[ARDF] tuning the Ron Graham RX-4 receiver

[Dale Hunt, WB6BYU]

   Could be due to vibration.  You could try some wax or a wrap
   of Teflon pipe thread tape around the core..

   Well, actually that used the 455kHz IF transformer core with an 
   internal thread, so maybe just a strip of sticky tape across the
   top of the coil can, presuming it also sticks to the top of the
   tuning slug.

   Though I'd be more inclined to look for other explainations, such
   as the telescoping antenna not being extended by the same amount
   or one of the wires coming lose on the antenna or switch.  If you
   turn the loop so it nulls a signal and switch in the sense antenna,
   if there is no detectable increase in the received signal level
   then I'd suspect an open circuit or gross misadjustment somewhere.
   (Might be in the adjustment pot also.)  If the pattern changes, but
   is no longer adjusted correctly, then it sounds like the coil slug
   may have slipped.

   You might consider measuring the resistance of the adjustment pot
   and recording the value on the inside of the case.  That will allow
   you to get one of the adjustments correctly reset with just an ohmmeter
   the next time you have to readjust it.

   Also, if you retune the loop antenna trimmer, you will probably
   have to readjust the sense antenna.

   And make sure you aren't holding the receiver with a finger on
   the mounting screw for the sense antenna, as that could throw
   things off, too.  But if you can detect NO CHANGE in the pattern
   (especially the depth and position of the nulls) when the sense
   antenna is switched in, then I'd make sure the sense antenna
   really is connected to the rest of the circuit.  I think that
   the resistance from the whip to ground should give you the
   information you need for that.

   Good luck!

       - Dale



Matthew Robbins wrote:
> 
> I had a set back with the RX-4.
> 
> I tuned the sense antenna several months ago, and it was great!  I had
> sense from 10m to 800m.
> 
> Saturday, I got it out for a demo event, and the sense didn't work *at
> all*.  No perceptible difference between front and back.
> 
> I've had it in the car for 3 or 4 trips to local ARDFs, so it has been
> exposed to some vibration.  I wonder if it's got a slug that's not
> tight enough to hold its position?  I remember it being pretty easy to
> turn.
> 
> Should I try some wax or Q-dope or something to lock it in place after
> I tune it again?
> 
> {Val: This might explain why you were having trouble with it.}
> 
> Matthew
> AA9YH
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