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Repeater antenna and feedline

repeater antenna feedline

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#1 krwheele

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Posted 11 September 2013 - 02:03 PM

Hi all. Need some help. New to the forums and i am thinking this is a good place to get some guidance. I have a Kenwood TKR-820 repeater that has been set up and tuned for GMRS 462.550/467.550. It is a turn key system and does not need any configuring by me. I also have a Comtelco BS450XL antenna that has been tuned for GMRS with a center frequency of 465.550.

 

http://www.comtelcoa...DF/BS450XL3.PDF

 

Now to bring this altogether i need some solid guidance on what kind of feedline to use to connect this to the repeater. I need to know what kind of lightening surpressor i might need to use. I need to know anything that would help me successfuly mate the antenna and repeater together for a reliable station.

 

The antenna will be mounted on the side of my house on a mast. It will be 26 feet above the ground. The antenna height is what it is and can not change. The feedline length between the repeater and the antenna is no more that 40ft and probably closer to 30 feet. I live in FL so its pretty flat. Not a Rocky Mountain in sight.

 

Any help you can provide would be much appreciated.

 

Regards,

Kris



#2 PastorGary

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Posted 11 September 2013 - 03:01 PM

Hello, Kris and welcome to the Forum.

 

One of the least expensive and good quality feed lines for that distance would be LMR400. 

 

You can also use Andrew Heliax Hardline, but there isn't much of a difference at 40 feet for cable losses.

 

This is one link below to LMR400 through Amazon.com's supplier...

 

http://www.amazon.co...ds=lmr400 cable

 

I have also used RG213 successfully at 50 feet or less and that is about the same cost as  LMR400  in many cases.

 

 

 

[ Lets give our new member some tips on cable and setup - Thank you. ]


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#3 JeremyM

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Posted 11 September 2013 - 04:28 PM

I agree with PG. LMR400 is what I use for GMRS and Amateur. N-Type connectors are best suited for frequencies above 400MHz, so that is what I recommend terminating those lines with.

 

LMR400 is a semi-rigid cable which means it has some girth, but also has good shielding. Avoid sharp angles at all costs, they will cause more loss. Make sure the LMR400 has a UV resistant outer layer. UV rays from the sun will cause the outer insulation (rubber) to crack allowing moisture to penetrate the cable causing all sorts of fun issues.

 

Through the research I have done, this is the best way to prevent damage to your equipment:

  1. Use a flat strap for the antenna ground connected to a strike plate (grounding bus bar)
    1. Lightning arrestor connected between the flat strap and the strike plate
  2. Make sure AC line has ground connected to lightning arrestor then to the same strike plate
  3. Run flat strap from strike plate to 8ft grounding rod at least 10ft from house or other structures

Everyone has their own way, but this seems to be pretty good.


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#4 Logan5

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Posted 11 September 2013 - 04:31 PM

Howdy Kris and welcome to the MyGMRS forums, As PastorG stated LMR400 is pretty good stuff and for a price point, well below 1/2" hardline cost. and only a fraction of db. difference in loss at 40feet.. I consider LMR400 use a minimum. No point spending all that money on top of the line equipment only to skimp on feedline. Also a properly tuned duplexer unless you plan to use two properly spaced, separate antennas. I also live in Florida and the flat topography is awesome, I run an Old Uniden 25watt repeater with 60' of LMR400 on a 50' pole currently only raised to 40' with a comet antenna factory tuned to 465. I use an RFS duplexer and I cover a 20 mile radius. I expect 25 miles when raised to 50'. Good luck and keep us posted.  Jim...


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#5 krwheele

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Posted 12 September 2013 - 02:53 PM

Well its unanomous. LMR-400 it is. That a good thing because i already have 50 feet of it. My biggest concern with using it was that i read it was bad for repeaters. Seemed like some of the reading suggested it causes desense issues. I have a short run to make with it so i will give it he old college try and see what happens. I have also read that some folks in Florida steer clear of grounding there antennas. What is the concenus on that?

 

KW



#6 PastorGary

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Posted 12 September 2013 - 04:12 PM

There is a nice, detailed thread on this topic located in the Forum link below.  If you have any questions after looking over those posts, please feel free to post in that thread and we'll help out as we can...

 

 

http://forums.mygmrs...enna-grounding/


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#7 Logan5

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Posted 12 September 2013 - 06:07 PM

Oh yes, I do not ground my antenna, as I do not want to attract lightning. I know others will disagree, however in 20 some odd years I have yet to be hit. Although I have had lightning come in on the telco and did thousands of dollars of damage to my "10baseT" network, to give you an idea of how long ago that was.


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#8 JohnE

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Posted 12 September 2013 - 06:17 PM

Well its unanomous. LMR-400 it is. That a good thing because i already have 50 feet of it. My biggest concern with using it was that i read it was bad for repeaters. Seemed like some of the reading suggested it causes desense issues. I have a short run to make with it so i will give it he old college try and see what happens. I have also read that some folks in Florida steer clear of grounding there antennas. What is the concenus on that?

 

KW

de-sense issues are caused by putting on connectors improperly, poor tuning of duplexers and poor weatherproofing of antennas. make sure you read the paper work that comes w/antenna, most have drain holes on the bottom. if you cover them up guess what happens.unless you get a bad piece of cable(it happens) or your running too long for for its abilities there should be no problem running 400 cable 50'. at 50 ' your line loss will be ~1.25dB or roughly 20%. the 820 is rated at 25W w/duplexer loss of 1.5 db and a line loss of ~1.25 to the cable your looking at ~13W into the antenna. these are just #'s off the top of my head you mileage may vary.

JE


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#9 JeremyM

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Posted 13 September 2013 - 09:27 AM

I might add, while I did provide the grounding method which seems to work well, I do not have my antenna grounded. When I am not at home my Astron SS-30M is disconnected from AC and my LMR400 is disconnected from the radio with the N connector in a glass mason jar.

 

I do not wish to attract lightning to my residence. I am up to about 24ft or so and there are other object at higher elevations, but I still don't chance it by leaving everything connected. With my luck I would get hit and burn my whole house down.


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