[Elecraft] New list member/T1 tuner questions

Sat Jul 11 11:26:09 EDT 2009

Unless you're planning to use your T1 as a wheel chock to keep your car from
rolling downhill, I think you'll find the stock case plenty strong. I'm not
sure exactly what plastic they used for the case, but keep in mind that
plastics can be stronger than many metals. (Most military and civilian
aircraft are held together in the air by plastics these days ;-) After
several years, my T1 still looks new. 

Even though toriods are nominally self-shielding, they aren't perfect, so a
metal enclosure might have some deleterious effect. 

You need to push buttons on the T1 to turn it on and initiate a TUNE cycle,
so if it's going to be where you can't reach it, you'll need some sort of
remote control cable. 

The T1 is excellent with random wire end-fed antennas. Like all tuners
today, you do need to avoid exactly 1/2 wavelength long wires. Keep in mind
that's *electrically* 1/2 wavelength, which is not always what the 468/f
formula says because of the effects of the surroundings. 

And there's the challenge with an end-fed wire: you want to be as close to
1/2 wave as you can for maximum efficiency since the power is divided
between the antenna and ground with the most power going to the higher
impedance load, but not so close to 1/2 wave that the T1 can't find a match.
And the closer you are to a 1/2 wave long antenna, the more important it
will be to have a 1/4 wave long wire attached to the case to establish a low
RF voltage on the outside of the case of the T1, the coax connecting it to
the rig and on the outside of the rig itself, to avoid "RF on the rig"
issues.

But don't get too upset if you can't get close to 1/2 wave up in the air for
an end-fed wire. Note that if your radiator is only 1/4 wave long, and your
ground wire is 1/4 wave long, you lose only 3 dB - half of your RF- to the
earth. That may sound like a lot, but many Hams in their home stations would
love to have an antenna that efficient; many, many Hams have much lower
efficiency antennas and get out just fine. Just keep in mind that as you
drop below 1/2 wavelength, the ground becomes more and more important. It's
not a linear effect. The losses start to skyrocket really fast as the
antenna length drops below 1/4 wavelength, so use 1/4 wave as a minimum
length wherever possible.

In this case we're talking about *physical* lengths, not electrical lengths.
Adding loading coils can change the impedance to something easier to match,
but does nothing to help the efficiency of a short antenna. A short antenna
with a loading coil is still a short antenna, Hi! 

73,

Ron AC7AC  

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of qrp_1 at juno.com
Sent: Saturday, July 11, 2009 7:08 AM
To: elecraft at mailman.qth.net
Subject: [Elecraft] New list member/T1 tuner questions

Hello to the group !
  I'm Rick - KC8AON, in Southern Ohio.  Just joined the Elecraft group
because I am thinking of buying a T1 tuner kit to go with my Yaesu
FT-817.  I have been reading some of the reviews of the T1 on the web and
most seem to be good reviews except for the enclosure they put the T1 in.
 I guess they use plastic to save on weight and expense ?  Anyway, was
wondering if anyone has mounted their T1 in a more robust enclosure to
offer more protection in the field and if so did a metal enclosure effect
the tuning properties of the tuner ?  I have a nice small modem case that
would make a very nice rugged enclosue for the T1 that has an extruded
aluminum chassis and a slide on vinyl covered steel top.  But again, will
a metal enclosure effect the tuning properties of the T1 ?  I would
rather go ahead and build it into the more rugged enclosure as I build it
than I would to put it in the plastic box that comes with it if it will
work ok in the metal enclosure.

  Also, does the T1 work well with endfed wire antennas ?  I'm thinking
maybe non resonant lengths with counterpoise wires to eliminate the high
Z of half wave length wires so the tuner will not be trying to tune a
very high impedance and to move the feedpoint to much lower voltage point
on the antenna.  So, if the T1 will work with end fed wires, what are
some good lengths that have been proven to work well with the T1 for 10
thru 40 meters, 10 thru 80, and 10 thru 160 ?  Most of my portable
operations are 10 thru 40 meters, but I do like to work 60 & 80 meters on
occasion, and even 160 on scarce occasions.

  Now, when using the T1 with the FT-817, is the special control cable
absolutely needed ?  If so, how long is the cable and can it be easily
lengthened ?  My planned purpose for the tuner is to put it at the
feedpoint of the endfed wire when operating portable to eliminate coax
feedline loss between the antenna and the radio, so if the T1 will work
fine without the control cable, that would be much better.  If not, the
cable would need to be at least 8 or 10 feet long to reach the feedpoint
of the antenna where the tuner will be.

Thanks for the bandwidth !

73 - Rick McKee, KC8AON
Southern Ohio - EM88sn
www.angelfire.com/electronic2/qrp
With God all things are possible ~ ><(('> ~
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