The AM Forum

OR....Bill Builds a Tuner
  Here are some pics of my latest project, an antenna tuner. This is a reversible L constructed in a rack mount UPS chassis. Hammer finish aluminum was used for the front panel. The roller inductor started life as a fixed value Gates broadcast coil. Plastic end caps with shaft bushings were added as was the roller and arms to follow the inside of the coil creating a roller inductor. Extra capacitance can be added via a rotary switch. The circuit board box on the back is the pickup for the SWR meter. The tuner can be switched in or out of line, reversed and there is a complete disconnect position. More pics in next message....

Here are the last two pics with a close-up of the coil.

Bill,

Nice work! 

I am using a reversible L network which also uses a Gates roller coil.  I built it with a vacuum variable and I used BC-375 "tap switches" for bypass, reversing the L configuration, switching antennas, and adding additional caps in parallel to the 1,000 pf vacuum variable.  I have been very happy with mine and the L network helps knock out harmonics.

Rodger WQ9E

Nice job!.....Larry

Nice looking.

Here is my project. The VFO and exciter with PS for the 813 rig.

Former VF-1 VFO feeding a 6AG7 to and 807


Carl
/KPD

Both y'all did some fine work there!

Hi Bill,
MFJ could learn a lesson from that tuner on making roller coils - the square stock keeps the roller shaft aligned with the main shaft, whereas on MFJ roller coils the roller shaft posts are just tightened by scews, in the manner of knob setscrews, to the round shaft - and they slip.

Carl, On the exciter, do you have the schematic available for the stages driven by the VFO?

I recognise the vfo as the guts out of a VF-1.

I once used one myself.  A modification that will improve the stability is to remount the coils so that they are mounted like the ones in the DX-100.  You will notice that in the VF-1 (as shown in the photo) the ceramic coil forms are mounted on one wall of the coil subassembly while the tuning slugs are mounted on the opposite side.  When the temperature changes, the copper plated steel box expands and contracts, moving the slugs in and out of the coils ever so slightly, but enough to cause some serious drift.  Take the  coils and tuning slugs out, and drill two  holes each, equally spaced on opposite sides of each slug bushing, spaced just far enough apart to accommodate the threaded mounting studs on the  coils.  Remount the coils in the new  holes and reconnect the wiring, so that coil and slug are mounted on the same wall of the box, and that will eliminate one source of drift.

This explains why the DX-100's VFO is more stable than a VF-1, even though both VFO's are practically identical.

What Bill didn't detail is that he machined the roller and fabricated the other parts to mount the shaft and roller assembly. This is a very hot lick since you can often find nice edge-wound inductors like this at fests for pretty reasonable prices. But finding a strapping roller inductor is much harder, especailly for low dollars. Rolling your own like Bill did is sweet!

Thanks for the nice comments. Having a lathe is a real plus.
One thing I probably will change is the SWR components. If I can find a cheap and not pretty Heatkkit AM-2 or HM-102 SWR meter I will change out the meter and pickup. I don't want to take a nice looking one apart. If the meter works and looks good I don't care about the case condition. There are several cheap on e-pay, but by the time you pay shipping you may as well have gone to a hamfest and bought one.

Bill

When is that indoor fester at the old pick-n-run store, Bill?

Very nice piece of work, Bill. Those edge-wound inductors are just the ticket, and as Steve pointed out - you did a most excellent job of upgrading it. Picked one up in the early 80s that the former owner (a BC engineer) had done this to, but nowhere near as elegantly. Nice to see it done right.

Hi Don,
Thanks for the idea
Current plans are to use it only on 160-40. Do you think I wwill need to do that mod for those freqs?

Also one of my other hobbies is insomnia. I tend to wake up late at night (2 AM or so) Eastern and listen to the bedside rcvr. Often here you on 75 with a nice sig. You are a real night owl!
73
Carl
/KPD