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Author Topic: 40 meter dipole works well on 80 and 20m  (Read 21147 times)
KF7DS
Member

Posts: 191




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« Reply #15 on: March 31, 2013, 10:49:58 PM »

I have the same antenna that I plan to hang this month and was thinking about using 450 ohm twin-lead too.

The antenna will be at 35 Ft on it's north end and about 60 Ft at the south end, and mid-point at about 45 ft.....feedline drop to ground is about 45 Ft and then another 50 Ft to a remote antenna switch.

Where should I change from twin lead to coax, when the twin lead hits the ground?

The only way to the switch is on the ground, but won't this detune the twin lead or is it ok to run along ground surface?

What adapter would I need to change from twin lead to coax at or before the switch (coax 8 port switch)?

Any other issues I should consider (e.g. attachment at antenna)?

Thanks
Don KF7DS
Portland, OR
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WB6BYU
Member

Posts: 13353




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« Reply #16 on: April 01, 2013, 09:57:11 AM »

If you are just using it on 40m, run coax all the way from the antenna to
the switch/shack.

If you want to use it on 20m and other bands, the proper adaptor between
the ladder line and coax is a balanced antenna tuner.

Unless you carefully choose the lengths of the antenna and ladder line to
give a low SWR relative to 50 ohms, a combination of coax and untuned
open wire line can cause significant losses in the coax due to high SWR.
It isn't difficult to lose half you power (or more) in moderate lengths of
coax with such a system.  For example, while a ladder line length of around
45 to 50' may give a low SWR on 20m with a 40m dipole, the SWR on 40m
and resulting efficiency will suffer.  It's quite difficult to find such a
combination that will give low coax losses over a range of bands, especially
if you have more than 50' of coax involved.  If you do use a remote balun with
coax to a tuner in the shack, I recommend that you keep the coax short -
inches rather than feet if possible.

Or use very low loss coax - this would have been a good use for some of that
RG-17 that I got rid of at the Salem Hamfest.  That might have kept your
efficiency over 50% across multiple bands.
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KF7DS
Member

Posts: 191




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« Reply #17 on: April 01, 2013, 09:35:24 PM »

Good feedback and good to know. Bought it for 40m and will play with it that way.

Thanks much,
Don KF7DS
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N0NZG
Member

Posts: 127




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« Reply #18 on: April 03, 2013, 11:26:41 PM »

proof qrp works.
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VE3FMC
Member

Posts: 987


WWW

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« Reply #19 on: April 04, 2013, 04:45:22 PM »

proof qrp works.

True enough, I have a 80 M coax fed dipole that tunes right up on 160 meters. Doesn't radiate with a damn but hey the radio sees a 1:1 SWR.  Grin 6 meter 3 element beam will load on 20 meters too!

Hey I have made contacts on my old Heathkit Cantenna that is sitting on the basement floor and that thing has a 1:1 SWR on all bands.  Wink
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