[Elecraft] OT: manual & automatic tuners

[Ron D'Eau Claire]

The first fully-automatic ATU for  HF that I "met" was a Collins unit
built for aircraft use on B-50 bombers in the 1950's. (The B-50 was a
B-39 "Superfortress" on steroids with bigger engines, propellers and a
taller vertical fin. It was among last of the piston-engine bombers used
by the US Air Force). 

The ATU was part of a Collins HF radio SSB/CW system that was truly
"state of the art" for the Korean War era.

That was decades before cheap logic systems were available to manage the
tuning process. Simple sensing circuits drove electric motors that wound
capacitors and inductors back and forth to find the lowest SWR on the
link to the transmitter. They were slow and 'clunky' with a great deal
of sensitive machinery to go wrong. 

It's important to remember that the "computer" of the future, in the
vision of folks back then, was a mechanical man who would bring you a
fresh-brewed cup of coffee while you operated late at night. Building
any truly "automatic" machinery was a major undertaking and expensive.
Having a fully automatic ATU to switch between Ham bands made about as
much sense as buying a Ferrari to drive to the grocery store, and darn
near as expensive. Tuning up the "finals" in a Ham rig was a natural
part of "firing up" to operate on any frequency. 

There were a few manually-tuned ATU's around then. They showed up mostly
to let ops using the new single-ended pi-net outputs of their post WWII
rigs feed their balanced open wire feedlines. Also, TVI was forcing many
hams to use a low-pass filter in the feed line. The low pass filter is a
fixed tuned affair that requires a low SWR on the line. Often an ATU was
the only way to provide that. Even so, the ATUs were expensive compared
to the typical transmitter or receiver. Most hams simply hooked their
antenna to the rig and operated very happily, "tuning" their finals to
match the antenna. 

Then came "no tune" rigs (like the K2 and all the factory-boxes the
preceded it). No tuning controls meant the operator didn't have to do
anything but spin the VFO to QSY, and it made for much smaller rigs.
(Think how big a K2 would be if it had large variable caps and
bandswitches with front-panel knobs on the inductors to cover all the
bands.) 

The problem with our modern rigs was that they are  NOT "no-tune", they
are "FIXED-TUNED". They are fixed-tuned to deliver power to a 50 ohm
non-reactive load or they won't work. Few popular antenna designs could
provide that over even one Ham band, much less several bands. 

Some Hams settled on operating only on a portion of a band or, at most,
on a couple of bands. Others bought fairly expensive antennas that had
all sorts of complex matching networks to present the required load to
the rig across several bands. 

Then came the WARC bands, which made the antenna design problem even
worse. That brought back the ATU, which is really just a replacement of
the "tuned" output network in the rigs of the 50's and 60's. And
following that came the modern "automatic" tuner. Now they were a bit
cheaper (I bet those early Collins units cost as much as several typical
Ham stations back in the 50's). 

Who said that things don't go around in circles? As Julian pointed out,
it was somewhere 1980 that automatic ATUs started becoming popular in
Ham stations. Now we're back to "tuning up" again, only instead of
swinging a knob and watching a meter, we push a button and listen to the
clicks. 

The modern ATU is a wonder with a built-in "computer" that tunes it up
in seconds and even remembers the settings for each band.

But it still can't make a decent cup of coffee.


Ron AC7AC
K2 # 1289


I don't know when they were first introduced but I've seen automatic
tuners that look to date from the 40's or 50's, maybe even
earlier...they look to be some type of commercial, military, or maritime
gear.t be done at operating power but again, if the settings are
recorded, you can usually just return to those settings and operate. 

Lou W7DZN