[FoxHunt] IARU controller question

[WBob]

Now I am confused.

A2A will generate a carrier and two sidebands that are in phase and will be limited 
out in a "good" FM receiver leaving you with no tones. F2A (narrowband FM) will 
generate two sidebands that are out of phase and will not make tones in a "good" AM 
receiver. SSB, with carrier, will work on both to make tones.

WBob

Marvin Johnston wrote:
> 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/
>>WestNet:  Connecting you to the planet.  805 884-6323
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> 
>