[FoxHunt] IARU controller question

[WBob]

FM squelch circuits measure the noise outside of the modulation band  and when the 
carrier (any carrier) causes any limiting in the IF amplifier the noise is reduced and 
the squelch opens. The only thing that might preclude the carrier from quieting an FM 
receiver is if there was enough signal coming through to the squelch filter to fool it 
into thinking it was noise. An off tuned carrier would do this (the squench filter is 
about 15-20 kHz in a well designed FM receiver) or a lot of over modulation...anything 
that would make stuff in this filter bandwidth.

WBob

Kuon & Dale Hunt wrote:
> Charles wrote:
> 
> 
>>It wasn't until I hunted using an AM transmitter to track an FM fox (slope
>>detection) that I realized the problem ,,,
>>
>>With an AM receiver I could only track the fox when a tone was being sent.
>>Which meant that only for a small fraction of the 1-minute cycle was I able
>>to actually track the fox...
> 
> 
> 
>     As those of you know who have attended ARDF events in other
>     Regions, keyed-carrier AM tone modulation is the standard.
>     (Though I did encounter the continuous carrier FM in Japan.)
> 
>     This provides an experience similar to hunting 80m signals -
>     you can only take a bearing during the tone portion of the cycle.
> 
>     One thing I noticed when hunting a keyed-carrier AM signal in
>     Victoria was that it would not open the squelch on my 2m HT,
>     regardless of how strong the signal was.  (I've had the same
>     experience listening for ELT beacons using a 2m rig with AM
>     receiver in the Aircraft band:  apparently the squelch was
>     still designed for FM.)  In both cases I had to hunt with the
>     squelch open.  This poses a bit of a dilema when we are trying
>     to gain experinence at international hunts while encouraging
>     newcomers to try the sport.
> 
>     Actually, one advantage of the keyed carrier transmission is
>     that you can tell which transmitter you are listening to even
>     when "whoopee" (tone "S"-meter) receiver mode.
> 
>     At this point I think we will all just use whatever transmitters
>     we have available, but it is a point to consider as we plan for
>     new ones.
> 
> 
> 
> 
>>When Region 2 writes its ARDF rules we should consider whether to require
>>that FM transmitters turn off their carriers between "MOx" transmissions.
>>This would level the playing field between those using AM receivers and
>>those with receivers equipped with S-meters.
>>
>>In the meantime I've reprogrammed my Montreal controllers to send the
>>callsign identifier first, and then they transmit standard code characters
>>and spacing until the end of their transmission.
> 
> 
> 
>     Actually the ID first is the proper method of ID'ing in Canada,
>     where the rules state each station must ID at the beginning of
>     an exchange of transmissions and at least every 30 minutes
>     thereafter.  Technically it would be legal under US rules as long
>     as you let it ID before turning it off.
> 
>     Meanwhile, a further technicality:  the US rules require any ID
>     sent automatically in Morse Code to be no faster than 20 WPM.
> 
>     Playing the ID at a different speed/tone freq is probably a good
>     idea when we have visitors from other Regions, since I've never
>     yet encountered a transmitter in Region 1 that had an ID on it.
>     This will clue in the hunter that this is NOT part of the
>     standard MOE/I/S sequence.  (Especially Charles, or they might
>     think every transmitter is TX #2!)
> 
> 
>          - Dale WB6BYU
> 
> 
> _______________________________________________
> FoxHunt mailing list
> FoxHunt@mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/foxhunt
> 
>