[SOC] A2A is legal on all HF bands but not on MF in EI

[Bry Carling]

Wow - thank you Dave - I was away and couldn't get to this for a few days. It is a wonderful and interesting read!

Glad you still have the freedom to use MCW in UK !

73 - AF4K / G3XLQ


________________________________
From: soc-bounces at mailman.qth.net <soc-bounces at mailman.qth.net> on behalf of g4jht <g4jht at eircom.net>
Sent: Saturday, October 6, 2018 8:43 AM
To: Second Class Operators' Club
Subject: [SOC] A2A is legal on all HF bands but not on MF in EI

That is the interesting the FCC prohibiting MCW, but not illegal under
the ITU Regs -see below.

However if the GMDSS fails to raise anyone, when you hit the DISTRESS
button. Or you send the WRONG message - as happened with the SS El Faro
who carried no Radio Officer. You are then free to use any mode on any
frequency to draw attention to your distress and summons help. you can
even modulate the nearest TV station if you think it will work. That has
always been in the ITU Radio Regulations. Plus if you hear such a
distress signal you must provide assistance or take action (phone the US
Coast Guard  etc) to notify someone who can provide assistance -- that
is the law still.

MCW  a good old fashion AM  double side band full carrier signal
modulated 80% with a 1000 cycle tone and keyed at 45 wpm still only
occupies 2.1 - 2.2 Kc/s according to the ITU Regs. But the ITU allocates
"channels" that are 3 Kc/s wide below VHF in the international frequency
database. With each "channel"   consisting of  a designated frequency,
the center frequency and extend plus and minus 1.5 Kc/s on either side.
So the MCW or A2A signal keyed at 45 wpm  and occupying  +/- 1.1 Kc/s is
well inside any allocated ITU "channel"; it is narrower than a 3 kc/s
SSB signal.

I also thought the ITU had banned A2A (or A2 in old money)
transmissions.   According to the new ham frequency and mode table just
issued by ComReg, our equivalent of the FCC. A2A tone modulated double
sideband signal is permitted from 1810 Kc/s all the way up to 47200 Mc/s
(47.2 Gigs)!

The great advantage of MCW was and is that it cuts through the static.
On MF, its use reduced fatigue for the mandatory watch on 500 Kc/s,
especially from the static in the tropics, where it performs
significantly better than plain CW.

The comment regarding 600 watt A1 signal becoming  1200 watt A2 signal
is not correct.
Since MCW is used for short range coasting communications ship to shore
out to 200 - 250 miles, too much power would cause interference to coast
stations adjacent to that being called/worked. Ships transmitters for
use on the old MF 600 meter band , and on 500 Kc/s were limited to a
maximum of 400 watts A2A or A1A by ITU Regs. So 600 watts or 1200 would
get the FCC and the US Coast Guard, plus US Navy down on you for a trip
to the slammer. that sort of power would damage equipment and operators
hearing.

As far as I can remember the the most powerful MF Tx  I ever had my
hands on  was the ITT ST1610 around 1976. With 1500 watts of A3H/A3J  on
HF bands 4,6,8,12,16-17, and 22 Megs.

But the output power was limited down to 400 Watts of A3H/A3J on the
2Meg MHF band and 400 watts of A1A or A2A on MF, with step reduction
down to 25 watts on MF. When the 500 Kc/s distress frequency was
initially selected the A2A mode was locked in, together with full power
- 400 watts.

But most cargo-ship marine transmitters operating on the old 600 meter
band produced something more like 100 watts of A2. The requirement range
for a Class I ship - a ship carrying more than 30 passengers was 175 sea
miles range on 500Kc/s from the  main Tx and 100 sea miles from the
Emergency Tx. In each case sufficient power to produce a signal with a
field strength of 50 microvolts per meter. This according the the
Merchant Shipping Radio Rules 1967.

The Marconi Marine  main MF Txs of the time had four  807s in parallel
which produce around 100 - 120 watts output to give the specified range,
modulated by two 807s in a self oscillating circuit produced 80% depth
of modulation at 1000 cycles. The emergency Tx had three 807s with two
more in the modulator and was only required to provide the 100 sea miles
range.

For normal cargo ships larger than 1600 tons the transmitter ranges were
reduced to 100 sea miles and 75 sea miles for main and emergent
transmitters. While for coasters of 1600 tons or below that never
ventured far into the oceans both transmitters only needed to reach 75
sea miles.

I taught marine radio for a couple of years in the early 1970s - my
memory is pretty solid some things you never forget.

Hope it is useful. Have a great weekend guys, keep smiling. :-):-)

73s, Dave and Pene G4JHT/EI0DB/VP8ART.

Friends all over the world by skywave wireless telegraphy; CW and MCW
the true arts, in an over-digified age.




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