Notices
Marine Electronics Forum

VHF antenna extra cable

Old 07-12-2014, 06:40 AM
  #1  
Admirals Club Admiral's Club Member
Thread Starter
 
Join Date: Feb 2014
Location: Louisiana
Posts: 1,762
Received 17 Likes on 15 Posts
Question VHF antenna extra cable

Installing galaxy 5225-xp. It comes with 20 feet of cable, which is quite a bit too much.

I think I read somewhere that the cable is actually the antenna--is that true?

Should i run the cable from the mount directly to my ebox and cut off the excess, or would I get better reception if I ran the cable around the frame of my t-top and took the long way back to the ebox (more cable exposed)and coiled up the excess?
Old 07-12-2014, 12:02 PM
  #2  
Senior Member
 
Join Date: Jun 2010
Posts: 4,458
Likes: 0
Received 27 Likes on 20 Posts
Default

Excess coax can be coiled rather than cut...the extra cable will not change SWR or add to significant attenuation of signal, unless the difference is drastic, like coax for a 100' boat coiled for a 17' boat...

When coiling excess coax, use a large radius coil, like 6" diameter for RG58 or similar small cables.

Coiling can actually be an advantage, acting as a "common-mode choke", too technical to explain here.

Coiling excess cable of any type is generally ugly, but seldom is detrimental.
Old 07-12-2014, 01:32 PM
  #3  
Senior Member
 
Join Date: Sep 2011
Posts: 5,216
Likes: 0
Received 1 Like on 1 Post
Default

I cut mine figured I had to soldier the connector on anyways, might as well get the benefits of that. I mounted my VHF in the TTop so I would have had 18' of 20' coiled in my TTop.
Old 07-14-2014, 06:00 AM
  #4  
djy
Senior MemberCaptains Club Member
 
Join Date: Dec 2003
Location: Babylon NY
Posts: 1,185
Received 42 Likes on 29 Posts
Default

cut it and solder on a pl59. no big deal cut a 20 foot length down.if you can't solder there are crimp on fittings that you can use.
Old 07-14-2014, 05:47 PM
  #5  
Senior MemberCaptains Club Member
 
Join Date: Jan 2005
Location:
Posts: 4,303
Received 309 Likes on 261 Posts
Default

Leave at least 3 feet, no problem cutting it back. I leave a little extra in case I need to change the connector or move the VHF in the future.

Jim
Old 07-14-2014, 05:54 PM
  #6  
Senior Member
 
Join Date: Sep 2013
Location: Greenville NC
Posts: 700
Likes: 0
Received 0 Likes on 0 Posts
Default

I would not solder it unless you know what you are doing. You can add a lot of attenuation if not done correctly.

Last edited by leftyNC; 07-15-2014 at 03:55 AM.
Old 07-14-2014, 06:41 PM
  #7  
Admirals Club Admiral's Club Member
 
Join Date: Mar 2013
Posts: 308
Likes: 0
Received 5 Likes on 4 Posts
Default

Karl in NY, you might want to study up on your coax. NMEA standards are against coiling coax. Also, the longer the coax, power is lost. Best to cut and terminate cable with enough for service loops.
Old 07-14-2014, 06:43 PM
  #8  
Admirals Club Admiral's Club Member
 
Join Date: Mar 2013
Posts: 308
Likes: 0
Received 5 Likes on 4 Posts
Default

Commode mode choke? You lost me.
Old 07-14-2014, 07:51 PM
  #9  
Senior Member
 
Join Date: Dec 2002
Location: Southeast Michigan
Posts: 3,009
Likes: 0
Received 253 Likes on 206 Posts
Default

Originally Posted by offshraddict View Post
NMEA standards are against coiling coax.
Originally Posted by offshraddict View Post
Commode [sic] mode choke? You lost me.
Since the NMEA seems to be your source of authority for how radio frequency coaxial transmission lines work and should be installed, you should probably ask NMEA about common-mode chokes.

If you want advice on Commode mode chokes, check with

http://www.thetford.com/HOME/PRODUCT...4/Default.aspx
Old 07-14-2014, 07:54 PM
  #10  
Senior Member
 
Join Date: Dec 2002
Location: Southeast Michigan
Posts: 3,009
Likes: 0
Received 253 Likes on 206 Posts
Default

Originally Posted by Akgoff4 View Post
Installing galaxy 5225-xp. It comes with 20 feet of cable, which is quite a bit too much.

I think I read somewhere that the cable is actually the antenna--is that true?
You are using "cable" to mean coaxial transmission line.

The transmission line connects the transmitter to the antenna. It is not part of the antenna. Changing the length of the transmission line does not change the resonance of the antenna or the VSWR on the transmission line.
Old 07-14-2014, 07:59 PM
  #11  
Senior Member
 
Join Date: Dec 2002
Location: Southeast Michigan
Posts: 3,009
Likes: 0
Received 253 Likes on 206 Posts
Default

Originally Posted by Karl in NY View Post
Coiling can actually be an advantage, acting as a "common-mode choke", too technical to explain here.
Yes, precisely. Here is a two-turn choke installed on a Marine Band yagi antenna I installed for my AIS base station:

Oops--Sorry for the bad link. See the coiled coaxial transmission line choke in one of the illustrations at

http://continuouswave.com/whaler/ref...S_Antenna.html

Note that such a choke is usually placed close to the antenna to suppress the flow of antenna currents down the coaxial transmission line outer conductor outer surface.

Last edited by jhebert; 07-15-2014 at 09:00 AM.
Old 07-14-2014, 08:14 PM
  #12  
Senior Member
 
Join Date: Jun 2010
Posts: 4,458
Likes: 0
Received 27 Likes on 20 Posts
Default

Originally Posted by jhebert View Post
Yes, precisely. Here is a two-turn choke installed on a Marine Band yagi antenna I installed for my AIS base station:

http://continuouswave.com/whaler/ref...aCoaxBalun.jpg
linky no worky...
Old 07-15-2014, 05:03 AM
  #13  
djy
Senior MemberCaptains Club Member
 
Join Date: Dec 2003
Location: Babylon NY
Posts: 1,185
Received 42 Likes on 29 Posts
Default

way to much info here for a simple install.glad to see all the fcc techs can gum up the works with a simple vhf install.
Old 07-15-2014, 05:22 AM
  #14  
Senior MemberCaptains Club Member
 
Join Date: Jan 2005
Location:
Posts: 4,303
Received 309 Likes on 261 Posts
Default

It is an old practice to wind a coil of coax to add some inductance to prevent static discharge or add some lightning protection, does work and is not a problem.

A common mode choke thought is two coils wound on a core, used to reduce electromagnetic and radio frequency interference. Not sure of that application here as there is no core, just a coil of coax.

Jim
Old 07-15-2014, 06:18 AM
  #15  
Senior Member
 
Join Date: Dec 2002
Location: Southeast Michigan
Posts: 3,009
Likes: 0
Received 253 Likes on 206 Posts
Default

Originally Posted by Akgoff4 View Post
...Should I run the [antenna transmission line] from the mount directly to my ebox and cut off the excess, or would I get better reception if I ran the cable around the frame of my t-top and took the long way back to the ebox (more cable exposed)and coiled up the excess?
More "exposed" (as you call it) antenna transmission line will not affect reception. A coaxial transmission line is a shielded transmission line. The transmission line is not intended to be part of the antenna that is receiving signals.
Old 07-15-2014, 06:40 AM
  #16  
Senior MemberCaptains Club Member
 
Join Date: Jan 2005
Location:
Posts: 4,303
Received 309 Likes on 261 Posts
Default

There were some marine antennas years ago that specifically stated not to cut the line, it actually was a part of the antenna, I had one but can't remember the make or model.

When you secure the cable with tie wraps do not deform the cable, this will impact performance. Just secure with minimum tension.

Jim
Old 07-15-2014, 08:39 AM
  #17  
Senior MemberCaptains Club MemberPLEDGER
 
Join Date: Feb 2004
Location: Atlanta, GA
Posts: 8,931
Likes: 0
Received 319 Likes on 248 Posts
Default

Maybe I'm a creature of habit but I have always coiled mine in the shape of an "8" and neatly zip tied. Never had an issue.

And - if you buy a Digital Antenna with the gold plated mini connector already installed, you really don't want to cut it off...it simplifies installation.
Old 07-15-2014, 08:54 AM
  #18  
Senior MemberCaptains Club MemberPLEDGER
 
Join Date: Nov 2005
Location: Central Jersey
Posts: 7,961
Likes: 0
Received 3 Likes on 3 Posts
Default

I'm amazed how often this same crap keeps coming back like a bad burrito lunch. Coil away. Or cut. Just make sure you know how to attach a connector properly and avoid sharp bends in the coax. .
Old 07-15-2014, 08:59 AM
  #19  
Senior Member
 
Join Date: Dec 2002
Location: Southeast Michigan
Posts: 3,009
Likes: 0
Received 253 Likes on 206 Posts
Default

Originally Posted by Parthery View Post
..I have always coiled [my antenna transmission lines] in the shape of an "8" ..
Making figure-8 loops means the inductance in cancelled because the turns alternate clockwise and counterclockwise. This is a good practice if you intentionally do not want to create any inductance. The purpose of coiling a coaxial transmission line is to intentionally create an inductance. Note that the inductance is created only for alternating current flowing on the outside of the outer conductor of a coaxial transmission line. For the current flowing inside the transmission line there is no effect.
Old 07-15-2014, 09:04 AM
  #20  
Senior Member
 
Join Date: Dec 2002
Location: Southeast Michigan
Posts: 3,009
Likes: 0
Received 253 Likes on 206 Posts
Default

Originally Posted by jfwireless View Post
It is an old practice to wind a coil of coax to add some inductance to prevent static discharge...
A coil of coax in an antenna's transmission line has no effect on static discharge. In order to drain static electricity from an antenna, the antenna needs to be at DC ground potential. In any case, draining static electrical charges from an antenna is generally to be encouraged, not inhibited.

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.