[TenTec] Slightly OT

[Rick - DJ0IP / NJ0IP]

Art,

Once the open wire reaches the shack, how do you connect to the 238B?
Directly using its built-in balun?

The first thing I would do it use an external balun, a good 4:1 current
balun if you have one, and then try it.

The next thing I would do is add 11 ft. more open wire to the feedline.
This is about 1/8 wavelength on 15m.

Although the 238B (or C, etc.) is my favorite matchbox on the planet, its
weakness (IMHO) is when the Inductor needs to be at minimum for best match.

I have has multiple cases (all on 40m if I recall right), where I had the L
set to minimum, but middle in the band I would have to switch between "Hi"
and "Lo" to get minimum SWR.  It just seemed flaky.
In these cases I used one of my other tuners; typically my MFJ-986.
On other bands, sparks would fly inside the 986 and the 238 would match it
like a champ.

For that reason I keep two matchboxes.  (For high power)

Unfortunately I cannot tell you exactly what is going on.  But I'm confident
changing the feedline length will fix it.

73
Rick



-----Original Message-----
From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
On Behalf Of Art Trampler
Sent: Sunday, September 18, 2011 3:32 PM
To: 'Discussion of Ten-Tec Equipment'
Subject: [TenTec] Slightly OT

Hi Gang,

 

This is an antenna/impedance transformation device question, but the devices
in question are a Ten-Tec 238B, and the (LDG) internal tuner on a Pegasus.

 

Antenna: 140’ sloping dipole, apex at 45 feet in a tree, ends around 28’. It
is fed with 10’ of LMR600 to a 4:1 current balun, and from that point with
about 100’ of near-600 ohm ladder line (4” spreaders from www.cnc73.com).

 

Symptoms: The internal tuner finds a match on all bands other than 160
(where the whole antenna is ¼ wavelength). With the 238B I cannot match 17,
15, 12 or 10. The best I might see if 4:1, and even then it is very
sensitive, such that any adjustments vary the displayed output in an Autek
WM-1 wattmeter as well as the calculated SWR. Measured output on the Autek
might fall to “0.” I tend to rely on the reverse power setting on the 238B
for tuning, but as SWR falls, so often does the measured output. 

 

The closest match on these bands is found in “bypass” on the 238B.

 

All this was done with 10 to 25 watts output.

 

Knowing that the 238B has a wider tuning range than the internal LDG tuner,
I am a bit perplexed. Could it be poor grounding? Beefing the grounding of
the antenna tuner is one of my next projects. Or could it be stray
inductance within the tuner that I cannot get rid of merely by setting the
inductor all the way counter-clockwise? That is what I tend to believe.

 

Your thoughts? 

 

In other news, all relays replaced on Pegasus and it works fine, and grid
protection circuit for 425 nearly ready to test and drop in.

 

73,

Art K0RO

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