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Re: [TenTec] Tuner

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Tuner
From: Richards <jrichards@k8jhr.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Mon, 08 Jul 2013 15:42:31 -0400
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
What type and length of transmission line are you using? I presume this is a regular old half wave dipole, right? If so, I believe the text book suggests that a regular old half wave dipole tends to work on its ODD harmonics, which would exclude 40 m on an 80 m antenna. Not that the tuner may not be robust enough to force the matter, but typically it is difficult to tune a coax fed half wave dipole on the first higher EVEN harmonic. (I use Off Center Fed (OCF) antennas because they tend to work on their EVEN harmonics...)

Now the textbook also suggests that 80 m dipole is a "doublet" when fed with open transmission line and used with an appropriate tuner and it is purportedly easier to match on any band using a tuner and open line.

So... what are you using?

I agree with JB's comment it may be you are just not seeing where it does tune on 80m. I recently acquired a Model 248C tuner and was struck by how narrow the tuning range is. Not that it does not match a wide range of loads, but that the sweet spot is very narrow, and requires careful handling or you can easily miss finding the sweet spot.

First thing to do is test the antenna with your antenna analyzer to see if impedance is hither or lower than 50 ohms at the point where the tuner is. You use information that to select either a LowZ or HighZ fixed capacitor setting. Set the Capacitor Knob to around the |3| position, and then work the inductor starting from 0 upward - and go slowly, it won't take much. The sweet spot is a narrow, almost pin-point range, so watch the cross nettle meter carefully and when you are close to the sweet spot, the Reflected Power needle will suddenly and sharply drop. Tune for the lowest reading, and then mess with the Capacitor Knob left and right until you find the lowest possible reflected power meter reading.

Do this for each of the five fixed capacitor settings, although after a bit you will determine the best or most likely capacitor choice 1 through 5, and repeat the procedure described in the paragraph above. Make an charter of the settings that work for each frequency band on each antenna, and you will find the best setting one in short order.

Because the sweet spot for each band is fairly narrow and sharply defined, it is easy to miss it. On the other hand, the best setting will be sorta obvious and dramatic, and the best bit is that setting should work for nearly the entire band, which means it is a sharp tuning point, but that point will cover all or most of the band, obviating the need to keep retuning as you QSY up and down the band.

Once you get this zeroed in, you will really like this tuner because it
is either tuned or not, with little ambiguity, and once tuned, works a wide operating segment of the band for which it is tuned.

Hopefully this helps you find that sweet spot.

================  K8JHR  ==================


On 7/8/2013 12:46 PM, Walt Stewart wrote:
I recently purchased a used 238 tuner. It will give me a perfect match on 40 
meters with my 80 meter dipole, but I cannot get it to match the 80 meter 
dipole cut for 3800 down to the CW area. What am I doing wrong?

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