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Author Topic: Coax Suitable for VHF/UHF  (Read 293 times)

N2SLO

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Re: Coax Suitable for VHF/UHF
« Reply #15 on: Today at 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: Today at 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.)
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