Setting the SWR
- Thread starter Lone Bear
- Start date
gary in ohio
Explorer
First you add a spring. Then your done, Not all antenna are tuneable. The 102 whip plus a 6" spring is the correct length.
Most of the fiberglass whips have no way to tune them either.
Most of the fiberglass whips have no way to tune them either.
08whitex
Adventurer
Most of the fiberglass whips have a wire running to the top of the antenna. You can trim that wire to set the SWR.
If you have a SS whip all you need is a SWR meter. If you need to remove some antenna cut it 1/8 inch at a time. If you need to add length get a spring.
gary in ohio
Explorer
Most whips DONT have tuning options, a few do and NO DONT cut anything off the 102" whip. You want the static ball at the top intact. Unless the antenna is on the roof he will not see 1:1 SWR. Any side mounted is going to add capacitance between the antenna and the meta body changing the SWR.
The average CBer isnt going to see a difference in range or reception in 1:1 or 2:1 when using a legal CB.
S
Scenic WonderRunner
Guest
Setting the SWR......
This site has lots of good CB info.
http://www.cbradiomagazine.com/
Get your SWR set as close to 1:1 as possible to be able to talk the longest distance possible.
Do you have a pic of your installation? If your antenna is not grounded well, and is lacking a "groundplane", and is setting right next to a camper......you won't be happy with it's performance.
You might want to consider a "no ground plane" antenna placed on top of your camper and using a tilt mount, so you can tilt it down while not in use.
http://www.wilsonantenna.com/ngk.htm
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This site has lots of good CB info.
http://www.cbradiomagazine.com/
Get your SWR set as close to 1:1 as possible to be able to talk the longest distance possible.
Do you have a pic of your installation? If your antenna is not grounded well, and is lacking a "groundplane", and is setting right next to a camper......you won't be happy with it's performance.
You might want to consider a "no ground plane" antenna placed on top of your camper and using a tilt mount, so you can tilt it down while not in use.
http://www.wilsonantenna.com/ngk.htm
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DaveInDenver
Middle Income Semi-Redneck
You need the spring to make the whip the right length. A 1/4 wavelength on CB frequencies is about 108". CB in the US covers 26.965 to 27.405 MHz. If you take the center of 27.185 MHz and convert to wavelength you get 36.181 feet, so 1/4 of that is 9.045 feet or 108.5 inches. Without a spring you will be short. You could put a 6" spacer I suppose, but everything has been designed to use a mount + spring + whip and it's been that way since probably 1950, so no reason to reinvent the wheel here.
I've personally never seen a full 1/4 wavelength steel CB whip that was tunable, they are usually fixed in the threaded base and have a non-removable ball at the top. Not having any loading coils will give you a fairly wide bandwidth. Get about the right length, it won't be terribly sensitive within about an inch or so. Just make sure to have clean connections on the coax and you probably don't need to worry much after that.
gary in ohio
Explorer
If the camper is metal you may not be able to get a good swr. If its fiberglass then it may be possible. YES you need the spring, Its part of the antenna length and it helps absorb the impact the antenna takes when it hits something.
gary in ohio
Explorer
Again with a legal CB, range is only a few miles and 1:1 or 2:1 will not make a difference. On top of that when mobile your SWR will bounce all over the place based on what is around you.
If the mount is bolted well enough to keep the antenna on the vehicle its grounded enough. Would be nice to see how its mounted and how much of the vehicle/camper impacts the antenna.
Basically smoke and mirrors. A ground plane antenna just use the coax as part of the ground side of the antenna. The same as other antennas with a poor ground.
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08whitex
Adventurer
Is there a reason you say not to trim a 102 whip. Every CB shop or forum I have had experience with say the proper way to tune a 102" whip is to trim it 1/8 inch at a time.
I am not trying to start a fight I just want to know if I have been told wrong and why.
DaveInDenver
Middle Income Semi-Redneck
There is no reason to trim a 102" whip, they are already 6" too short for a proper installation. With a spring I suppose you could conceivably need to trim it, but really unlikely. If you need to trim a 102" whip without a spring then you have a mount or coax issue that is being masked.
DaveInDenver
Middle Income Semi-Redneck
An end-fed 1/2λ monopole will not need the ground to radiate correctly, just like a dipole. It will need a matching network to get the feedpoint impedance right. In any case using the coax as part of the antenna indicates that you have a problem in your installation.
gary in ohio
Explorer
Which is why its smoke and mirrors. The so called no-ground plane antennas are really not.
DaveInDenver
Middle Income Semi-Redneck
I'm not sure what you're calling it smoke and mirrors. A 1/2λ monopole doesn't need a ground plane or radials.
S
Scenic WonderRunner
Guest
I pick THIS Answer....!
"Some men think the Earth is round, others think it flat; it is a matter capable of question. But if it is flat, will the King's command make it round? And if it is round, will the King's command flatten it? No..."
-- Robert Bolt
Oh wait! I think Dave already answered it in his Profile! How cool!...:elkgrin:
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