[Elecraft] KAT3A Question

[Tox]

Ft-991 (pre-A samples at least) has trouble tuning some multitrap verticals
for all the expected bands, this may explain why

On Sat, Apr 11, 2020, 7:57 PM Mark Goldberg <marklgoldberg at gmail.com> wrote:

> On Sat, Apr 11, 2020 at 6:09 PM Bob McGraw K4TAX <rmcgraw at blomand.net>
> wrote:
>
> > My 6M yagi shows a 5.3:1 SWR as indicated on my K3S on 28.3MHz with the
> > ATU in Bypass mode.   When the KAT3A ATU  in the radio resolves a match,
> > the indicated SWR indicated is 1.1:1 on the radio.
> >
> > Using the same antenna but using my KAT500 ATU the best SWR resolved is
> > 1.6:1 as indicated on the radio.
> >
> > Now my antenna analyzer on 28.3 MHz with my 6M yagi connected shows and
> > SWR of 7.5:1, a Z value of 16.6 ohms, and R value of 7.3 ohms and the X
> > value of 14.7.
> >
> > That same antenna on the analyzer at 50.2MHz shows the SWR at 1.2:1, Z
> > at 39.9, R at 40.0 and Z at 0.0
> >
> > My conclusion:  although the SWR values may be indicating acceptable
> > values, the 6 meter Yagi operated on 10 meters would make a very lousy
> > antenna.   You'd be much better off to use an 80 meter dipole or better
> > yet, just a 10 meter dipole.
> >
>
> In addition, a Yagi operated at a non resonant frequency, especially below
> it's design frequency is likely to not act like a Yagi at all. The pattern
> depends on the elements being close to resonance. More wire / aluminum is
> usually better. A physically short antenna may be tunable but it won't be
> efficient. Much of the power will be dissipated in the tuner or balun or
> feedline as losses. A physically short antenna + tuner + high power often
> results in smoke somewhere! I use a 300 foot horizontal look and it can be
> tuned from 80 to 6 meters. Who knows what the pattern is at high
> frequencies but I can make contacts!
>
> So, a tuner is a good idea, but it won't solve every problem. Because it is
> easy to understand, Hams use SWR, but in actuality the same number for SWR
> results from an infinite number of impedances ( R and X), not all of which
> can be handled by the tuner the same way. ARRL has done some comparison
> testing with tuners with various impedances, I believe. I don't know if the
> losses have been measured, but you can take two different impedances that
> result in an SWR of 4:1 and only some can be tuned, depending on the tuner.
>
> 73,
>
> Mark
> W7MLG
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