little confused on using link coupled tuner.

[NR5P]

I've got a link coupled tuner put together, no capacitor in the input just a parrelel vac variable.  I was having trouble getting it working so i used a gdo and with the taps on the very ends of the coil to capacitor it is resonate on 8 mhz.  I'm going to go to town and buy some copper tubing I guess. 

I understand it is necessary to play with it but what is actually going on when properly tuned?  Do we want the tank circuit to be resonant with antenna and all connected?  Ofcourse the tank would be high impedance so the link going to transmitter would be a typical transformer and the taps going to the antenna is another transformer in that a low impedance would be less taps and a high impedance might take up most of the coil.  Am I thinking of this correctly?  Should the first thing I do be to find resonance on different bands with nothing connected and start there?  Sorry some simple questions I just want to make sure I'm understanding correctly.

[Ed/KB1HYS]

Need more information, what band/freq were you using?  What type antenna/resonant frequency?  Also the dimensions (diam & turns) for the coil and size of the cap (pf) would be handy. 

IIRC but you should probably be able to resonate the tuner as a tank at the lowest frequency intended.

Yes, the tuner is an impedance transformer, but it won't always work in parallel configuration. Some loads you will need to connect the output coil and cap in series with the feedline ends to get a match.  Usually for lower impedance loads, like a short (for the frequency) dipole.  Older handbooks will have good explanations on this.

[NR5P]

2.25 inch diameter coil 8" long.  about 60 turns 14 gauge wire.  cap is 1000pf.  Antenna is a g5rv 102' around 31 ft. 450 ohm line to it.  Just wanted to use the coil stock I had until I can get some 1/8 inch tubing to use.  just for 100watts for now

[k4kyv]

If you use a split stator capacitor, the easiest way to series tune is to split the  coil at the exact midpoint, and place the line across the split in the coil.  Otherwise, two separate capacitors are required, to keep everything balanced.

Self resonance with just the coil and capacitor might be a good starting point, but leave a margin of error by including extra turns and expect the possibility that you might need extra capacitance.  Sometimes reactance introduced into the circuit by the feedline may require extra inductance or capacitance to keep the circuit in resonance once the feed line is connected. Or you might find that you have too much inductance and/or that the circuit will resonate with the capacitor set near minimum.

[WD8BIL]

http://amfone.net/ECSound/K1JJ13.htm

[NR5P]

also I read in an old arrl handbook that for an input link capacitor it should be about 100ohms of reactance at frequency if L1 reactiance is about 120ohms.  So if I split the coil down the middle I would have to use a split stator cap?

[K1JJ]

http://amfone.net/Amforum/index.php?topic=18054.0

Here's more info on using a simple, balanced link coupled tuner for both series and parallel operation. With a low feeder impedance, use series - with a high impedance use the parallel config as shown in the schematics.
 
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