[BC] ATU broadband tuning

[Ronald J. Dot'o Sr.]

From: "Dave Dunsmoor" <mrfixit at min.midco.net>
>
> I asked this question the other day, and it seems to have gotten 
> lost in the
> ether-shuffle. ... or something. At least I never saw it, and have 
> not seen
> any replies either. So anyway, here goes again:
>
> How do you guys who know this stuff well, adjust an ATU for not only 
> low
> reflected power at carrier, but also at +/- some amount of khz to 
> effect a
> clean match for good sideband response?

First off I wouldn't say that I "know this stuff well", just enough to 
be dangerous.

I just tune the ATU for max performance (Min reflected) on the carrier 
frequency with no modulation and trust that the sidebands will take 
care of themselves.

Think about it, with two or three coils and a cap or two I think you 
would have a very hard time trying to narrow band it without a lot of 
other components.  Generally I would think that @ 1Mc the 10kc 
sidebands should cause minimal reactance, but that's just my 
uneducated opinion.

Common sense dictates that if you tune the ATU to the exact center 
that the sidebands should be equal.

I have heard of some very narrow bandwidth towers causing problems but 
not being a PE I'm not sure of that.

If you read the tower +/- 25kc either side of Fo and the readings 
progress the way they should then I don't see a problem.

I would think that if you read the ATU input +/- 25kc of Fo then that 
should tell you how even the sidebands will be for ATU and the tower.

The biggest problem that I've encountered is getting the down time at 
the best time of day to read the tower and ATU.

The above is just common sense nuts and bolts engineering.

Ron D