[FoxHunt] IARU controller question

[Jay Hennigan]

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)

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