I need/want an antenna for 80 meters. I don't have quite enough room.
So, here's what I'm thinking about building and wonder if it will work.
I need 134' of antenna and about 10 feet on both ends for cord and insulators to hang it. I have about 90 feet.
What if....
I wind 30 feet of wire, evenly spaced, around a piece of PVC pipe about 2 feet long, attach wire of approximate 19 feet to either side of the pipe. for 1/2 of the dipole and duplicate for the other side.
Will it work?
The overall length of wire would be the same as an 80 meter dipole. But, am I going to run into inductance issues with the wire wound around the PVC pipe?
TIA
Ed
NC5S
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Not a good idea. You can't just "wind wire" and expect it to behave as though it was straight. It won't.
However, you can definitely just let the ends of a wire dipole hang down straight, vertically, to reduce the horizontal space required.
For example: You have 90' horizontally but really need 120'. That means you're 30' short.
Install insulators 15' from each end of the dipole. Continue the 120' dipole wire past the insulators and let each end hang down towards the ground. Tie off each insulator to a high support with rope.
Now, you have an "inverted U" antenna, where most of it is horizontal, but the ends are vertical.
Works fine, and almost no difference from having it all horizontal, as long as the very "tip" of each wire (the "ends") are high enough above ground. Usually only 15'-20' is enough to make this work. And of course you do not want any conductive supports holding the wire up; if you do, you need to be farther away from them to prevent undesired coupling/detuning. But trees, houses, utility poles, etc. work fine.
I wind 30 feet of wire, evenly spaced, around a piece of PVC pipe about 2 feet long, attach wire of approximate 19 feet to either side of the pipe. for 1/2 of the dipole and duplicate for the other side.
Will it work?
The overall length of wire would be the same as an 80 meter dipole. But, am I going to run into inductance issues with the wire wound around the PVC pipe?
Yes, it will work, but if you build it exactly as you proposed it will not work on 80m. It will be resonant on some other frequency.
You have described a classic shortened dipole loaded with inductors. Your coils are inductors, but, as WB2WIK stated, you can't just coil up the extra wire - the inductance will be wrong. The inductor does not replace the "missing" wire in this design, it cancels out the capacitive reactance that exists in a short antenna.
Described therein, in excruciating detail, is how to design a shortened, inductively loaded, dipole. Enter your parameters, it will calculate everything you need. Follow the "Coil Design" or "Custom Coil" links on that page, and you will be taken to another page that will help you design and build your coil.
I have never seen the HEX beam concept applied to 80M but seems like it should work.
That works, but ......
..... if you needed 134ft East-West for the linear dipole, you would need only 67ft E-W using the hex shape; however you would also need 67ft North-South to accomodate it!
73,
Steve G3TXQ
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If you can handle open wire / ladder line then you might want to consider simply making it a center fed 90 ft doublet. It's not ideal on 80 but it would work okay and work well on higher bands.
Might I suggest you look up the "shorty fourty" antenna. It is a center loaded half wave with a tapped 50 ohm feed.
Good suggestion as well.
Quote:
Originally Posted by KR2D
Yes, it will work, but if you build it exactly as you proposed it will not work on 80m. It will be resonant on some other frequency.
You have described a classic shortened dipole loaded with inductors. Your coils are inductors, but, as WB2WIK stated, you can't just coil up the extra wire - the inductance will be wrong. The inductor does not replace the "missing" wire in this design, it cancels out the capacitive reactance that exists in a short antenna.
Described therein, in excruciating detail, is how to design a shortened, inductively loaded, dipole. Enter your parameters, it will calculate everything you need. Follow the "Coil Design" or "Custom Coil" links on that page, and you will be taken to another page that will help you design and build your coil.
Great web site. Gives me the information that I need to make the coils and build the antenna.
Quote:
Originally Posted by KJ4IIF
You could try a trapped dipole using purchased traps or buy comercial made traps, quite a few manufactures sell kits for multui band antennas.
Yep, I could do that.
But the enjoyment of building it would be gone and I wouldn't learn anything.
Quote:
Originally Posted by KB1KGA
If you can handle open wire / ladder line then you might want to consider simply making it a center fed 90 ft doublet. It's not ideal on 80 but it would work okay and work well on higher bands.
I've though about that type of antenna. However, ladder line won't work for me as I have to bury the feed line for a ways to keep it out of sight.
Thanks to all for the suggestions and info.
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Would this work?????
Linear Mode
