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Cable for duplexer and repeater connection

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xccess

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nashville, TN
Hi all,

I am new to this stuff and want to get my ham technician license. I had my GMRS license. I am in the middle setup a private GMRS repeater and had a few questions,

my equipment is.

ICOM FR-4000 repeater radio

Comet Original CA-712EFC 460-470Mhz UHF Base Station Antenna

N-Male to N-Male 50 Foot LMR-400 Cable | Times Microwave Ultra Low Loss 400 Coax

2 of MPD Digital D0-I27S-DRXN N-Male to N-Male LMR-400 Cable Ultra Low Loss LMR400 Coax (6-Feet)

UHF Compact Band-Reject Duplexer 50W MICRO-4201-C6

PolyPhaser - Bulkhead Arrestor N/F (IS-B50LN-C2)

I plan to connect the 50foot cable from the antenna to PolyPhaser Bulkhead Arrestor for lighting strike protection, and from PolyPhaser Bulkhead Arrestor I will connect it to the UHF duplexer (which I still need one more cable to this connection) from duplexer I will use 2 of MPD Digital D0-I27S-DRXN N-Male to N-Male LMR-400 connect to the radio.

my questions are this. since the 2 of MPD Digital D0-I27S-DRXN N-Male to N-Male LMR-400 from duplexer to the radio seem to be hard not to flex. can I user any other shorter cable like 2 feet to connect to radio from duplexer without the signal loss? the radio also have room to put duplexer inside, should I put the duplexer inside the radio or it will be too hot when I put it in the garage? I live in Nashville area so weather may get hot a time.

as far as the connection from PolyPhaser - Bulkhead Arrestor came from the antenna I have not purchase the cable. but the radio should be about 30-40 feet from it. should I stick with LMR-400 cable or get something else?

and how far radio ground and PolyPhaser - Bulkhead Arrestor should be from ground to protection it from light strike?

TIA
 

lmrtek

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Sounds like a pretty sweet set up!

The duplexer will be fine inside the repeater cabinet, I do it all the time

LMR 400 should be fine for feedline

Install the polyphaser where the feed line enters the building
 

prcguy

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LMR400 or any coax with foil/braid shield is not recommended for full duplex repeater use. 50ft would be considered a very long run for LMR400 at UHF in my book with about 1.6dB loss. Try to cut that in half if you can and look into Commscope/Andrew Heliax, LDF4-50A or at the very worst, FSJ-50B.

Its best to use double shielded coax for jumpers in a repeater system and common small coax used in the industry is RG-142 and RG-400, both RG-58 size but with silver plated conductors, double shielding and Teflon dielectric. Double shielded RG-214 is large but a bit more flexible than LMR400. For very short runs like under a foot, RG-223 is ok.

Your repeater and duplexer will make an ok bare bones repeater if its in an area with no other UHF repeaters or UHF paging transmitters around. If you skimp on anything else in the system like the antenna or feedline, any performance capability you have now will go down the toilet fast.

You probably can't ground your system well enough to survive any kind of direct lightning strike so unless you want to spend a couple grand having professionals build you a ground system, ground to NEC article 810 and be aware that a direct hit will more than likely wipe you out.
prcguy
 
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AK9R

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Assuming 50 feet of LMR-400 at 462 MHz and 50 watts transmitter output, the actual power at the end of the coax will be about 36 watts.

Step up to 1/2" hardline and the power at the end of the coax would be about 42 watts.

Step up to 7/8" hardline and the power at the end of the coax would be about 45 watts.

This is just loss in the coax and doesn't account for loss in the duplexer and other losses in your system.

The issue with LMR-400 is that the shield consists of dissimilar metals Over time, you may develop some distortion in the system caused by corrosion between those dissimilar metals. Yes, there are lots of repeaters using LMR-400 in various parts of their system and they seem to be getting away with it. prcguy made some suggestions for good system engineering practices. They aren't hard and fast rules, but they are very good guidelines.
 

xccess

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nashville, TN
Assuming 50 feet of LMR-400 at 462 MHz and 50 watts transmitter output, the actual power at the end of the coax will be about 36 watts.

Step up to 1/2" hardline and the power at the end of the coax would be about 42 watts.

Step up to 7/8" hardline and the power at the end of the coax would be about 45 watts.

This is just loss in the coax and doesn't account for loss in the duplexer and other losses in your system.

The issue with LMR-400 is that the shield consists of dissimilar metals Over time, you may develop some distortion in the system caused by corrosion between those dissimilar metals. Yes, there are lots of repeaters using LMR-400 in various parts of their system and they seem to be getting away with it. prcguy made some suggestions for good system engineering practices. They aren't hard and fast rules, but they are very good guidelines.
I believed what you are saying, but I am new to this scene and still learning. so after reading this and how much lost I may have in the line. What you think better? UHF amplifier or spend more money to get Commscope/Andrew Heliax cable ?
Also when should I use my isolator or if there is a need for it ?
 

kayn1n32008

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What you think better? UHF amplifier or spend more money to get Commscope/Andrew Heliax cable ?
Invest in the antenna and feed line, an amplifier will not help you on receive.

You can have the best repeater and duplexer going, but if you have lousy feed line, and a crappy antenna you WILL have crappy results.

The issue with LMR400 is that it is not the proper tool for the job. spend the money and step up to at least 1/2" hard line. you will not regret it, and will have less issue down the road.
 

xccess

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Location
nashville, TN
Invest in the antenna and feed line, an amplifier will not help you on receive.

You can have the best repeater and duplexer going, but if you have lousy feed line, and a crappy antenna you WILL have crappy results.

The issue with LMR400 is that it is not the proper tool for the job. spend the money and step up to at least 1/2" hard line. you will not regret it, and will have less issue down the road.
going to get some 1/2 line

you think this will work

CommScope - 1/2" Foam Heliax Cable from Tessco

https://www.tessco.com/products/dis...X9hWPRZdr3jNQb5fR4uHG-x4ctcb_CHe3IBoCSYPw_wcB
 

AK9R

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Yes, that cable would be a good alternative to LMR-400.

For an extra fee, Tessco will install the connectors onto that hardline for you.
 
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