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New Antenna and Feedline for GMRS Repeater


n4gix
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I have a new Bridgecom repeater ordered and am now thinking about replacing my existing antenna and feedline with something more efficient for a $1500 repeater!

 

I was initially thinking about 1/4" Superflex heliax, but according to the specs I've found loss is around 4.5db/100' <Yikes!> The one major advantage is the 2" bend radius.

 

Next for consideration is 1/2" Superflex with only 1.4db/100' loss. That's more reasonable I think. Price is $1.69/ft. The 5" bend radius is an issue though. The coax enters through a pass through tube below my desk, but has to make about a 2" bend and travel up the wall about 2' and then make another 2" bend to the back of the repeater's antenna port.

 

What I'm wondering is if I could bring the 1/2" heliax down to my lightning arrestor, then use about 6' of 1/4" Superflex to bring it into my house, and if that would cause any serious issues. Alternatively I could simply use the 6' of LMR400 cable that's already in place.

 

I'm somewhat challenged for height at the moment, so I'm thinking a 6db gain antenna would help compensate for the lower height. Any recommendations for antenna choice?

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I have no experience with hardline yet. but I went with Times LMR600 and like it very much, however it has an even wider turning radius. I like your idea of switching cable at entry, something more flexible, but unsure of any issues it might cause. I think I would place the repeater and drill a hole in the wall directly behind it. so no bends at all. make sure you got a drip loop though.

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What I'm wondering is if I could bring the 1/2" heliax down to my lightning arrestor, then use about 6' of 1/4" Superflex to bring it into my house, and if that would cause any serious issues. Alternatively I could simply use the 6' of LM400 cable that's already in place.

thats the route to go. how many feet are we talking about.

https://forums.mygmrs.com/topic/252-cable-types-and-losses/

 

gain will not make up for height but it will be a slight help.

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John, I found that 1/2" regular heliax actually specs out to even lower loss than Superflex, and is a bit less expensive as well. A 60' length calculates out to 0.87 db loss. I haven't found specs for the connector loss but they shouldn't be too horrible.

 

I'll have to use a N male at the antenna end, and a UHF male at the arrestor end. That should be less loss than a N male and adapter to UHF to match the arrestor's connection.

 

I think for the time being I'll simply use the existing 6' length of LMR400 and use my new spectrum analyzer to do a sweep VSWR test of the new cable and whatever antenna I decide to install.

 

I really only need about 45' where the antenna is now, but since I may be able to raise it up another 10' to 15', I'd rather have more "slack" than to have to patch in another section to lengthen it.

 

I'm trying to decide betweek a Laird FG4507 7db gain @ $199.95 or a Comet CA-712EFC 9db gain @$129.95.

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Okay, after a lot of thought, here is what I've ordered tonight for the new Bridgecom repeater. I sure hope this works out well!

 

60' of 1/2" LDF4-50A and connectors should have ~1.36 db total loss. A really conservative estimate calculates that 40 watts into the system should put about 28.6 watts into the antenna. With 9db gain, that should be around 228 watts ERP.

 

My new Rigol spectrum analyzer will be delivered tomorrow and the rest of the stuff I've ordered should be delivered by Wednesday of next week. I plan to do a full sweep VSWR analysis of the new antenna system before the new repeater is even connected!

 

http://puu.sh/npaXv.png

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Okay, after a lot of thought, here is what I've ordered tonight for the new Bridgecom repeater. I sure hope this works out well!

 

60' of 1/2" LDF4-50A and connectors should have ~1.36 db total loss. A really conservative estimate calculates that 40 watts into the system should put about 28.6 watts into the antenna. With 9db gain, that should be around 228 watts ERP.

 

My new Rigol spectrum analyzer will be delivered tomorrow and the rest of the stuff I've ordered should be delivered by Wednesday of next week. I plan to do a full sweep VSWR analysis of the new antenna system before the new repeater is even connected!

 

http://puu.sh/npaXv.png

If you purchased the base model Rigol spectrum analyzer with the sweep generator ($1500 Bucks) it will not do VSWR without an additional license key as well it requires a VSWR bridge. The 2 options Cost another $1325 purchased as accessories.

 

Corey

 

Corey

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If you purchased the base model Rigol spectrum analyzer with the sweep generator ($1500 Bucks) it will not do VSWR without an additional license key as well it requires a VSWR bridge. The 2 options Cost another $1325 purchased as accessories.

 

Corey

My best friend has two of the 815-TG, and owns the VSWR bridge and software license. He told me he'd loan me his so I won't need to buy it myself. Aren't friends handy things to have? :)

 

There is also an alternative method that frankly will work "good enough" using a Mini-Circuits ZFDC-20-5+ directional coupler. It's not a "one button solution" but will serve most people's needs quite well. See James Eagleson's video here: https://www.youtube.com/watch?v=X50qybdiLuk

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I'm new to heliax cable use also........can someone explain the bend radius and superflex vs standard cable?

 

It's a bit confusing. Never having used it I can't get a sense of how flexible these cables really are.

 

For example.......will either cable be able to go over a roof edge & straight down a outside wall without damaging it?

 

Can it bend @ the entry point of a wall and form a drip loop without damage?

 

Thanks

Chris

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I'm new to heliax cable use also........can someone explain the bend radius and superflex vs standard cable?

 

It's a bit confusing. Never having used it I can't get a sense of how flexible these cables really are.

 

For example.......will either cable be able to go over a roof edge & straight down a outside wall without damaging it?

 

Can it bend @ the entry point of a wall and form a drip loop without damage?

 

Thanks

Chris

the super has a different corrugation to make it more flexible as opposed to the standard,

both can go over a roof edge but make sure it is properly secured.

as to the drip loop it can be done but don't kink it or you'll have to cut and terminate at that point.

I will grab some "scraps" I have laying around and post some pics of bending radii, that way you might have a better clue as to what to expect when you do the work.

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Well the new repeater finally arrived. I'm seeing a solid 45 watts out of the duplexer into a 50 ohm dummy load. I just got notice that the new heliax and antenna have been shipped. Hopefully they will arrive and I can arrange for my 'roof guy' to install them. In the meantime, it's running on my existing roof mounted high gain dual band antenna...

 

http://puu.sh/nsGVe.jpg

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The new Comet CA-712EFC antenna arrived yesterday and it is partially assembled and ready for fair weather to allow me to gather my "crew" together for an antenna party. The heliax was shipped separately and will not be delivered until Monday or Tuesday via UPS.

 

If the specs are honest, this antenna is tuned to 460-470 MHz, 9.8 dBi gain...

 

...which is -if my math is correct- equivalent to 7.65 dBd which is pretty respectable still. (dBd = dBi - 2.15 dB)

 

The antenna on the left in the other room is a Workman dual-band antenna to replace my nearly twenty year old one currently being used for my office 2m/70cm radio.

 

http://puu.sh/nvQ0E.jpg

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Corey, tones are listed in the myGMRS.com entry. I've given up on finding anyone local to help install my antennas, so I'm waiting on a professional installer to give me a quote. He's supposed to call me today and arrange for a visit.

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I would totally help if I were local.

Bill showed up this morning on time, quoted me $250, and I approved. Two hours later both the new Comet and Workman antennas are up and working. Unfortunately, the hardware on the middle (old) tripod was too rusty to be safely reused, so I had him put the Workman 2m/70cm on one of the chimney mounts. He took down a really old dual-band that had the top element broken off some years ago during a nasty storm.

 

In the left picture you can see the unity gain J-Pole on the ground mounted mast. This is what the repeater's been using up until now. In the right picture from left to right, the Comet CA-712EFC (460-470), the "old dual-band", on the chimney forground is the new Workman dual-band, and on the far side is an old backup dual-band antenna.

 

http://puu.sh/nD77M.jpg

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So have you tested range on the new repeater yet?

I was actually somewhat surprised, since $250 is about what I'd have charged myself...

 

...20 years ago! ;)

 

I'll be doing some preliminary range tests on my way to the LCARC monthly meeting in Crown Point, IN this evening.

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I could still receive about 2 S units at the intersection of Calumet Avenue and US 30, which is about 10 airline miles from the antenna to my mobile's rear end. On the return trip with my car facing north, reception was about 4 S units. That's no surprise since that's where the major lobe of my trunk mounted mobile antenna will be found.

 

With a limit of about 50' for the repeater's antenna, I had calculated about a 10 mile radius for 70% coverage. I still have some "weak spots" in the antenna system, not the least of which is a 20 year old lightning arrestor, and a 20 year old LM400 8' jumper from the arrestor to my desk. I've had to add another 6' of really shitty RG-58U coax with nickel-plated crimped connectors to reach the repeater's temporary location.

 

Interestingly enough I was able to work the repeater from inside a Food-4-Less this afternoon on my MD-380 5 watt HT. That's about 5 miles airline from the repeater, from inside a large grocery store.

 

I'm pretty confident that once I've replaced the lighting arrestor and the feedline into the office, performance should improve, especially on reception. In the meantime, I'm casting around looking for some prime "vertical real estate!" I wish I had my best friends connection (W9CTO). His 2m and 220 analog, and 440 DMR repeaters are sharing a receive antenna at 580' and a transmitter antenna at 500'. Talk about a H U G E footprint! :o

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I would bet if you get rid of the LMR400 and RG58 things will improve significantly. Good luck on the tower hunt, look around and see if you have any independent tower owners in your area. I rent my space from a locally owned tower company and the rates are far better then places like Crown Castle and American Tower. Some local radio stations may even let you put up a community repeater for little or no cost.

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