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Author Topic: K1JJ Tuner Efficiency  (Read 5157 times)
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N7ZDR
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« on: February 16, 2019, 02:26:12 PM »

Hello,

I am wondering about the efficiency of the JJ tuner. I have a few questions that I am sure someone here on the forum can answer.

Antennas are the following--

135' dipole at 100 feet east / west fed with 100 feet of  DX Eng 450 Ohm ladder.
135' dipole at 100 feet north / south fed with 100 feet of  DX Eng 300 Ohm line.
The middle tuner is
80 meter delta loop with the apex at the bottom (top wire at 100') fed with 92 feet of DX Eng 300 Ohm line.

The current photos are showing all three (3) wire antenna tuned on 40 meters of 1 to 1.5 swr or less

You can see that all 3 tuners have their output caps at or near their minimum value.
Is this minimum value of capacitance ok?
Do you see any changes that can be made to be "more efficient"?
I would naturally prefer the tuners to be as efficient as possible.

Thank you in advance.
Larry
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* IMG-0982.JPG (351.41 KB, 1280x960 - viewed 395 times.)

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W1ITT
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« Reply #1 on: February 16, 2019, 02:58:37 PM »

The fact that your capacitors are close to minimum capacitance is not, in itself, necessarily a problem.  Those good old high voltage bread slicers have a fairly high minimum capacitance simply because of their geometry.  That's partly why vacuum variable capacitors came into fashion.  They often have a lower minimum, aside from the advantage of higher voltage ratings in a more compact package.
Try tapping across less inductance and see how bandwidth works out for a given setting.   One can often find a match with different L-C ratios.  I go for the one that tunes up smoothly, rather than a sharp critical tuning condition.   And see what warms up or arcs.  Depending on the length of the transmission line back to the shack, the antennas you have described will generally present moderate impedances back at the matching network on 80m and beyond.  From experience, I  only worry about tuner efficiency problems when trying to match into very low impedance loads, and when the sizzling blue arcs start dancing across the components.  Or when I smell something cooking...  Otherwise, life is good.
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Steve - K4HX
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« Reply #2 on: February 16, 2019, 03:32:01 PM »

Generally, the closer to the center of the coil the feed line is tapped, the higher the Q of the parallel tank circuit. High Q means higher circulating currents and more loss. So, for best efficiency, tap the feedline as far from the center of the coil as possible. The added benefit is that the tuning won't be as critical too.

If efficiency is of concern, consider replacing the ladder line with open wire line made with #12 or larger conductors. This could impact efficiency more than the tuners.

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K1JJ
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"Let's go kayaking, Tommy!" - Yaz


« Reply #3 on: February 16, 2019, 03:37:29 PM »

Hi Larry,

Norm and Steve  pretty well covered it in their posts above...  I'll add some comments too.

I used to have a multi-tuner setup like that... five tuners before switching over to all hardline. What a inexpensive and convenient way to pull it off, huh? Your setup is the poster child for what this simple tuner design is all about.

You are concerned about getting the most efficient set up since you have some great antennas at 100' for DX.  Good.

I realize this is 40M and needs little C - and minimum capacitance mesh will work most efficiently, however, I generally like to see a little more tuning capacitor mesh, (slightly higher Q) if simply to have more C in the equation for swr tuning stability.  IE, on 75M, a tank with only 35 pF will change in the wind or be affected more with your hand near it than say the same circuit with the cap at 150 pF.   So as Norm says, try moving the antenna taps and the capacitor taps around to find a new 1:1 match and using somewhat more C mesh.  There are usually several combos of taps for 1:1 swr.   If not, no big deal and stick with what you have already.

How far do the caps mesh on 75M?

For best efficiency, I also prefer homebrew #10 open wire that uses conventional ceramic or high quality plastics to give less loss when the post-tuner swr is high and for better environmental stability. The absolute best OWL is two wires pulled taunt off a tower with NO spacers at all, spaced 12" apart. Near zero loss and the wx has no effect. I've done it here on many big wire arrays.

 That brown slotted plastic OWL has never worked well for me in the rain or snow/ice.  The losses are higher too at the high currrent points, so that I have seen 1KW melt the brown OWL on the higher bands.  This loss is exhibited in receive too, of course.

Another consideration is: Do you have the series tuner conection info?  Sometimes this tuner operates much better in the series config (for lower impedance antennas) compared to the parallel config. It's easy to change it over on the fly if you set up the taps. Between the various taps and series/parr configs I've never seen an antenna this tuner did not like... :-)

BTW, there's no metal in that window jam where the OWL goes thru, right?  If QRO, watch out for fires, even if wood.  Don't axe me how I know.

T
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N7ZDR
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« Reply #4 on: February 16, 2019, 05:33:58 PM »

Thanks for the great information guy's

Yes, at the last QHT I used 12 gauge aluminum fence wire pulled taunt and spaced about 8 inches apart. Wind, snow and ice had very little effect on it unlike ladder line which flops like a flag along with build up of snow and ice.

We moved to this Idaho location in November and ladder line was all I had time to throw up before the arrival of snow (to date we have 6 feet on the flat) and where sick of winter!

So lets see if I am thinking right----

Always try to tap further out on the coil if possible?
More capacitance is better (if possible)?
Choose a smoother tune rather then a sharp and quick dip (if possible)?

FYI-- two (2) of the tuners are split in the center for a series tune configuration (very seldom ever used)

Tom-- Below is a shot of a quick tune for 80 meters. The cap is bridged so its using almost the full amount.



Thank you


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Steve - K4HX
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« Reply #5 on: February 16, 2019, 06:12:52 PM »

Consider using different clips, preferably ones with flat (not serrated) jaws or even soldering on tabs. With tabs you can use slip-in type clips like those shown in the attached photo. You want a large contact area for lowest loss.

Another option for the clip.

http://k3rrr.com/homebrew-ham-radio-antenna-coil-clips/


Tom mentioned series tuning. You'll need to consider using the arrangement if you must tap the feedline very far in on the coil. I've only ever needed to do this when using a short dipole on 160 meters.


* MantennaTuner.jpg (94.07 KB, 600x496 - viewed 664 times.)
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N7ZDR
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« Reply #6 on: February 16, 2019, 09:38:14 PM »

K3RRR does come up with a great type of clip for sure. I usually will try to flatten out the tip of the Mueller 60C clips to give a bit more surface area. I also may clean up the interior feed line mess by using 8 gauge copper ground wire mounted nicely to the wall and spaced appropriately.

Thank You for all the input and or suggestions.

Larry
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AG5CK
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« Reply #7 on: February 17, 2019, 09:36:54 AM »

I used an RF ammeter to find the combination that gave me the most current on the feedline. With the tuner set up for series configuration and feeding a short antenna I found less inductance and more capacitance seem to transfer more power to the antenna.

I don't  use the capacitor on the input link coil. I did in the beginning but I found myself having it set to minimum to get a good match with the analyzer and things would go crazy with over 100 watts. If you keep the cap on the input I would leave it set at max and only use it as a last resort.

I also suggest that you connect the feedline to the outside turns of the coil and use jumpers to short out the unneeded turns. That will keep it from ringing or possibly arcing at high power.

I use the Mueller 27C clips on 1/4 and 3/8 tubing. They seem to have enough surface area to do the job. My K1JJ tuner is mostly used for feeding a short antenna on 75m. I've put legal limit into that same 70 ft doublet on 160 and the clips hold up fine.

I don't know about efficiency but have an idea since you have more that one. Take two identical tuners that are adjusted for the frequency of interest and connect them output to output. Connect a dummy load to the input of one tuner and a transmitter to the other. Measure power in vs power out and divide by 2 to estimate the loss in each tuner. I've never done this but it might work.
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N7ZDR
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« Reply #8 on: February 18, 2019, 01:14:29 PM »

Thanks for the tips-AG5CK

I have never tried tapping the feed line like you are saying but will try now and see if there may be any difference.

One interesting thing I seen yesterday--- I tried a series tune on one of the tuners (found a match pretty quick) and noticed the screen on one of the PCs was quite garbled at 100 watts. Then change back to the parallel tune with no noticeable PC screen garble.

"I don't  use the capacitor on the input link coil. I did in the beginning but I found myself having it set to minimum to get a good match with the analyzer and things would go crazy with over 100 watts."

I have never not used a input link capacitor----however I will now experiment a bit and remove it.

I also do not have any means of measuring RF current----I guess I need to build or squire something.




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AG5CK
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« Reply #9 on: February 18, 2019, 08:32:53 PM »

I made a pick up with a snap on ferrite core and a digital multimeter. Not calibrated but it still seemed to work as a reference. Once I got the same amount of current out of the link coupled tuner as my balance L I called it good.

It also allowed me to fix the imbalance that was causing rfi on the upper frequencies with the balanced L.

I copied this to build the pick up.
https://www.w8ji.com/building_a_current_meter.htm

I was using parallel configuration on 75m but had some heating. Cutting the coil and using series configuration did the trick.





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