[BC] Tuning a SS rig vs tube

[dynotherm at earthlink.net]

Willie,

The problem was the SX's, and their simplified siblings sold 
as the Gates model, did not sense VSWR at the PA board output 
where the load needs to be non-reactive. Most of these boxes 
I've worked with exhibit some small degree of rotation that 
makes the box "like" a little compensating rotation in the 
opposite direction. 

There is also the output network that may or may not be dead 
center. Twenty years ago this was not considered important. 
Today, with newer bandwidth considerations, there is more 
focus on rotation and instrumentation error such as you see 
in the SX/Gates is less tolerable. 

Curiously, I rebuilt a DA transmission system and phasor
a year or two ago that was driven by a SX-1. We installed 
excellent CP controls so we could adjust exactly, and a CPB 
to measure continuously. Using a FIM-41 as an external bridge 
detector with the gain cranked to maximum and the bridge 
nulled to the bottom of the 100 uV scale I set the CP to 
exactly 50 j0 and the SX-1 loved it. It tuned purrrfectly. 
Go figure. <g>

If you are in Las Vegas next month, or have a chance to see 
it elsewhere, take a look at the way Nautel has approached 
the VSWR indication and sideband balance problem (first in 
their new 50 kW shown a year ago).

Remember that it is the PA's that need to see a non-reactive 
load, and they are far removed from the output spigot.

Phil Alexander, CSRE, AMD

-----Original Message-----
>From: WBRadiolists at aol.com
>
>Hear, hear! The Gates 5 at WFIF LIKED to see a little reflected power. >Tune it for center-of-null, and it splattered all over the place! 
>Bring the tuning control about 1 /4 turn to the right of null, and 
>it purred like a kitten... passing NRSC with flying colors!