Balanced linked tuner turns ratio

[DMOD]

If the topology is the one I mentioned earlier... Where the link is required to absorb the antenna reactance (inductive) and there is NO tuning on the balanced transmission line side, then this results in the schematic attached. Note, counter intuitive, the link inductance is larger than the balanced side inductor. There is only the 50 ohm side of the tuner with a series cap to tune out the reflected impedance. The result is the consequence of absorbing the reactance of the termination. Obviously different results will occur dependent on the 600 ohm side of the balanced line Z and the selection of circuit Q values. Finding a set of component values is easy using the Matlab script and the full linked coupled equation from the prior post. You might consider the balanced tapped inductance with link as I think showed in your photo. K1JJ tuner. I have not analyzed this from design to component value. Perhaps someone has already.

I think Alan's schematic and analysis is the most sensible approach to this question.

Phil - AC0OB

[AMLOVER]

If the topology is the one I mentioned earlier... Where the link is required to absorb the antenna reactance (inductive) and there is NO tuning on the balanced transmission line side, then this results in the schematic attached. Note, counter intuitive, the link inductance is larger than the balanced side inductor. There is only the 50 ohm side of the tuner with a series cap to tune out the reflected impedance. The result is the consequence of absorbing the reactance of the termination. Obviously different results will occur dependent on the 600 ohm side of the balanced line Z and the selection of circuit Q values. Finding a set of component values is easy using the Matlab script and the full linked coupled equation from the prior post. You might consider the balanced tapped inductance with link as I think showed in your photo. K1JJ tuner. I have not analyzed this from design to component value. Perhaps someone has already.

W4AMV,
The attached is the usual set up (jj tuner) which I am also intending to use. The link coil value is known for the frequency as 4.3uH but could be used larger with the addition of a capacitor in series with the coil link to ground. The balancing inductor and it's parallel capacitor are resonating the also known 120+600jx ladder line impedance. The question is what is the critical L and C values for transforming 120+600jx to 50+-0jx with a reasonable Q and efficiency factor?

Chuck,
Yes, it is for 160m. Frequency is not that critical because by using terms in wave length all can be scaled with a reactance calculator and the wave length scale factor.

[W4AMV]

I did not do an extensive derivation of Tom's tuner.
However, there are notes in the attached as to the procedure applied.
To do it justice, need to consider the tapping of the main balanced inductor and probably treat it as a symmetric tapped inductor (auto transformer). I simplified and allowed the inductor to be larger than required to adopt tapping if needed. You can get by with a smaller size if desired. The element values and response are attached. You need to build and verify your coupling coefficient, k. Easy to do. You need close to unity, 0.85 should be fine and not difficult to achieve.  If a smaller k is desirable to aid in construction, could visit the script in Matlab. The main inductor floats...balanced... did not show it that way, got lazy.

[W4AMV]

After back of the envelope inductor size and value, I suspect you are not going to be happy so here is another run....

Change the 270 uH to 54 uH, change the 4.3 uH to 1 uH and the tune cap to 276 pF. The same range of K is desirable.

The return loss is still quite fine from a min of 15 dB to a best case of over 30 dB. A larger L (than 54 uH) however, would be more flexible so as to accommodate symmetric tapping. In any case you could start with this set of values.

[DMOD]

"The question is what is the critical L and C values for transforming 120+600jx to 50+-0jx with a reasonable Q and efficiency factor?"

From your circuit diagram above and posted pictures, it appears you are wanting some type of air coil RF transformer system, unbalanced in, balanced out.

I ran some calcs on MatLab as well and here is my put.

Updated 9/22: Calculated Coil Values and Dimensions

Phil-AC0OB

[Steve - K4HX]

If I'm seeing your photo correctly, it appears you are tapping WAY down on the coil. If so, you may want to consider the series tuning arrangement rather than the your current arrangement, parallel tuning.

W4AMV,
I read the QST article you reccommended me and saw that it is for linked coupling of the tube output to 50 Ohm. It is advised to keep K less than 0.4 and when did that the Q should be 12 or more. Anyway in that article both parts of coupler are considering as resistive. In order to use those equations I have to cancell the reactive part of the ladder line. This is not however the mainstream technic. I see now that things become easier with k=1 but still the series cap is a must. This cap is not involved in any balanced linked couple tunner consideration.

Joe,
I have studied very carefully your program's results but I can't understand why the LI which is on the ladder side facing 118 Ohm is smaller than LR which is on the link side facing 50 Ohm. Normally should be opossed.

Chuck,
It is for the low band as I have mentioned in my first post. 300 Ohm line seems much better in calculations but it is not very safe because the wires (12 gauge) have to be less then 2'' closed together, this distance needs more spacers per foot and is unsafe to winds, rain and snow.    

In conclusion I think that the parallel cap must be on the edge of a sufficient for the frequency inductor to keep the Q and the circulating currents low and the line should touch the inductor where the resistance is correcttly transformed. I wonder if I can manage to use a not so big inductor without sacrificing much gain. My tuner should look like the one in the photo  http://amfone.net/Amforum/index.php?topic=36685.0 where the antenna set up including the OWL length is like mine. I only wish not to have so many turns in the main inductor.

[ka1bwo]

"The question is what is the critical L and C values for transforming 120+600jx to 50+-0jx with a reasonable Q and efficiency factor?"

From your circuit diagram above and posted pictures, it appears you are wanting some type of air coil RF transformer system, unbalanced in, balanced out.

I ran some calcs on MatLab as well and here is my put.

Updated 9/22: Coil Values and Dimensions

Phil-AC0OB

Phil,
What k factor did you use for your analysis

Joe 

[DMOD]

"The question is what is the critical L and C values for transforming 120+600jx to 50+-0jx with a reasonable Q and efficiency factor?"

From your circuit diagram above and posted pictures, it appears you are wanting some type of air coil RF transformer system, unbalanced in, balanced out.

I ran some calcs on MatLab as well and here is my put.

Updated 9/22: Coil Values and Dimensions

Phil-AC0OB

Phil,
What k factor did you use for your analysis

Joe 

I used a k = ~0.8 assuming the coils were placed end to end and separated by 1/8 inch.

The coupling is highly dependent on how you place and orient the adjacent coils.

One could conceivably have a coil-over-coil (primary over secondary) arrangement, for example, by increasing the diameter of the primary to 2.25," decreasing the number of primary turns to 7, and decreasing the length to 10mm close wound.

[AMLOVER]

W4AMV,
It is important to keep the link coil value at 4.3uH. The balance inductor (54uH) seems to be very big with your calculation considering 1uH link coil.

Phil,
This is what you attached is what I had also in my mind from the begining.
To cancel the +jx and then to transform the resistance with the coupled inductors.
In the meantime I started read more and more and found out that the gurus (Cebik ect) proposed a better way.
They add turns to the balance inductor in order to increase its inductance and connect the capacitor from edge to edge. This lowers the Q and the losses because the circulating currents 'see' a lower rf resistance.
They definitely find the right turns ratio somewhere in the inductor. I didn't meet anywhere this you and me thought which is to cancel any positive or negative reactance from the OWL and then to care for the resistance with the linked coupler.
It is possible they didn't do so because they designed a multipurpose tuner for many bands and not a single band narrow use one as in my case.
I am thinking after your post to mix somehow both technics, to triple the balance inductor (3x9uH=27uH) to get better efficiency with less circulating currents and resonate the parallel sircuit with the capacitor at 1.85Khz. Using the 300pf caps in series with the OWL legs I'll have to deal only with the 120Ohm OWL's resistance and I'll find the right points on the balance inductor (I hope around 8T/9uH) to get an efficient matching. Schematic attached.

Steve,
Around 15 years before I constructed a link coupled tuner like this but for an endfed Zeppelin resonant low band antenna. In that time my OWL was 1/4 wl.
The result was that 4000-5000Ohm from antenna edge was transformed to about 60-80Ohm at OWL edge before the tuner. I started with the parallel configuration (wrong for this low resistance) and found a matching point on the balance inductor but very closed to the link, as in the photo you saw. After some thinking I decided to try the series topology and cut the inductor in the middle, connected there the OWL and I never managed to get a good matching again. I even added a cap in series to the link coil but nothing.
So before I split the inductor I'll try all the ways with the cap in parallel.  Series will be my last decision.

Joe,
My balance inductor is on a 4" PVC form and the link over it on a 5" PVC form. I leave the forms in both as far they don't get any heat, I don't know if this influences the efficiency/Q of the inductors. I can't also guess the K factor.  

[W4AMV]

This is series tuned per Steve suggestion.

The balanced link inductance value is constrained by the reactance presented at the 600 ohm end of line port. The k is 0.95. Smaller k
limits return loss, however, you could get by with 0.8.  That requires a
larger inductance balanced side inductor. At 0.8, 18 uH. Re tune the balanced C and the return loss is in excess of 30 dB.

[W4AMV]

And the other arrangement is:

[W4AMV]

Joe,
My balance inductor is on a 4" PVC form and the link over it on a 5" PVC form. I leave the forms in both as far they don't get any heat, I don't know if this influences the efficiency/Q of the inductors. I can't also guess the K factor. 


WHY NOT MEASURE IT? IT IS EASY. DO YOU HAVE ANY TEST GEAR?
YOU WILL NEED TO MEASURE INDUCTANCE AT 1.8 MHZ.

[AMLOVER]

W4AMV,
I have a LCR meter for inductance and capacitance measures.
I also have a grid dip meter and an osciloscope 100Mhz double trace.
I can test the effieciency with some laser gun temperature tests.
How I could measure the K factor with these instruments?

[W4AMV]

The GDO will work fine.

You will need to resonate the PRIMARY, that is the larger inductor.

Use your LCR meter to get an approximate inductance reading, will neglect the fact that the LCR does not take a reading at 1.8 MHz, but lower.

Now using the L reading, figure out the shunt C needed to resonate the PRIMARY L at 1.85 MHz... All this is done with the LINK OPEN circuited. Now use the GDO to measure the resonate frequency of the primary with the LINK open and then measure the primary again resonate freq with the link shorted. Keep wires and all that connection stuff as short and direct as possible. The calc for K is as follows:

K = SQRT (1-(Fopen/Fshorted)).

So clearly if the freq with the link shorted moves HIGH.... compared to Fopen, then K is approaching 1.

Any questions, flame away...
 

[AMLOVER]

If it is so straigtful I'll try to measure K factor first to a simulation sircuit -much smaller dimensions but same frequency- and then to the final one.
Thank you very much for the knowledge you shared to me.

[W4AMV]

Great. No problem. Keep in mind the GDO is one of those instruments that requires skillful art to provide accurate measurements. Couple it to the coil under test at a distance where you get a nice dip.  But then BACK AWAY as much as possible and accept a more feeble dip. The GDO, oscillator can be PULLED a bit and that upsets the measurement. Once I get the dip, I carry the GDO over to my frequency counter and jot down the number. If you have no counter, maybe use your receiver to pick up the GDO signal and record its digital reading or lastly try reading the GDO dial as best you can.

[AMLOVER]

I am very familiar with the GDOs. I own 3 different portable/batteries ones which I used to measure in many instances.
I also have a frequency meter to check whether it dips or oscilates in the right frequency.

[aa5wg]

The 1/4 wavelength feedline connected to a halfwave doublet will provide high voltage at the feed point of the transmission line.  
This is called voltage feed which favors the parallel configuration for the link antenna coupler.  ARRL antenna books from the 1950's and 1960's provide inductor and capacitor data to build this antenna tuner in the parallel configuration per your desired band. 

Chuck

[W4AMV]

Here is DMOD solution, Phil...

Quite reasonable. The series caps are fixed, not series tuned, however serve to cancel the reactance of the Z balanced port. The shunt C is tuning and fine adjustment. A k of 0.9 is preferred, you can get by with 0.85, dropping to 0.8 is still an acceptable 16 dB return loss.

[DMOD]

Note, these are for 2" Dia. coils. in a linear, side by side arrangement.

If you use other diameter coils or coils with different wire gauge, the coil parameters such as number of turns, length of coil, diameter, wire gauge and winding pitch will need to be recalculated.

I think the coaxial Tp over Ts configuration probably gives the highest coupling coefficient k; for example, having the Tp coil 2.25" to 2.5" and the Ts coil 2" in a coaxial configuration.

Phil - AC0OB

[AMLOVER]

The 1/4 wavelength feedline connected to a halfwave doublet will provide high voltage at the feed point of the transmission line.  
This is called voltage feed which favors the parallel configuration for the link antenna coupler.  ARRL antenna books from the 1950's and 1960's provide inductor and capacitor data to build this antenna tuner in the parallel configuration per your desired band. 

Chuck

The antenna where I used the 1/4wl feedline was a Zepp not a doublet.
It was fed on the edge where the voltage and the resistance were very high.
So on the end of the 1/4wl line  appeared low voltage and resistance so series feeding was the propriate way but for some reason it didn't fit to my needs.
 

[aa5wg]

The neat thing about the link antenna coupler is its flexibility to make the appropriate impedance match for the complete antenna system (one half the doublet, feedline length and antenna tuner).  This system theoretically works best at multiples of 1/4 wavelengths at any given band.  These lengths change when using different bands.  Thus, having the flexibility to tune the capacitive or inductive reactance via parallel or series tune is achievable with link coupling.  Parallel tuning is used for a high voltage point at the tuner or series tuning for a high current point at the tuner.

When the total antenna system length (one half of doublet, length of transmission line plus antenna tuner) is a measurement of multiple 1/8 wavelengths instead or 1/4 wavelengths extra high reactance is present and it may be difficult to tune out this extra high inductive or capacitive reactance.  

When this happens a rule of thumb is to shunt (connect) across the left and rights sides of the transmission line an additional variable reactance at the output of the tuner.  This is going to be a variable capacitor to tune out the excessive inductive reactance or a variable inductor to tune out the excessive capacitive reactance.  

The transmission line impedance dictates the theoretic maximum value for this shunt inductor or capacitor.  Example: A 600 ohm open wire feed line would have a theoretical maximum reactance of 600 ohms for the shunt inductor or capacitor.  600 ohms worth of capacitance at 3.5 MHz is just less than 80 PF.  600 ohms worth of inductive reactance at 3.5 MHz is about 27 uH.  It is best if these shunt capacitors and inductors are variable.

This same link antenna tuner works great for the end fed ZEPP antenna fed with open wire feedline.  

Another neat thing about link antenna coupling is there are no ferrite transformers that can saturate/heat up under reactive loads.  Antenna systems always have resistive and reactive components such as inductive or capacitive reactance.  This is why we need to "tune" the "antenna system" for maximum flexibility and efficiency.  

Chuck

[AMLOVER]

W4AMV, Phil, Chuck and all,

Ithink that should be better to make a test tuner with a dimensionally small but sufficient inductor (50uH+), a link coil with the right reactance for the frequency loading it with 120 Ohm resistor in series with 52uH inductance and check the possibilities.
I'll try first with 270pf caps in series with the load (120+600jx) to precancel the inductive reactance.
I'll also try without the caps and check if the OWL impedance can be handled by the parallel cap in co-operation with the inductor.
I'll also check the efficiency and measure the K factor.
It is true that my case is 'special' because of single band use and 3/8wl as total length of one leg of the dipole+OWL.
In case the results are dissapointing, I'll rethink about using the single band super efficient cap loaded dipole antenna.

Thank you all for simulations suggestions and possible solutions.
Stefano

[KL7OF]

I have followed the thread with some interest....... I have nothing to contribute, but I am very interested in how the tuner works after construction.  Good Luck.   Steve

[aa5wg]

Build a link antenna tuner with correct capacitor and inductor values for the band in use.  Make sure you can change from parallel to series tune with your tuner.  Don't use larger inductors that are greater in value for the band in use.  This will degrade the tuners performance.   Don't use resistors because they will give you false performance indications.  Rather, use the antenna system (antenna, feedline and tuner) which provides true conditions for the tuner.  The input inductor for the tuner, that receives power from the transceiver or transmitter, should have a variable capacitor in series connected to ground.  Sometimes it makes a difference if the this capacitor is first or after the inductor.

Chuck