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W8AMR
04-13-2005, 07:45 PM
I am new to this and have a few questions. Where I live I have electric services on 3 sides so putting a tower up along side the house is realy out of the question. Not that I couldn't put it up but if mother nature took it down there could be BIG problems. So heres my question how far can I run my coax ,or what lenght of coax can be run between the radios and the antenna. Also if I can go any distance should the coax be buried in the ground in a PVC pipe I wouldn't think running coax in the air would be good for it. Any help would be appreaciated.
Thanks Charlie KD8BHQ http://www.qrz.com/iB_html/non-cgi/emoticons/rock.gif

AI4IJ
04-13-2005, 07:56 PM
Maybe, it would be better to approach this matter from a different direction:

How far would you need the coax to run to get to where you intend to install your antenna(s)? If it's less than 200 ft., there are several options available that will not present big losses. On the otherhand, if the run would need to be 500ft., you will need more expensive, better quality coax, or use balanced feedline, which generally has less loss at HF than coax.

But, yes, you can certainly run coax through buried PVC pipe. And, running it through the air is also fine. You may, however, run into problems if you bury the coax without the PVC pipe, especially in certain soil types.

73
Richard
AI4IJ

KB1KIX
04-13-2005, 08:06 PM
I agree with Richard totally.

I'd also look at the higher quality coax and look at it's dB loss per 100'. Attenuation for LMR400 is around .9 dB per 100 feet (if I recall correctly) - so, 200 feet of that should be fine - IMHO. Since you're putting up a tower - you can more than make that up in a decent antenna.

hey, I only run 50', but I can't do jack for a tower!!!! ARGHHH, I'd trade positions anytime!

Jonathan

WB2WIK
04-13-2005, 08:36 PM
Quote[/b] (ai4ij @ April 13 2005,12:56)]But, yes, you can certainly run coax through buried PVC pipe. #And, running it through the air is also fine. #You may, however, run into problems if you bury the coax without the PVC pipe, especially in certain soil types.
Re: Running coax "through the air."

This might be fine, but might not be. When feeding a dipole or such, the coax usually self-supports for a vertical drop, and not much horizontal span, and may or may not survive the application, depending on the type of coax you use.

Most coaxial cable used by hams is not rated to self-support at all, other than short incidental lengths between equipment or between stacked antennas. For longer spans, normally you'd need a steel messenger cable running from point "A" to point "B," and that cable should be drawn taut using appropriate hardware and a turnbuckle for tensioning. Then, you "hang" the coax from that messenger cable, so the messenger takes all the physical stress (weight) of the coax, and the coax isn't self-supporting at all.

The coax used by the cable TV companies to run between poles or from a pole to a house (a "drop") has the messenger cable built right into the coax, molded into the jacket material.

Ordinary coax made of copper conductors and soft dielectrics cannot withstand this kind of stress.

WB2WIK/6

K0RGR
04-13-2005, 09:06 PM
If you live in an area where it gets extremely cold, like Minnesota, or Antarctica, or places like that there, as the old wine cooler commercial used to say, running the coax through a pipe could cause a problem if water is allowed to collect and stand in the pipe. Make sure the pipe has weep holes in the bottom and can and will drain - otherwise, the freezing water could crush the coax.

KC9AWD
04-13-2005, 09:26 PM
Quote[/b] (KB1KIX @ April 13 2005,08:06)]I agree with Richard totally. #

I'd also look at the higher quality coax and look at it's dB loss per 100'. #Attenuation for LMR400 is around .9 dB per 100 feet (if I recall correctly) - so, 200 feet of that should be fine - IMHO. #Since you're putting up a tower - you can more than make that up in a decent antenna.

hey, I only run 50', but I can't do jack for a tower!!!! ARGHHH, I'd trade positions anytime!

Jonathan
Agreed, just not IF your not running 200 foot of LMR 400 on VHF/UHF

200 ft @ 146 mhz = Total Run Attenuation(dB) 3.0 Efficiency (%) 49.8

200 ft @ 449 mhz = Total Run Attenuation(dB) 5.4
Efficiency (%) 28.7

On HF

200 ft @ 28.5 mhz = Total Run Attenuation(dB) 1.3
Efficiency (%) 73.8

200 ft @ 1.9 mhz = Total Run Attenuation(dB) 0.3
Efficiency (%) 92.5

Coaxial Cable Attenuation & Power Handling Calculator (http://www.timesmicrowave.com/cgi-bin/calculate.pl)

I just love playing with that calculator #http://www.qrz.com/iB_html/non-cgi/emoticons/biggrin.gif #http://www.qrz.com/iB_html/non-cgi/emoticons/tounge.gif

W8AMR
04-13-2005, 10:06 PM
Thanks guys
I beleave 150' to 200' is going to be the limit. If I put the tower behind the house the land falls about 10' so I have to add 10' to the tower just to get 50' so I think I'll be taking out elderberry trees they are just a messy tree anyway and provide nothing to the landscape I think a 50' tower would look MUCH better. Now whaty to put on top that tower?http://www.qrz.com/iB_html/non-cgi/emoticons/rock.gif? Man I hope my wife dosen't try to decorate it this winter I can only imagen what tinceil would do for a signal.

KB2VXA
04-13-2005, 10:38 PM
Hi CANDC and all,

The guys have it pretty much right but frankly I don't recomend sky wire except for the antenna of course. Not only does the coax weather badly and even the UV resistant jackets aren't what they're cracked up to be, but the main consideration is lightning. The more you have out there the greater the chances of something getting whacked.

If you have a very long run to a balanced wire antenna then open wire ladder line is recommended but then a protective, well grounded along it's entire length "stringer" above it will protect it just like the ones above power lines and the old commercial HF stations. Yes, they're grounded at the foot of every pole.

Coax in buried PVC won't be as well protected however, it provides a better ground than earth as scientific studies have shown. It's not likely to get whacked considering the odds but buried utilities oddly enough get it more than above ground ones, lightning bores right down forming fulgarites, fused glass tubes.

I just tossed that stuff in in case you want to work ground wave from a deep mine or cave, otherwise you can take your chances with the rest of us. (;->) The serious bit is I don't like the idea of hanging coax in mid air.

W8AMR
04-13-2005, 10:53 PM
No I didn't like that either to much ice around here and winter is NOT the time to be working on a tower to replace broken anything.

K9KJM
04-14-2005, 07:39 AM
The length you can run coax depends on the frequency. For normal length runs of coax for VHF/UHF Times LMR-400 is the good stuff to use. (Avoid Belden 9913 series, lots of problems with some versions of it)
LMR 400 will work great at lengths up to 75 feet or so.
If you really need to run 150 to 200 feet on VHF/UHF you have a problem. Your best choice for that long a run would be a nice used length of Andrew 7/8" Heliax.
Used to be hard to find and super expensive, But nowadays it is available at most all swapfests for reasonable prices, along with the correct connectors.
Also seen on Ebay lots of times, But watch out for shipping charges!
A low buck feed line could be a "spool end" of cable TV trunk hardline (3/4"- 1") this stuff is 75 ohm, But can be used with 50 ohm systems if care is taken cutting a proper length of 50 ohm cable for each end to connect to your radio and antenna. This coax is usually available for "a few cold ones" from a local cable TV construction crew.
HF is a different story. RG-8X, Plain old RG-8 will work fine for pretty long lengths. And open wire feeder will be very low loss.
The top coax for HF use is good old Belden 213.

WA9CWX
04-14-2005, 09:16 PM
All good advice,
One other ,similar, comment. #DO NOT run the cheap 'CB' type coax for ANY runs, and do not use even the really good Belden RG58 1/4" coax for any runs over 50 feet or so (160 or 80 meters being the exception).
I have used RG213 on a 2 meter/440 ant at a 160' foot run, it worked, but I will never do that again. I now use hardline, which ain't cheap, but you CAN find it cheap if you try. OTHERWISE, for VHF use the BEST coax you can find. For upper HF use the best coax you can afford, and for lower HF, use what you will, but keep it protected and accesable (PVC), so you can change it later if needed.

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