Good Afternoon,
I have a few questions regarding my 40-80-160 dipole installation. It resembles
something in between a parallel and a fan dipole.
I have a 1:1 current balun at the end of a piece of LMR400 cable, tied off the
face of my tower at approximately 80ft above ground. From this balun, I have
three sets of 14ga wire leaving each side. One pair approx. 32ft for 40m,
another pair approx. 62ft for 75/80m, and a third pair approx. 120ft for 160m.
Let's look at one side of the balun (as both sides are the same) - I have the
160m leg tied off to the farthest fence post in the far corner of my property.
The 75m leg ties off the the next (closer to the tower) fence post approx. 8ft
closer. The 40m leg then ties off to the next fence post after that. So
another words, there is approx. 8ft between each band segment leg of the
antenna. Repeated for the other side of the antenna.
Now here's my concern. On 160m and 75m, I obtain a resonant point where the
SWR is 1.05:1 or so. And I can shift it up or down by playing with the point
where I transition from the 14ga wire to the 3/16" tie rope of each leg.
HOWEVER, on 40m, no matter what I try, I can not get the SWR below 1.5:1. Even
if I try to place the 40m legs on a further fence post, bringing them further
away from the 80m legs, or even bringing them closer in to the 80m legs, I can
not get better than 1.5:1. Although it will change with different spacings.
You may ask, why bother - well, first off the amplifier doesn't like anything
much higher than 1.5:1, and second, this also results in reaching 2:1 or worse
that much faster when deviating from the "cut" frequency.
Is this simply a result of interaction between the 80m or 160m legs?
Or could it be the balun itself having some sort of resonant issue on 40m?
Will this problem only go away if I use a separate feed and balun for the 40m
legs? I'd hate to have another balun tied off of the tower, due to the added
weight of another balun and associated down-weight of another 80ft of LMR400
hanging from it.
Thanks for any and all thoughts and suggestions, and Happy Thanksgiving to all.
Eric
K2CB
Now here's my concern. On 160m and 75m, I obtain a resonant point where the
SWR is 1.05:1 or so. And I can shift it up or down by playing with the point
where I transition from the 14ga wire to the 3/16" tie rope of each leg.
HOWEVER, on 40m, no matter what I try, I can not get the SWR below 1.5:1. Even
if I try to place the 40m legs on a further fence post, bringing them further
away from the 80m legs, or even bringing them closer in to the 80m legs, I can
not get better than 1.5:1. Although it will change with different spacings.
You may ask, why bother - well, first off the amplifier doesn't like anything
much higher than 1.5:1, and second, this also results in reaching 2:1 or worse
that much faster when deviating from the "cut" frequency.
Is this simply a result of interaction between the 80m or 160m legs?
Or could it be the balun itself having some sort of resonant issue on 40m?
Will this problem only go away if I use a separate feed and balun for the 40m
legs? I'd hate to have another balun tied off of the tower, due to the added
weight of another balun and associated down-weight of another 80ft of LMR400
hanging from it.
Thanks for any and all thoughts and suggestions, and Happy Thanksgiving to all.
Eric
K2CB
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