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Author Topic: Is a simplex repeater useful in a disaster situation?  (Read 9126 times)
HS0ZIB
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« on: April 13, 2012, 05:14:02 PM »

I have one of the Argent units; bought it many years ago and used it to increase the range of the VHF HTs in a city area where I worked as a volunteer police officer (in Thailand).  The unit seemed to work very well - no complaints.

Now after the recent, (but thankfully small) tsunami here on Phuket Island, I've found this Argent unit again and was thinking if/how I could use it in a disaster siutation.

My first idea would be to permanently mount it atop my QTH antenna mast, allowing 2M HTs a greater coverage range in the vicinity of the international airport (I'm located 300 meters from the runway).  There is no 2M duplex repeater coverage in this area.

Or would it be more useful in a 'go-bag', and to deploy in a remote location?

My feelings are that if there were a major disaster in my area (tsunami/earthquake), then I/my equipment would be better-used to provide local and national radio comms from the region of the airport, which would probably be the first point of rescus/contact from outside the island.

Your thoughts/advice appreciated

Simon
« Last Edit: April 16, 2012, 01:11:29 AM by HS0ZIB » Logged
KG4RUL
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« Reply #1 on: April 14, 2012, 09:39:30 AM »

I would make it part of the Go-Bag along with a simple ground plane antenna that can be easily assembled/disassembled, a length of coax and some rope to hoist the antenna into a tree.
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K1CJS
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« Reply #2 on: April 15, 2012, 06:31:24 AM »

The very principle of a simplex repeater would preclude it from being used in any sort of situation when many people could be transmitting at once.  It is very possible that such a repeater could cause communications fowl-ups rather than help.

A simplex repeater works by recording the incoming, then retransmitting it.  If many people were to try to get into it all at once, the result would be garbled hash instead of legible voice being retransmitted--if the machine didn't lock up from the possible many units trying to access it at one time.

Now, for a single person--maybe two--using it to get into another repeater, there would be no problem, but for a stand alone repeater for general comms use, it simply isn't suited.
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K5LXP
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« Reply #3 on: April 15, 2012, 07:54:44 AM »

A simplex repeater works by recording the incoming, then retransmitting it.  If many people were to try to get into it all at once, the result would be garbled hash instead of legible voice being retransmitted

You mitigate that a bit by using coded squelch.  Only folks aware of how it's set up will be able to access it and would understand the issues of unheard stations on the frequency.

Which brings to light the overall fallacy of the op's goal - he's trying to be a one man first responder.  No emergency service operates with individuals in a vacuum.  For a simplex repeater, or any deployable communications resource, there needs to be coordination and efforts in concert with others along with training and practice to realize any advantage.  Without this, "when all else fails", this will too.

A simplex repeater might add value but only within a group with capabilities and training to use it.  Start with the group first, and implement what the communications goals require are rather than randomly setting stuff up with the idea it might be useful.


Mark K5LXP
Albuquerque, NM
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HS0ZIB
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« Reply #4 on: April 16, 2012, 01:08:33 AM »

Mark, your comments are absolutely sound, but not realistic in this developing country.  As part of the foreign volunteer police in Thailand (responsible for looking after the many foreign tourists who visit), I and my foreign colleagues have tried to work with the Thai authorities to organize formal processes, procedures etc for evacuation, disaster management.  Unfortunately, for reasons that are best not detailed here, we foreigners tend to be given rather short shrift by the Thai authorities.  (I say that after living and working here for 10 years, with a Thai wife and family, and including 6 years work as a police volunteer).

Take a simple example last week when the (thankfully small) tsunami hit the island.  The international airport was closed and the local Thai police was advising the many hundreds of stranded foreign passengers that the airport would remain closed all night, and to take an expensive taxi ride back to their hotels.  I went to assist and using my 'common-sense' about the time for tsunami waves to arrive after earthquakes, advised that the airport should reopen in 1 hour unless the wave was large.  Sure enough, the airport reopened 1 hour later and the passengers were very grateful for my good advice.

It is simply not possible or realistic to rely on the local authorities or citizens to act coherently in a time of disaster.  Sorry, the truth hurts...

(I was here during the major 2004 tsunami and the OneTwoGo air crash a few years ago, so I base my comments on experience)

Therefore, unless I find like-minded persons to assist, I have to use whatever skills I possess to provide some form of assistance in relative isolation.  The most realistic way to help is to ensure that my amateur radio station at the airport has the capabilities to offer off-grid Echolink-L connection from HTs in the locality, long-distance mobile HF comms from my car, and possibly some form of extended range repeater facility for the local 'CB' HTs that many locals use.

But I agree fully that a simplex repeater will confuse the hell out of those who are unfamiliar with it's use, or where many try to use it.  Far better to use it via coded squelch to provide extended coverage for 'those in the know'

Simon

PS - there was some suggestion from colleagues that I actually install a 2 meter repeater at my location, since it's generally outside the coverage area of the island repeater.  I wonder how 'cheap' a 2 meter, home-brew repeater would be?  (I guess the filtering/diplexer is the expensive part?)

PPS - 5 minutes after posting this there was another sharp aftershock which sent people running for the hills again.  I really must get my comms equipment fully sorted out and ready
« Last Edit: April 16, 2012, 05:29:38 AM by HS0ZIB » Logged
VA3NMI
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« Reply #5 on: April 20, 2012, 12:51:24 PM »


PS - there was some suggestion from colleagues that I actually install a 2 meter repeater at my location, since it's generally outside the coverage area of the island repeater.  I wonder how 'cheap' a 2 meter, home-brew repeater would be?  (I guess the filtering/diplexer is the expensive part?)


Depending on your skills and equipment, you may well be able to create a duplexer yourself for not high cost.

Our club put a 6m repeater on the air using a homebrew helix duplexer.  A quick google found at least one similar hit for 2m ftp://80.162.76.78/radioer/repeater-filter/2M%20Heliax%20Duplexer%20Design%20(Two%20Meter%20Duplexer)%20by%20WB5WPA.htm

The only special equipment used was a mini-VNA to tune the resulting assemblies before soldering them together.  We used a bit of donated helix, which while it may be hard to find, can come cheap as the end of some other cable if you have friends in the right places and/or find a really good dumpster.

Good Luck - and keep up the good work
Scott  VA3NMI
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