I have a 20 meter dipole that I decided to add 10 meters to. I have added 8.5 feet of wire on either side of the balun. I can now get it to tune on 10 meters but not all of the band. I am using the limited built in tuner in the FT-450AT which can tune 3:1 or better. I can get it to tune up on 28.5 mhz all the way to 29.6 mhz. Below 28.5 mhz the tune fails, I'd like t get it to tune down to 28.3.
Do I cut the wire or does the wire need to be longer in order for me to be able to tune it to a lower freq? How much should I cut or add roughly?
They are both in an inverted V (attic installation) The 20 meter wire is on top with the 10 meter wire underneath. The ends of the 10 meter wires are about a foot directly below the 20 meter wire section. Up near the balun the wires are fed from the same point.
Quote:
Originally Posted by WB2WIK
Longer.
3-1/2" per "side" of the dipole, per MHz at 10m.
If you want to lower the resonant frequency from 29 MHz to 28 MHz, you need to add 3-1/2" of wire to each "side" (or leg, or half) of the dipole.
However the problem you have isn't guaranteed to be that -- could be something else, like the influence of the 20m dipole screwing it up.
How far apart are the 20m and 10m wires? Sounds like they are "together" at the feedpoint, but how far apart at the wire ends?
They are both in an inverted V (attic installation) The 20 meter wire is on top with the 10 meter wire underneath. The ends of the 10 meter wires are about a foot directly below the 20 meter wire section. Up near the balun the wires are fed from the same point.
That should work. Try making the 10m wires longer and see what happens.
Putting up a good antenna is partially science, and partially magic ! You start with the calculated figure, and then you "tweak" the lengths a bit to get the best all around compromise.
I always cut my antennas long, so I can end up clipping off the wires to achieve the desired match.
It is a lot easier with a device such as the MFJ antenna analyzer, but back in the "olde days" we used SWR meters, or some kind of relative RF field strength meter.
Good luck! Jim
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The only problem you would experience is that the 16 ga will not be as strong as the 14. But if the 14 is carrying the weight, you are probably better off using the 16 for the shorter antenna, as the total weight of the system will be less!
Are you installing this as a "flat top" or "inverted VEE" style antenna ?
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10 meters is a large band and difficult to cover all of it without retuning your antenna. Consider making a two wire per side cage dipole for 10M which can be made to have a VSWR bandwidth that covers the entire band. Use about a 12 inch spacing between the wires. The length will end up a little shorter than a single wire dipole for resonance due to the additional capacitance.
Trim the 20 meter element for the lowest VSWR first and then the 10meter one because of the interaction.
73,
Terry, K7FE
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10 meters is a large band and difficult to cover all of it without retuning your antenna. Consider making a two wire per side cage dipole for 10M which can be made to have a VSWR bandwidth that covers the entire band. Use about a 12 inch spacing between the wires. The length will end up a little shorter than a single wire dipole for resonance due to the additional capacitance.
Trim the 20 meter element for the lowest VSWR first and then the 10meter one because of the interaction.
73,
Terry, K7FE
Terry, I doubt he needs to cover higher than about 28.5 MHz...unless he wants to use the same antenna for FM above 29 MHz. I admit I'm a boat anchor lover and also use 10m AM around 29 MHz when the band is really open, but the last time that happened was probably in 2003. Hopefully we're looking forward to those "AM times" again -- maybe.
When F2 comes back to 10m, my AM station gets fired up again!
We appreciate your support.
10 meter wire length question.
Hopefully we're looking forward to those "AM times" again -- maybe.
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