Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: antenna feed line  (Read 474 times)
WD4KPD
Member

Posts: 57




Ignore
« on: February 17, 2009, 09:20:41 AM »

i need to run my vert feedline several hundred feet out to the back property line.

i think it is a bit much for coax at the higher frequencies.  i intend to run balanced line via a pair of baluns.  i also need to run the line down low to keep the neighbors as happy as possible.

how high off the ground must the balanced line be placed? the lower the better.

david/wd4kpd
Logged
KB1NXE
Member

Posts: 290




Ignore
« Reply #1 on: February 17, 2009, 10:02:54 AM »

Coupla of questions that may help you decide for yourself:

Do you have to mow under it?
Will it be accessible by small, curious hands (not just yours)?
How you going to support it over it's length?
Will it present a tripping hazard?
What's the substrate it needs to travel over (dirt/grass/pavement/the living/thermonuclear warheads)?
Will it be open wire or ladder line (insulated)?

I'd make that second question the most important.  No need to fry the curious.  Just messes with your SWR anyway ;~)  But you also need to address the safety of the installation.  

You theoretically can leave it inches off the ground as long as no grass or other material will come in contact.  Tripping hazard is a huge consideration if you need to stay right with your family and insurance company.  Assuming open wire, if grass will come in contact, not only will it screw up the match, it could become a fire hazard (unless you run QRP).  However, if the grass is damp, it may load better:~).

Logged
WB2WIK
Member

Posts: 20395




Ignore
« Reply #2 on: February 17, 2009, 10:59:23 AM »

I've done long runs of balanced line (window line, open wire line) but always by supporting it with a messenger line made of rope, and always putting it far enough overhead that nobody could possibly bump into it or even touch it.  This means about 8' or so above ground.

My messenger line is usually double braided Dacron polyester rope.  It's strong, UV-resistant and stretches very little.  I take up slack/stretch using long turnbuckles.

I wouldn't run this stuff on or too close to the ground -- the hazard isn't worth it.

WB2WIK/6
Logged
AA4PB
Member

Posts: 12343




Ignore
« Reply #3 on: February 17, 2009, 12:27:07 PM »

If you keep the SWR down, RG213 is only 1dB per 100 feet at 30MHz. LMR400 is 0.667dB per 100 feet at 30MHz. It'll be much less on the lower frequencies. I'd tend to trade the loss for the convience of coax unless you are talking more than 200 feet or so.
Logged
WW5AA
Member

Posts: 2088




Ignore
« Reply #4 on: February 18, 2009, 04:42:09 AM »

Better help would be available if you tell us what antenna you are using, however since you say "several" hundred feet, parallel feeder and a carrier line would be the only way to go. Have fun.

73 de Lindy
Logged
WA7NCL
Member

Posts: 625




Ignore
« Reply #5 on: February 18, 2009, 08:14:54 AM »

If you are talking UHF VHF you might need to consider it.  If you are talking HF as one of the other posters pointed out, some very low loss coax is available.  Also you need to understand the meaning of dB.  On a typical receiver, an S unit might be between 3 and 6 dB so if your losses are under 3db you will barely notice it on HF because QSB and QRN will make it hard to tell.  Thats in spite of the fact that 3 dB loss is half the power and it sounds really bad.

You also need to remember adding a bunch of baluns to go between coax and open line will not be lossless.

I would suggest you pony up the bux for good quality coax.

For UHF, VHF you should consider antenna mounted preamps for RX and on transmit, you just add more power to overcome the loss.
Logged
K3GM
Member

Posts: 1705




Ignore
« Reply #6 on: February 18, 2009, 11:50:21 AM »

"....higher frequencies...."

What's the maximum frequency you plan to use with this feedline?  I use 1/2" Heliax out to my antenna site located about 165' from the panel entrance.  It has about .35dB loss per 100' at 30 MHz. It just lays on the surface of the field grass, and is slowly sinking into it.  I drive over it with a 2000lb tractor, mow over it, and walk on it without damage. You cannot deny the convenience of using it.
Logged
WD4KPD
Member

Posts: 57




Ignore
« Reply #7 on: February 18, 2009, 07:38:22 PM »

Gentlemen....

as usual for me i think a simple question should have a simple answer...but i guess not this time.

all replys were well within "good amateur practice"
i had just assumed everyone had no childern around, and a full circumferance privacy fence !

i had intended to run it close abroad the fence just above the mower height, where neighbors couldnt see it unless they stood on a ladder.

i do have some of that 5/8 tv line, so maybe just burying it may be best.

tks all.....

david/wd4kpd
Logged
K9KJM
Member

Posts: 2416




Ignore
« Reply #8 on: February 19, 2009, 03:17:11 AM »

For HF, The 5/8" cable TV hardline should work out well. But if you are going through the trouble of digging a trench to bury it, I would find some more surplus cable TV hardline and put it all in the same trench right away.   (The price is usually right, Close to free) So you have a few "spare" runs of coax for future use....  

For VHF/UHF, Several hundred feet is just too long for anything but something like some surplus 1 5/8" Heliax. (Which is now showing up on the ham used market from cellular tower sites that are being upgraded)

If you do dig the trench and bury, I would also get some cheap corrugated plastic drain pipe (4 inch) that sells for about 20 bucks a hundred foot roll to put the coax inside of for extra protection. AND run  a bare copper wire OUTSIDE the conduit to bond grounds together, Adding a few ground rods along the way also.

Sometimes it is just easier in the long run to use a radio like a Kenwood TS 2000 and put the radio in a little shelter or box of some kind out by the antenna tower and remote control the radio from your shack.
Logged
W3LK
Member

Posts: 5643




Ignore
« Reply #9 on: February 19, 2009, 07:34:00 AM »

<< i need to run my vert feedline several hundred feet out to the back property line. >>

Why? What's the reason you can't place the antenna closer?

73,

Lon - W3LK
Naugatuck, Connecticut
Logged

A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!