On 10/27/2013 11:01 AM, Jim Lux wrote:
Whether it will take the SWR to 1:1 is a function of the step size in
the tuner design (if it's a switched L and C) and the control algorithm.
Most autotuners stop when the SWR is below, say, 1.3:1 or 1.2:1.
What you might want is a way to manually configure the L and C, and
then store that for the frequency (most tuners can do this now.. the
AT200PC can, for sure), or have a computer that knows what frequency
you're tuned to, and then set it up.
(this is what I was doing with my active phased array.. I used AT200s
as essentially computer controlled LC networks)
If you are shooting for really close to 1:1 VSWR to keep an super
finicky SSPA happy, you probably want something with continuously
variable matching components in it. RF Concepts (aka Alpha Power) is
working on one to handle a wide impedance range:
http://www.rfconcepts.com/PRODUCTS/New-Products/Alpha4040
I think they are still struggling with making it work reliably over what
amounts to a fairly ambitious impedance range, but I am sure it as it
stands now it would pull in the VSWR of a Tennadyne LPY from 2:1 down to
1:1 without breaking a sweat. While it's not exactly the same, the Alpha
87A and 9500 as well as the Acom 2000 already do this sort of thing -
that is - automatically bring in a <3:1 VSWR (<2:1 for the 87A) into
something close enough to make the finicky ceramic tubes with delicate
grids happy. The auto tuning of the stepper-motor driven variable caps
on these products is very fast.
In this case of more forgiving PAs that don't need super low VSWR, the
discrete tuning step approach is as you suggest perfectly fine.
73, Mike W4EF.........
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