The AM Forum

Okay, so I finally made the jump to 600 ohm ladder line, a 125' doublet, and its been great so far. I have a KW Matchbox but the "Matching" cap arched and now wont stop arching.(The tuner sat in my fathers barn for 20 years before I took it home with me, so it was kind of expected) I am currently using an MFJ-989C Versa Tuner V and its working pretty good. The 1:1 current balun isn't getting warm so there doesn't appear to be much loss. Anyway, I want to homebrew a tuner. I have been reading up on Balanced L-Network tuners and I think that's the route I am going to go. I don't want to have to mess with alligator clips and all that because I band cruise almost every band and It wouldn't be practical. So, who has homebrewed a balanced L-network tuner and what tuners are you guys using? Any info an constructive criticism is welcome!


Perry
W3MMR

I have built a couple different balanced L-network tuners and they work well.  Don't scrimp on the input balun.  Keep the L and C mounted on standoffs well above any metal chassis so that you don't add any too much stray capacitance to ground.  This would tend to unbalance the output side that you have carefully maintained during construction of the antenna and transmission line.
I have tuners built for different bands to facilitate fairly quick band changes.  On my two element driven 80 meter array, there's even a CW tuner and a Phone tuner.  PA0FRI has an interesting design on his web page that I might try this winter. 
As for that Johnson Flashbox, you probably have a burr on a capacitor from that arc, which makes it "want" to arc there even more as the E field concentration provides a breakdown point.  Get in there with one of those sandpaper files that women use on their fingernails and clean it up.  You can never have too many tuners.
de Norm W1ITT

Hey Perry,

Look at the post from Bruce W2XR in this archived topic:

http://amfone.net/Amforum/index.php?topic=29563.0

Jeff W2NBC

Let me help.....

1) You could prune that doublet to 105 or 110 feet.

2) Drop a 135 foot Zepp feeder from it.  Make the Zepp feeder out of insulated #14 save for the last 40 feet or so near the ground.

3) Make a balanced L, fed with a high performance 1:1 current balun.

4) Go from the tuner to the Zepp feeder with 600 ohm OWL made out of #1 insulated, stranded copper.

Depending on the band, the Impedance at feedpoint will be less than or greater than 600 ohms.

If less than, short the Zepp at 1/2 lambda or 1 lambda, and feed end to side with the 600 ohm OWL a few feed above the short.  Experiment with short position and feed position above short to get 600 ohms at the tuner output.

If greater, do the same at an odd multiple of 1/4 lambda.

Have fun!

ER, I meant to say #16 stranded copper, insulated.

Sorry!

In case you did not see it:

How to make FB current baluns.

I would use the 2.4 inch #31 toroids, two in series.  Pick the frequency response you want.

http://k9yc.com/2018Cookbook.pdf

Zepp feeders.....people should use them more often.

The last 40 feet or so of the feeder is bare solid copper.  This allows you to attach the OWL end to side with copper gator clips, and, of course, put a short bar across it.

You need not hit 600 ohms spot on at the tuner.....just something within the tuner's transformation limit.

For each band, you will have a short bar location and a feeder location.  Pretty easy.

The only hassle is going outside to move the short bar and the 600 ohm OWL tap point when you change bands.

Sorry it took me so long to reply. Unfortunately, thats not going to be practical or even feasable at my QTH. I had a hard enough time just being able to get the ladder line to the shack window. I live in the city, I have a small lot, the antenna stretches from one corner to another, and the OWL is draped across the roof, over the gutter, then into the front window of the shack.

Awesome info. Thanks!I did not see that, thanks Jeff!

W3MMR

  330 ft center fed, home made 600 ohm  feed line , have seen 2,000 pep go thru it many times, no arcs, no sparks, no case on it. Several mods, the fixed stator plates on the bottom differential
cap, cut the grounding wire lose from chassis ground.   2nd mod , a 500 mmfd variable cap in
series with the ground side of  the input link of the main tank coil. It is mounted on a piece of wood mounted  above ground on top of the frame of  the main  capacitor. Stator plates to ground side of link, rotator plates and shaft to chassis ground. We are now matching the link input impedance to  the transmitter. From what I have read, experienced, and have heard, , perfect, matched balance feed line is a must, each side matches to the inch, no sharp 90 degree turns, , no touching of metal gutters, no duct taping to sides of towers so it won't blow in wind. I saw your pictures  and  I see problems.
      Last winter , rf in audio on certain frequencies  check all connections good, looked out the window and the rubber tension line had rotted and slack in the open wire and one side of it was in the snow, other side  wasn't. Corrected problem no rf audio. Touching snow and unbalancing feed line, was the problem.  Converted another matchbox to 160, replaced tank coil with 43mmh edge wound  coil,  padded 100 vac cap across main tuning cap, 500mdf cap in series with link, works wonderful.
      One test I tried, disconnect one side of the open wire from the matchbox, tuned to 40 watts out, perfect swr 40 watts out, disconnected other side on same teminal, same output and  swr.
  Bob  W8LXJ

You say you see problems, what problems do you see? I cant do much else with the position of the feedline, with the exception of getting it up off the roof more or getting it away from the gutter more. I dont have any other options really. I dont really have any RF issues, with the exception of 20m, at 1kw, I get some RF into my computer to where I cant type while transmitting, but thats it. I get zero RF in my audio at all, zero RF into my PC speakers, which are the speakers for my Anan, And mind you, thats using an SDR. And any RF Im getting into the shack Is coming from the antenna itself and not the feedline radiating because the one leg of my antenna is only 15'-20' outside the shack. So how much better can I really make things?

 You said the matching cap is arcing and won't stop. I assume you mean the  the cap on the right side of the cabinet. It is either a completely unbalance feed line, or an internal short in the matchbox component. Do you have the cabinet off the match box? If so, check the 4 small
ceramic stand offs this cap  is mounted on . One might be destroyed. Also the band switch, blew one apart, the center ceramic coupler between the 2 sections of the band switch arced across
leaving a carbon trail between both ends of the tank coil. Ended up taking ceramic ring out a built
one from plastic.  You might try , disconnecting feed line from box, , attach a light bulb or 50 ohm dummy load  to the matchbox open wire feed throughs and see what happens.  Arcs, problems in the box, no arcs line problems

Bob

Oh, i thought you were seeing problems with my antenna and feed line setup. The feedline isnt unbalanced, well not much if any. I should have said that the arching happened with a coax fed dipole, not the doublet. But it also did it with the doublet when I tried it. Like I said, the tuner was in my fathers barn for 20 years and was taken out of service for a reason and I had issues with it immediately. Anyway, I am buying a Ten-Tec 238A off a friend for next to nothing so Ill try that out for a while until I build one.

Here    https://pa0fri.home.xs4all.nl/ATU/Smatch/smatcheng.htm  is a very interesting balanced tuner that seems to work very nice. Heard good things about it. I like to build one, but can't get the cores here in Costa Rica and I don't have them in stock

http://www.somis.org/bbat.html

http://amfone.net/Amforum/index.php?action=printpage;topic=12059.0

Good ideas for a simple tuna there.

And you can use Jim Browns ideas for a choke balun to make it force balance....

--Shane
KD6VXI

I came across this several years ago. Seems like a nice design. Can also be used as a tank circuit for push-pull tube final.

I've wanted to build a balanced L-network tuner for a while.  I went a different way as shown in my QRZ page.  Good luck.

Best regards,
Fox
W7FOX

   I wanted an antenna that would give me multiband coverage and was easy to deploy and take down. I built a 130 foot dipole using 450 ohm window line as feedline and a WA1FFL dipole center. This antenna was used at both of my sisters homes in MA while visiting. I purchased a used Palstar BT-1500A tuner, this gave 80 to 15 band coverage and worked very well especially since at one location is was hung out a second floor window and only 25 feet above ground.

   I was so pleased with the antenna I built one for my DPRK QTH which is a bit more challenging, a 50 X 100 Bay Area urban lot. I have a 50 foot tree 10 feet in from the property line which is my antenna support. Construction was the same, 450 ohm window line, WA1FFL center support, height is at 45 feet. I had a tree climber clear some limbs and put a bracket with pulleys in the tree. I bought another used Palstar 1500A tuner and also got a lightening protector from Array Solutions that is made for window line. Because of my small yard the antenna is in a lopsided V, see picture.

   I have 80 to 15 meter band coverage, almost all of my operating is on 75 meter phone, either AM or SSB. Coverage is good North to South, the sides of the V are North South. This gives me good signal into LA and Southern California plus Arizona and Southern Nevada. I also get into Oregon/Washington and BC OK too. Coverage to the East of me is OK, one of the nets I check into is run out of Reno area and they hear me OK and I can also hear one station from Colorado that checks in on occasion. I don't think coverage to the West is very good.

   Considering my limitations of space I'm happy, my urban noise floor is S7 on a good day and S9 is often the case. This antenna works much better than the coax fed 80/40 fan dipole it replaced.

Playing with the Bal-Bal Tuner. Had some Air-Dux coils and a 300pf cap. Resonates fine on 80m and 40M. Still have to play with 160M. Best I get is 7:1 with full mesh of the breadslicer. Going to pad it with 500pf and see what happens. I made this to test out. I will use my inductance meter to give me the best values then go shopping for a pair of rollers. Then will make it belt driven like the Measures design. I like this better than the big K1JJ tuna. Once I get it fine tuned, no clips.

I am using a DX Engineering 160M doublet with their 300 ohm ladder. Trying to decide if I should go with 600 open line. This 300 ohm stuff is easier to get into the shack downstairs and is more agreeable with the XYL HOA.

John

"I like this better than the big K1JJ tuna. Once I get it fine tuned, no clips. "

Hi John,

That tuner seems like a nice design and convenient to tune around the bands with the roller inductors and capacitor.

Though there are no free lunches.   The balun costs $174, the roller inductors will cost probably over $125 each if you get big ones that will handle the power... and the output cap will need to be a vacuum variable if you plan to handle the pair of plate modulated 813s at 3KV.

That's around $600 for parts if you do it right.   See below the kind of roller you will need. I doubt the MFJ roller will handle it.

In contrast, the JJ tuner requires one vacuum variable cap and a copper fixed coil, but that's it for virtually unlimited power. Made to be simple and cheap. It is good if you build several tuners to stay "pre-tuned" on various bands like I did. I had 5 tuners at one time - all from junk parts.

For your balun design tuner, look around for something rugged like the roller inductor linked below. To gang them together, they need to be identical.  Make sure there is enuff inductance to cover 160M. Notice the fat finger stock contacting the coil. Also, a very heavy-duty wheel works well too. Flat coil stock is the way to go. The currents and voltages on the various bands for a perfect match can be brutal - especially for a big plate modulated AM rig. Many marginal roller inductors develop "hot spots" between the coil stock and roller contact. It depends on ratings and actual power levels, but generally, never rotate the roller inductor with full power going thru it.

Sample roller inductor:

https://www.ebay.com/i/143246306942?rt=nc&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D20160908110712%26meid%3Dc722ccb104954d49924505df4efc2786%26pid%3D100677%26rk%3D13%26rkt%3D30%26sd%3D283494476263%26itm%3D143246306942%26pmt%3D0%26noa%3D1%26pg%3D2385738

T

Nice layout. I would advise against use AirDux or other coils designed for use in transmitter tanks. For use in tuners, where the circulating current can be far higher than in a transmitter tank, the size of the conductors is too small. The result is loss.

Well, this is a fun experiment. Easy to throw together with parts laying around the shack.

I hear what you both are saying. Big tunas matter with big power. JJ it is.

I mainly threw this together to play with the Drake. With only one 3-500Z this may work ok for now.

John

I agree with Steve on AirDux.......if you are using a high Q tuna.

If you use a balanced L with a Zepp feeder, things will be "prematched" to about 600 ohms at the tuna. Thus, your tuna will never be asked to wrangle with a large transformation ratio.

A balance L with a current balun will be fine with AirDux or something similar, as the Q of the tuna will be around 3 or 4. Thus, currents in the inductors will not be excessive. 

If you are using modern gear, harmonic suppression by the tuna is not a concern, so a low Q L is fine.  If you are running a high powered class C beast, consider something else, like a low pass balanced Pi with #8 bare copper wire, or copper tubing.

Have fun!

How so, across multiple bands? Where did the 600 Ohms come from?

The Zepp feeder is shorted at 1/2 wave or 1 wave if the feedpoint of the doublet is less than 600 ohms at frequency of interest.  If higher, short at 1/4, 3.4, etc.  Tap into the feeder end to side with 600 ohm OWL.  The feder itself is OWL, with the bottom 25 to 35% bare copper so you can connect anywhere.

Pick a connection point, and slide the short bar around until you hit the real axis.  Move the feed point up or down, and slide the bar again until you eventually hit 600 ohms, or something close.  For each band, you will have a short bar position and a feed point above the bar.  That is the drawback: A trip outside when you want to change bands.

The 600 ohm line will present 600 ohms to the tuner.  For a balanced L with a good current balun on the input, this is within reach. 

You will quickly recognize this as the stub matching problem with a shunt, shorted stub.  Instead of looking for a 50 ohm match, you are looking for a 600 ohm match.

Make sense?

Here is what to do:

1) Get a pair of 300 ohm carbon comp (or other noninductive) resistors, and string them in series.  Match them well.  1 watt is fine. The junction of the two will be your neutral point.  Bond the two free ends to the tuner's balanced output.  Looking into the tuner's 50 ohm input with noise bridge, VNA, etc., find 50 ohm match at frequency of interest. You might want to apply a low level RF signal to the tuner's input, say enough to give you a couple of RF volts across the load.  Get a VTVM with RF probe, or a scope with probe.  Using the junction as a neutral point (ground lead or clip), check the voltage on each output terminal.  The two voltage should be very close if balance is good.

2) Once this is done, HANDS OFF the tuner controls.  Remove the 600 ohm load, and connect the 600 ohm OWL to the tuner on one end, and to the trial feed point on the Zepp feeder.  Slide the short bar up and down, noting where you cut the real axis of the Smith chart.  Move the feed point up or down, until you get your 50 ohm match back at the tuner input.

3) Have fun!

I have used a similar technique, but even simpler...

Start with a 70 ohm hardline or 50 ohm coax from the shack out to the OWL antenna area.  I once had a 36 element wire 20M Sterba curtain array (with reflectors) all fed with openwire. 150' wide by 90' high.  And also had a 75M Zepp fed with open wire... it makes no difference.  

Now, how to easily go from a "whatever" OWL impedance to a 50/70 ohm coax to the shack?

Use a 2" donut toroid (or a few stacked to increase power capability) and wind a 1:1 balun.  Unblanced to balanced.

Connect the coax to the unbalanced balun side and then connect the balanced toroid side across the antenna openwire. The toroid will hang right at the OWL. Use the same shorting bar and balun tap experiment that WA4WAX describes to find a perfect 1:1 50 ohm tap on the OWL.  The taps and shorting bar must be changed for each band, of course, but there is just one unbal to bal interface from 50/70 ohms to 50/70 ohms on the OWL  - plus no tuner needed.  Using the shorting bar technique I have always been able to find a perfect 1:1 50 ohm match for the 1:1 balun tap no matter what the OWL antenna may be. Just have enough bare OWL to work with so you can find the proper tap points. It may mean adding some to find 50 ohms.

If you set up the OWL run properly, the coax length can be very short and tap right outside the shack.

Using an MFJ 259 antenna analyzer makes the two adjustments quick and simple by expeimentation.

T

Sure. Makes complete sense. This is not how most people and MMR for sure, will run their open-wire fed dipole. So, large impedance swings will occur across the bands.

I have posted this picture before but thought I would again-- Why! because these simple tuners work great and are very fast to tune. I have two (2) Palstar balanced tuners and both are sitting in the closet. Fiddling with the dual roller inductors and buttons on the Palstar was a pain in the butt. Once I got use to using this type of "JJ tuner" going to anything else was a burden. No flashing leds or blinking lights required and you can count on most, if not all your power will be transferred to your antenna.

(https://i.imgur.com/7MiYZ2p.jpg)

Hi Larry,

Looking closely at your picture, I see you have THREE separate "JJ tuners" with three separate antennas. Cheap and easy way to pull it off. Quick band-switching. Very cool.

BTW, just to be clear for the record....  The original schematic came from an old Handbook from the early 1930's. Back in the 1980's I was looking for a design where I could build five tuners cheaply that would handle multi-KW with good efficiency. I used open wire for all antennas back then. Wanted instant band-switching.

There is nothing unique about the current design except the implementation of the single section vacuum  variable cap and the big copper tubing coil you can wind yourself. The 50 ohm input link variable cap is optional, though most use them and they are small variable air caps. All easily available parts.

What other design will handle 5KW+  using one single section vacuum variable cap? Single section caps are very common and vac caps are ALL single section. They can handle the high voltage easily whereas an equivalent air cap is rare and huge and may lack the capacitance to do the job on 75/160M.  

We are paid well for using a highly efficient tuner, even with a 1 watt QRP rig. DB loss is dB loss no matter what power we are running.

It could just as easily be called a link coupled balanced tuner, but the "JJ Tuner" nickname and implementation simply caught on as a convenient reference after I used them for many years - guys started building them and referring to them on the air this way.

The only downside is that the harmonic rejection is not as high with the single floating HV cap - as with tuners having (dual) caps to ground, but in this day and age with pi-networks,  more harmonic rejection is not needed.  I believe we are talking about -25 dB vs: -40 dB or so.

T  

neat tuners shown here...one question though:

so if I have two 3" diameter, 4TPI, 10AWG, each 9.5" long airdux'es I shouldn't use them for a balanced L ?

That AirDux would be just fine, as long as your are not attempting large impedance transformation ratios.

With a 600 ohm Zepp feeder scheme, you will be fine.  Loss will be negligble.

You will be shooting for a Q of around 4.

Remember:

Current balun on the input side!  Balun should have at least 6K of CMR.

:-)

What antenna system will you be "tuning" with it?

My little experimental balanced L Airdux tuner is working fine with a 220ft doublet fed with 100ft of 300 ohm ladder. I pre-tune it at low power. Running 700 watts CW with no arcing. My coils are 1.5in in diameter and 3.25 in long at 10 tpi. I measured them at around 20uH. I am using a commercial DX Engineering 1:1 Current Balun that I was previously using with my lower wattage commercial tuner. 300pf breadslicer. Won't tune 160M. I am sure it would arc if I tried. I used my MFJ-259 analyzer to preset the tuner to get it close on 3.885 and 7.290. Once you set the taps the cap tuning is smooth and fairly wide.

I would think your larger ones should work just fine if you have a well behaved antenna. Give it a try, nothing to lose.

John

right now I have a 67 foot doublet up at 40 ft fed with window line and tuned with the smaller Johnson link tuner...I'll sweep its R&X tonight with an analyzer and post here.

Hopefully soon I will be increasing the length of that antenna to 84 feet so that it's an EDZ on 20, I hear there's AM action on 14330 these days but I can't hear it on the 67 footer.

I have these two coils, a 1:1 un/bal to feed them, and a 50-500pf 15kv vacuum variable.

Do it. 30min of work and then test it. I am using alligator clips for part of it.

I'm in the process of breadboarding it...meanwhile, here's a sweep of the 67 foot doublet. The window line goes through a 1:1 bal/un to the antenna analyzer and to the laptop on battery. The setup is floating.

Running a sim and transmission line calculator for 67 foot center fed with 40 feet (it's probably more) 450 Ohm ladder line, your tuner will see something like 290 -j600 impedance on 7.290 MHz.

14.3 MHz: 61 -j400
21.3 MHz: 133 -j250
29 MHz: 56 +j82

Of course, 75 meters, the antenna is quite short, so the numbers get really ugly. But maybe you don't even use the antenna in the band.

3.885 MHz: 4 -j14.


I'll run the numbers for your 84 foot system tomorrow. Also, what is the exact length of your feed line?

Thanks 'HX ! the present feed line is 42.5 feet of the supposedly 450 window line. I'm looking at it now and there's a lot of sag...looks like the tree branch on one end broke and the rope landed on a branch below bringing the wire about 4 feet above the attic roof...

the unsimulated house below the ant (late 1800's brick and stucco cement) probably explains the big difference between what I measure and what you simulate.

There are some difference in our numbers but the trends across the bands are pretty similar, except for 40 meters. I used a generic 450 ladder line in my sim. If you know the Wireman part number, I can probably go a better sim.

Why are you moving away from the Johnson tuner?

just playing with parts on hand...

I breadboarded it and the results are kinda
funny...40 meters tunes with just one and a
quarter turn of coil  ;D  see the pic...the cap
is at about 50pf.

What is the load?

How about checking the RF voltage on each feeder lead, using a reference.  If cap is dual section, use the rotor.  Other wise, use the common on the input connector.  VTVM or scope probe ought to do.  Use low power, such as a signal generator.

I have enjoyed this thread and the photos.  In answer to the first question, I use a Heathkit SA-2060 with my Apache and DX-100B transmitters from 160m up, which has worked well for six years.

I'm about to put my Globe King 500B back on air, but don't know if the SA-2060 would be sufficiently robust for longer transmissions with the 500B. Anyone here using a 2040 or 2060 with a 250W AM transmitter?

N7ZDR's set up is very interesting.  Any more pics?

If you do search on  "k1jj link coupled tuner" you will get tons if information.

In today's plug and play world the days of seeing this type of thing are long gone.

If you need anything let us know----73

Check out the Google image results too. More copper tubing than a backwoods distillery.

If only we could distill Whisky at the same time we would be in heaven...

John

ps. look at my tag line...

Thanks. One of the photos on your QRZ page is what I was looking for. Nice work.

I showed someone the rough layout of a link coupled tuner built around some BC-610 coils.  The miscreant said it looked like a moonshine still.  Uggh!


https://www.youtube.com/watch?v=WE5pM1HXxlI