Remote Control Tuner

[flintstone mop]

I would like to get some ideas for a radio controlled tuner. Instead of buying 400 feet of 4 conductor #18 or #16 stranded wire. Besides the solid or stranded wire I have to replace for the chewed up radial system from this past Summer's mowing.
I would have to run a healthy extension cord to the antenna/tuner to power up the receiver/power supplies to drive the 12VDC auto window motors. Would wire still be cheaper?

OR move the antenna closer to the house. Right now it's about 400 feet from the shack. I use an MFJ antenna switcher to switch between an 80/40 M vert and the 160M vert.
 
I have heard of running DC over the coax, but how would I switch controlling a variable capacitor and variable inductor?

The tuning network was a neat trick used in another familiar shortened vert. The capacitor is in series with the center conductor and the "HOT side" of the vertical antenna.This "electrically lengthens or shortens the vert.
The inductor is ACROSS the Center Cond and Shield, at the antenna, to act as a form of transformer to get to the magical 50 ohms (radiation resistance). Adjusting the two components will magically create a match. The MFJ antenna god will be hooked to the coax sending the desired on air freq.
The coax will be a "transmission line" not a transformer.
What are some thoughts from all of the great resources here?

Fred

[KB2WIG]

 ' I have heard of running DC over the coax, but how would I switch controlling a variable capacitor and variable inductor? "

Off the top o my head, a couple of  flip flops that toggle between each L and C ,shoot a pulse down the line on top of the dc.......  its late, but maybe that the idea

klc

[w4bfs]

Hi Fred ... lets see ... you could run these simultaneously down a coax (with appropriate decoupling) ... rf, low freq ac, dc ...if your tuning cap were an air variable without a rotational stop (could be continuously rotated) then feed its motor from 60 Hz ac ... the dc sent down the coax could have it's polarity flipped to motor-drive a roller inductor both directions ... how to keep up with the roller is a problem ... crudest way is to add end limit switches to know when you are at limits or an ammeter on the dc feed to see the locked rotor current increase ...will depend on how everything is made ...hope this helps ...73 ...John

p.s. I just noticed the mfj remote switch in your description ... this complicates things ...about the only thing left is multiple voltage level dc ... most likely the mfj would have to modified to tolerate this ... point of diminishing returns ...beefus

[flintstone mop]

Ok That was good stuff using a continously turning variable cap. And DC for the inductor.
The MFJ antenna switch is just some heavy duty relays. I don't think it would bother anything sending these voltages through the relays.
Good food for thought.

Fred

[Opcom]

On the same subject but addressing the tuning system itself, what if a variable capacitor of the kind that can be rotated continuously were placed on the same shaft as the inductor? It would go through a 360 degree min-max-min each revolution of the inductor. (or it could be geared to turn 4 or more times per coil turn). This would permit the use of but one motor. A perfect 1:1 SWR might never be reached, but considering 1.5:1 is a 4% reflection and 2:1 is an 11% reflection (right?), it might be practical.

Has anyone ever tried this scheme?

[w4bfs]

hey fred ...lookit at this months Qst ... the all band dipole is interesting with its remote changing scheme ...beefus

[K3ZS]

The GRC-27 unit had a UHF transmitter that had what was called a Hubbard tuner.   It was both a capacitor and inductor on the same same shaft.   However, it don't think it went through several 360 turns of the capacitor along the range of the inductor.

[flintstone mop]

It would seem that inductor and capacitor need to be individually controlled as the values would be extremely different as the operating freq will change. The capacitance and inductance will not track each other.
I want my cake and eat it too. Use the entire 160M band with the one vertical. I have had excellent sig reports with this particular antenna.
I heard of sources that would have surplus zip cord (18G cheap stuff...doesn't need to be the monster oxygenated wire) , but because I'm looking for it, it is non-existent.
Fred

[Steve - WB3HUZ]

Use relays with appropriately polarized steering diodes. Plus DC controls the cap and minus DC controls the inductor (or vice-versa). You could control a third element with 60Hz AC.

[Opcom]

could run the free spinning cap with AC and the inductor direction with DC? The inductor having limit switches.

Another crazy idea would be to separate the a commercial autotuner into the brain and switch/tuning sections. Serialize the relay data. Send AC up the cable for power, then a low data rate serial DC signal to be fanned out up there by logic to control the relays. A conventional automatic tuner in the shack to sense SWR and send data up. The up-pole part could be a beefed up version.. That's a pretty complex thing to try as an experiment though.

[WBear2GCR]

It would seem that inductor and capacitor need to be individually controlled as the values would be extremely different as the operating freq will change. The capacitance and inductance will not track each other.

Fred

Fred,

Think about it more...

Each turn of the inductor is like moving the tap along the length of the inductor.
For each tap we can assume that the cap is a full mesh.
So L = 1 to N (where N is turns)
while for each L, C = max ufd (when the cap is fully meshed).

...same as a variable L, with a fixed C.

Now as we rotate the L between N, and N +1, the cap will go from fully meshed to unmeshed in 1/2 turn.
So for each value of L you can "rock" the cap back and forth to get all values of ufd between "0" and "C" (max ufd)!
The only down side is that for fully 1/2 of a rotation of L there will be 1/2 turn where the values of C repeat in reverse order (as you go toward full mesh, and then away from full mesh). (but the values of L will be slightly different... maybe a plus?)

So, it seems workable, but the thing will dip and peak if you are rolling through the range... seems best to tune at low power for the sake of the transmitter's finals...  although maybe you could tune for best match using an antenna analyzer or noise bridge??  And maybe you need a "fast/slow" feature too...

                   _-_-bear