[Elecraft] New list member/T1 tuner questions

[Don Wilhelm]

Rick,

The question and discussion has mentioned end fed half wave antennas, 
and has also mentioned that the half wavelength end fed types have a 
high impedance feedpoint that must be dealt with.  There is an 
alternative that is resonant and also end fed.

If you are looking for something end fed that is lightweight and easy to 
put up for the upper bands, consider the classic "Zepp" antenna.  I know 
that the term has been construed in ham usage, and most any dipole has 
been referred to as a zepp antenna.
BUT what I am talking about is "The Classic Zepp" - a half wave dipole 
and a quarter wave piece of parallel transmission line.
YES, if you look at a J-Pole antenna, you can see what I am referring to 
- a J-Pole is nothing more than the classic Zepp antenna that was used 
to trail behind zepplins - lighter than air craft, it does not have to 
be vertical to work well.
You can use that antenna in a straight line, or you can bend it at the 
point where the transmission line ends and the halfwave antenna section 
begins, either configuration works.
It can be easily built from 300 ohm parallel transmission line - either 
solid dielectric or window line, or it can be made of 450 ohm ladder 
line, or even your own constructed parallel transmission line.
Measure out a 3/4 wavelength of the 300 ohm line (do not cut yet, just 
mark it) using your antenna analyzer to determine the electrical length 
or if you really know the velocity factor of the line, you can 'do the 
math' and use a measuring tape.  Divide that length into thirds - the 
length from the end to the first third should be 1/4 wavelength, so cut 
one side of the parallel line there - this is the 1/4 wave transmission 
line.
Now from that cut point, measure a full half wave dipole length (the 
velocity factor of the transmission line does not count for this half 
wave piece, but the insulation will have some effect on the length 
required) - this piece could be regular wire or it can be an extension 
of the transmission line with only one conductor used, take your pick.
You can either feed the open end of the directly from a tuner (the 
impedance will be low), or you can do as is normally done with a J-Pole, 
short the end and tap up on the conductors a bit to achieve a 50 ohm 
match and feed it there with coax.

A J-pole is not only for UHF, they are handy for portable operation too 
- but they are single band antennas, so plan to build and carry one for 
each band you intend to operate.  The size is practical for 20 meters 
and up and depending on the tree situation, 30 or even 40 meters is not 
difficult.

73,
Don W3FPR

qrp_1 at juno.com wrote:
> 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.
>   
>