Mark,
Sorry I didn't see this question earlier...
Quote:
Originally Posted by MarkJ
I am involved in a committee making recommendations about the radio capabilities of a particular Caribbean country's Coast Guard.
They do monitor HF.
What HF frequency/s do you think I should be advising them to monitor? They are certainly well within 100nms of the island nations to the north and south.
I would have thought 2182. But now?
|
1) 2182khz was really never a good choice....well maybe in the 1950's....but since the late 60's/early 70's, most users found the HF freqs (the new "Hi-Seas" channels) to be much more useful....and in the 1970's there was a steady, and rapid, decline in use of the 2mhz/MF freqs, 2182khz, etc...
And, since January 1999, there has been NO requirement for VOICE radio watch / monitoring of 2182khz...by vessels at sea nor coast stations...
And, further, even years before that most merchant vessels and coast stations (except for the USCG), used "2182 watch receivers" which did NOT listen for "voice" signals, but rather for the "two-tone
alarm signal", and only when they received this "alarm signal" did they un-squelch and then the watchstander could hear the vessel calling (although most of the time there was plenty of static as well!!!)
2) Since vertical antennas are/were required (by rule)on vessels for MF/2mhz, to maximize their groundwave
communications abilities, for all practical purposes this also reduces the effectiveness of Near Vertical Incident Skywave (NVIS)
communications...
And unfortunately, these vertical antennas are also very "noisy" receive antennas...
"Ground wave" communication range is very similar on 2mhz and 4mhz, and with 4mhz being much quieter AND usually having better NVIS signal strength, especially daytime...4mhz soon took over the functions of the old 2mhz MF maritime channels...
Overall daytime 2mhz (2182khz) communications, especially in tropical areas (with many hours of sunshine and hence high ionospheric "D" layer absorption...AND with scattered T-Storm activity on a regular basis), has always been poor, with ranges of usually 100 miles....
{In the mid/late 60's, I remember my Dad NEVER being able to raise "Miami" from the
Exumas (200 - 250 miles away), nor even
Nassau on some days...on 2mhz, using 150 watts and a 23' whip w/ a metal
hull ground/counterpoise....and in 40 years of my own sailing/radio career, I've only tried 2mhz ONCE....and unsuccessfully...}
3) The GMDSS rules require vessels at sea to maintain a
DSC radio watch on 2187.5, 8414.5khz, and "one other
DSC frequency" (to be determined by the vessel's master, based on vessel location,
route, time-of-day, radiowave propagation,
weather, etc.)....
However, in actual practice all the GMDSS
gear (and even the M-802) has six-channel DSC scanning receivers, so vessels that comply with GMDSS rules are monitoring/scanning all six DSC freqs (2187.5, 4207.5, 6312.0, 8414.5, 12577.0, and 16804.5), so if I were in need of assistance and desired to raise help, etc. from vessels in my area, I'd be sending out a 6-channel DSC distress...(but if I had to pick only one channel, it would 8414.5khz first, and then 4207.5 second....and if then no joy, I'd send out a 6-channel DSC distress signal...)
So, here it's 8mhz first, 4mhz second, and then probably 6mhz third...
4) As for recommendations for what HF frequencies to monitor, that's actually an easy answer!!!
For local/regional coverage...typically from 25/30 miles to 500 miles daytime, and longer ranges at night....
For VOICE monitoring:
8291khz, 4125khz, 6215khz....(these are 3 of the 6 GMDSS Voice Distress, Urgency, and
Safety channels)
For DSC monitoring:
8414.5khz, 4207.5khz, 6312khz....(these are 3 of the 6 GMDSS DSC Distress, Urgency, and
Safety channels)
Although exact ranges and communications capabilities (radiowave propagation) vary with time-of-day, time-of-year,
solar flux, sun-spot activity, earth's magnetic field activity, etc....as well as local/regional T-storm activity affecting receive
noise, etc....here are the typical ranges/capabilities...
Daytime should yield excellent coverage out to ~ 500 (or more) with fairly low-noise, on 8mhz....and from 100 - 2000 miles at night...
Daytime should yield good coverage out to 100 - 200 miles, with some
noise, on 4mhz....and usually 25/30 miles - 1000 miles at night....
Coverage on 6mhz, typically falls in the middle between 4mhz and 8mhz....
5) My
advice:
a) Make SURE that whatever your committee recommends, it INCLUDES DSC-watchkeeping....
This is not only part of the GMDSS (unlike voice radio watchkeeping) and will move whatever island is considering this into the 21st century!!
But is also increasingly being equipped on pleasure boats and is actually being understood and used by them!!!
And, depending on
where the actual receiver is, it can allow even busy administrative staff / bureaucrats in an office to maintain a DSC watch, as the radio is silent until it gets a DSC message...
b) If there are
budget concerns, an
Icom M-802/At-140, with a 250' loop of wire for the main
antenna (strung up horizontally, about 50' - 60' above ground, in a square or triangle shape), with one end of loop to "antenna" terminal on the AT-140 and the other end of the loop to the "ground" terminal...will
work fine for this application....
And, a second similar loop
antenna, just fed directly with coax, for the DSC receive antenna...is a great idea.....or, if space (and/or money) is at a premium a short, 40' sloping single wire antenna (fed directly with coax), is a good second choice for a DSC receive antenna....
This set-up allows 24/7 monitoring of all 6 Int'l DSC channels as well as whatever HF channels they choose to "Scan"....
c) If
budget allows the Sailor / Thrane & Thrane series 6300 HF radios are really great...The 500 watt model 6350 is a super radio, but will set them back about $15,000 USD...
And they can put together complete GMDSS consoles and coast stations, etc...including antennas....
Loops, LPDA's, verticals, etc...all have their place/application....all it takes is money!!!
6) Have a look at the thread I started, a week ago, on the USCG and MF/2mhz comms on the SSCA disc boards...
http://www.ssca.org/forum/viewtopic.php?f=5&t=15726
Even years before this:
Quote:
Effective 01 August, 2013, the U. S. Coast Guard will terminate its radio guard of the international voice distress, safety and calling frequency 2182 kHz and the international digital selective calling (DSC) distress and safety frequency 2187.5 kHz. Additionally, marine information and weather broadcasts transmitted on 2670 kHz will terminate concurrently.
The Coast Guard will continue to maintain a continuous watch on VHF FM channel 16 (156.8 MHz) and on existing voice and DSC frequencies in the 4/6/8/12 MHz bands as described in the Coast Guard Navigation Center website http://www.navcen.uscg.gov/?pageName=cgcommsCall.
|
The USCG (and many others) has been discouraging the use of MF/2mhz maritime frequencies for many years now....
Quote:
Mariners are advised that calls to the U.S. Coast Guard on the international radiotelephone distress frequency 2182 kHz or the Digital Selective Calling (DSC) frequency 2187.5 kHz
may not be heard or may be severely degraded.
Instead of using 2182 kHz for distress calls, mariners should use high frequency (HF) radiotelephone or DSC in the 4, 6, 8, and 12 MHz distress or calling bands
|
BTW, Mark, I envy you....being in on the ground floor of such a useful and humanitarian
project, and dealing with RADIO at the same time!!!
How cool is that!!!
If you need more help, please let me know...
Fair winds...
John
s/v Annie Laurie
Linear Mode
Recent Discussions