[TenTec] Tuner

[kb4srn at yahoo.com]

Thanks for the advice.  The antenna is the old dipole fed with 8x coax.  I did have a doublet up that was fed with ladder line in the past and it was great.  Wife just doesn't like the idea of me cutting a hole in the wall to get the ladder line out of the shack.

My tuner matches great transmitting on 40 with the 80 band dipole.  Where I have the problem is tuning the dipole that is cut for 3800 down into the CW portion of the band.  I just can't seem to find the combination.  I'll try your suggestions and watch the meter closely as I may be missing the sweet spot I'm looking for.

Again, thanks for the advice.




________________________________
 From: Richards <jrichards at k8jhr.com>
To: Discussion of Ten-Tec Equipment <tentec at contesting.com> 
Sent: Monday, July 8, 2013 3:42 PM
Subject: Re: [TenTec] Tuner
 

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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