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Author Topic: Feedline Options - 370' run  (Read 1993 times)
WG5J
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Posts: 21




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« on: December 29, 2008, 06:25:29 PM »

I wheeled it off tonight and I am looking at a 300' run from my shack to the tower base.  Then another 70' up there and then up the mast, etc.  

I am looking at surplus hardline.  1/2"+

What kinds of feedline can I bury?  I don't want to go aerial - more stuff to mow around, etc.  Trenching it won't be a problem - ditch witch does wonders.  

Comments on bury?
Which feedlines should I consider.

Mostly HF - 1.8 -> 30

Will probably around with some 6mtr and up later on.

Thanks,
Darin
WG5J
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WA7NCL
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Posts: 625




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« Reply #1 on: December 29, 2008, 08:29:29 PM »

How much power do you want to lose?  3 db loss is half, 6 db is 3/4 lost.  Say you have a beam antenna with 6 db gain.  I should think you what to keep the loss to 3 db or less.  So you have some noticeable net gain.

So look up the loss of your proposed feed line per 100 feet matched and see what it takes.

I bet you are looking at big dia hard line.  You then need to figure out how to keep the water out of the system.  Hopefully there are some folks here who are experts at that stuff.
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K9KJM
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Posts: 2415




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« Reply #2 on: December 30, 2008, 01:47:00 AM »

Some surplus cable TV Trunk line "spool ends" would work well for HF and 6 meters, As would some surplus 7/8" Heliax.    1/2" Heliax should work well for the lower HF bands.

I would not bury it until you have at least several runs of Heliax and/or cable "hardline" so your trench will contain several runs.....
Also, Be sure to lay in a bare copper ground wire outside any conduit to bond your tower ground system with your shack ground system.  (#6 or heavier) A few ground rods along the way should also be installed.

Some type of cheap plastic pipe can be used for conduit, I have had good luck using the flexible corregated drain pipe in 3 or 4 inch diameter. Very low cost, Just over 20 bucks for a hundred foot roll.

(For VHF or UHF, The distance is simply too far for any normal type coax. IF I were doing it, I would also lay in a few CAT 5 wires so you could someday remote a VHF/UHF radio at the tower base if desired)
Other wires should also be put in the trench before you backfill.   wires for possible rotor, Power to the tower site, etc.)

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WG5J
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Posts: 21




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« Reply #3 on: December 30, 2008, 08:54:21 AM »

Well in an ideal world I would like to loose no power but in a world of compromise...  I do mostly HF work and it seems that 1/2 hardline will work fine.  I am planning on some VHF and UHF stuff, but I am not really into it.  I am considering a couple runs of 1/2 for the HF stuff and a single run of 7/8" for the others.  It is twice as good.  I suspect 1/2 across the board would suit my needs but if I can get a run of 7/8" to the tower - I'll do it.  

Thanks,
D.
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WG5J
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Posts: 21




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« Reply #4 on: December 30, 2008, 09:04:11 AM »

Some surplus cable TV Trunk line "spool ends" would work well for HF and 6 meters, As would some surplus 7/8" Heliax. 1/2" Heliax should work well for the lower HF bands.
----

Exactly what I am looking to purchase.  


I would not bury it until you have at least several runs of Heliax and/or cable "hardline" so your trench will contain several runs.....
Also, Be sure to lay in a bare copper ground wire outside any conduit to bond your tower ground system with your shack ground system. (#6 or heavier) A few ground rods along the way should also be installed.
---------

I am thinking at least 2 runs for HF, maybe 3 depending on what I can get my hands on.  1 run for VHF/UHF - hoping 7/8"  I want to have a spare in there in case one goes bad.  I am thinking of an array solutions 6 pack for HF - so that will take 2 runs.  Then put a switch on the 7/8" that will handle VHF/UHF stuff.  Then I will have a spare 1/2 hardline run in there in case.

Interesting point no the ground wire.  Do I really want the tower grounded back to the shack (in addition to the grounding at the tower base?  I have not thought that thru.  Thanks for bringing that up.  For that length run I suspect I will be considering a direct bury aluminum run.  If it is a complete run with no splices and I prep the ends correct - that should work.  



Some type of cheap plastic pipe can be used for conduit, I have had good luck using the flexible corregated drain pipe in 3 or 4 inch diameter. Very low cost, Just over 20 bucks for a hundred foot roll.
----------
Good call on that - easier to work with.  I assume it does not have drain holes in it.  The ditch witch I have access to will do a 4" tranch I believe.  So, I think 3" would be easier to work with.  How do you splice the 100' segments together?

I need to see how I can splice a 3" into the box I mounted on the outside of my shack.  When the electricians were out adding a sub-panel for my Alpha, etc I have them put a couple 2" conduits thru the wall to a box on the outside.    Always something to sort thru.  I was originally thinking PVC electrical conduit due  tot he ease of ends, etc.  would splice in just fine to the boxes, on both ends.  



(For VHF or UHF, The distance is simply too far for any normal type coax. IF I were doing it, I would also lay in a few CAT 5 wires so you could someday remote a VHF/UHF radio at the tower base if desired)
Other wires should also be put in the trench before you backfill. wires for possible rotor, Power to the tower site, etc.)
------
7/8" for the UHF should be OK.

 I will be putting in a bunch of control cable for coax switches, 80 mtr relay on the optibeam, rotator, steppir, etc.   I had not planned on Cat %, but that is a good idea.

I won't pul power out there, I have a generator if I need juice.  

Thanks for the input,
D.
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W0FM
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Posts: 2055




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« Reply #5 on: December 30, 2008, 11:39:02 AM »

Hi Darin,

Look up your local commercial two-way radio dealers in the phonebook (Motorola, Kenwood, MA/Com, etc) and stop in to see the shop manager.  Often times they will have large spools 1/2", 7/8" or 1.25" hard line taken out of service when they disassemble old paging systems, IMTS mobile phone systems (pre-cellular) dispatch systems... whatever.  Most shops will keep what they can but when storage space becomes an issue, they usually will sell it quite inexpensively simply to get it out of the way.  Just something you might try.

73, Terry, WØFM
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WB2WIK
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Posts: 20595




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« Reply #6 on: December 30, 2008, 07:22:15 PM »

Ditch witches are great, but I run cables overhead, always (after 43 years of trying different approaches at a lot of installations).

Buried lines are impossible to inspect and difficult to service.  Simple as that.

I can run a line overground for 300' in a couple of hours, no digging required, and then can inspect the length of the line from one end to the other.  Use a messenger cable (like EHS guy wire and turnbuckles) and hang the hard line from that.

If I can't run a line elevated, I won't run it.

Just 43 years of tower installation experience.

WB2WIK/6
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WG5J
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Posts: 21




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« Reply #7 on: December 30, 2008, 07:30:12 PM »

I hear ya - done that before but with our current home - not happening.  

D.
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K9KJM
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Posts: 2415




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« Reply #8 on: December 31, 2008, 01:41:28 AM »

You DO want to run a bare COPPER ground between the tower ground and the shack ground systems.  Think it over. You are ALREADY bonding them together via the coax shields!   So you DO want an external ground line that is in contact with the earth (Along with a few ground rods along the way to provide a better lightning ground.)  Brand new copper wire is not needed. Old, Used copper wire will work just as good. As would some old used copper tubing, etc.
Aluminum will NOT work out well at all in most all soils!

If you are even thinking of a VHF/UHF run, Also try to get some even larger size heliax.  The 1/2" and 7/8" are available at most all larger swapfests nowadays for a very reasonable cost, Check with cellular tower construction crews for some old used 1 1/4" or 1 5/8" heliax for UHF, (Along with a few runs of (Cheap) CAT 5 wire to remote a VHF/UHF rig at the tower base, With the control head in your shack as an alternative to a really long RF run.

Some really large size cable TV trunkline "hardline" would also work for VHF/UHF.  Dont worry about the 75 ohm to 50 ohm bump.

The corrugated drain tubing comes in either non perforated, OR perforated at about the same price.
For all the coax you are considering, I would go with the 4 inch.   Plastic connectors to join the 100 foot rolls are available where you buy the tubing, At most any farm and fleet type store, Or larger home supply store.
I agree that once it is buried, Service is next to impossible. You want to do it right the first time.
Elevated lines, While very easy to service, Usually look pretty ugly.
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K9KJM
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Posts: 2415




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« Reply #9 on: December 31, 2008, 11:31:04 AM »

Don't be timid about searching for some really good, Large size heliax.

A quick search on Ebay found this:

http://cgi.ebay.com/300-ft-of-Andrew-VXL7-50-1-5-8-Coax_W0QQitemZ200257208822QQihZ010QQcategoryZ48704QQtcZphotoQQcmdZViewItemQQ_trksidZp1742.m153.l1262

300 feet of Andrew 1 5/8" for just over a buck a foot!!!!   Brand New!!!!!
If you search around, Good used is available at even better prices.  Connectors are also sold cheap if you wait and watch a place like Ebay.

Local nearby cellular companies are usually even a better source.  When they upgrade sites, That old heliax is going for scrap prices.  And with the foam dielectric, That price is far lower than #1 copper......

(If you do get some really large heliax like this, I would not try to run it inside your plastic conduit. It is simply far too large. This really big stuff can be directly buried with no problem, The outer plastic jacket being VERY thick and tough.)
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EC158
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Posts: 1




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« Reply #10 on: January 01, 2009, 04:53:49 PM »

Definitely go with hard line…I ran 200 feet with conduit, ran rotor cable in same conduit, used remote antenna switch on the tower.

Found this on ebay, price looks good at the moment…

http://cgi.ebay.com/360-ft-Andrew-Heliax-FSJ4-50A-360kt-1-2-Coaxial-Cable_W0QQitemZ200293297587QQihZ010QQcategoryZ96966QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


I used your zip code and found the conduit at your local home depot, 30 ten foot lengths plus a few extra should do it….thats around $100..

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100348473&N=10000003+90016+528216

The remote antenna switch is an Ameritron.

Good luck!

Doc,
EC158
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EC158
Member

Posts: 1




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« Reply #11 on: January 01, 2009, 04:54:36 PM »

Definitely go with hard line…I ran 200 feet with conduit, ran rotor cable in same conduit, used remote antenna switch on the tower.

Found this on ebay, price looks good at the moment…

http://cgi.ebay.com/360-ft-Andrew-Heliax-FSJ4-50A-360kt-1-2-Coaxial-Cable_W0QQitemZ200293297587QQihZ010QQcategoryZ96966QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


I used your zip code and found the conduit at your local home depot, 30 ten foot lengths plus a few extra should do it….thats around $100..

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100348473&N=10000003+90016+528216

The remote antenna switch is an Ameritron.

Good luck!

Doc,
EC158
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EC158
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Posts: 1




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« Reply #12 on: January 01, 2009, 04:55:18 PM »

sorry for the double post Smiley
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NA0AA
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Posts: 1042




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« Reply #13 on: January 03, 2009, 01:13:33 PM »

I would consider a second option:  In the trench run a 240 circuit of 100 amps capacity, a phone line extension, a cable TV extension.  Then I'd use short coax to my now RF isolated shack!

But that's just me -  toughshed with some insulation and paneling inside and you are good to go!
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KB0TXC
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Posts: 79




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« Reply #14 on: January 07, 2009, 11:34:28 AM »

How about an option that no one mentioned...

Rather than burying lossy coax, even hard line which even surplus is not cheap, what about hanging a balanced open wire feed to the tower, then a balun at the tower to convert it back to coax, good coax up the tower and voila! a much less loss feed system. There is a lot of info in the antenna handbooks about open line (IMHO, "real" open line made with insulators and wire, not that plastic fantastic second cousin of TV twin line). If you want modern, use plastic insulators, for retro (me) use 1/2" dowel rods that have been boiled in paraffin. (Do that outside please, away from the house, and have a fire extinguisher handy...)

Suspend your feed high enough that the kiddies wont touch the wires, and have at it!

Just my two cents worth, probably worth what I charge for it.

Best and 73,

Joe KB0TXC
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