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Author Topic: coax  (Read 2004 times)
KE3LB
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Posts: 39




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« on: February 28, 2010, 08:15:47 AM »

i need some input on coax giong to run 80 to 100 ft of coax to a elk antenna on a tripod thninking on lmr400uf or lmr600uf or i saw belden7810a which it think is cheaper but loss factor are about the same as lmr 400 and comments would be appreciated 73
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WD8LIC
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Posts: 32


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« Reply #1 on: March 18, 2010, 04:12:24 AM »

I use RG-6 cable TV coax.  Very low loss.  75 ohm but the mismatch is negligible.  1.3 vswr with no tuner.

Cable company runs it to my house from the street 300 ft. away.  Good stuff and very inexpensive.  Buy a good name brand such as Phillips.

Bob
WD8LIC
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K6LCS
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« Reply #2 on: March 18, 2010, 11:38:56 AM »

Describe the 80-100 foot run. What are the weather extremes in your area? Will this be buried ... in pipe ... or all above ground?
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Clint Bradford, K6LCS
http://www.work-sat.com
K5MBV
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Posts: 265




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« Reply #3 on: March 26, 2010, 09:02:00 PM »

If you will use the feedline for 432 Mhz you really
should run at least LMR600. Ideally 7/8' Heliax
should be used for a run that long on 432.
Otherwise an amplifier and a LNA could be
used at the antenna end
and you could use any old coax like RG8 etc.

For 2 meters, you could get by with LMR400.

Ken  K5MBV
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AA4HA
Member

Posts: 2384




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« Reply #4 on: March 27, 2010, 04:39:52 PM »

Here are the losses at 433 MHz for 100' of feedline;

Times Microwave LMR-240 1/4"     5.20 dB       $1.00/foot
Times Microwave LMR-400 3/8"     2.63 dB       $1.15/foot
Times Microwave LMR-600 1/2"     1.69 dB       $1.85/foot
Andrew LDF4-50A Heliax 1/2"        1.48 dB       $2.60/foot
Times Microwave LMR-900 5/8"     1.08 dB       $5.30/foot
Andrew LDF5-50A Heliax 7/8"        0.82 dB       $6.30/foot

Prices given are Tessco list.

Selecting a coaxial feedline is a tradeoff between price-difficulty to install and tolerable losses.

You just need to remember that every 3 dB of difference is a doubling or halving of power. This affects your transmitter EIRP as well as your receiver threshold. Gains and losses affect both sides of a radio's performance.

If you have plenty of antenna gain, great receiver sensitivity and power output you could probably afford to deal with more losses in the feedline.

I prefer Heliax as I have alot of experience in putting on connectors, the connector end flare prep tools and a bunch of N connectors salvaged off of commercial sites. LMR-400 is probably the most familiar to most hams and you can find '259 connectors for the ends and do the work with a razor blade, snips and a soldering iron. So it is also about what you are comfortable with and what environment you are putting it in.

Heliax hates being kinked, if you crush it you might as well cut out the bad section or replace the span. It is much more finicky but if you do go that route it should last +20 years with proper weatherproofing.

LMR type connectors can cost anywhere from $0.50 up to $5.00 each depending upon the size and construction. Heliax connectors can cost anywhere from $25.00 to $200.00 each, depending upon size and construction.

Tisha Hayes, AA4HA
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
Free space loss (dB) = 32.4 + 20 × log10d + 20 × log10 f
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