What coax cable for repeater.

[WSHH555]

Hello everyone.  Slowly working to put up my own repeater and currently in the coax stage.  I understand LMR400 is not the best for repeaters as the metals don't play well with it.  I am running approximately 50ft so nothing crazy.  What have y'all been using that works well?

[WSFF627]

As lots have mentioned here Heliax is the ideal choice. However you need to decide how much you want to spend. LMR400 is cheapest, LMR600 is more expensive but loss wise more comparable to 1/2 Heliax. For your length the dB loss doesn't justify the cost of 7/8 Heliax in my opinion. Yes the LRM types risk noise in full duplex operation, however that's more prevalent in wattages much higher than 50 watts and when there is a bunch of cable flex. I ran a test on a 100 watt 70cm HAM repeater for a while on 65 feet of LMR600 and didn't see a noise issue.

Yes 400 will work but is not the best choice due to higher loss. Everyone thinks about TX and power out loss, but not many talk about RX loss, and a pre-amp cant do something for what never makes it to it. In high RF environments or with poor filtering, or a combination of both, they can do more harm than good. If your going to try one, get if from AdvancedReceiver.com I have several of them, they work great, and if you have a service monitor and the knowledge, can adjust them.

Large Heliax is the best performing choice, and the most expensive, the connectors alone are $35 each.

LMR600 is a good economical and good performing choice. Its actually in service in a lot of commercial setups on short runs, so is LMR400. But you wont find either going up a commercial tower due to loss and the noise issue at high wattage. Andrews and Times Microwave also offer grounding kits for LMR600. I recommend grounding the cable shield as well as a good quality (not a cheap amazon) lightning arrestor. A good one will run you $100 or so.

Check repeaterbuilder.com It has lots of good info and a copy of the Motorola site standards, which you may find very helpful.

I own and operate a GMRS repeater with a 60 mile radius as well as a 70cm DMR HAM repeater that can go farther (both have site elevation to their advantage, they are high). I've also put together other large footprint repeaters at commercial sites.

[WRUE951]

22 minutes ago, WSFF627 said:

As lots have mentioned here Heliax is the ideal choice. However you need to decide how much you want to spend. LMR400 is cheapest, LMR600 is more expensive but loss wise more comparable to 1/2 Heliax.

LMR 400-600 will work just fine for distance less than 150', of course if you have some decent height on your antenna.   We used Helix on super long runs for our UHF radios at work on antennas at the upper portion of a 300' tower.  From 150' down we used 600 and so did everyone else leasing space on the tower from mid point down.    

[LeoG]

LMR600 is more expensive ($2.69/ft) than 1/2" Heliax ($1.99/ft) and has greater loss.  It has the advantage of being more flexible. (antenna farm prices)

https://theantennafarm.com/images/specs/34/lmr-600-coax-cables-datasheet.pdf

https://theantennafarm.com/images/specs/36/ldf4-50a-product-specifications.pdf

The fittings for both run about the same although the LMR has a wider variation.

[WRYZ926]

1/2" Heliax if you can afford it. Otherwise LMR400 will work even though it is not optimal for repeater use. 

Here are the losses for LMR400 and 1/2" Heliax for a 50 foot run on 462.600 using 50 watts out and antenna with 6 dBd of gain:

Power loss per 100 feet

• LMR400 - 48%
• 1/2" Heliax - 30%

ERP -effective radiating power

• LMR400 - 143 watts
• 1/2" Heliax - 166 watts

You will not see 50 watts out of the repeater due to the duplexer. Most will output 25 to 35 watts. Here is the numbers for 35 watts out.

EPR

• LMR400 - 86 watts
• 1/2" Heliax - 99 watts

Those numbers are from using the kv5r.com coax loss calculator.

@WSFF627 is correct when he talks about receive signal strength. You have to keep that in mind too. 

 

You will be okay with either LMR400 or 1/2" Heliax. Go with what fits your budget. Don't skimp on any of the components such as coax fittings, etc.