I changed the title because this is no longer 80m Loop specific.
Don, I hope I didn't shock you by implying it was something new
and you had missed it. As Mike pointed out, LB Cebik (W4RNL) has
done an excellent job of comparing the two circuits in his
article on Link Coupled Tuners. You'll find it on his web site.
Most people probably won't tell a difference between the two and
for TEN-TEC users (at least the ones running barefoot) it
probably doesn't matter whether one runs the original Johnson
circuit or the Annecke circuit. In fact if you have a good tube
amplifier, it won't matter either. It's just the hams with
transistor power amplifiers who will see a great benefit from
modifying the Johnson to an Annecke.
The Johnson was designed in the days of tubes where every radio
and amp had a PI-filter in its output. If the matchbox brought
the antenna's impedance down to 150 or 200 ohms, that was just
fine because the PI-filter could do the rest.
Once transistors came along, the need was redefined to tighter
tolerances. Before we had the WARC bands, it was no big deal
because it was usually possible to find several lengths for your
antenna which the Johnson could pull in to almost 1:1.
What Annecke did was make the 50 ohm side switchable and add a
270 pF variable in series with the link. With that, you can
pretty match anything to 50 ohms. The trade-off is that you have
one more knob to adjust.
So, if you don't have a TEN-TEC and your transceiver requires
exactly 50 ohms, the Annecke circuit is a little bit better.
LB shows a picture of the insides of the Annecke but he chose the
wrong Annecke matchbox. He showed the QRP version (200w). I
have the "real" version. Go to my web site www.dj0ip.de and
click on the picture at the bottom titled "Home of Orion".
You'll see the matchbox just above the TFT monitor which is just
above the Orion. Note the 4 big knobs. The one on the right
titled "Sender" (meaning transmitter) is the additional variable.
I've been running both the high power and low power version of
this matchbox for about 20+ years. However, often in contests
when I'm running lower power, I substitute a "Differential-T"
tuner because there's less knobs to tune. For high power,
nothing beats the Johnson/Annecke circuit.
I wanted to build a second one but parts are difficult to find.
I was also considering the Z-Match designed by Lloyd, VK5BR.
I've been discussing the pros and cons with LB. LB felt the
Z-Match probably will not be as efficient. In the meantime I see
that he has included Lloyd's Z-match on his web site too. I hope
someone smarter than me takes the time to measure and report on
the efficiency of the Z-match.
I've scratched the idea of building another one and will simply
purchase a used Johnson. One of the OM here on the reflector was
kind enough to reserve one for me. Now all I have to do is get
to the states and pick it up!
Finally, I would like to pay tribute to Mr. Annecke who passed
away a couple of years ago. Altogether, I think he designed
about 15 or 20 different matchboxes of various sizes and shapes
and circuits. He sold them as kits, ready built, or just the
components (which is what I bought). Unfortunately his son who
took over his business, dropped the line of ham gear because it
probably was not a lucrative business.
I have all the circuit drawings of every matchbox Mr. Annecke
produced. If I ever find time to work on my Ham website instead
of my work web site, I want to exhibit what he contributed to the
ham community. Right now I can't even find time to use my Orion.
73
Rick
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