Autotuner and dipole
 

I recently acquired an ldg lz 100 and hooked it up as soon as I got
it. The dipole I have now will tune with a manual tuner to below
1.5:1 on 40m-10m. The autotuner won't tune to below 1.5:1 in any
band. Am I doing something wrong or did I just not get a decent
tuner. I oftentimes won't even get an SWR green light to show it has
tuned and when I do, the SWR is high. Should I put a balun on or
what? The dipole is 66 feet long in my attic... but as I stated, it
tunes awesome with the manual tuner. If you want to email me, please
email to The email here is incorrect.

Greg wrote:
I recently acquired an ldg lz 100 and hooked it up as soon as I got
it. The dipole I have now will tune with a manual tuner to below
1.5:1 on 40m-10m. The autotuner won't tune to below 1.5:1 in any
band. Am I doing something wrong or did I just not get a decent
tuner. I oftentimes won't even get an SWR green light to show it has
tuned and when I do, the SWR is high. Should I put a balun on or
what? The dipole is 66 feet long in my attic... but as I stated, it
tunes awesome with the manual tuner. If you want to email me, please
email to The email here is incorrect.


You should be able to tune the antenna on 40 meters, as it is resonant
around 7.1 mHz to start with. 20 meters - maybe. 15 meters should tune okay.

Your manual tuner tunes okay because it will tune a much higher range
of mismatches, assuming it is a "T" type tuner.

The autotuner I have seen that has the widest range for tuning
mismatches is of all things, an MFJ.

This doesn't mean your tuner is bad, From what I have seen of the LDG's
- they are nice well constructed units. I'd keep it and modify the antenna.

- Mike KB3EIA -

Greg,
Most 'auto-tuners' have limited tuning 'range' when
compared to 'manual' tuners, that's because of expense,
size limitations, and so on. Since I know nothing about
your 'LDG' tuner, that's what I'd have to guess is happening.
Doesn't mean that there's necessarily anything wrong with
it, just that it can't 'do' what you're asking of it...
'Doc

Thks for replies. I am going to keep it. I think it will come in handy for FD
when I run a random wire up a tree. I will certainly look into some of the
specs for this tuner and adjust the antenna accordingly. Shows my ignorance
that you can just throw up an antenna and tune it with an autotuner. Thanks
again. Always a big help!!


73
Greg

Gregg,

Measure the SWR without a tuner on the various bands. you should be able to
tell whether the autotuner will tune that.

Tam/WB2TT
"Greg" wrote in message
om...
I recently acquired an ldg lz 100 and hooked it up as soon as I got
it. The dipole I have now will tune with a manual tuner to below
1.5:1 on 40m-10m. The autotuner won't tune to below 1.5:1 in any
band. Am I doing something wrong or did I just not get a decent
tuner. I oftentimes won't even get an SWR green light to show it has
tuned and when I do, the SWR is high. Should I put a balun on or
what? The dipole is 66 feet long in my attic... but as I stated, it
tunes awesome with the manual tuner. If you want to email me, please
email to The email here is incorrect.

The LDG tuners will tune a fairly large range and should work in your
application. Look at the QST reviews of a collection of auto tuners for
details. Are you using a balanced feedline? If so, you should use a
1-1 or 4-1 current balun to make the connection to the tuner. If you
are using coax feed use a 1-1 current balun at the feed point.

Knowing just the SWR does not give you the feed line input impedance
which you need to know to understand if the tuner will match. You can
use Eznec to tell you the feed point impedance and a program like TLW to
model the input impedance and calculate the L and C values for a L
network tuner (LDG is a L network tuner). Of course, if you can borrow
an analyzer you can just measure it. Depending on the feed line length
you may just be unlucky and a change in the feed line length will
transform the impedance into something that will match. TLW will help
you figure that out.

I use a LDG RT-11 to feed my 136' dipole and it will match on 160
through 10. I use a length of 450 ohm ladder line to a 4-1 current
balun to the tuner and of course coax to the radio. I selected the
length of the ladder line to insure the match.

Larry

Greg wrote:

I recently acquired an ldg lz 100 and hooked it up as soon as I got
it. The dipole I have now will tune with a manual tuner to below
1.5:1 on 40m-10m. The autotuner won't tune to below 1.5:1 in any
band. Am I doing something wrong or did I just not get a decent
tuner. I oftentimes won't even get an SWR green light to show it has
tuned and when I do, the SWR is high. Should I put a balun on or
what? The dipole is 66 feet long in my attic... but as I stated, it
tunes awesome with the manual tuner. If you want to email me, please
email to The email here is incorrect.