A question never seen addressed

[Sandy W5TVW]

At 07:00 AM 11/24/98 -0800, you wrote:
>Hi All,
>
>I'm fairly-well experienced in both tube and solid-state circuitry.
>What am I overlooking?
>
>Solid-State rigs require no tuning of the Driver nor the Final.
>Just select Band and dial in Frequency.
>
>Tube equipment requires both Driver and Final tuning.
>Why?
>Why couldn't tube rigs have been designed so as to be as
>convenient to use as S-S turned-out to be?

        First, because when most tube stuff was designed, the use of broadband
ferrite cored transformers were not in use at that time.

Why couldn't a Tube rig be designed to be tune-less?

        They were in some instances!  The Central Electronics 100V and 200V
exciters and the 600L linear amplifier were entirely "tuneless".


        I do hasten to add that the new rigs are not without drawbacks!  Most
modern transceivers are designed to work into a 50 ohm NON-REACTIVE
load at less than a 1.5:1 or 2:1 VSWR.  Most antennas DO NOT show this
characteristic, except at a very narrow range of frequencies.  Most that
*seem* to are generally lossy or inefficient!  The higher the "Q" of the
antenna system, the sharper it usually tunes.
        With modern rigs with "no-tune/broadband" output networks, some form
of antenna tuning unit or "transmatch" is needed to properly match the non-
reactive 50 ohm port of the transceiver to whatever complex impedance the
antenna is presenting to it.  In simple terms: "The antenna coupler makes the
antenna look like a 50 ohm non-reactive resistor to the rig".
        Although all the tuning and loading controls of tube rigs may seem
inconvienent, they allow a much wider range of "loads" to be catered to,
including reactive ones.  In some "pi" section tuning networks employed
inearlier trasnmitters, it was entirely possible to match a "random wire"
antenna on virtually any band and achieve usable results.  With a newer
transceiver, this is impossible without some external antenna tuner/coupler
unit.  I include the transceivers with the so-called "built-in" antenna tuners!
These are only designed to tune a somewhat limited range of impedances
and fall way short of what a reasonable external antenna tuner/transmatch
can accomplish.
        One of the best discussions of antenna tuner/transmatch devices I have
EVER seen, was written by Walt Maxwell, W2DU called "Reflections",
and published by ARRL.  It is fairly easy reading, uses a minimum of
mathematical "explanations", and is based on sound theory and practice.
It is a great myth-buster as regards the great SWR bugaboo.  I'd say it
was almost "must reading" for anyone who wants to seriously improve his
radiated signal!
        Hope this helps.
73,
Sandy W5TVW

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