Dave,
If you look at the LB Cebik information, he has long recommended 44 foot
dipoles as a back-up antenna for 40 through 10 meters and 88 foot
dipoles for 80 through 20. The main reason for his recommendation is
that the radiation pattern does not break up into lobes over that range
of frequencies, and all the radiation is broadside to the antenna wire.
Now, take that dipole and stand it on end - the radiation pattern will
be low to the earth.
As a second step, remove the lower portion of the antenna and install
radials (22 or 44 ft long) to balance out the vertical section. If the
radials are run in opposing directions, any radiation from them will
cancel leaving all the radiated power from the vertical element, and it
will be at a low angle when operated within the frequency range that
keeps the radiation pattern in single lobe (below 10m for the 22 ft
vertical and below 20m for the 44 ft vertical).
If the vertical element is mounted well above the ground, 4 radials (2
pair oriented in opposing directions) should be sufficient, but if
ground mounted, a lot of radials are needed to form a ground screen.
An antenna of this nature will not have an impedance suitable for
feeding with coax. A remote auto-tuner or an L section designed for
each band will be needed at the base to provide a suitable match or the
coax. If the feedpoint is transformed to something coax can easily
match, most all the power will be delivered to the radiator and the
feedline loss will be small, but if directly fed with coax, the losses
can be rather high - just how high depends on the feedline length.
73,
Don W3FPR
dyarnes wrote:
> Paul and All,
>
> This is very interesting! Thanks for bringing that article by VK1OD to our
> attention.
>
> I think I agree with you about trap losses. I have used a Cushcraft R7, and
> now an R8, for years with surprisingly good results. What appealed to me
> about both of these models is that they emulate a 1/2 wave antenna, thus
> making radials more or less unnecessary. These antennas only cover 40 and
> up however.
>
> What now intrigues me about the 43 ft. antenna is connected to some comments
> made to me by Jim Duffey, KK6MC ("Dr. Megacycle") when he visited here some
> time ago. I think most of you are familiar with Jim, and respect (as I do)
> his technical expertise. Anyway, Jim suggested that I might be even better
> off with a 22 ft. vertical on my roof, with as many radials as I could
> reasonably lay out. He said I should also use a remote tuner and balanced
> feedline. Jim felt it would perform adequately on 40 meters, and better as
> you go up. I believe he said the "magic" about 22 feet was to try and keep
> the radiation angle from getting too high on the higher bands.
>
> So, now I'm wondering if a 43 ft. antenna would bring 80 meters, and
> apparently 160 meters, into play under more or less the same concept that
> Jim was espousing. He didn't really mention that the 22 ft. version might
> get you on 80, so maybe not, but the mathematical relationship sure has me
> wondering. Probably I'm extrapolating his comments incorrectly.
>
> I think Jim does monitor this reflector, so maybe he will jump in and make
> some comments. I will probably pass that article to him though, and see if
> I can prod him for some insight.
>
> By the way, I'm guessing that if you could roof mount, or otherwise elevate
> the 43 foot version, you might not have to worry quite so much about having
> so many radials.
>
> Anyway, this motivates me to do a little digging!
>
> Dave W7AQK
>
>
> ----- Original Message -----
> From: "Paul Christensen" <w...@arrl.net>
> To: "Steve Ellington" <n...@carolina.rr.com>; <Elecraft@mailman.qth.net>
> Sent: Sunday, March 15, 2009 7:07 AM
> Subject: Re: [Elecraft] 43' Vertical and the K2 tuner
>
>
>
>>> The 43' vertical is recent fad and it makes no sense at all. Virtually
>>> any trapped multiband vertical should easily outperform it.
>>>
>> Steve,
>>
>> I thought the same until I read this:
>>
>> http://vk1od.net/antenna/multibandunloadedvertical/
>>
>> According to the author, the so-called "magic" of the 43-foot length is
>> that
>> radiation resistance remains quite high across the HF spectrum and thus,
>> system losses are minimized. Compared to a 33-foot vertical, system
>> losses
>> are much lower across the spectrum.
>>
>> But to your point, a trapped multi-band vertical can offer similar
>> performance. Personally, I think the negativity associated with trap loss
>> in multi-band antennas is grossly overblown. Other systematic losses mask
>> what little loss exists in most trapped antenna designs.
>>
>> Anyway, not sure how valid all this data really is, but the data presented
>> is interesting
>>
>> Paul, W9AC
>>
>
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