[TenTec] Zepp?

[Rick - DJ0IP / NJ0IP]

Bob,

As long as you are using a manual tuner, that suggestion works.
If you are using an automatic tuner AND running high power, then the
impedance on several of the bands may be above the matching range of the
tuner.  

Most of the common high-power ATUs max out between 600 and 1200 Ohms, which
is not high enough for matching a center-fed Zepp on even harmonics, unless
you happen to have a feedline length that is near a quarter wavelength (or
odd multiple thereof) long.  

You can change the feedline length, but that is frequency dependent.
The suggested formula is to add 1/8 wavelength of feedline on the band
causing the trouble.
My problem usually seemed to be on 40m (my favorite band).  I found that 13
ft. of feedline does the trick on that band (assuming openwire between .8
and .9 VF).

Here is a trick the ALWAYS WORKS but many of you will be uncomfortable with
it.
My suggestion is, don't moan too loud before you have tried it.
MOVE THE FEEDPOINT
Instead of feeding it at 50/50 (in the middle), feed it at 43/57.
That way the maximum impedance on all bands is under 1000 Ohms, regardless
of feedline length and nearly every external ATU on the planet will match it
on all bands.

All other things equal, Common Mode Current rises, the farther away from the
center you place the feedpoint.
When you move it just 7% off center, the impact on CMC is very little, but
the impact on the impedance of the antenna on even harmonic frequencies is
significant, dropping it from over 2000 Ohms to below 1000 Ohms.  That's the
trick.
Voila!

4:1 vs. 1:1 balun.  Besides the 4:1 balun losing its ability to impede CMC
under high SWR conditions, it also prohibits you from running your Zepp on
lower bands.  For instance a 40m Zepp works just fine on 80m when you use a
1:1 balun, but don't try to do that with a 4:1 balun.  The 4:1 balun is
transforming the impedance in the wrong direction and the result is often an
impedance seen by the ATU of 5 Ohms or less. 

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)


-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Bob McGraw
- K4TAX
Sent: Sunday, September 14, 2014 3:13 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Zepp?

My take is to bring the balanced line all the way inside to the tuner. 
There is certainly no harm in that.  At the tuner output use a 1:1 current
balun between the tuner and the balanced line.  A short piece of RG-213
between the tuner and the balun.  And then a common mode choke on the input
of the tuner between the tuner and the amp/transceiver output.  The fact the
tuner locks up is an indicator of circulating currents.  The common mode
choke should help in this regard.

Another thought is to add 10 ft or so to the balanced line or maybe shorten 
the balanced line 10 ft or so.   The ~ 100 ft of line is acting like some 
odd wavelength matching line for some bands.

73
Bob, K4TAX


----- Original Message -----
From: "Richards" <jrichards at k8jhr.com>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Saturday, September 13, 2014 2:04 PM
Subject: Re: [TenTec] Zepp?


> Should he be using a balun AND a remote tuner?
> I removed the balun and replaced it with a remote tuner.
>
> ------------------------- K8JHR ------------------------------------
>
>
>
> On 9/13/2014 2:01 PM, Ken Brown wrote:
>>
>>> One strange misbehavior I have found that my MFJ 929 auto tuner lockup 
>>> if placed near the 4:1 balun (i.e. using a 2 ft jumper of RG213). 
>>> requiring power to be cycled to regain its brain.
>> An auto tuner that gets locked up when exposed to RF???  Oh it's MFJ.
>> _______________________________________________
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>
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