Trying to tune duel antenna's (buddies rig)
05-01-2006, 11:24 AM
#1
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Trying to tune duel antenna's (buddies rig)
Hey guys,
So SkyRat was nice enough to send me his SWR meter and I was able to achieve a 1.3 SWR reading on ch1 and 1.8 on ch40! I was stoked.
Now, my buddy has a '73 CJ-5 and wanted to run duel antennas. So we got everything mounted and wired correctly, and when we went to tune the SWR, it was reading 10!!!
We double checked the connections, and tested with the pos or neg wire on each antenna, and SWR change would occur to show we had everything wired up correctly and that there was hopefully no continuity through the mount.
So for about 2 hours we tried everything.
We finally achieved a SWR reading of 1.5 on chan 1 and a 3.0 on chan 40.
This is whats weird:
We had to remove the tip completely on antenna #1 and take off the ground. On antenna #2, the tip is screwed all the way down and both connections are attached.
If we attach the ground to antenna #1 it will read 10swr on all channels. Once the ground is off, its fine.
What does this mean?
Any help?
So SkyRat was nice enough to send me his SWR meter and I was able to achieve a 1.3 SWR reading on ch1 and 1.8 on ch40! I was stoked.
Now, my buddy has a '73 CJ-5 and wanted to run duel antennas. So we got everything mounted and wired correctly, and when we went to tune the SWR, it was reading 10!!!
We double checked the connections, and tested with the pos or neg wire on each antenna, and SWR change would occur to show we had everything wired up correctly and that there was hopefully no continuity through the mount.
So for about 2 hours we tried everything.
We finally achieved a SWR reading of 1.5 on chan 1 and a 3.0 on chan 40.
This is whats weird:
We had to remove the tip completely on antenna #1 and take off the ground. On antenna #2, the tip is screwed all the way down and both connections are attached.
If we attach the ground to antenna #1 it will read 10swr on all channels. Once the ground is off, its fine.
What does this mean?
Any help?
05-06-2006, 08:38 AM
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Couple of things you may want to consider -
dual antennas will give you a much different radiation pattern if you are running co-phased. He may get some dead spots where his radiation pattern is weak. If he wants to be able to talk equally (or mostly equally) in all directions, he may want to reconsider.
Are you running them f/r or s/s? Ideal spacing on a Suburban is 6' apart, with 6' of coax.
are you using the proper coax? Cophased coax has a different resistance. (I am assuming that you made your own custom coax instead of buying pre-fab co-phase coax).
Ground, ground, and more ground. Check to make sure that both mounts are solidly grounded to frame.
Also - general rule of thumb is to tune the first antenna for as close to 1:1 as you can get. Disconnect (remove physically from mount) and tune second antenna for as low SWR as possible. Reconnect and you should be good.
With one antenna ungrounded, it sounds like you are running a backdoor setup. You will see a lot of gain in one direction, and not a lot of signal behind the backdoor (assuming you are running f/r setup). I don't think this is what you are after?
One last point - dual ants may look cool, but are not always the best setup unless you are going to compete in keydowns. They are (as you have discovered) a pain to tune properly. If it is not necessary to have duals, you may want to consider changing to a singleton. (sorry - I know this isn't what you wanted to hear).
Best of luck,
Merlin
dual antennas will give you a much different radiation pattern if you are running co-phased. He may get some dead spots where his radiation pattern is weak. If he wants to be able to talk equally (or mostly equally) in all directions, he may want to reconsider.
Are you running them f/r or s/s? Ideal spacing on a Suburban is 6' apart, with 6' of coax.
are you using the proper coax? Cophased coax has a different resistance. (I am assuming that you made your own custom coax instead of buying pre-fab co-phase coax).
Ground, ground, and more ground. Check to make sure that both mounts are solidly grounded to frame.
Also - general rule of thumb is to tune the first antenna for as close to 1:1 as you can get. Disconnect (remove physically from mount) and tune second antenna for as low SWR as possible. Reconnect and you should be good.
With one antenna ungrounded, it sounds like you are running a backdoor setup. You will see a lot of gain in one direction, and not a lot of signal behind the backdoor (assuming you are running f/r setup). I don't think this is what you are after?
One last point - dual ants may look cool, but are not always the best setup unless you are going to compete in keydowns. They are (as you have discovered) a pain to tune properly. If it is not necessary to have duals, you may want to consider changing to a singleton. (sorry - I know this isn't what you wanted to hear).
Best of luck,
Merlin
06-12-2006, 02:29 PM
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Dual antennas are a total waste of time and $.
The only time they are at all useful is on a semi tractor where you are trying to establish a decent radiation pattern around an object (the trailer). Also they need to be around 9 ft ( 1/4 wavelength at CB frequency) apart to work properly - again you can do this on a semi. Even then the mounting location, on the mirrors, is less than ideal. To work properly an antenna should be mounted on a large flat surface area of sheet metal. This area creates a groundplane (not to be confuse with an eletrical ground) which acts as the second half of the antenna.
Anywhere else the extra coax just creates signal loss. The tuning issues you have already encountered. Also, if you don't use the proper type of coax and lengths for the co-phasing harness you'll have additional tuning problems
Sorry it's not what you wanted to hear, just reality.
The only time they are at all useful is on a semi tractor where you are trying to establish a decent radiation pattern around an object (the trailer). Also they need to be around 9 ft ( 1/4 wavelength at CB frequency) apart to work properly - again you can do this on a semi. Even then the mounting location, on the mirrors, is less than ideal. To work properly an antenna should be mounted on a large flat surface area of sheet metal. This area creates a groundplane (not to be confuse with an eletrical ground) which acts as the second half of the antenna.
Anywhere else the extra coax just creates signal loss. The tuning issues you have already encountered. Also, if you don't use the proper type of coax and lengths for the co-phasing harness you'll have additional tuning problems
Sorry it's not what you wanted to hear, just reality.
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