Batboard

hello everyone,
i want to put up a small repeater i made but i am not sure what coax to use. the feedline will be a 100 ft stretch on uhf. is rg-8u good or should i go w/ lmr-400?

thank you
otto

The higher the frequency, the more loss per foot for any transmission line. However, the smaller the cable (RG-8U), the more loss; the larger the cable (LMR-400), the less loss. I can't quote you the exact loss figures for the two choices, but the RG cable will have more loss. Transmission cable is one of those subjects where 'bigger is better', esspecially at higher frequencies.

LMR400 has a bonded jacket, making water ingress more difficult. This ingress, or water getting into the coax, will render the coax useless--so any sealant that slows or prevents such makes the coax a better deal in the long run. Also, be aware that there is no "official" specifications for "RG-8"--you will often see "RG-8 type" on coax making the specifications it will meet that much more vague. RG213 perhaps, but NOT RG8. Go with the LMR 400, it's good line. Blitz.

Go with the LMR400 for sure. Also use the "EZ-400" connectors. They are very reliable and have captive pins, so no assembly problems. You will need a crimp tool with a .429 die.

Gone

ok thank you all i really appreciate the input

i did some checkin and i can get lmr400 for $140 and heliax for $200 100' l

but the loss between the two different feedlines are very close around 2.7bd

does anyone know a good place to buy either cable?

thanks again
otto

well after further reading of posts on the board i came across a thread that said radio shack rg-8 is garbage and that is what i am using ..(not for long)....so i guess it is safe to say that using lmr-400 over the radio shack garbage would have a pretty dramatic difference?
what is the loss for r/shack rg-8?

any opinions?

thanks again
otto

If this a permanant instalation, then by ALL means go with heliax, not just any heliax, get the Andrew 1/2" at the least.

"i can get lmr400 for $140 and heliax for $200 100' l "

Go for the heliax, you will be better off in the long run, and at that price, if it is the genuine Andrew, is well wort it. You will not have to go back and change out the cable.

We use name brand Mil Spec RG213 for the portable repeaters on UHF.

It has been mentioned here on the BatBoard, avoid the unknown brands and markings, there is a lot of low should I say very poor cables out there labled simmularly to the RGx and LMRxxx.

Will

We generally use either Times Microwave LMR-400 or RG214. The RG214 is the same physical size as RG213, but is double shielded for lower loss & is more flexible than LMR-400. I do like LMR because it has a bit better specs & is stamped with length measurements every 4 feet (handy when you're trying to figure out how much to bill the customer). We basically use whatever we can get our hands on the quickest.

Todd

i did some checkin and i can get lmr400 for $140 and heliax for $200 100' l

but the loss between the two different feedlines are very close around 2.7bd

The Time Microwave LMR400 is 2.7 dB/100 ft at 450 MHz. The 1/2" LDF4-50 is 1.45 dB/100.
http://www.andrew.com/catalog38/default.aspx Go to page 496
http://www.timesmicrowave.com/cgi-bin/calculate.pl

The difference is about 1.25 dB. I reality, you probably won't be able to detect a difference of 1.25 dB.

If this were a comercial installation on a comercial site, I would really lean to the Heliax. It is a more sturdy cable and will stand up to wear and tear longer.

I would focus some attention to whats at the bottom of the antenna cable. What type of duplexer? What type of cable between the duplexer and the RX/TX. make sure that is dual shield. RG214 is best. RG142 is good for the RX,

yea allan i looked at the wrong heliax.........the stuff i saw for 200 was
some other brand cable experts had and was close to the same specs as lmr400........the andrew heliax is alot more money and yes less loss
i think i am gonna go w/ the lmr 400
i have a sinclair duplexer w/ rg-8u cables but i am goin to change them aswell
thanks for everyones help
otto

LMR cable is a bad choice for a repeater antenna feed line.
See these previous posts.

http://batboard.batlabs.com/viewtopic.php?t=24173

Nand.

As Nand and others have pointed out, repeater service brings out the worst in site problems. If you dig far enough, you will find documented cases where hams and two way shops have found out the hard way that LMR cable is a poor choice for repeater feedlines.

Those that have tried using it have had all sorts of strange noise, intermod and desense problems over time. They have tried all sorts of things to resolve the noise. Bottom line came down to replacing the coax feedline with some form of heliax type cable.

Do what you want, just don't come back here complaining about all sorts of weird noise and intermod problems. The money you save now will come back many times over to bite you in time and material. Repeater noise problems can take months to find and solve. If 35 years in the radio field ever taught me anything, it was to do it the right way the first time.

Jim

Nand wrote:LMR cable is a bad choice for a repeater antenna feed line.
See these previous posts.

http://batboard.batlabs.com/viewtopic.php?t=24173

Nand.

ok nand and jim can you tell me it this stuff is any good

http://cablexperts.com/cfdocs/cat.cfm?I ... ship=1&c=0

not the andrew stuff the 1/2 in corragated

thanks
otto

Gone

http://www.timesmicrowave.com/content/pdf/engdisc.pdf

LMR cable is great for a lot of things but not for use as a repeater feed line. Times Microwave suggests that it is good for tower runs and base stations. I have not found any place where they mention repeater use. I also didn’t find any suggestion on their web site as to what cable they suggest for repeater use.
There are pages where they talk about noise, but not the noise in their cable.

http://www.timesmicrowave.com/content/pdf/tl14/75.pdf
http://www.timesmicrowave.com/content/pdf/tl14/76.pdf

Nand.

http://www.cablexperts.com/cfdocs/cat.c ... ship=1&c=0

Since it appears that you are not familiar with using this type of cable it is best to pick one of the pre-assembled cables listed on that page. Make sure you pick the model that has the right male or female connectors on it for you configuration. It isn’t clear that the pre-assembled cable is Andrew Heliax, even though the top of the page suggest that it is, but it is likely as good as Andrew and better than LMR for repeater use.

You will also need a connector sealing kit and solid antenna type suitable for repeater use. Some antennas come with pigtails, others have just a solid connector mounted on them. So you may need to get a small jumper cable between the antenna and the Helix to take care of any connector strain. The jumper can be a good quality RG-214 preferably the silver-plated type. Also use quality cable ties if you can’t afford hangers.

Nand.

I think the problem with LMR400 is that people use the standard LMR400 instead of the LMR400-DB....the DB is much more durable, waterproof, etc....

a quote from the Times Microwave site:

"LMR® - DB is identical to standard LMR plus has the
advantage of being watertight. The addition of
waterproofing compound in and around the foil/braid
insures continuous reliable service should the jacket be
inadvertently damaged during installation or in the future".

I had it on the GMRS repeater and it worked perfectly. I have it connected on both my UHF and VHF radio's in the house, its been up there for 4 years, no problems and it looks like new.

I gave some to a local club for use on a new repeater they put up, that was over 2 years ago and its been working great. I don't remember if I gave them 400DB or 600DB....

I have quite a bit of it I bought awhile back if anyone is interested. I think I have 400DB, 500DB and 600DB, although I'd have to check.

dave

Hi all...

I recommend to him in this order:

a.- Belden 9913

b.- Timex LMR-400


Bye....

Belden 9913? I thought he was looking for feedline, not garden hose... (I became a believer after watching a TDR get filled up with water from a long section of 9913 garden hose).

What Mr.?

if you know some cable 9913 I enter water to him, she is because they did not isolate well....but I believe that you must respect my opinion on the use of cable Belden 9913.

I prefer not being isolated from her either...

A place with a good price on andrew cable is http://www.componetconnectionsurplus.com/

hey guy lemme start by saying thank you very much for all your advice and knowledge....i really do appreciate it.

i decided i was goin to save my pennies and break open piggy bank for heliax but as luck would have it i wont need to. i met a guy who lives very close to me, i noticed he had a tower in his yard, so i stopped to talk, as it turns out he gave me a 100 ft piece of andrews heliax 1 inch for $50 i couldnt pass it up. now i just have to get jumpers made up and a new duplexer all in n connectors.

once again thay you all
otto

Now that's a real man's coax.

I too have no idea what magc06 is talking about.

He will also need grounding kits (minimum of two per feed).

Just for everyone's information, I just got in 100 feet of Belden 9913 from Allied, their P/N 216-0212, Belden #9913-010100 CX/100, and it cost me $109.98 plus UPS of $11.72. It's intended to serve as a feedline to my 900 mHz Larsen 12db beam with a cable run of about 65 feet with 13 watts or so from a GTX M11W radio. When I do one of these I use more damn RTV on the connections than the RTV factory has stuff in stock, and after years of use the connections are always dry (and still good) when I cut them open.