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Author Topic: Coax Suitable for VHF/UHF  (Read 526 times)

N2SLO

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  • Posts: 123
Re: Coax Suitable for VHF/UHF
« Reply #15 on: April 02, 2023, 07:49:20 AM »

LMR 400 minimum for UHF/VHF. Expensive probably for what you  are using it, but do it right the first time. Do not use 9913, has a history of water issues (I had that years ago).
You can do a google search on DB loss, just off of memory I think 100 feet at 144 is a 1.5db loss.
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WB6BYU

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    • Practical Antennas
Re: Coax Suitable for VHF/UHF
« Reply #16 on: April 02, 2023, 09:18:13 AM »

A couple tips:

As Steve WB2WIK used to say here on eHam,
“No coax is too long if it runs vertically.”

Height generally will make the biggest
difference in coverage area.  Don’t skimp
on height just to reduce coax loss.


The impact of cable losses is more important
when using weak signal modes, like CW, SSB,
or FT8, where a 1dB difference can make or
break a contact.  On FM, which works best on
strong signals, it may make a difference between
40% copy and 60% copy, or improve quieting
on a weak signal, but won’t bring a signal
you can’t copy at all up to full quieting.

If you are trying to work simplex stations over
difficult paths, it may help.  If you just want to
work the local repeaters, then, once you have
enough signal strength, reducing losses any
further won’t make any significant difference.


For reference, the typical S-meter range of
the FM mobile rigs I have tested is about
12 dB from no indication to full scale,
regardless of the markings.  Often the meter
will only have 7 or 9 steps (even if each
step lights multiple marks), so about 2 dB
for each step.  So a 1 dB change might not
be enough to see on the meter.

Or it might be:  in one case the meter read
“S7”, then I increases the signal by 1 dB and
both the “S9” and “S9+20” indicators lit up
(they were controlled by the same step on
the meter - you couldn’t get one without
the other).

The point of all that is not to trust the meter
readings on FM radios for anything more
than relative “stronger” or “weaker” readings.
I’ve seen a number of antenna articles that
reported fantastic gains when measured
that way (32 dB!!! for the previous example,
when the actual difference was 1dB).


And, when comparing the losses for different
types of cables, the number to look at is the
difference in the losses for the length you need,
compared to the difference in price (as well as
other factors like flexibility, cost of connectors,
how big a hole you need to drill in the wall, etc.)

WA3SKN

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Re: Coax Suitable for VHF/UHF
« Reply #17 on: April 02, 2023, 02:47:31 PM »

How long a coax run?

-Mike.
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N5XJT

  • Posts: 93
    • HomeURL
Re: Coax Suitable for VHF/UHF
« Reply #18 on: Yesterday at 10:08:21 AM »

Lots of information here but......at the end of the day LMR400 is low loss, durable, cost just a tad more than RG8 and will give good long lasting performance.
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KD6VXI

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Re: Coax Suitable for VHF/UHF
« Reply #19 on: Yesterday at 10:17:42 AM »

Myself, I use LMR400.

At my disposal, I have LMR240, LMR 400 and LMR600.  I also have CommScope 1 5/8 heliax.

The tradeoff with ease of use, cheap connectors, ease to bend to come off the tower, etc. vs dB loss made it a no brainer.

Belden 9913 is just fine, if you get it made by someone who KNOWS what they are doing and they use recently manufactured coax.  As someone who was burned a couple decades ago, I won't use it again.  However, I know many that have (civilian and military....  Incidentally, military air comms at 2xx mhx use LMR400...  I installed a system 2 years ago before moving to the island at Edwards) and report no issue.

If I was purchasing all new, and had to buy from a distributor, it would be Davis RF, hands down.  His Buryflex is as good as anything else on the market, is priced at lower prices and will stand head to head with anything LMR or 99xx.



My vote is LMR400 or Buryflex 400.

--Shane
WP2ASS / ex KD6VXI
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K6JH

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  • Posts: 701
Re: Coax Suitable for VHF/UHF
« Reply #20 on: Yesterday at 02:03:29 PM »

Speaking of buryflex, I understand this is a flooded coax. Is there any sort of special cleaning preparation involved to clean off the flooding goo when mounting connectors? Solder PL259’s vs. crimp?

I’ve always wondered but never got around to asking Davis, as I’ve never used it.
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73
Jim K6JH

W9IQ

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Re: Coax Suitable for VHF/UHF
« Reply #21 on: Yesterday at 02:24:41 PM »

Bury Flex is another foamed PE dielectric cable with a 9.5 AWG stranded bare copper center conductor. As such, you can safely presume that its losses on HF and higher frequencies are just slightly more than LMR-400 (non UF) coax.

Bury Flex is not a flooded cable and it uses a standard PE jacket.

- Glenn W9IQ
« Last Edit: Yesterday at 02:29:49 PM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

K0UA

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  • Posts: 9588
Re: Coax Suitable for VHF/UHF
« Reply #22 on: Today at 08:37:57 AM »

Speaking of buryflex, I understand this is a flooded coax. Is there any sort of special cleaning preparation involved to clean off the flooding goo when mounting connectors? Solder PL259’s vs. crimp?

I’ve always wondered but never got around to asking Davis, as I’ve never used it.

I use Davis RF Buryflex for most everything  including My VHF antennas. It is NOT flooded. It uses standard Connectors. It is really good coax and is under $1 per foot. I have been paying $0.89 per foot lately for it. There are plenty of other good coax out there too. Some of my old runs of RG213 are used on 160 and my 40 and 20 meter verticals out in the woods. Mainly because I had it and it was long enough :)
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73  James K0UA
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