Yes, I know that automatic tuners are the marvel of the age, and I may
have one someday. However, I grew up in a different age. Tuners designed
for about 100W used relatively large components. Tuners like the Johnson
Matchbox and homebrew tuners made from salvaged ARC-5 transmitters used
large diameter air wound or ceramic coils and the biggest breadslicer
capacitors we could find. Internal wiring was at least number 18. The
idea was too keep the losses down.
Today, the autotuners use tiny caps and inductors on a PC board. How can
they be efficient?
Inspired by the good QST review on the Ten Tec 238, which is an "L"
network, I homebrewed a small "L" myself to go with my Scout. I used a
Ten Tec box (almost as big as the Scout) and the variable toroid
inductor that was used in Ten Tec's small tuners. I don't know if Ten
Tec still sells these, but it cost about $25. I used a surplus 400 pf
variable cap and a switch to throw in some fixed capacitance.
The Collins tuner (180L-3?) is also an "L" network, but it has an extra
variable capacitor that can be set up in shunt or series with the "L".
Collins used no switches in this design! Everything is configured by
external jumpers and shorting bars.
The main tuner in my shack is a Drake MN-7, which amazingly, is a
perfect styling match for my Corsair.
Still, I'm tempted to try an auto tuner, especially with the Scout, but
why argue with success?
73,
Bob WB2VUF
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|