[FoxHunt] IARU controller question

[Marvin Johnston]

It looks like you are both right. The specs used for International
competition is on the web at:

http://www.ardf-r1.org/html/ardfrules26b_rev1.htm

>From that spec for 2M ARDF, "Mode A2A (keyed carrier modulated by AF
tone or continuous carrier modulated by keyed AF tone)."

Jay Hennigan wrote:
> 
> On Wed, 14 May 2003, Kuon & Dale Hunt wrote:
> 
> >     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.
> 
> I'm not sure I understand this.  There's A1 which is straight CW,
> and A2 which is a continuous carrier with an AM tone which is keyed.
> 
> My understanding was that 2 meter IARU foxes used A2.  During a
> given transmitter's one-minute interval it has a continuous carrier,
> and the morse M-O-x identifier is sent as tone modulation of that
> carrier.  During that transmitter's "off" time, it's off.  In other
> words, just like the typical USA 2m foxes, but AM instead of FM.
> 
> The above statement implies that the spaces inbetween the CW elements
> and words are without carrier, that BOTH the MCW tone and the carrier
> are keyed on and off with each code element.  Is this true?
> 
> >     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.
> 
> Most integrated circuit receivers with a squelch circuit use a noise
> gate squelch which involves a limiter and FM detector, even if the
> audio demodulator used to drive the speaker is AM.  Typically the
> RSSI (S-meter) is also a function of the limiter used with the FM
> detector.  I would think that a regular 2m FM HT squelch would work
> on an AM signal.  If the carrier is indeed being keyed with the code
> elements, the squelch circuit integrator and logic might not be fast
> enough to function reliably at higher code speeds, but this shouldn't
> be that much of an issue at least on the M-O characters with the speeds
> normally used.
> 
> >     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.
> 
> That's where a stereo headset with whoopie and receiver audio is a nice
> feature.
> 
> >     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.
> 
> If there's a standard, we should migrate towards it, especially for the
> more advanced hunts.  Practice hunts to get folks with only a 2m HT hooked
> on the sport are a different ballgame.
> 
> >     Meanwhile, a further technicality:  the US rules require any ID
> >     sent automatically in Morse Code to be no faster than 20 WPM.
> 
> Actually, that's only true if the automatic device is used only for
> identification.  Although I suppose that technically the M-O-x sequence
> is a form of "identification" in the strict sense of identifying which
> transmitter is on, it isn't "station identification" as defined in the
> rules.  Kind of a gray area.  If the M-O-x is over 20 WPM, then the ID
> probably can be as well.  M-O-x at 5 WPM and the CW ID at 40 WPM would
> not IMHO be a legal ID.  97.117(b)(1)
> 
> --
> Jay Hennigan - CCIE #7880 - Network Administration - jay@west.net
> NetLojix Communications, Inc.  -  http://www.netlojix.com/
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