circuit modifications such as an RF preamp
     or a lower noise replacement for the MC3340 variable gain chip
     in the IF.  Also the temperature stability can be improved a bit
     by rewiring the VFO coil, and a bigger improvement by using a
     different coil a bit more surgery.  (On a hot day in the car, 
     the signal drifted out of the tuning range.)

        I had a few other changes I was going to try, but since 
     I've built other receivers I don't have much incentive to
     spend time on it.  But the basic receiver line-up with the
     NE602 - NE602 - LM386 is what I use in my "plastic pipe"
     receiver and it works quite well, so it may be worthwhile
     upgrading one if you have it.


> 
> One thing I considered was to ignore the 1-4 tone and just mark some
> small graduations on the RF gain...

     There are two distances that I am particularly interested in:
     when I am 4 minutes from the transmitter and when I am 1 minute
     away.  You can mark these with colored tape on the face of the
     receiver, then move them to fit your measurements on the model
     transmitters if needed.  Pacing off distances should be close
     enough if you don't have a good map, even if it means walking 
     out of the nominal practice area.  I do the same with transmitter and
     beacon frequencies on my tuning dial (and especially for Kuon.)

    - Dale


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