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Author Topic: Is this possible?  (Read 658 times)
CERTNEAL
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« on: September 29, 2009, 11:51:45 AM »

I have been brainstorming some ideas on how to get the best portable repeater system in the event of a disaster. One thing I am hoping works is a system of cross band repeater radios like the FT-8900. This would be cheaper than a conventional repeater and more mobile.

I am new so please forgive me if I am way off but it seems to me that one radio set to recieve on 2m and transmit on 70cm, then spacing the next radio a little off and have it the reverse would give a similar effect to a standard 2 meter repeater. Also that the second radio would be a shifted 2 meter frequency.

These would both be on small towers but would allow handhelds a good way to get out of the area should it actually work.

Any and all comments appreciated.

Neal
KJ4OPC
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K0BG
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« Reply #1 on: September 29, 2009, 04:39:34 PM »

That's what regular repeaters are for.

Cross band repeat is just a feature that's easy to add in most dual band radios. For its intended use, I guess it's okay. However, from my perspective, it's a toy with little added benefit over a real in-band repeater.

Alan, KØBG
www.k0bg.com
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KE4DRN
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« Reply #2 on: September 29, 2009, 05:25:10 PM »

hi,

many dual band radios will work, however,
they are not designed as a repeater.

they will not handle the duty cycle a repeater demands
and you don't have the filtering that a repeater needs.

you'll need to have your radio ID per FCC rules.

73 james
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N8EMR
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« Reply #3 on: September 30, 2009, 03:40:18 AM »

The ft8800 will "cross band" out of the box. The problem is in the cross band mode you cant legally id all the transmitters involved. Now occasional use where your near the car is one thing but putting it up on the tower, Might want to check your fcc rules regarding  repeater and auxiliary operation.

heck for the price of a 8900 you can get a bottom of the barrel UHF repeater on ebay.
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CERTNEAL
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« Reply #4 on: September 30, 2009, 06:41:21 AM »

Thanks for the comments guys, I will try to answer some and ask a few more hehe.

First off let me clear up why I would even think of using this method. This would be for very temporary use, 3-5 days or so. This won't be used for rag chew, only vital communication. This is an option when all other repeaters are gone in a disater.

I was thinking of erecting 2 small towers one recieve on 2 meters send on 440, this one would run low power. The 440 signal would basically act as a long feed line, perhaps 500 yards to avoid interference from the next tower. Then the next one will recieve on that same 440 signal and send at a shifted 2 meter signal to act similar to standard repeater. The second tower would send full power to reach people at a base station outside the disaster area as well as giving a good signal in the area.

We would have multiple teams using handheld radios, these would for the most part be 2 meters, that is why I want to stay on that band mostly.

Alan, A regular repeater may be better in most ways, but how easy would it be to set one up in this situation? Also what else is required when using a standard repeater? I suppose I was thinking that two radios would also be more redundant, in the event one person is in the disaster and equipment is destroyed, at least we would have 1 radio left capable of voice messages at the least or cross banding a signal to the base on...6 meters perhaps.

James, The duty cycle is a bit of a concern, but filtering is more to me at this time, would the seperation distance in the towers help at all?

N8EMR, A standard repeater may be the best option, we are just at the planning phase and looking for all options in an emergency.

Still working on the ID problem we would have with this.

If I may, what would be needed to set up a repeater, not the tower but just the radio equipment needed to run it properly?

Thanks a bunch,
Neal
KJ4OPC
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WB2WIK
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« Reply #5 on: September 30, 2009, 10:22:09 AM »

If you're serious, a far more functional, utilitarian repeater would be one where input and output are on the same band, so far more people would be equipped in an emergency to actually use it.

Inexpensive repeaters are available with built-in controllers and automatic ID systems, etc, specifically for such needs.  An example is this one:

http://www.hiprorepeaters.com/Model%20R1.htm

Just add a duplexer and an antenna, and you're up and running.  This model will operate from a deep cycle lead-acid battery for 1-2 days (24-48 hours) even with pretty heavy activity.  Whole system, other than antenna "support," can be set up in 10 minutes.

WB2WIK/6
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K5LXP
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« Reply #6 on: September 30, 2009, 12:14:01 PM »

Technically you can do exactly as you describe.  It's the practicality that's in question.

I've done split sites for repeaters and it works.  The biggest downside that I observed is you're running separate antennas and sites for transmit and receive.  So the range of each may not exactly line up with each other and it can be confusing to users.

The other issue is the link frequency.  It becomes a 2nd opportunity for interference or other problems.  Unless you take pains to equalize the link you're adding a 2nd emphasis/deemphasis step, which compromises the repeated audio.

You need four times as many antennas.  With a duplex repeater you need one, with a back to back linked split site setup you need four- 2 2M and 2 440.  Plus twice the supports and 4x the feedline.  You need two power sources instead of one and if you filter eacj band at each site to the point it's somewhat reliable, you've got way more into it than a set of duplexer cans.  Plus the above mentioned ID and duty cycle requirements.

Conceptually it would work great.  It's the details that catch up to you.


Mark K5LXP
Albuquerque, NM
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CERTNEAL
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« Reply #7 on: September 30, 2009, 01:23:31 PM »

I appreciate the replies thus far.

One question I had for Mark is what is the need for 2 antenna per unit? Couldn't we use a dual bander and if we needed say 6 meters we can use a tri bander?

One reason I must admit this would be feasible is that two people can spread out the cost of it. Also we can have two usable rigs to play with, and if one unit were disabled we could still have a relay unit of sorts, very nice for a HT to reach a longer distance.

Thanks again,
Neal
KJ4OPC
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WB2WIK
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« Reply #8 on: September 30, 2009, 08:39:19 PM »

Two people does not make an emergency communications network.

You need more people, who have equipment unknown before the event occurs.

A small crossband repeater for real "emergency" service is folly.
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CERTNEAL
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« Reply #9 on: October 01, 2009, 06:43:00 AM »

In reply to WB2WIK

Thanks for your reply, but I never said 2 people were the only ones in the network. This would be simply to aid in reliable communications for handhelds in disaster area, as well as providing a way to reach much further out.

If we had say 20 teams using handhelds in an area, this would be to give them a longer distance communication link similar to a standard repeater. Also can possible reach a base outside the area that a handheld cannot. Please elaborate on why this idea is folly, I am reasonable and willing to change should it be needed.

Cheers,
Neal
KJ4OPC
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K0BG
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« Reply #10 on: October 01, 2009, 10:08:49 AM »

Neal, one of the biggest problems is proper ID. The FCC has issued several bulletins about this very use. That is, cross band repeat from radios like you describe.

I can't speak for Steve, but what he said is very straight. The radio won't handle 100% duty cycle use, like a properly designed repeater would. And, repeaters have ID, COR, TOT, and a few other features missing in your radio. All of these to conform to the FCC R&R.

As Steve noted, you can buy a complete repeater, even the duplexer, for about $1,000. With the right antenna, set up in a portable communications van, it will run circles around cross band repeat. And as Steve mentioned, open of the communications link to more users.

To assume otherwise, is the folly.

Alan, KØBG
www.k0bg.com
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