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Author Topic: Need advice on coax  (Read 2997 times)
AC6IJ
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« on: September 25, 2011, 11:53:13 AM »

 Can you advise me on what is the type of coax to use on a Hy-Gain AV-640 vertical antenna that will require about 60' of coax to my transmitter? I have noticed lots of change in coax over the years and help on this would be appreciated for sure. I would order it from AES but I need suggestions on this. Thanks, Bill.
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AC5UP
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« Reply #1 on: September 25, 2011, 11:54:50 AM »

RG-213

Durable, reliable and cost effective.
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WB6BYU
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« Reply #2 on: September 25, 2011, 12:38:50 PM »

You can't go wrong with RG-213 - solid, rugged, and low enough loss that you won't notice any
difference going to a more expensive cable.

You can also get by with smaller cables such as RG-58 or RG-8X if cost or availability is a factor
(or if you happen to have them on hand.)   With RG-58 you'll have about 1dB more loss on 10m
than you would with RG-213, and less on the lower bands - only you can make the decision
about the tradeoffs between cost and loss, based on your personal preferences.
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N6AJR
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« Reply #3 on: September 25, 2011, 12:54:47 PM »

I usually buy coax when I find it as a deal, I got 2300 feet of lmr 400 for $600 delivered, as an example.  I use the lmr 400 for most of my longer runs.  Almost any good half inch diameter  coax will do OK for 60 feet.  Even rg8x or rg 58 would be ok on the longer wavelengths.  something like gr 58 has a lot of loss at 6 or 10 meters, but almost  has the same loss as others on 80 and 160 m.  go to belden and look up there loss per 100 feet tables, and you will get a good idea.  the best practice is to use the best coax you can afford to get the most signal  both up and down the pip
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W5JON
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« Reply #4 on: September 25, 2011, 01:27:24 PM »

Simple, for HF and VHF all you need to remember is: LMR400.

73,

John 
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AB3NK
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« Reply #5 on: September 25, 2011, 05:05:29 PM »

Basic reception 101
Antenna's exhibit gain, everything beyond the antenna is expressed as loss.
Even pre amplifiers are not expressed as gain + because they also inject some internal noise into the equation which degrades the signal.

At the same time, frequencies below 30 mhz do not exhibit as much loss (db) as does the higher frequencies / above 300 mhz...

The end result is if you want a clean signal, you use as good a coax as you can get.   LMR 400 or Belden 9913 is the two highest rated coax for the money for that frequency range.. Beyond that - you get into communications grade stuff like Belden 9913F7 which is sweep tested to a couple Ghz..

Just think of your signal like a small child, you want to protect your signal as much as possible.  Keep the good signal in and the noise out and not loose half the signal in the coax - if your goal is to have as much signal available to you as possible.

Buy the good stuff and leave the junk alone - it will only cause you grief.  At the same time, the connectors plays a large role in how the signal is transferred from the coax  to the radio.
You want to stay away from the cheap radio shack crap connectors / anything with plastic center insulators is no good.
Buy Amphenol connectors the ones with the colored insulators...

 
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KG4NEL
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« Reply #6 on: September 25, 2011, 08:49:16 PM »

By Times Microwave's calculator: http://www.timesmicrowave.com/cgi-bin/calculate.pl, losses are:

RG-213: 0.6dB
LMR-400: 0.4dB

at 28MHz, worst case. Both are inaudible.
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K4RVN
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« Reply #7 on: September 25, 2011, 09:24:25 PM »

AC6IJ

This link may be of help. The type coax you need depends on how far the antenna is from the shack and how much power you want to run. I looked at a manual for the antenna and Super mini 8 low loss (RG8x)probably would be OK.
Here is a link from the wireman. I have bought from him many times on the net, by phone and recently at a ham fest.
I use RG8x for runs of 100 ft or less running a max of 1000 watts pep. It cost about half of some of the larger low loss
and is suitable for HF and the warc bands. I don't operate vhf but short runs of 50 ft should work ok for 6 meters.
Look at the products table , prices and losses and decide what you need based on your station .

http://www.thewireman.com/coaxp.html#101

Frank
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W8JX
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« Reply #8 on: September 25, 2011, 09:30:21 PM »

By Times Microwave's calculator: http://www.timesmicrowave.com/cgi-bin/calculate.pl, losses are:

RG-213: 0.6dB
LMR-400: 0.4dB

at 28MHz, worst case. Both are inaudible.

I agree. Unless you are using runs of several hundred feet on HF, you will never begin to see the difference between 213 and LMR 400 anywhere but pocket book. LMR400's need for HF is greatly over rated.
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K9KJM
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« Reply #9 on: September 25, 2011, 10:20:22 PM »

Belden RG 213 is generally considered the "Cadillac" of coax for HF use.....   Some real tough stuff, And plenty low loss for HF at those lengths.   And as pointed out, Something like RG 8X will also work out just fine, At a lot lower cost, But like all foam dielectric coax, Will be somewhat more fragile than the solid dielectric of RG 213.

Times LMR 400 IS great coax, Especially for VHF/UHF, But for HF is somewhat overkill as far as loss goes........
Belden 9913 had lots of problems with many of it's different "versions".....

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AA4HA
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« Reply #10 on: September 26, 2011, 08:10:42 AM »

By Times Microwave's calculator: http://www.timesmicrowave.com/cgi-bin/calculate.pl, losses are:

RG-213: 0.6dB
LMR-400: 0.4dB

at 28MHz, worst case. Both are inaudible.

I agree. Unless you are using runs of several hundred feet on HF, you will never begin to see the difference between 213 and LMR 400 anywhere but pocket book. LMR400's need for HF is greatly over rated.

You can also use the Times Microwave calculator to look up how RG-8 will behave;
RG-58      2.38 dB/100'@28 MHz        57.7% efficiency    0.57 KW average power
RG-59      1.73 dB/100'@28 MHz        67.2% efficiency    0.53 KW average power
RG-8X      1.89 dB/100'@28 MHz        64.7% efficiency    0.36 KW average power
RG-8        1.05 dB/100'@28 MHz       79.3% efficiency     2.02 KW average power
RG-213     1.05 dB/100'@28 MHz       79.3% efficiency     2.02 KW average power
LMR-400   0.65 dB/100'@28 MHz       86% efficiency       3.45 KW average power (3/8")
LMR-600   0.41 dB/100'@28 MHz       91.1% efficiency     5.7 KW average power   (1/2")
LDF4/50A  0.35 dB/100'@28 MHz                                   5.8 KW average power (1/2")
LDF5/50A  0.19 dB/100'@28 MHz                                  14.0 KW average power (7/8")

The LMR cables will be stiffer than the RG cables and you may have some bend radius issues, watch how much of a loop you have on a rotator if using a tower or how much bend you can work around your shack. I can work LMR-400 into tight bends but you have to work at it so you do not kink it (only seen that done once).

The shielding effectiveness of the lower end RG cables is highly variable and you may find the cable acting more like a radiating element in your shack. I would stay away from the stuff that is second or third hand and was left coiled up in someone's basement for 20 years in a puddle of water.

I only included the two references to Andrew (Commscope) semi-rigid coax as a comparison since it does come up from time to time. Going with semi rigid cables are really only of benefit when you are >VHF and up to a few GHz. The connectors are also expensive, tricky to install and the cable does not like being kinked or flattened at all.
« Last Edit: September 26, 2011, 08:18:45 AM by AA4HA » Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
W8JX
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Posts: 5904




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« Reply #11 on: September 26, 2011, 09:01:10 AM »

Once again the difference between 213 and 400 at HF frequencies is very very small and if you consider most work 20m and below the difference is even smaller yet. Many look at total loss rather than difference between them. Realistically it is much more of a ego thing than a necessity on HF unless runs are several hundred feet and if they were it would likely do more than LMR 400 for a biggest difference over 213 on HF. LMR 400 has merit on VHF and UHF within its limitations too.  

I have a mix of 8x and 213 here and I guess I should not be getting out at all at times because of my lossy coax. (Even though I get good signal reports.)
« Last Edit: September 26, 2011, 09:02:54 AM by W8JX » Logged

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WB6BYU
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Posts: 13288




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« Reply #12 on: September 26, 2011, 09:07:43 AM »

You can also use VK1OD's transmission line loss calculator here:

http://vk1od.net/calc/tl/tllc.php

This lets you look at the loss (including that due to mismatch) for different cable types, lengths, and
frequencies of interest.  For example, you can see what the loss of 60' of RG-6 CATV coax is feeding
a 50 ohm load on each band, and see what the SWR would be (as well as choosing a feedline length
that gives a low SWR on any band.)

Cable loss might be important if you are trying to optimize performance on 10m, but by the time you
get down to 20m and lower frequencies, the differences are negligible.
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N4NYY
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« Reply #13 on: September 26, 2011, 10:00:50 AM »

All good advice. If you plan on running along the ground or underground, I would get Davis Bury-Flex. The thing about Bury-Flex, is I think it has that dielectric that does not deteriorate with moisture. In my situation, I have in excess of 100 ft underground, and also some in a wet swamp.
 
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WA3SKN
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« Reply #14 on: September 26, 2011, 10:19:46 AM »

60 Ft of coax at HF frequencies is not really a loss problem, so pick because of other reasons.... cost, durability, etc.

-Mike.
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