[ARDF] US ARDF Championships: 2m AM receivers...

[Dale Hunt, WB6BYU]

Jay Hennigan wrote:
>
> AM vs. FM isn't as significant to me as keyed vs. continuous carrier.
> Most ARDF receivers have an audio S-meter (whoopie) function.  With
> continuous carrier the tone is audible for the entire cycle.  Keyed
> carrier causes the tone to follow the code elements.  This takes some
> adjustment for people used to continuous feedback.
> 


   This certainly makes a big difference.  The keying on the
   original Montreal controllers is very slow with extra space
   between the sets of characters (except for TX #5).  This
   makes it particularly difficult to hunt as the carrier is
   off for comparatively long periods at a time.  But no worse
   than using the same controller on 80m CW, of course.  I may
   be converting a couple of my transmitters to keyed carrier FM
   for practice.


   One other note on receivers:  some like the VK3YNG use the RSSI
   (signal strength) output of an FM receiver chip for the AM
   demodulator.  The problem with this is that the apparent audio level
   does NOT vary with signal strength the way it does for a 
   conventional receiver with a diode detector.  (The DC output level
   changes, but the AC component remains constant.)  So it is
   easier with most of the European sets to find the strongest
   signal by ear while listening to an AM signal, while the VK3YNG
   sniffer requires the use of whoopee mode.


      - Dale
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