Sorry I need to add some thing I left out.
The ATR-10 modification I am using is without the series capacitor sorta
speak.
The MFJ 989B is fed into a tap on the coil. Cause of the T network on the
tuner
There is series capacitance on the input to the external components.
So the external components is an inductive L network with a cap from the
antenna going to ground.
100pF seams to give the MFJ 989B a bit more tuning range than the 250pF
cap.
Jim K9TF
On Tue, Oct 8, 2013 at 12:56 PM, Jim GM <jim.gmforum@gmail.com> wrote:
> 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
>
--
Jim K9TF
_________________
Topband Reflector
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