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: coax feedline  (Read 356 times)
KB1NKJ
Member

Posts: 10




Ignore
« on: October 06, 2007, 07:12:08 PM »

my feedline is 16 ft. longer than what I need. It is RG213  with connectors already attached for a 2meter vertical antenna.I hate to cut and resolder end on the line.Can I coil excess line at base of mast before entry into house?
                       73
                      KB1NKJ
Logged
W5GNB
Member

Posts: 419




Ignore
« Reply #1 on: October 06, 2007, 07:42:08 PM »

Yes, you can simply coil the excess coax.  You should have no appreciable additional losses provided your SWR is as low as possible.

73's
Gary - W5GNB

Logged
W7AIT
Member

Posts: 487




Ignore
« Reply #2 on: October 06, 2007, 07:49:26 PM »

Yes, can coil.  At VHF!

Beware, GAP Challenger HF vertical DO NOT COIL COAX!  Chokes off 80 meter as the coax is used as part of the counterpoise.  Coiling makes a RF chocke and cuts off the counterpoise making the antenna unuseable on 80 meters.

Coax Coil Balun:  5- 10 turns around a 1 liter coke bottle is often used as a RF balun for 10 meter - 40 meter HF dipoles and such.  Works well when you don't have a balun.
Logged
K9KJM
Member

Posts: 2416




Ignore
« Reply #3 on: October 06, 2007, 07:56:36 PM »

What is the overall length of the RG-213 coax from the antenna to the radio?
If more than 30-40 or so feet I would cut it off.
RG-213 is great coax for HF use, But pretty lossy at VHF/UHF........    While an additional 16 feet may not be the end of the world, It WILL affect VHF performance where you need the least loss possible.

(There is a lot more to the overall loss of feedline than the paper charts show. Those charts are for brand new feedline under ideal conditions and do not take in to account connectors, Age, etc)
Logged
N1LO
Member

Posts: 1039


WWW

Ignore
« Reply #4 on: October 06, 2007, 08:38:59 PM »

  Neat tip about the GAP Challenger. Otherwise, go ahead a make a choke coil. 16 feet won't be too much. A large coffee can or gallon paint can makes a handy form.

  If you bond the coax shield to the mast (which should have its own grounding system) and place the choke coil betwwen the mast and shack, then you have created a preferred, low impedance path to ground for any surges or noise impressed on the outside of the shield.

--...MARK_N1LO...--
Logged
K7KBN
Member

Posts: 2754




Ignore
« Reply #5 on: October 06, 2007, 10:42:25 PM »

I wouldn't use a one-liter Coke bottle as a coil form for RG-213 - WAY too small a bend radius.  I'd use the Navy's rule of thumb for coax:  bend radii have to be at least 12X the cable's outside diameter.  For 213 @ 0.405 inches OD, that would be about five inches RADIUS, or 10 inches diameter.
Logged

73
Pat K7KBN
CWO4 USNR Ret.
WA9SVD
Member

Posts: 2201




Ignore
« Reply #6 on: October 07, 2007, 06:56:16 AM »

Unless you need the extra coax in the shack for interconnections, just leave it.  (You CAN coil it with at least a 12" diameter coil; think: size of a reel from the manufacturer...)

    The additional loss in only 16' will be only a few tenths of a dB at most, it will not be significant or noticable; barely measureable.  (Even with a high SWR; and if you DO have a high enough SWR to make the loss of 16' "significant" you will have wasted most of your signal in the other portion of the coax.
    Some people obsess over a tenth or so of a dB in feedline loss; if it's THAT big a deal, then a better feedline and better antenna should be considered.  If a person wants to split hairs on loss on VHF, better feedline would more than make up for the loss in 16' of RG-213/U.
Logged
WT0A
Member

Posts: 922




Ignore
« Reply #7 on: October 07, 2007, 11:10:11 AM »

http://www.ocarc.ca/coax.htm
Logged
K9KJM
Member

Posts: 2416




Ignore
« Reply #8 on: October 07, 2007, 10:57:10 PM »

Those who say it is just dandy to coil up the excess coax really are not up on today's lightning protection standards and info:
Quote the Polyphaser site:
"This could elevate the equipment cabinets to deadly voltages. Deadly for both people and components.

Even though inductive properties of the coax cable appear to be beneficial, and some extra inductance can be created by adding a few turns to the coax; don’t do it. The added turns can also act like an air wound transformer that can couple more energy into the line. This is just the opposite of the desired effect. Instead, make sure that coax lines leaving the tower remain at right angles to the magnetic field surrounding the tower."

Read all about it here:

"http://www.comm-omni.com/polyweb/hamradio5.htm



Logged
WA3SKN
Member

Posts: 5420




Ignore
« Reply #9 on: October 08, 2007, 05:33:14 AM »

Simple solution!
Move your antenna 16 feet, preferrably UP!
Really, 16 feet of RG213 is not enough to worry about.

-Mike.
Logged
KE3WD
Member

Posts: 5694




Ignore
« Reply #10 on: October 08, 2007, 09:45:35 AM »

>>Beware, GAP Challenger HF vertical DO NOT COIL COAX! Chokes off 80 meter as the coax is used as part of the counterpoise<<


Not if you put RADIALS underneath the thing.  


You will also improve the antenna's performance quite a bit.  

Of course, this assumes ground mounting and using the vertical "like a vertical" in the first place.  


KE3WD
Logged
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!