It just occurred to me that if you shunted the input of the
amplifier with a capacitance who's reactance is say 1/5 of the input
resistance the auto tuner will try to match it and thus you will get a Q of
about 5. It would require switching capacitors but one capacitor could
easily cover an octave in frequency.
It's possible that one capacitor could serve to cover a 9:1 range say from
3.5 to 29.7 MHz but it might. That would be a Q say 3 on 80 meters and 27
on the top 10 meters. The only down side of the high Q is that the auto
tuner would be retuning more often. If you want 160 to 10 meter coverage
you could get by with only 2 capacitors. One for 160 to 40 meters and one
for 40 to 10 meters. Each only a 4:1 range.
These L-tuners work well with capacitive loads but usually associates
with a lower resistance such as the impedances encountered in short (length
less than 1/4th wavelength) vertical antennas.
At 10:53 AM 1/20/2006 -0500, Roger D Johnson wrote:
>Tony King - W4ZT wrote:
> > I don't know if any of you have looked into this particular product but
> > at first glance it appears that this is one solution for the tuned input
> > problem many of us face and at the right price too:
> > <http://www.ldgelectronics.com/manuals/AT-100AMP%20Manual.pdf>
> > 73, Tony W4ZT
>The purpose of the tuned input is to provide a "flywheel" effect to
>smooth out the variations of amplifier input impedance over the
>operating cycle. The Q of the circuit determines how much "flywheel"
>effect we have. The lowest recommended value I've seen is 2. Solid
>state transceivers want even more...perhaps 3 to 5.
>The LDG tuner is an L network in which the Q is dependent on the ratio
>of impedances to be matched. For normal input impedances, the resulting
>Q will be very low. It's hard to write the formula in text format but
>in words it's as follows: divide the higher impedance by the lower,
>subtract 1 and then take the square root. For example to match an
>impedance of 100 ohms to 50 ohms, the resulting Q is only 1!
>With a 3 terminal network you can choose the Q independently of the
>matching and would seem to be the way to go.
>Remember the USS Liberty (AGTR-5)
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