[TowerTalk] Fwd: Tower and antenna decisions

Michael Tope W4EF at ca.rr.com
Mon Oct 28 03:31:00 EDT 2013

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:


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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