CB antenna placement - Page 2 - Rubicon Owners Forum
 30Likes
Reply
 
LinkBack Thread Tools
post #11 of 17 (permalink) Old 12-20-2019, 09:34 AM
Administrator
 
johncanfield's Avatar
 
Join Date: Oct 2010
Location: Texas Hill Country
Posts: 10,422
Garage
Any mass of metal near an antenna could detune it and/or change its radiation pattern. With our Jeeps it's almost impossible to have an ideal antenna placement, as long as the SWR is 2.0 or less the radio should be happy. Where Art installed his Wilson is about as good as it gets. For an RF ground I used an aluminum strap from my tailgate to the aluminum corner guard (GenRight tub armor.) John, WB5THT.
Desert Dog likes this.

John - WB5THT
=======================
2006 LJ, not stock
johncanfield is offline  
Sponsored Links
Advertisement
 
post #12 of 17 (permalink) Old 12-20-2019, 10:34 AM
Rubi Crawler
 
Join Date: Feb 2009
Location: Durango CO in summer. Baja in winter
Posts: 287
Garage
True, with my vhf antenna 2' from the A pillar I get a bit over 1 SWR at 35 watts and 2+ SWR at 75 watts. My SWR meter tells me the cause is because of degradation of the reflected signal because of being too close to the A pillar.
The mass of metal at the back of the Jeep degrades the signal. This is why my top load coil is so good with my carrier mount. Guys using the generic fiberglass antenna mounted the same way get a resulting less signal strength due to how the antenna works where the radiated signal is distributed over the length rather than the top above the coil. Still not a big deal for a 5 watt CB radio not designed for long range communication.
PaulW KEOVZC
johncanfield and Desert Dog like this.
pwmac is offline  
post #13 of 17 (permalink) Old 12-26-2019, 09:12 PM
Rubi Noobie
 
Join Date: Dec 2014
Posts: 14
Quote:
Originally Posted by pwmac View Post
True, with my vhf antenna 2' from the A pillar I get a bit over 1 SWR at 35 watts and 2+ SWR at 75 watts. My SWR meter tells me the cause is because of degradation of the reflected signal because of being too close to the A pillar.
The mass of metal at the back of the Jeep degrades the signal. This is why my top load coil is so good with my carrier mount. Guys using the generic fiberglass antenna mounted the same way get a resulting less signal strength due to how the antenna works where the radiated signal is distributed over the length rather than the top above the coil. Still not a big deal for a 5 watt CB radio not designed for long range communication.
PaulW KEOVZC

Either your SWR meter is malfunctioning or you are interpreting the results incorrectly. SWR is constant at a particular frequency regardless of power. That is unless there is so much power you have voltage breakdown, corona, or whatever. Not likely with 75 Watts. Also, the bulk of the radiation from a top-loaded antenna is from the lower section of the antenna where the current is high and relatively constant along the length up to the loading coil. Current above the coil tapers to zero rapidly and contributes little additional radiation.
johncanfield likes this.
Jim1 is offline  
 
post #14 of 17 (permalink) Old 12-27-2019, 11:12 AM
Rubi Crawler
 
Join Date: Feb 2009
Location: Durango CO in summer. Baja in winter
Posts: 287
Garage
Two different antennas one degrades at 75W due to reflect signal and top load does not.
If you think an antenna next to a metal object does not have signal degradation you are mistaken.
pwmac is offline  
post #15 of 17 (permalink) Old 12-27-2019, 01:29 PM
Rubi Noobie
 
Join Date: Dec 2014
Posts: 14
My point is that VSWR does not change with power. I flagged this because you said you get close to 1.0:1 at 35 Watts and over 2.0:1 at 75 Watts. This did not make any sense. Apparently you were talking about two different antennas, one which happened to be measured at 35 Watts, and the other at 75 Watts (not that power level makes any difference). You are of course correct that placing the antenna near a metal object (or even a non-metal object in some circumstances) will affect performance.
Jim1 is offline  
post #16 of 17 (permalink) Old 12-28-2019, 09:47 AM
Administrator
 
johncanfield's Avatar
 
Join Date: Oct 2010
Location: Texas Hill Country
Posts: 10,422
Garage
Quote:
Originally Posted by Jim1 View Post
My point is that VSWR does not change with power. ...
I do believe this is accurate. The only way I can think power could affect SWR would be if it breaks down the transmission line (coax or ladder line) somehow.

John - WB5THT
=======================
2006 LJ, not stock
johncanfield is offline  
post #17 of 17 (permalink) Old 12-28-2019, 06:33 PM
Rubi Noobie
 
Join Date: Dec 2014
Posts: 14
Yeah, that or corroded connectors or ground connections.
johncanfield likes this.
Jim1 is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Rubicon Owners Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome