[TowerTalk] Tune 160/80 Vertical

[Michael Baker]

Hi Dick,

	Don't think in terms of SWR. Think Rs with no Xs. Which means the
wire is too long. It is basically resonant at 1770. Not too unusual to see
impedances in the 16 ohm range with shortened antennas and that is what the
trap coil is doing.

	Wind up an Un-Un that converts 50 to various impedances. I have one
I purchased that gives me a bunch of range from (If I remember correctly) 3
ohms to 36 ohms output range. If I remember correctly I got it from
CWSBytemark. It is a Jerry Sevik design.

	Here is what I found that I have managed to copy and paste from the
PDF file.

	POWER RATING: 1 KW CONTINUOUS, 2 KW PEAK.
UNBALANCED CO-AXIAL INPUT: 50 OHMS SO239
1 MATERIAL: UL RECOGNIZED 94V-0 FOR FLAMMABILITY
CORE: COATED FERRITE TOROID, K MATERIAL
CWS BYTEMARK OR OTHER APPROVED PART
WIRE: UL RECOGNIZED 200°C RATED MAGNET WIRE
MARK PART NUMBER AND REVISION
2
SPECIFICATIONS:
WHERE SHOWN
APPLICATIONS:
4
50 O : 12.5 O (4:1) CONNECT COAXIAL B(12.5 O) TO COAXIAL D (50 O)
50 O : 5.56 O (9:1) CONNECT COAXIAL C(5.56 O) TO COAXIAL E (50 O)
50 O : 4.08 O (12.25:1) CONNECT COAXIAL C(4.08 O) TO COAXIAL F (50 O)
50 O : 3.13 O (16:1) CONNECT COAXIAL C(3.13 O) TO COAXIAL D (50 O)
50 O : 36.76 O (1.36:1) CONNECT COAXIAL A(36.76 O) TO COAXIAL F (50 O)
50 O : 28.13 O (1.78:1) CONNECT COAXIAL A(28.13 O) TO COAXIAL D (50 O)
50 O : 22.22 O (2.25:1) CONNECT COAXIAL B(22.22 O) TO COAXIAL E (50 O)
50 O : 16.34 O (3.06:1) CONNECT COAXIAL B(16.34 O) TO COAXIAL F (50 O)

About $60.  

>From what you describe if you shorten the wire to resonance at the freq you
want (middle of where you intend to operate) and then use a matching method
(like this transformer matcher) you should be good to go.

If you want to have a good match AND 50 Ohms or there about, other methods
of tweaking the operating freq will be necessary. Tunable loading coil at
the bottom and switched in and out as needed for 160 operation.

Have fun... BTW, I use that matcher for mobile where low impedance is normal
and sometimes very low. 4 Ohms?

Michael Baker  K7DD
k7dd at cox.net

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of w3oa at roadrunner.com
Sent: Saturday, November 20, 2010 9:36 AM
To: towertalk at contesting.com
Cc: sturpe at gmail.com
Subject: [TowerTalk] Tune 160/80 Vertical

I'm helping a friend who has an 80 meter 1/4 wave vertical.  At the top, he
has a 160 meter trap then a wire extending horizontally for 160 meters.  It
is therefore an inverted L on 160.

The SWR on 80 is good and can be adjusted nicely by changing the length of
the vertical component.  160 meters, however is somewhat of a problem.

The minimum SWR he can achieve on 160 is about 1.7:1.  Of course the object
here is to lower the SWR on 160.   Here are some readings we took with my
MFJ -269 antenna analyzer in case this helps anyone.

1.770, Rs 16, Xs 0, SWR 3:1
1.800, Rs 27, Xs 15, SWR 2:1
1.825, Rs 45, Xs 26, SWR 1.7:1
1.85, Rs 79, Xs 31, SWR 1.9:1
1.875, Rs 128, Xs 2, SWR 2.5:1

Can anyone point us in the right direction to find a solution?

Thanks,

Dick, W3OA
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