Being automatic doesn't constrain the network topology or
implementation; you could add servos and a controller to the 180s-1.
However, most typical automated tuners are L networks, and differ from
the aircraft one described in using switched combinations of fixed
inductors and fixed capacitors, which means they have a finite number of
settings. The Elecraft ones cover wide range of values (256 equally
spaced inductance values and 256 equally spaced capacitance ones), but
some built into other transceivers have a limited range.
In circumstances that require a load end capacitor, the Elecraft type
design reverses the L network, rather than converting to a Pi topology.
All L (and Pi) networks, are designed to feed unbalanced loads fed
against the same ground reference as at the transmitter output. If
possible, they should be at the antenna end of the feeder, so should not
be driving a feeder themselves.
You don't need a tuner when driving a matched line and an unmatched line
can present a very wide range of impedances.
Actually, looking at the circuit of the 180S-1, in
<http://collinsradio.org/archives/manuals/180S-1_2nd-ed-02-62_.pdf>, the
transmitter side capacitor topology is a hybrid of a pure variable
capacitor and the switched lumped capacitors that are used for all the
capacitors in the Elecraft type designs, although they only provide for
two fixed values, in addition to zero, from two switches (500 and
1,000), whereas the Elecraft type design would give 500, 1,000, and
1,500. I guess capacitors were expensive.
--
David Woolley
On 02/07/2022 23:13, Mister Mike wrote:
The 180S-1 consists of an L network which is formed by a variable air-capacitor on the
input, and a variable roller inductor as the series coil. It is then possible to expand
this network (by means of a jumper) with a vacuum capacitor on the output of the
"PI", in cases where the tuning solution would call for this. The vacuum
variable capacitor can be either shunted on the output, or placed in series with the
inductor. This configuration allows for virtually every kind of antenna to be tuned.
The “automatic” antenna tuner is a completely new concept for me. They appear to
be designed to tune unbalanced coaxial feedlines and not an end-fed wire. I have
one in my K3 but prefer to use the 180S-1 or my B&W VS1500A which is a
“transmatch” based on the design by Doug DeMaw, W1CER/W1FB SK in the 1960s.
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