The AM Forum

Hi to all,

I am preparing a linked balanced tuner for a 1/8 wave length 600 ohm ladder line feeding a resonant low band monobander dipole.
I have calculated the resistive part of the impedance on the edge of my ladder line to around 118 ohm and the reactive part to about +615jx.
As far my tuner space is limited and the antenna is monobander I am wondering if the turns ratio of the inductors is transforming the resistive part and the capacitor cares for the reactive part.
If so I'll only need few turns for the big inductor. Let say 118 ohm:50 ohm =2.4 and sqr 2.4=1.55 which will be the turns ratio factor for multiplying the link's turns. Per example 5 turns for the link inductor and 1.55X5=8 turns for the big inductor. For safety I'll make 20-24 turns which will save me lot of space in comparison with the 45 turns for a multiband tuner.
Is this makes any sense or somewhere I miss something and I'll anyway need a 45 turns inductor?

Greetings
Stefano

See Cebicks article:

http://www.antentop.org/w4rnl.001/link.html

or see 4. Link Coupling

https://www.dj0ip.de/antenna-matchboxes/symmetrical-matchboxes/

Taking into account some of us build with balanced output right from the finals, a balun isn't necessary in the circuit.

I usually copy the output section of the Raytheon AM BC transmitters. Yes, they were able to match 50Z all the way up to 600Z.

73DG

Stefano, I hope this will help you. Image 1, circuit diagram.  L is a modeled 75 meter dipole at 50 feet with an overall length of 125 feet, T1 is 1/8 wavelength of 600 ohm line. Image 2, impedance at the end of the 600 ohm line vs frequency. A is the link, C1 is the tuning capacitor to match the antenna from 3.5 to 4Mhz and G is the transmitter model. Image 3, SWR vs frequency vs C1, C1 was swept from 66p to 141p. Maximum SWR is 1.53:1 at 4 mhz, C1=66pf.      

Wrote a short script in MATLAB to solve
for the link coupled transformer where
the load is complex and the source is
real. Like your case where the reactance
is not tuned out. There is an exact solution
but the values are not practical. If you
resonate out the j615 ohm at at say
3.75 MHz, then the link coupled match is
nice. The series C is 69 pF and the
balanced side L is 6 uH and the 50
ohm side L is 1.35 uH. The coupling
k value is reasonable and easy to set
and measure. An exact match on the
50 ohms side requires a shunt C.
The Q values are low and the response
pretty broadband.

The response is shown below,
with schematic and S parameter response. 

This is the equation being solved in the script.

I use T.J. Maresca paper in QST Oct 1959 to seed
the MATLAB script with initial values. See his case
equations for Parallel-Resonant Primary Untuned
Secondary on page 30 of QST.
 

DMOD,
Very usefull info at the provided links, I spend time to learn more in deep.

W7TFO,
This is a succesfull technic but as far I use a narrow band (50-100 Khz) I try to find out the right turns ratio in order to keep the inductor, if possible, as small as possible.

Ka1bwo,
Your calculation is almost as mine but I use a cap (C2) in parallel with the balance inductor and a link coil with reactance 50 ohm (per example 2.1225uH for 3750Khz) so there is no need for C1. With C2 in parallel with balanced inductor I would expect no reactance such as the X=450 Ohm in your scheme. Redrawing your scheme is how is my set up and follows in the attachment with some modifications.
The perfect scenario is to cancell the +588jx or +615jx in my case with C2 and the 118 Ohm resistance to 50 Ohm with the ratio of the balanced inductor to the link coil. Could you please recalculate with the C2 in this place?
In this case the balanced inductor will be not that big and the tuner will be of course usefull only for a narrow band.

W4AMV,
This is a very nice set up. I have never seen the parallel to the link coil 1.7nf cap.
All schematics have it in series with the link in order to cancel if needed some of its reactance.
Could you please explain me if the 69pf cap which cancells the +615jx at 3750Khz is in parallel with the load as it is drawn in the 2nd attachment (TUNER) as C2? or it should be in series with one of the ladder line legs?

Greetings
Stefano

To clarify. I took your stated measured or calculated impedance at the end of the 600 ohm line to be 118 ohms series with j 615 ohms. That series Z is the R2 + jX2 value across the secondary link L2. The reflected Z is calculated  via the equation I posted using the MATLAB script and the resulting reflected Z is in addition to the primary inductance on the low Z side, namely the 50 ohm side. I convert the series Z on the primary side to its parallel equivalent and hence the parallel C that you spoke of results. The result is the primary side is REAL and matched to 50 ohms.

Oh, the Z load you stated is a series Z. I assume that is the case. Correct me if wrong. So yes, the 69 pF is in series tuning out the j615 ohms at 3.75 MHz.  Now the problem is just taking the 118 ohm and transferring it to 50 ohms at the desired frequency. If I desire to use no secondary tuning C and reflect the complex load to the primary, that is possible. However, the resulting component values are not nice. This is partially drive by the fact that the Q of your load is higher than desired.

Ka1bwo,
Your calculation is almost as mine but I use a cap (C2) in parallel with the balance inductor and a link coil with reactance 50 ohm (per example 2.1225uH for 3750Khz) so there is no need for C1. With C2 in parallel with balanced inductor I would expect no reactance such as the X=450 Ohm in your scheme. Redrawing your scheme is how is my set up and follows in the attachment with some modifications.
The perfect scenario is to cancell the +588jx or +615jx in my case with C2 and the 118 Ohm resistance to 50 Ohm with the ratio of the balanced inductor to the link coil. Could you please recalculate with the C2 in this place?
In this case the balanced inductor will be not that big and the tuner will be of course usefull only for a narrow band.



Stefano, here is the rev schematic and SWR chart. Your scheme will be more efficient due to less series resistance
 in the inductors. Link turns ratio = 7.538

Joe

You can convert your series antenna Z to its parallel equivalent. This provides yet another solution. The basic configuration follows the link coupled topology from the QST paper discussed as resonant primary non resonate secondary, see figure. However, the author of this paper did not address the complex load. If you convert series to parallel then the 69 pF cap is in shunt with the balanced line and secondary winding and a new set of primary and secondary inductance values emerge. As well, the k factor can change as desired as you alter the matching bandwidth or Q of the source and load side of the link coupled network.

W4AMV MATCHING SOLUTION:

This follows the QST paper guideline, parallel resonant primary,  series resonate secondary. The solution is not unique. You can vary the Q on wither side of the network despite the give antenna complex Z. So you can vary the coupling coefficient, k, of the link coupled coils. The only mod from the paper is tuning out the reactance of the antenna. Another solution is obtained by converting the antenna Z from its series to parallel equivalent. Then proceed again with the link coupled equations. I encourage you to read the paper.

Here is the network for the parallel equivalent Z. The coupling is light. Easier to implement. Increased coupling is possible, just  decrease the Q of primary/secondary sides. The antenna equivalent Z highlighted in box
and the shunt C to resonate is absorbed into the shunt C that results from solving the link coupling equations. Plotted the return loss as REAL RETURN LOSS as a positive number. 

sim smith provides a solution with k = 1. This simplifies the prior posted equation and I suppose you can choose a Q for the primary and secondary loop within some constraints. Need to visit those details. Anyway, if you get a k of 1, great. A k of 0.8 or greater is needed otherwise the match deteriorates as shown in this plot. I assume one is able to enter a desired k into sim smith. Nicely done.

 

Hi Stefono,

What band is this mono-band antenna for?

And, you might consider using 300 ohm instead of 600 ohms for your feedline impedance.  This lowers the high voltages on the feedline and thus a lower voltage stress on your link antenna output components (inductors and capacitors - potential arcing of capacitors).  

Let us start with above and move on from there.  What do you think?

Chuck

Yes, you are correct a k of 1 was used for the analysis you can enter the desired k. Here is a plot of the ideal power delivered to the 600 ohm transmission line vs k, with a transmitter output of 100 watts.

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.

Perhaps you can clarify with a schematic the exact circuit topology you desire. The limited view of the hardware requires quite a bit of extrapolation!

After a careful re read of your post, is this the topology desired?

No tuning on the secondary implies the secondary reflected Z will also be complex and reactance cancellation on the primary should permit the primary port Z to be 50 + j0.

Stefono,

When you say low band do mean 160 meters?

Thank you.

Chuck

Hi aa5wg...

per prior posts, looks like... 80 meters phone.

(per example 2.1225uH for 3750Khz)

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

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.

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.

"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

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,
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.  

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.

And the other arrangement is:

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.

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?

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...
 

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.

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.

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.

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

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.

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

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

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

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

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

Why not try a full size, unit-scale link coupled tuner with this circuit,
which uses a 2.5" Primary link coil OVER a 2" Secondary coil. These component values and sizes have been verified by simulation.

This Coaxial arrangement should provide the highest coupling coefficient.

See coil detail notes in lower left-hand corner.

This is essentially what you requested graphically in a previous post.

Phil-AC0OB

Wrong circuit design.  A variable capacitor needs to be added to the input inductor.  This will give you much more flexibility in tuning the antenna coupler, matching.

For some reason I can't reply any more. :-X

That's good, I can post but I can't attach the photos of my just finished tuner. I'll try to find out what is wrong and come back with the photos.

Just a test photo, nothing to do with this conversation.

I found out the reason but I'll fix it tomorrow and I'll add the photos of what I have done till now.
Excuse me for the inconvinience.

Phil, Joe, Steve, Chuck and all,

I fixed my problem with attachments. My photos archives were jpeg and I had to transform them to jpg.
I hope this time to get attached.
The main inductor is 34 turns 1/8'' spacing 3/8'' copper tube on a 5.5" pvc form and the link coil is 4 turns 3/8'' spacing 3/8'' copper tube on a 7'' form.
Due to dog house small dimensions I can't get any bigger. In any case I'll adjust OWL or antenna length to get the most efficient taping.
Plenty of taps for experimenting tunings.

When you say 5.5" and 7" forms, are those length dimensions?

If so what are the coil diameters?

Phil

5.5'' and 7'' are the diameters from center to center of the 3/8'' tubes. The dimensions are 21.2'' for the 34 turns coil and 2.1'' for the 4 turns link coil.

Your 5.5" Dia. 34-turn Output coil has an inductance of 35uH and an XL of 415 ohms. About 220pF in parallel will tune it to 1.85MHz.

Your 7" Dia. 4-turn Input coil has an inductance of 3.5uH and an XL of 41 ohms or 9 ohms below the 50 ohm target.

I think when there is a coupling between two coils, the inductance of the outer coil is increased because of the mutual conductance.
I will count it however when it is in its final place and I'll adjust, as possible, its inductance by squeezing the turns spacing.

The design is based on the self inductance of primary and secondary. The mutual inductance is controlled by the coupling factor and so these items are chosen somewhat independent of each other. No issue, just put a tiny squeeze on the L if need be. Initial values might compromise best case return loss slightly.

possibly a naive question: all those designs here have low to very low L/C ratios, is that desirable ?

peter

Hi Peter,

What values would you propose for L and C in a sircuit like the one in the attachment?
Single band use p.e 1850Khz, 50Ohm to 120+600jx impedance.

Stefano

The L/C ratio is driven by the complex line Zo with the antenna attached and the desired matching bandwidth, that is operating Q. A good treatment of the details is in the handbook, example the '63 treatment in the chapter on transmission lines. See copy of excerpt attached. There in Ch 13, the series and parallel balanced line tuning is addressed.

In my calcs, the calculated coil inductances were for free coils by themselves.

If one is concerned with the Mutual Inductance, then
M ~ = (Ns X Np X Area)/length of coil.

M also is = k X SQRT(Ls X Lp)  where k is the coefficient of coupling.

If k ~= 0.9 for a coaxial set of coils, then M = 0.9 X SQRT(3.5uH X 35uH) = 0.9 X 11.1uH = 10uH.

Even if it is a coaxial set up, the two coils have a distance of 3/4'' between them so K could be less then 0.9.

I used 4 turns for the link coil because this number was right in a previous linked tuner I made for an EFHW (4000Ohm +).

In that case I had the link coil (4 turns) around the cold side of the long inductor (44 turns). It worked perfectly without capacitor in series to ground.

In that case coupling was much better and K was for sure closer to 0.9. The long inductor was factory made and I managed a very tight coupling, may be less then 3/8''.

In any case if I'll count around 10uH when in place then with a var. cap and 1300pf in series to ground  I'll adjust it to the desire XLS.

Some more comments on this and to put this design approach in perspective.

Choosing Lp and Ls might be driven by the loaded
Q of the primary and secondary inductance. On the
50 ohm side, a Q of unity is realized at 1.8 MHz
with an inductive reactance of 50/(6.28*1.8 MHz)
or 4.4 uH, hence its value. On the balanced side
consider the magnitude of the Z termination, about
612 ohms, At a Q of unity, Ls would approach a
value of 54 uH. However, if the reactance of
600 ohms is tuned out at 1.8 MHz, the remaining
112 ohms is set by an inductance of 10 uH. A
range of 10-54 uH with suitable C to tune the reactance
is reasonable. It is the coupling factor, k, that
will significantly alter the final quality of the
match and the return loss. Recall in the earlier
designs of balanced matching tuner systems, a swinging
link was always touted as an ideal final adjustment.   

Should be 120 ohms, real, anyway still ~ 10 uH.

Alan - W4AMV, good material.


[/quote]

as the handbook text posted above says, as a first approximation use the LC values of the transmitter plate tank.

the 160M B&W balanced (for push-pull PA) coils are 94 uH and resonate at the bottom of 160 with 90 pF. The handbook recommendation is that the LC tuner tank resonates at 80% of the intended operating frequencies so max of 100-120 pF would be used in a parallel-feed balanced link tuner for 160 using the B&W hdvl or tvl coils depending on power. From what Stefanos is seeing at the input end of his ladder line he should use the parallel configuration.

and make the link variable to dispense with the capacitor on the link side.

If Charles and Peter have some analysis and schematics they would like to submit, I am sure we could all benefit.

This is sort of a work in process. I found it interesting to look at the linked coupling transformer modeled as its "conductively coupled equivalent circuit". The results for a simple impedance matching system are interesting. More to follow while digging deeper.

I'm just diving into this thread. 1.4 picofarads at 160 meters; 60,000 Ohms? Doesn't look like a comma to me at 7:30 p.m. - tired.

Hi Tom... Yes sir... Keep in mind, there just numbers. Some notions are counter intuitive. Not necessarily practical.  However, it is the concepts and making sense of the mechanics so that practical and useful design paths are  obtained.

94uH inductance is much but logic for a 160m final PA which can vary from 1000-10000 Ohm depending on plate voltage to current, Q of the tuning network and working class. When the impedance, as in my case, is considerably low the inductance in conjuction with the proper capacitance can be much smaller.

Added the interactive Smith chart tuning tool which was the motivation in using the T equivalent transformer arrangement. The added pages now become more realistic You could embellish all this with parasitic components if desired. This is now version ONE. 

Used the tune feature in the Smith chart tool with the ideas presented in the paper pdf and constraining to values close to those discussed in the thread. However, kept the k factor realistic at k ~ 0.5. There is an asset in using the series cap input in order to achieve a reasonable response for small k factor.

Stefano,
From your link coil dimensions, 4 turn link coil= 3.73uh, 34 turn coil= 37uh, k=.9
Circuit L is the feed point impedance vs frequency of a modeled centered fed 160 meter dipole at 100 feet, with an overall length of 247 feet of #12 copper wire, sweep from 1.8 MHz to 2 MHz. T1 is a 1/8 wavelength at 1.9mhz of 600 ohm line.  The antenna can be match to 50 ohms across the 160 meter band.  Shown are the values of C1 and C2 for matching at 1.8, 1.9 and 2Mhz.  

Match 1.9 MHz

Match 2Mhz

Simulations and S graphs are nice but I think what experimenters really need and want are real schematics and component values.

Phil-AC0OB

Hello to all.

Below are component values for the 160 meter (1.8 MHz) link antenna tuner calculated for a 600 ohm feedline.  

Because this link input coil (connected to the transceiver or transmitter) is fixed (cannot be tuned) you need to add a variable capacitor in series with this coil to achieve input tuning flexibility.  This variable capacitor can be connected ahead or after the inductor.  If it is after the coil then is is connected to ground. If it is placed in front of the coil then the coil is grounded.  Some times it can be placed in parallel with the input inductor.  Each antenna farm is unique and testing of the input variable capacitor placement is required to determine it's electrical location.

INPUT components:

1. Input link capacitor value is 1768 pf.  A variable 300 - 500 pf capacitor with added (padded) home brew or commercial capacitors in parallel will get you up to the 2500 plus pf range.

2. Input link coil is calculated at 4.4 uH.

OUTPUT components.

SERIES circuit configuration:

1. Total inductance is 106 uh.  

2. Total capacitance is 74 pf.  Use a 150 pf variable capacitor.

PARALLEL circuit configuration:

1. Total inductance is 27 uH.

2. Total capacitance is 295 pf.  Use a 500 or 600 pf variable capacitor.  

If the total antenna system length is a multiple of 1/8th wavelengths instead of the desired multiples of 1/4 wavelengths then you may need to connect a capacitor or an inductor to the left and rights sides of the transmission line at the output of the tuner.  This is called a shunt capacitor or a shunt inductor.    

1. The shunt capacitor is calculated at 147 pf.  Use a 300 pf variable capacitor.  

2. The shunt inductor is calculated at 53 uH.  Make this inductor variable with taps.

Above components with less challenging values can be achieved with a 300 ohm transmission line.  The 300 ohm transmission line also lowers the high voltages encountered at the antenna coupler in the parallel configuration which is dependent upon total antenna system electrical length.  Lowering these voltages helps prevent high voltage induced arcing of the capacitors.  

73,
Chuck

 PARALLEL circuit configuration:

1. Total inductance is 27 uH.

2. Total capacitance is 295 pf.  Use a 500 or 600 pf variable capacitor. 

If the total antenna system length is a multiple of 1/8th wavelengths instead of the desired multiples of 1/4 wavelengths then you may need to connect a capacitor or an inductor to the left and rights sides of the transmission line at the output of the tuner.  This is called a shunt capacitor or a shunt inductor.   

1. The shunt capacitor is calculated at 147 pf.  Use a 300 pf variable capacitor. 

2. The shunt inductor is calculated at 53 uH.  Make this inductor variable with taps.

I am exactly on Chuck's road. If I am lucky and this is the value I'll need then I have doorknobs 150pf few Kvars, I have also increased the link coil inductance by bringing the turns much closer each other. 

I will see if I can re-calculate the output series components using capacitors instead of inductors.  This may make it easier for component selection.  Give me a little time to crunch the numbers.

It is VERY important to utilize the input variable capacitor.  You need four tires to operate your car efficiently and the same goes for the link antenna coupler regarding this input variable capacitor.

1. Try not to use door knob capacitors.  They can heat up and turn the tuner into a microwave oven.  Fixed home brew plate capacitors work much better; they run cool.

2. Be careful when decreasing the spacing of the coil windings.  This increases inner winding capacitance and some times messes things up.

The output windings work well when spacing is the diameter of the wire or tubing in use.

If possible, use 1/4 inch or 3/8 copper tubing or flat copper stock to make parallel 300 ohm open wire feeders.  It may be possible to make a four wire open wire feeder that uses smaller wire to accomplish the preferred 300 ohm impedance for open wire feeders.

73,
Chuck  

Hi Stefano,

Given your current link coupled physical configuration per your prior pictures, would recommend you take a measurement of the coupling value, k. This significantly drives the possible solutions and component values of the tuner. Some of this can be accommodated by the series C on the link side. However,   knowing in advance what k is  possible helps target a closer set of all component values.

Here is an Excel SS. Not fancy, but seems to correlate well with measurements on push pull link coupled tanks that I have constructed in the past. Any issues, please let me know.

See article by O J Russell.  Good luck.

https://www.worldradiohistory.com/UK/Practical-Wireless/50s/PW-1955-08.pdf

Excellent and thanks. Another is:

https://www.worldradiohistory.com/Archive-Electronics/50s/Electronics-1952-05.pdf

W. Bruene from Collins Radio had some nice pieces on the subject.
73'