I have used an SGC 230 automatic antenna tuner in a maritime mobile
application.

It is basically a PI-network tuner. However the capacitors on the input
or output side of the PI-network need not be utilized, so it self
configures as:

1. PI-network

2. L-network with an input capacitor for matching low Z loads.

3. L-network with an output capacitor for matching high Z loads.

The switched input capacitor values are 100, 200, 400, 800, 1620, and 3200
pf.

The switched output capacitor values are 25, 50, 100, 200, and 400 pf.

The switched inductor values are .25, .50, 1, 2, 4, 8, 16 and 32 uh.

The capacitors are switched in and out in parallel. The inductors are
switched in and out in series.

The input C can assume values from 100 to 6320 pf in steps of 100 pf. The
output C can assume values from 25 to 775 pf in steps of 25 pf. L can
assume values from .25 to 63.75 in steps of .25 uh.

The ARRL antenna tuner analyser software calculates the impedance ranges
such a tuner can match.

When the 230 tuned up, it worked well. When it didn't, often tuning up on
an alternate frequency and then tuning up on the desired frequency would
solve the problem. Sometimes, but not always, pactor would drive the unit
crazy. It would launch a tune up sequence for each packet. SGC has a mod
that locks the tuned position disabling repeat tune ups. Our 230 was too
old for the mod.

Unfortunately the 230 died when it was stored in tropical Australia for 3
years. Water condensed inside the sealed unit, totally filling it and
corroding the circuit board. Three monsoon seasons can do that. Furuno
RADAR domes have flexible plastic breather tubes designed to prevent
condensation. I wish SGC had done that too or filled them with
pressurized nitrogen or taken some other measure to prevent condensation.

Live and learn. I am looking for a replacement tuner.

The MFJ website states they are L-network tuners. Are they C input or C
output L's?

What are the impedance ranges an MFJ tuner can match?

Are the MFJ units designed as a hefty tuner for use at the antenna or a
light weight used to flatten the SWR at the transmitter?

Since they are not weather proofed, I suspect they are designed for use at
the transmitter. Ditto for LDG tuners.

How would an MFJ tuner stack up against a SGC 230 or ICOM AT-120 tuner?

Tnx

Greg, ve0acr
gblair _at_ sympatico _dot_ ca

On Mon, 17 Jan 2005 10:06:12 -0500, Spam
wrote:

What are the impedance ranges an MFJ tuner can match?

Are the MFJ units designed as a hefty tuner for use at the antenna or a
light weight used to flatten the SWR at the transmitter?

Hi Greg,

These, and other questions, are answered at:
http://www.mfjenterprises.com/man/pdf/MFJ-991.pdf

At a minimum:
"256 values of capacitance and 256 values of inductance are
available. With the inductance switched
between the input and output side, this provides a total of
131,072 L/C tuning combinations. The nominal
tuning ranges are 0 to 3900 pF and 0 to 24 µH."

73's
Richard Clark, KB7QHC

"Richard Clark" wrote
Spam
wrote:

What are the impedance ranges an MFJ tuner can match?

Are the MFJ units designed as a hefty tuner for use at the antenna or a
light weight used to flatten the SWR at the transmitter?

Hi Greg,

These, and other questions, are answered at:
http://www.mfjenterprises.com/man/pdf/MFJ-991.pdf

At a minimum:
"256 values of capacitance and 256 values of inductance are
available. With the inductance switched
between the input and output side, this provides a total of
131,072 L/C tuning combinations. The nominal
tuning ranges are 0 to 3900 pF and 0 to 24 µH."

73's
Richard Clark, KB7QHC

I use an MFJ-994 in a Maritime Fixed-Land. It is advertised to handle 12-800
ohms. It has its quirks too, but is easy to shift from line-flattening every
transmit to memory-only.

Jack Painter
Virginia Beach, Virginia