JJ Tuner question

[N7ZDR]

Hello All---- New to the forum here so here it goes.

I have put together the JJ tuner using 40 turns of .25 copper tubing on a  4 inch pvc pipe.
Primary is about 5 turns of 12 gauge stranded directly wrapped on the secondary.
Capacitor is a 500 Pf
Antenna is a 265' center feed dipole with about 65' fed with cheap ladder line.
(Soon to be changed out this fall)

I can find a match pretty quickly with the 259B, but there only seems to be about 50% power transfer on the rig.

On 160 meter the LL in taped fairly close to the center of the big coil with the cap about 1/3 in from the ends.

I have also installed a cap on the primary across the ground>> But still getting about 50 % power transfer.

I have looked at most all the postings on this tuner and haven't seen anything relating to this issue. I am sure this is a easy fix though!

Any help would be great.

Regards,
Larry
N7ZDR











 

[K1JJ]

Hello All---- New to the forum here so here it goes.

I have put together the JJ tuner using 40 turns of .25 copper tubing on a  4 inch pvc pipe.
Primary is about 5 turns of 12 gauge stranded directly wrapped on the secondary.
Capacitor is a 500 Pf
Antenna is a 265' center feed dipole with about 65' fed with cheap ladder line.
(Soon to be changed out this fall)

I can find a match pretty quickly with the 259B, but there only seems to be about 50% power transfer on the rig.

On 160 meter the LL in taped fairly close to the center of the big coil with the cap about 1/3 in from the ends.

I have also installed a cap on the primary across the ground>> But still getting about 50 % power transfer.

I have looked at most all the postings on this tuner and haven't seen anything relating to this issue. I am sure this is a easy fix though!

Any help would be great.

Regards,
Larry
N7ZDR

Hi Larry,

Welcome to the forum with your first post!

Let's see if we can figure out what's the problem...  It's a simple circuit, so should be easy to figure out.

How are you measuring that only 50% of the power is being transferred?  Is the coil getting hot or is the rig just not showing full power when loaded into the adjusted 50 ohm tuner?

Sounds like it is working OK if the MFJ-259B ant analyzer shows a 50 ohm match into the tuner.

Do you have the input loading cap in series with the input link coil, and then going to ground?  What value is this input cap maximum?  On some matches it may need to be at least 1500 - 2000pf to work correctly on 160M.  The higher bands will require less C there.

You have the 5 turn input link electrically insulated from the main coil and is in the center of the main coil, right?

You might also try the tuner in series config as shown in the schematic near the beginning of the tuner thread.  If the OWL taps are near the center of the coil, then is sounds like a low impedance feed and needs to be series config.  The parallel config is for a high impedance feed and the OWL taps would normally be out on the ends of the coil.

Now try tuning it up on both 75M and 40M and see how it performs.


Let's start with these questions and go from there.

Tom, K1JJ

[AB2EZ]

Larry
Tom (FYI)

When measuring the input match with the MFJ analyzer:

Is one side of the tuner's input connected to the same ground bus in your shack as the transmitter is connected to?

If the shack's ground bus is not connected to one side of the tuner's input when using the MFJ, but is connected to the transmitter's ground... then the impedance that the transmitter looks into will be different from the impedance that the MFJ analyzer looks into

Stu

[N7ZDR]

Tom,

Were only running 100 watts for now, so no way to heat anything up.

Yes, the rig is not showing full output power on the external meter. I have tried this on 160,75 and 40 meters. If I set the rig to 50 watts out, the external meter only shows about 10-20 watts out. I am using RTTY mode for this test.

The input cap is a air variable with a max of 500 Pf. It is in series on the ground side of the 50 ohm coax.
The primary is located at the center on the secondary and is directly wound on the large coil.

The other main cap is a large  500 max Pf 9kv air var.

I have not looked at the series configuration yet (didn't want to cut the coil in half till I was sure it was needed)

Can you direct me to a location of a schematic showing the series configuration? I know I have see it some where here.

Thank You,

Larry

[N7ZDR]

Attached is a picture show the tuner in its current state. Will get it mounted and looking better once I get it working.

I did remove the input winding on the coil and re-installed on some insulators around the big coil.
There was no change on the rig meter- showing only about 50 watts out (rig set to 100).

Notice the jumper settings? This is on 1.825, swr shows flat on the 259B.

FYI-- I did hook up the dentron T match tuner and is shows a full 100 watts out.
I also checked the rig into the dummy load---all ok on that also.

Thanks
Larry

[AB2EZ]

With the primary wound the way it is (large diameter, half of the turns between the OWL secondary taps, half the turns to one side), the tuner is not well balanced. I.e. some of the magnetic field lines, produced by the current in the primary winding, will leak out of (wrap around) the windings of of the secondary coil before they pass through all of the secondary coil's windings that are between the OWL taps.  This, combined with any asymmetry in the physical layout of the antenna (including its relative position to the shack ground system), will exacerbate the effect of measuring the SWR with the MFJ analyzer by opening up the coaxial cable connection between the tuner and the transmitter... which (at the same time) disconnects the shack ground bus from the tuner's primary winding.

Can you measure the SWR looking into the primary of the tuner with and without the shack ground bus connected to the shield of the tuner's input coaxial cable?

Stu

[K1JJ]

OK Larry -

Could the different, open RF environment be affecting the transmitter swr fold-back circuit?  The dummy load may be quieter for stray RF.  Maybe you have a different rig to try.  If the MFJ-259B shows 50 ohms J0 into the tuner, then something is strange.

What does the swr meter or internal transmitter swr meter show between the transmitter and the tuner when the problem occurs?

In place of the OWL antenna taps, try using a 600 ohm load resistor and then 200 ohm resistor to see if that works.   Be sure the resistors are non-inductive and can handle the power, or at least use reduced power.


There was a very comprehensive thread on the AMfone forum about the tuner including schematics for both series and parallel configs. But I either can't find it or it has been deleted.  It started with WB3HUZ's two schematics of the tuner.  Can anyone locate it or the schematics?

And thanks for the suggestions, Stu.

T
 

[K1JJ]

Another test to try:

Tune the rig up for 50 watts into the dummy load. Note the power, current and swr readings.   Then hook up the tuner, keep the transmitter settings the same and experimentally find the proper tuner settings and taps to get the same transmitter power output and meter readings as the dummy load showed before.  

This will tell you there IS a 50 ohm tuner match and the tuner is working even if the MFJ-259B is not reporting it correctly. (As Stu suggested)


**  The tuner's output is floating and balanced.  To keep it balanced so not to affect the feeder balance, keep everything symmetrical. This means away from objects, and using balanced taps on the main coil for the tuning cap and OWL feeders. IE, if one feeder is tapped in two turns from one coil end, then the other feeder needs to be tapped in two turns on the other end. The input link should be in the exact center between all taps.

In the parallel config, you CAN ground the main coil exact center tap. Try it and see if it has any effect. It should make little to no tuning difference if everything is balanced.

Some guys use little light bulbs on each feeder or RF current meters to insure perfect equal feedline current and balance.

T

[Steve - K4HX]

Tuner schematics.

http://amwindow.org/tech/htm/160smallants.htm

[W3GMS]

Yes, the rig is not showing full output power on the external meter. I have tried this on 160,75 and 40 meters. If I set the rig to 50 watts out, the external meter only shows about 10-20 watts out. I am using RTTY mode for this test.

Hi Larry,

I am a bit confused on your term external meter.  Most watt meters are only accurate when place in a 50 ohm circuit.  If you have the tuner adjusted for a flat SWR as viewed on the input link of the tuner then that is your only 50 ohm point that you can count on!   So where is this external metering point your referring to located?  Both it and the internal meter in the rig should read approximately the same if each one is reasonable calibrated.   

Since your 160M antenna is likely current fed, its not unusual for the taps to be near the center of the coil.  As the feed point looks more voltage fed, you will need to move the taps out further on the coil.   That will likely be the case if you load the antenna up on 80 meters.   

I have used this tuner topology many times in the past and it works great. 

One check I do is to measure the RF current in each side of the ladder line.  Real antennas tend not to be exactly balanced since they are not perfect antennas.  In that case you can tweak the tap location a bit until you get equal currents in each side of the line.  Doing this lessens line radiation and life is good!

Have fun!

Joe, W3GMS     

[N7ZDR]

Here is a update on the coil project----
I now have 7 turns closely wrapped and centered. The insulators are about 3/8" in thickness.
This did change the tap location by a small amount @ 1.825 MHz.

This organization seemed to cure the issue-- 50 watts out on the dummy load now shows 50 watts through the tuner.

The radio meter and external meter both show the same power output. The external meter is of course inline between the tuner and rig.

My next goal I guess is to check for balance using the light bulb trick.

Thanks for all the pointers!

Larry

[Steve - K4HX]

Good to hear you've improved things! That's a FB looking tuner.

Looking at the photos, I see that you have the feedline tapped WAY in on the coil. This will work, but could result in losses in the tuner. See if you can achieve tuning with the feedline tapped out further. If not, make a long transmission at high power. Then check for heating on the coil. If you get some, you may want to consider series tuning.

[K1JJ]

Good going, Larry!

The lightbulb trick - just in case you or someone is not familiar with it....   Use two small flashlight bulbs with two wires soldered to each.  Spread the wires about 2" apart and connect one bulb to each leg. The 2" spacing samples the IR drop on each leg.   The bulbs do not go across the two legs, but one on each leg.  You can use test clip leads to find the right wire spacing for your particular arrangement.  It may need a LOT of spacing at the current point on 160M, and little spacing on 75M for your test get the bulbs to barely light. The eye is most sensitive to dimmer range changes.


As Steve said, your OWL feedline taps are close to the center.  On 160M, with a 1/2 wave dipole and 63' long feeders it uses 1/8 wave feeders, so closer to a current (series) feed.   You will find that when doing the lightbulb adjustment,  one coil turn tap change has a big effect when the taps are close to the center.   But on 75M it will be more a voltage feed with the OWL taps out towards the ends of the coil. So the coil taps will be easier to balance on 75M.

Keep us informed how it all works out.

T