[Elecraft] New list member/T1 tuner questions

[Ron D'Eau Claire]

Rick Asked: So, what magic wire lengths work well on all bands with the T1 ?

Answer: There are no "magic" wire lengths. Since you understand feed point
impedance concerns, the "point" is to choose a wire as close to 1/2
wavelength on the lowest frequency as is convenient and which will still
allow a match with the T1. 

Probably something in the range of 90 to 100 feet or 150 to 175 feet will
work FB.

As you know, the only real important band where 1/2 wave really helps is the
lowest frequency band. Even if you hit an exact multiple of 1/2 wave on the
higher frequency bands, the feed point impedance will be a lot lower than it
is at the 1/2 wave band, so it should load FB. You are probably aware that
as you go up in frequency, the feed point impedance tends to settle down so
something in the range of a few hundred ohms which the T1 handles easily. 

There's nothing "special" about any particular length of antenna as long as
it's long enough for the tuner to match on the lowest-frequency band. All
tuners have some minimum antenna length that's needed because the impedance
of the antenna drops to a very low value as it becomes shorter in terms of
wavelength. For example, many high-end commercial tuners required at least
22 feet of radiator at 2 MHz. There's sure to be some minimum length you'll
need with the T1 on the lowest band you use but "Longer is Better" still
applies, at least up to 1/2 wave. 

Use "counterpoise" wires, especially on the lower frequency bands; one cut
1/4 wave for each band. Probably one 66 feet, one 33 feet, and maybe one 16
feet. If you want perfection, you might include a 30 meter wire if you use
it a lot, but I find little to gain over having the 40/20 meter wires by
doing so. 

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Rick Asked: Do I need to use a balun with the endfed wire to make it work or
just
feed it direct to the T1 ?

Answer: No. Used on an end fed wire like that, a balun often makes loading
up the antenna easier by introducing some loss. It's sort of a "dummy load"
in parallel with the radiator that limits the impedance excursion so the
tuner has a better chance of finding a good match. So don't bother to throw
away power. Remember that the RF coming out of the BNC connector is
"balanced". The currents in the center and shield are equal and opposite.
You can feed a balanced load at that point without any concern. 

There are two useful things a balun can do: 1) Reduce the impedance of some
antennas to bring them within range of the tuner and 2) Help isolate common
mode currents from the tuner and rig when they are a problem. That's usually
when there's a ground problem. 


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Rick wrote: Also, I now find that the T1 requires the push of a button
before
starting to transmit, so is there no full autotune mode that cause it to
tune whenever the swr goes above a certain level ?  When changing bands ?
 If not, kind of messes wit hthe idea of having an utotuner in the first
place !  Hmmm ?

The "automatic" part is that it finds the best match automatically, once
it's been commanded to do so. Since you can destroy the tuner - virtually
*any* tuner - by having it tune at full power, the *last* thing you want one
to do is tune "automatically" by launching into a tune cycle when the SWR
runs above some limit. 

You can arrange simple external command either with a single two-conductor
cable (coax is recommended for RF isolation purposes) or by using the data
remote cable with your FT rig. I think you'll find the most comprehensive
answers to your questions about this and other issues relating to the T1
manual in the T1 Owner's manual. You can get it at:

http://www.elecraft.com/manual/T1%20owners%20man%20rev%20A2.pdf

Ron AC7AC