Feedline suggestions for deployable repeater

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KB1JHU
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Feedline suggestions for deployable repeater

Post by KB1JHU »

I'm looking to set up a deployable repeater for my EMS agency for use at special events or large incidents. Some of our events span enough area that simplex on portables just doesn't cut it and we don't like tying up the primary channel. We have a UHF GR1225 and I have found a portable mast and an antenna but I'm not quite sure what to go with for feedline. The mast is about 30ft fully raised so I'm thinking that I would only need 50ft max.
KB1JHU
B.S., Conservation Law Enforcement, Unity College
Jim202
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Re: Feedline suggestions for deployable repeater

Post by Jim202 »

KB1JHU wrote:I'm looking to set up a deployable repeater for my EMS agency for use at special events or large incidents. Some of our events span enough area that simplex on portables just doesn't cut it and we don't like tying up the primary channel. We have a UHF GR1225 and I have found a portable mast and an antenna but I'm not quite sure what to go with for feedline. The mast is about 30ft fully raised so I'm thinking that I would only need 50ft max.



Can't go wrong with RG-8 or RG-213 for the coax. Stay away from the LMR type cables. I shouldn't have to go into the details on the LMR type cable for repeater use. It has been discussed in so many threads I wish I could collect a dollar for each one.

Jim
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Bill_G
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Re: Feedline suggestions for deployable repeater

Post by Bill_G »

213 is more supple than LMR. Rolls up nicer. Even low loss RG58 would be acceptable for this application. Whatever you use, have a spare cable made.
KB1JHU
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Re: Feedline suggestions for deployable repeater

Post by KB1JHU »

Thanks for the quick replies. I had come across many instances where people have said that the LMR cables were not appropriate for repeater use.
KB1JHU
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Bill_G
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Re: Feedline suggestions for deployable repeater

Post by Bill_G »

And you'll find plenty that say it's just fine for repeater use.

Including myself. We use it all the time. It's the connectors that can cause you grief. Especially the way you intend to use it. If you use these often, the day will come when someone walks up with a connector in one hand and the rest of the cable in the other asking you what to do.

Your question was for a portable repeater - something with moderate loss, but is easily handled by the average person. LMR (and Belden 9913) is a bit stiff. RG213 is much more supple and easy to handle. Low loss RG58 is even easier to handle, and 50ft won't present even losses to worry about.

On the other hand, you can buy bagged connectorized tested 50ft lengths of LMR400 from many places on the net. If a cable fails, it's a quick fix to grab a new bag from your kit.
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N4DES
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Re: Feedline suggestions for deployable repeater

Post by N4DES »

I/4 inch superflex works good as well.
Will
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Re: Feedline suggestions for deployable repeater

Post by Will »

RG213, but make sure it is REAL Mil Spec RG213. Not just "RG123 type". There is a very big difference.
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nukedude
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Re: Feedline suggestions for deployable repeater

Post by nukedude »

Where I work, we have portable repeaters (using CDM1250's) and have used 50 foot lengths of RG-213, RG-58, LMR-400 and LMR-240 depending on who built them and which part of the country.

Each region pretty much used what they had on hand cable and connector wise. The ones that have held up the best, were using RG-213. The were used on portable crank up masts and WilBurt pneumatic masts at some sites.

LMR-240 was better for one site that needed to run the coax through a NyCoil cable management unit on a 50 foot WilBurt mast.
tvsjr
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Re: Feedline suggestions for deployable repeater

Post by tvsjr »

Assuming you need 50' and are at 450MHz:
LMR400 - 1.35dB
LMR400-UF - ~1.5dB
1/4" Superflex - 1.955dB
RG213 - ~2.5dB
LMR240-UF - ~3.1dB
RG58A/U - ~5.5dB


As you can see, from garden hose LMR400 to RG58A/U is a whopping 4.15dB. For an event repeater, that's a pretty small number. So, you have to consider if it's worth 3-4dB to deal with the pain of LMR400, or if you'd rather have something more transportable.

I'd also be concerned about the allowed bend cycles on LMR400 or even 1/4" Superflex. How many times can you coil the coax up until you fracture a center conductor?

LMR240 Ultraflex would be my choice. It's very flexible and easy to work with, not too much larger than 58 (it's an RG-8X class coax), and a hell of a lot easier to deal with than LMR400/9913.
Will
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Re: Feedline suggestions for deployable repeater

Post by Will »

Check out Davis Bury Flex cable. A RG8 size cable with stranded center that holds up in temp installations, field deployment.
It has a sauce between the two shields so it does not have the problems of IMD like the LMR 240, 400 cables.

http://www.davisrf.com/buryflex.php
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PRR
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Re: Feedline suggestions for deployable repeater

Post by PRR »

Two considerations from years of experience deploying temporary systems on a weekly basis:
1) Larger diameter coax (RG213, RG214, 9913, 9913F7, LMR400[-UF]) tends to hold up better, if for no other reason than it tends to command a greater psychological respect from users.
2) Coax of any type in this application is a perishable; expect to test and replace it on a regular schedule based on your usage.

A more flexible coax is definitely an advantage, especially in the colder weather and at the end of the night when everyone is tired and hungry and wants to go home. I too don't subscribe to the idea of braid over foil shield design to be inherently bad in single channel repeater applications, especially temporary deployments, as long as the connectors are installed and strain relieved properly (as Bill_G stated). Given that, we've had good success (longevity vs. price) with 9913F7 and Wireman CQ106. It's with multi-channel TX combined feed lines, we've found the braid over foil design to be more noisy than RG214.
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wavetar
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Re: Feedline suggestions for deployable repeater

Post by wavetar »

I prefer the double shielded RG214 over the standard RG213. There's not a big difference in loss spec, but there's a lot more braid to really make both clamp and crimp connections very solid. Much more flexible than LMR400 as has been said, especially in the cold! Get below zero and the LMR seizes right up! The RG214 tightens up a bit, but still very manageable.
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