Tom W8JI made some measurements back in 1997 on the ATR-15 when it first
came out. Not sure how this will print out.
*
*
*The ATR-15 measures as follows for load R and loss on 1.8 MHz:
12.5 ohms 21.8% (27.8%)
25 ohms 16.5% (22.9)
50 ohms 10.6% (11.0)
100 ohms 8.9% (10.7)
200 ohms 8.1% (10.4)
400 ohms 7.4% (10.1)
800 ohms 6.9% (8.8%)*
Doubling the value of C cuts low impedance losses in half. I put 500 pF
air variable caps in the ATR-15 and the 12.5 ohm loss was 13.1 percent.
I don't even come close to the MFJ-989 results they published. I
measured the values (they are the ones in brackets above) for the 989
using both an HP 4191A analyzer and a Harris RF voltmeter, as well as
confirmed on meters.
My question is where in the tee match was the extra capacitance installed?
was it going to ground?
N4XM commented in 1997 on the MFJ 989 review.
>*>>T network tuners (like the 989, Xmatch, Vectronics, Tucker, *
>*>>Murch, etc) handle the least power on 160 and with capacitive*
>*>>reactance low resistance loads. T network tuners handle MORE *
>*>>power into higher resistance loads or loads with some amount *
>*>>of inductive reactance. *
w8JI comments
>*L network tuners (like the Ten-Tec, Nye Viking, etc) handle more*
>*power into impedances near 50 ohms, but often do a poor job *
>*matching reactive or very low impedance loads on low frequencies. (Sometimes*
>*these tuners are called Pi-networks, even though*
>*they do not really function as a pi except perhaps on 15 or ten*
>*meters) *
>**
>*In a T network tuner, maximum efficiency and power handling *
>*generally occurs when maximum and equal amounts of *
>*capacitance are used in the capacitors, and the least amount of*
>*inductance is used. This is true even though many other settings*
>*will produce a low SWR.*
I later read more archives. What came up was the ATR-30 How beefy it was.
What the plate spacing on this tuners capacitors? I would think on a
short antenna like mine it is not enough.
So back to the ATR-10. The W8JI design with variable taps seams to handle
high power with nor arcing problems.
I just do not know why this is working for me. Can some one please explain
this to me I am confused? All this reading
requires a younger mind.
Jim K9TF
On Sat, Oct 5, 2013 at 1:54 PM, Jim GM <jim.gmforum@gmail.com> wrote:
>
> My antenna is a 99 foot inverted L for 160M with 95 short radials 2000
> feet of wire.
>
> What I am trying now is W8JI suggested modification design to improve the
> ATR-10 design by taps on the coil for adjustment. Works well.
> http://www.w8ji.com/antenna_tuners.htm
>
> Had my MFJ-989B at the feed point, I had to add a capacitor to ground
> 250pf so it could work. Inductance was at max farthest away from ground.
> Voltage was so high at 300 watts in, the 0.125 meshed plate spacing arced
> over, it has a T network and I had expected this to happen.
> http://www.mfjenterprises.com/support/MFJ-989B/MFJ-989B.pdf I run 500
> watts.
>
> What I was looking at is removing the coil and the input would be at the
> top of C1. I made a test with QRP using 2 small spaced caps taken out of an
> MFJ-901A. Works well. Because of the high voltage situation would there be
> an issue with this and I need to go to a 0.25 inch spacing between plates?
> Vacuum variables are out of my price range.
>
> ATR-10 with W8JI modifications is a high pass tuner or is it? Removal of
> the coil would make this a low pass circuit. Besides that on 160M which one
> would be more efficient, and off the top of your head what would be the
> percentages? If you had my make do with what I have setup, what tuning
> network would you use?
>
> Does any one have an email address for MFJ Service department? I have the
> wrong one. I sent my MFJ 998RT to their Service department, the High
> voltage that was developed with 300 watts pretty much done it in. The
> ATR-10 W8JI redesign has greatly reduce the High voltage that I was seeing
> with out the inductor.
>
> --
> Jim K9TF
>
--
Jim K9TF
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Topband Reflector
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