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Author Topic: Long coax feed line required across the house, looking for advice  (Read 1613 times)
KD0ZGW
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Posts: 128




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« on: April 01, 2014, 06:43:51 AM »

New ham setting up my shack.

West end of house has trees and TV mast over garage. 

after some research it seems a lower level bedroom on the opposite end of the house from most of the antennas will be best location for shack.  (That end has easy access to ground and 220v. in case I ever go with a big amp.)


My plan is to have a remote switch for HF at the east end and a single coax to the shack.  The run will be in excess of 100' from switch to shack.  I will probably also run a multiconductor cable for eventual use with a rotator at the same time.

any roof mounts for UHF could be on the same end of the house as the shack.  Not sure about VHF.

questions:

Can the coax be run along/under the gutters for part of the run?

Is it worth the expense to buy low loss coax for the long run?  if yes, what is recommended?

anything else I should be thinking about?

thx in advance for suggestions and help.

KD0ZGW
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NI0C
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Posts: 2400




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« Reply #1 on: April 01, 2014, 08:28:07 AM »

Check out the loss specs at your frequency bands of interest (usually given per hundred feet) for various types of coax.  I use mostly hardline, but my coax run is about 300 ft.

I also use my antenna analyzer to measure the loss of my entire feedline system at least once per year, just to check for any degradation caused by water, rodents, etc.

73,
Chuck. NI0C
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WB6BYU
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Posts: 13234




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« Reply #2 on: April 01, 2014, 09:43:45 AM »

For HF you'll be fine with any of the "half inch" (actually 0.4") coax types such as
RG-213.  Some types such as LMR-400 may have lower loss, but the difference
is relatively insignificant in actual operation, and probably not worth any expense
(though there is nothing wrong with using them if you already have them, or if
you can get them for the same price.)
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W5WSS
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Posts: 1724




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« Reply #3 on: April 01, 2014, 10:24:25 AM »

The routing of the coaxial antenna feed line to service your antenna system though is perfectly fine relative to ease of installation to your switch is subject to additional losses above and beyond matched condition attenuation for a normalized 100 ft.

So do be aware of the mismatch additional losses of your brand of antenna coaxial feed line.

It is important to be aware that for minimal loss for 100ft of the antenna feed line the antenna system must present a match to the antenna feed line in your case the run from the switch and any additional line from there up to the antenna is included in that calculation.

If you need to avoid such loss as is the case with an antenna system pressed into multi band service will present dramatic feed point impedance differences depending upon the band chosen.

The best solution is a multi band antenna that is exhibiting close to 50 ohms feed point impedance per band.

IF not then the next solution is: using an antenna tuner placed in a location closer to the antenna.

To avoid antenna feed line additional loss an antenna tuner can be placed closer to the antenna where the additional antenna feed line is removed an operated as a coaxial patch cable operated in the proper characteristic impedance.

73
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KD8GEH
Member

Posts: 465




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« Reply #4 on: April 01, 2014, 10:55:41 AM »

Good advise all around.  100ft is alot of coax too like the other OM said. I use the best I can afford for my runs, mostly RG-213 for HF, LMR400 for VHF and UHF.  Its a different deal if you plan on running multi band di-poles type, for those u use RG-8X with a home brew choke.  I run mine thru the cheapo gray electical conduit for a little extra protection.

Welcome to the hobby!  Its a blast, and dont be afraid to just jump in and get your feet wet. Feel frfee to drop me a line direct if you like, always happy to help.

73  Dave   KD8GEH (at arrl dot net)
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KB4QAA
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Posts: 2367




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« Reply #5 on: April 01, 2014, 11:27:14 AM »

http://www.qsl.net/co8tw/Coax_Calculator.htm

Here is a calculator that will allow you to estimate and compare losses.
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WA2ISE
Member

Posts: 143




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« Reply #6 on: April 01, 2014, 01:20:43 PM »

If at all possible, I'd try to run must of that coax inside the house.  This means you have to find a path to snake the coax from your shack to the attic/crawl space just below the roof.  Then have it go thru a hole in the facia board just under the gutter where the antennas will be. Look for internal chimneys, sewer pipes and such you could snake the coax thru with a minimal amount of hole cutting in walls and floors.  What this would get you is that coax lasts longer out of the weather, and you avoid unsightly (to your significant other!) cables attached to the outside of the house.  
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N7WR
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Posts: 38


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« Reply #7 on: April 01, 2014, 03:13:18 PM »

Way too much trouble trying to run it inside for what little benefit you might gain because of no weather exposure.  High quality coax with connectors properly installed and sealed will last a LONG time outside.  I have a 175 ft run of 9913 (outside) to my remote switch and then RG8 or 8X to various antennas that are within 50 feet of the switch.  All of that has been exposed to weather extremes (ice, snow, wind, rain, sun) for well over 11 years and still works fine.  I work all the DX I want (a lot) and haven't run an amp for quite awhile.
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AA4PB
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Posts: 12832




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« Reply #8 on: April 01, 2014, 04:24:39 PM »

I guess it's all a matter of what you are used to. 100 feet (especially on HF) doesn't seem that long to me. I have 100 feet out to the base of the tower and then 60 feet up the tower. On 20M I worked about 12000 miles while feeding 10W PEP into the shack end of the feed line (RG214).

Of course coax works better when its all run vertical  Wink
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W5WSS
Member

Posts: 1724




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« Reply #9 on: April 02, 2014, 04:08:59 AM »

If the line is operating at it's own characteristic impedance and matches the antenna feed point impedance, then even if it is an antenna feed line the loss can be considered close to the line specification per lineal foot.

When those conditions are met then 100 ft of coaxial antenna feed line can be considered to be as specified.

The tuner positioned and located at the antenna end of the 100 ft indoor run will match it and remove the loss if a mismatched line is operated as an antenna feed line.

It is not about the 100 ft it is about the 100ft operating as either a matched antenna feed line or not.

The tuner resolves this issue because it matches the line traveling from itself to the equipment.
Place the tuner ahead of the 100 ft and loss is low

Or

ensure that the antenna presents a 50 ohm match per band.

73
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