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

[William Kennedy]

Back in the early 70s I served on several “Ocean Station Vessels” in the USCG. One of our missions was to provide beacon service to aircraft crossing the Atlantic. and deep ocean rescue.There were ships stationed from south of Greenland, Ocean Station Bravo and on south to Station “Echo.” The ships were approximately in the mid Atlantic. We provided a radio beacon in A2 in the MF aeronautical beacon band. As I recall, power output was about 400W to a fan antenna.

We also held watch on 500Kc (obviously) and a MF “working frequency” to communicate with ships sending “OBS” data for the AMVER program. In the radio room one would see a watch stander standing a “split-phone watch.” One ear of the earphones to one receiver and the other ear to a second receiver - and keeping a log of traffic on both circuits with a manual mill. Certain ops from flagged vessels from the USSR and Poland would occasionally try to “burn” the US op buy sending so fast that the US op had to send “QRS.” This was during the cold war of course, and was a little “gotcha.” But, experienced US Radiomen would give it right back to them!

Maybe it’s just me, but as a GMDSS operator, I am not particularly impressed with the system. Some aspects are good but a deck officer has many other important duties to attend to and skill levels with the various GMDSS functions varies widely. It’s been a number of years for me, so maybe it’s changed. I hope so.

CW radio was and is relatively simple and efficient. Poor countries and poor shipping companies can effectively communicate without the huge outlay in money to equip their vessels and train every deck officer in the entire fleet.

I’m kind of a fan of keep it simple, stupid.


On Oct 6, 2018, at 7:43 AM, g4jht <g4jht at eircom.net> wrote:

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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