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Author Topic: Introduction to Drift Net Fishing beacons...  (Read 2843 times)

Offline Looking-Glass

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Introduction to Drift Net Fishing beacons...
« on: April 22, 2019, 0648 UTC »
Let me state before I delve into this subject, I am no expert, what you are about to read is from personal observations only and thus numerous variants can and will apply. 

The DNB (Drift Net Beacons) band I am covering here is 1.6 to 2.8MHz and while a lot has been written about these DNB's little is really known about them, various comments cover this subject via Google and you will read various opinions and theories.

Basically, a DNB is a small transmitter within a sealed barrel with a whip antenna, anchored to a very long drift net launched by a fishing trawler and left to ride the waves until the vessel returns to pick up the said net.

The Japanese fisheries authorities and radio licencing department have an allocated block for DNB's which are 1.825 to 1.907MHz designated Tropical Ocean Tuna Longline Buoy. The segment 1.912 to 2.000MHz and 1.834 to 1.890MHz are designated as "secondary service".  As on 24th of July 2018 there were some 491 Japanese fishing trawlers having a current licence for "Fishing Radio Buoys" according to authorities in Japan.

Not withstanding that other major Asian fishing nations (South Korea, Taiwan, China and Indonesia etc) have their own frequency blocks outside of what we consider the "normal guidelines" and then, in addition,  we have the European system to consider also.

There are four major manufacturers of these beacons in Asia/Pacific region and they are Kato/Wenden of Taiwan, Dong Yang of South Korea, Taiyo Japan and across in the Americas is Blue Ocean Tackle of Florida USA who sell these beacons. Basically, the power output ranges from just 05 watts to around 25 watts maximum.

Kato/Wenden of Taiwan sell DNB's covering 1.600 to 2.850MHz with either a four or ten watt version weighing around 22kgs, the company rates the battery life of around 500 hours and a service range of 200kms.

Dong Yang of South Korea
(http://www.radiobouy.co.kr/) sell two main models, the first being the PR-30 "Standard Bouy" 1.606MHz to 2.850MHz, no transmitter power is mentioned but a service range of 50-150kms is quoted.  The second model is the PRSC-30 equipped with "Selcal" and these beacons only answer/transmit when called by the mother ship, again, no transmitter power is mentioned nor a service range.

Taiyo Japan offer a 1.600 to 4.000MHz DNB of only eight watts of transmitter power with a suggested battery life of 720 hours and a service range of 270kms.

Ryokuseisha Electronics Company, Japan have an energy efficient dry cell  type battery DNB with a maximum power output of just three watts.  This DNB is set on just two frequencies A1A emission on 1978.5MHz and F1B emission on 1922.5MHz.  The Japanese authorities have a restriction on this DNB with a movement range of Pacific Ocean only.  The authorities have also issued a call sign block: FQ851 to FQ862 and HG308 to HG311 inclusive also some variants have been issued since on 1978.5MHz with FK and FO prefixes noted up until late May 2019.  Unlike normal DNB's this model does not have a preceding or ending carrier and doesn't transmit on a key on/off cycle, they appear at random, possibly activated by Selcal from the Mother Ship.

Blue Ocean Tackle, Florida USA (http://www.blueoceantackle.com) offer the KTUS-1L model range on DNB's with power output of three watts, eight watts and 14 watts with a service range of 400kms. These cost USD$995-00 each.

Transmitting times: Some of these DNB's are heard nearly every opening and I have been keeping a log on some of them. They start the transmission with a brief carrier and then the callsign three times and a concluding carrier before keying off.  The key off period is usually four minutes before the sequence begins again.  On odd occasions I have came across some of these beacons transmitting continuous for hours on end and thus ignoring the four minute key off period usually experienced.

I presume the ones that are transmitting continuous are activated into this mode via Selcal from the mother ship as it begins the process of tracking the net via Direction Finding and then the retrieval of the net.  There are Selcal activated models available, this would be sensible to conserve battery power.  The Japanese have two exclusive Selcal frequencies for this purpose, and thus these beacons never appear on what is considered the four minute cycle.

The strange thing about many of these beacons they are being heard for days and often weeks on end (my personal record is one beacon being heard for two months), this brings into question the Battery Life quoted by the manufacturers.  Maybe they have a small solar panel that recharges the battery, I cannot see this on the models featured at the sites previously mentioned. Maybe the mother ship only activates them at certain times of day?

1.713MHz  PO2   first heard 1646z on 17th March 2019, last heard 0921z on 16th of April 2019, so has been on for around a month, has been heard in between those dates at various times.
2.122MHz  DO63 first heard 1114z on 11th March 2019, last heard 1810z on 20th April 2019, so it's been around for well over one month now.
3.335MHz  EZ2  first heard 1745z 0n 16th March 2019, last heard 1225z on 19th of April 2019, also been on for around one month.

Call signs:  The DNB's mainly, in this region (Asia/Pacific), adhere to the two letters and one number prefix (QG5, OA0, DP3, UW5, VC9, CC1 etc.), however, there are variants to be found, and not restricted to any frequency block either, some variants are:

1.750MHz 3NRS
1.766MHz 2AFFG
1.767MHz 3FNY
1.817MHz 4QVZ
1.918MHz JU02
2.122MHz DO63
2.123MHz DB37
2.153MHz AFVEE

Now and again I have noticed a sequence in a particular frequency block too, maybe the DNB's belong to the same mother ship or company? Below are a detected call sign sequence in a particular frequency block, the only ones missed are PO4 and PO0.  Also detected was the OB series.

1.713MHz  PO2  0921z 16th April 2019
1.725MHz  PO3  0820z 04th April 2019
1.747MHz  PO5  1300z 11th March 2019
1.761MHz  PO6  0822z 16th April 2019
1.771MHz  PO7  0815z 16th April 2019
1.782MHz  PO8  0902z 04th April 2019
1.789MHz  PO9  1258z 11th March 2019

1.831MHz  OB2  1254z 18th March 2019
1.842MHz  OB3  1156z 02nd March 2019
1.853MHz  OB4  1453z 19th March 2019
1.863MHz  OB5  0859z 12th April 2019

Misfiring/defective DNB transmissions:

Sometimes you will hear a "misfiring" beacon which gives out a garbled or jumbled mess of CW, this I think is a DNB with either a transmitter fault or a battery near totally flat. An example of this was on 2.205MHz TEEE, or TETT, or TTEE etc logged on 2.205MHz 1929z 22nd of March and was noted again still in the same state on 24th of April at 1145z, also in mid April BS4 appeared on the same frequency 2.205MHz. Another was noted on 1.817MHz for well over a week transmitting either TTT or TET etc and is was also 50Hz off frequency. The call sign stutters and there is often a slight frequency shift which to me indicates the battery is about flat.

Unique calls and multiple frequency usage:

In the period March/April 2019 so far I have logged 203 unique call signs between 1.700 and 2.720MHz so there are a lot of them out there, virtually one every one Kilohertz.  Of note, that here in the Pacific region the two letter by one number call sign is the most dominant by far. Sometimes you will come across two or even three different beacons on the same frequency either in the same monitoring session or over a couple of nights.  A perfect example of this is:

2.565MHz  CU9  0854z  04th April 2019 539 report.
2.565MHz  GS0  1615z  23rd April 2019 529 report.
2.565MHz  DN3  1618z  23rd April 2019 549 report.

2.305MHz  DZ3  1221z  19th May 2019 529 report.
2.305MHz  GX6  1222z 19th May 2019  549 report.
2.305MHz  UI6   1224z 19th May 2019  519 report.

Note that DN3 appeared only three minutes after GS0 had keyed off.  Once or twice I have heard two beacons transmitting at the very same time on the same frequency too, maybe this is propagation?  I would think the trawler company would avoid having two of its own beacons transmitting on the one frequency to avoid problems DFing at retrieval time.  Three beacons, same frequency, but at different times unlike 2.305MHz in detail below.  Maybe three different companies with beacons on the same frequency but audible at the same time due to propagation.

Interesting with 2.305MHz with all three beacons on that frequency heard within three minutes, virtually one after another.  The question I have to ask within regard to 2.305MHz is whether the three beacons are in the same area, close to each other, or are we experiencing extended propagation (ducting?) and thus via extended distance factor over lapping paths via enhancement?  Very rare to hear three beacons on the same frequency within a minute or so of each other.

Distance factor and propagation variants, twist and turns abound...

This is a hard nut to crack, I have tried monitoring Grey Line but amazingly have logged two or three around 2.00pm local time which is 0400z well prior to Grey Line and in broad daylight as sunset not expected until 6.00pm local or 0800z, so either those beacons are off the coast of Sydney NSW some 110kms (direct line) away or are travelling by some unique mode of propagation?  Remembering that these DNB's are low powered ranging for 03 to 25 watts at best.

On May 19th 2019 I received BS4 on 2.205MHz from 0410z (2.10pm afternoon time in broad daylight) and CI7 on 3.308MHz and both were around the same strength slowly building as time passed, both were also transmitting continuously at the time. So I am at the conclusion that these two beacons are somewhere off the coast of NSW probably between Wollongong-Sydney-Newcastle sector.  Low powered NDB on 209KHz SCO Scone NSW was just audible at the time for a distance of 155kms with just 15 watts output. BNA on 206KHz at Ballina NSW, also low powered 15 watts at 590kms was not audible.

I have also tried to compare the paths to what is being heard on the NDB band by monitoring the aviation beacons but with little success. Maybe the 2MHz separation of frequencies is too much?  I figured if I was hearing New Zealand NDB's quite strong I would be hearing more of the DNB's, not so. Even comparing the low powered 25 watt New Zealand and Australian NDB's between 200-416KHz with DNB's being heard around 1.700MHz offers little comparison. Some nights the band is flooded with DNB's and the next night virtually nothing although the 200-416KHz NDB band is wide open with many low powered NDB's noted up to 2,400kms away.

Recently I have also tried to make comparison with amateur radio transmissions on the 160 metre band, especially when Pacific Island amateur stations and New Zealand are active, but then again a lot of the 160m diehards use much more power and more efficient antennas that the DNB's so it's back to square one.

Also I looked at WWVH signal on 2.500MHz to try and make a comparison as to what path is open etc, and to no avail, the Pacific is a huge expanse of ocean to cover.  Also WWVH runs quite a lot of transmitter power through dedicated antennas, even when propagation is poor WWVH is usually there but some DNB's have been logged 579 report at the same time.

Don't think these DNB's are weak in signal strength due to their low power, I have logged some in recent weeks up to 579 signal report, and sometimes 599 report just the other night 2.695MHz VF0 was 539 report at 0505z and had built up to 579 report by 0622z, ground wave across the ocean or enhanced propagation?  Another oddity is the fact I am located some 110kms inland from the ocean (direct line) and have a mountain range between me and the sea.  So how are the mid to late afternoon beacons making it across to me?

In conclusion:  That is about all I know about these fascinating little beacons that bob about the great expanse of our oceans, as to where they are?  Well, only the mother ship captain or the catch officer can tell us that.  It would be interesting to know as I am fascinated as to what distance is being covered by these drift net fishing beacons.

Comments most welcome... ;)
« Last Edit: June 27, 2020, 1156 UTC by Looking-Glass »
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Offline ChrisSmolinski

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Re: Introduction to Drift Net Fishing beacons...
« Reply #1 on: April 23, 2019, 1200 UTC »
Thanks for the well done summary!

Any thoughts about collecting all the logs into one central repository? I could try to throw together an online database, if you think it would be useful. Or perhaps the Wiki would be more useful? We have this (horribly out of date) page now: https://www.hfunderground.com/wiki/index.php/Fishnet_beacon

The basic format could be followed, perhaps with a notation as to the last date heard, and listener location, for each entry?
« Last Edit: April 23, 2019, 1223 UTC by ChrisSmolinski »
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Offline Teotwaki

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Re: Introduction to Drift Net Fishing beacons...
« Reply #2 on: April 24, 2019, 1318 UTC »
Great summary! Needs to be a sticky or in a Wiki.
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