As a comment on this TOPIC:
In the case of a vertical or a dipole, the point of adjusting the length to
'resonance' or low SWR is to be "nice" to the transmitter.
Anything thing that does this should be acceptable (placing a dummy load
across the antenna terminals is specifically excluded).
One method that I am using and that has not been discussed is the use of
coax transformers and/or stubs to provide this switching between high and
low portions of 40, 80 or 160 meters. ( I guess on 160 we might be talking
between 1800-1840 AND 1840-1880 as being "low" and "high", but the principle
is the same. Although using the stubs at the base of the vertical or at the
point at which the dipole feed line reaches the ground is best, one could
use stubs at the shack end as long as the losses in the feed line are not
excessive. Open wire feed lines or CATV feed lines help in this regard.
Interestingly, stubs and coax line transformers can use RG-59 or RG-58 or
similar small diameter coax. They can be switched remotely by reasonable
relays (generally). They are considerably cheaper than the large coils and
capacitors that one finds hard to locate for antenna tuners. Discussion of
this topic is found in ON4UN's books on Low Band DXing and in the ARRL
Antenna Book. There is a program available (I think from ARRL but I am not
sure) called "winSmith" which allows one to insert circuit elements (stubs,
transformers, coils, capacitors) and use a computer to estimate the values
one should employ to get the results one is interested in. It will certainly
help you to learn how to use a Smith Chart!
While I have not done it, I believe it may be possible to design a network
of stubs and transformers which 'switches' automatically as one moves from
the low to the high end of the band. I do not think the stub tuning will
always be applicable to tuned antenna arrays, but it should be universally
applicable to single element verticals and to dipoles. (I could be wrong).
Tod, KØTO
-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of n4kg@juno.com
Sent: Wednesday, November 14, 2001 2:24 PM
To: TOWERTALK@contesting.com; Stephen.Reichlyn@ryansci.com
Subject: Re: [TowerTalk] 80m Vertical ssb/cw switching
On Wed, 14 Nov 2001 Stephen Reichlyn
<Stephen.Reichlyn@ryansci.com> writes:
> Tom:
>
> If you had your choice, would you make an 80M (cut to 3510) vertical
> the correct length and use a transmatch to operate on 75M (3890)
> or cut the vertical for 3890 and use the transmatch to tune on 3510?
>
> 73, Steve AA4V
>
Hi Steve,
It probably doesn't make much difference. If you tune
it for SSB, you could add a small coil to tune for CW
using a aligator clip or leave the coil in place and short
it out with a wire / clip or relay.
If I didn't want to switch at the antenna, I would tune
it for CW and use a tuner on SSB.
My 80M wire vertical has a double dip at 3525 and 3800.
It consists of one half a bow tie, 62 ft high with 2 ft separation
at the top. I used a wooden spreaded and supported by an
upside down Y and a rope over a tree limb. It is fed with 1/4 WL
of 50 ohm RG58 followed by 400? ft of75 ohm CATV line to the shack.
I'm copying my answer to TowerTalk
since this question has broad interest.
Tom N4KG
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