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Question About The 4 States Antenna Tuner

Dave W0DCX
 

I recently completed a 4 States Tuner kit and gave it a try.  Sadly, it is not behaving correctly.  The red REV light come son and stays brightly lit no matter how I adjust the inductor or capacitors.  The green FWD is only weakly on when the inductor is at the higher inductance setting and then dims whenever either capacitor is adjusted.  It is off whenever the inductor is set at lower inductances.  Is it possible that the red LED was installed backwards? Anything else?
Thanks to anyone who might have some insight.
Dave W0DCX

Jeff Logullo N0̸MII
 

If the LEDs are lighting at all, then they're not installed backwards I wouldn't think.

Have you tried it with a dummy load connected to the antenna output? Might be good to start there, eliminating antenna variability while you're troubleshooting.

Jeff N0MII



On Jun 5, 2020, at 1:15 PM, Dave W0DCX <cwqrp73@...> wrote:

I recently completed a 4 States Tuner kit and gave it a try.  Sadly, it is not behaving correctly.  The red REV light come son and stays brightly lit no matter how I adjust the inductor or capacitors.  The green FWD is only weakly on when the inductor is at the higher inductance setting and then dims whenever either capacitor is adjusted.  It is off whenever the inductor is set at lower inductances.  Is it possible that the red LED was installed backwards? Anything else?
Thanks to anyone who might have some insight.
Dave W0DCX
_._,_._,_


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Jeff N0̷MII

n5ib_2
 

Hi Dave,

First thing to do is determine if the problem is with the SWR bridge part or the tuner part. Unfortunately with this circuit you can' t test the just the bridge into a dummy load without having the tuner in-line.

Do you have an antenna analyzer or a separate SWR meter that will work at QRP power levels? If so, connect a dummy load to the ANT jack and switch the bridge OUT. Excite the tuner with your analyzer or with a QRP transmitter through your other SWR meter and see if you can tune for a match. If so, the Ls and Cs of the tuner part are OK and the problem is almost certainly with the bridge part. You could even do this with the antenna connected if you don't have a suitable dummy load.

NM0S used some cleverness in devising the bridge indicator, and I don't profess to understand it fully :^)) but that's not a new thing. It almost seems like yours is working "backwards" with the red LED showing forward power.

As someone else commented, if the LEDs light at all it's pretty sure they are installed correctly. But check that the other diodes (D1 and D2 in particular) are oriented correctly. And also double check that Q1 and Q2 didn't get swapped. Q1 should be a 2N3904 (NPN), while Q2 is a 2N3906 (PNP).

Also double check R5 and R6 ... easy to miss the color codes if the light is poor... R5 is 150 K (brown-green-yellow) while R6 is 1.5 Meg (brown-green-green) .

Keep us posted what you discover.

Jim, N5IB

Dave W0DCX
 

Thank you all for those great suggestions.  I feel like my electronics IQ rose a few points just by reading your posts.  I do have a dummy load and I recently acquired a NanoVNA so I will follow all of your suggestions and see what I can come up with.
Dave W0DCX

n5ib_2
 

Dave (NM0S..... get ready to chime in here... I'm going to risk violating Mark Twain's advice ("keep silent and be thought a fool, or speak and remove all doubt) ... and try to explain the workings of the 4 State Tuner's SWR bridge operation.

First, D2 steals, and rectifies, a bit of the RF drive which is filtered by C3 to provide a "positive supply voltage" that is connected via R4 (1 k) to the collector circuit of Q1 (NPN) and also the emitter circuit of Q2 (PNP) .

That positive supply voltage is also applied, via R6 (1 meg), to the base of PNP transistor Q2, thus biasing it OFF, and preventing, for the moment, the red REV LED from lighting.

But if the 47 ohm resistive bridge (R1, R2, R3) is unbalanced because an impedance other than 47 ohms resistive is presented through the tuner elements, then an RF voltage will be developed across the C4 - D1 combo. D1 is oriented so as to rectify the RF and develop a negative DC voltage across C4, which acts as the filter capacitor.

That negative voltage is applied via R5 (150 k) to the base of Q2, counteracting the positive bias voltage applied through R6. If the bridge unbalance is large enough, the negative bias will overcome the positive, and Q2 will begin to conduct, causing the red REV LED to illuminate. D3 serves to produce a "dead band" so that the REV LED can be seen to extinguish clearly when a match is accomplished.

The greater the load mismatch, thus the greater the bridge unbalance, the greater will be the negative bias applied to Q2 and the brighter will be the REV LED.

While all this is going on the base of Q1 (NPN) is looking at the collector of Q2. As Q2 is driven to conduct, its collector voltage decreases towards ground, turning OFF Q1 and dimming (or even extinguishing) the green FWD LED.

When a matched condition is achieved and the bridge is balanced, there is no negative bias on Q2, and it is turned OFF. Q2's collector voltage then rises in the positive direction, which forward biases Q1, turn it ON and lighting the green FWD LED.

OK Dave .... did that "remove all doubt" LOL

Jim, N5IB

Dave W0DCX
 

I ran the dummy load test this morning.  Attached is a table in MS Word showing the results.  At least with the dummy load there is a semblance of functionality.  When I first tried the Tuner I had the Elecraft AX1 20-meter vertical whip antenna attached which I know has an SWR of about 1.3:1 but then I saw nothing but the RED LED illuminated which seemed wrong to me.  Totally different behavior with the dummy load attached.  I would be interested in your interpretations of this data.  Thanks.
Dave W0DCX

n5ib_2
 

Hi Dave,

I looks like something is working as it should... but the trouble with that test is you're still testing two things at once - the bridge part and the tuner part. You need to isolate the functions to home in on the problem.

Since you have a Nano VNA, set it at some fixed frequency, say 7050 kHz, and connect it to the tuner. Set the bridge to OUT, and connect the dummy load in place of the antenna. Adjust the L/Cs to attempt to find a 1:1 match as indicated on the Nano.

If you can make a match close to 1:1, then leave the L and C settings right where they are, disconnect the Nano and connect up your transmitter, set to the same frequency, still with the dummy load in place, but with the bridge now IN. When you key the transmitter it should see the match that you found, and the LEDs should confirm it - REV off or very dim, FWD on and bright. If that's not the case then something is amiss in the bridge part. It's possible you might need very slight adjustments to perfect the match, but only very slight.

Jim, N5IB

n5ib_2
 

BTW ... of interest to many... There is a simulator of the T network tuner at:
http://fermi.la.asu.edu/w9cf/tuner/tuner.html

It's a great way to practice adjusting the beast without smoking too many finals. Also has an optimized "autotune" function that can predict what your own tuner settings may need to be for a given load condition ( R +/- jX that the Nano VNA can tell you about). For example - it predicts that at 7 MHz the 50 ohm dummy load (50 + j0) should match with both caps at near maximum, and the inductor near minimum.

To run your computer does need to have JAVA installed, so it may not be everyone's cup of "tea"

Jim, N5IB

Dave W0DCX
 

The new attached MS Word file contains updated finalized chart including SWR analysis.  Thanks for everyone's input!  I have yet to follow up by switching to to my transmitter after finding a good SWR match with the NanoVNA.  Will do that next and report back.

Oh, I also ran the NanoVNA on 20-meters.  Similar pattern but the best SWRs were not quite as good as soon on 40-meters.  Data not shown in chart.

Dave W0DCX

Dave W0DCX
 

Well well well.  This has been pretty interesting, somewhat humiliating, and rather humorous.  I followed Jim's directive and, at least with the dummy load in place, the Tuner at last seems to be behaving as one might expect. So maybe I did assemble it correctly!  Who would have thought!  In the final step, as per Jim's advice, I replaced my NanoVNA with my transceiver set on 40-meters at 1 watt and obtained the same LED pattern on the Tuner.  Interestingly, when I switched to 20-meters at first it seemed not to work well.  But I was assuming there was an incremental pattern of tuning to be expected when adjusting the inductor.  I had previously assumed that I could "bracket" the inductor settings to more quickly figure out the best tuning, but I guess not.  I think one has to try each and every inductor setting more methodically.  Lo and behold I found that 20-meters gave me the green light when I had the inductor at the B position, Cap-L at 10 and Cap-R at 0.  B is the next to highest setting of A which worked well for 40-meters.  Lesson learned is that I need to be completely empirical when trying to adjust the tuner for the best match and not assume any patterns will emerge.  But the big question now is how will this all work with an actual antenna instead of a dummy load?  I was flummoxed when I first tried it on my AX1 vertical whip, but maybe now that I understand the tuning process better I can get it to work with that and other antennas too.
Thanks!
Dave W0DCX

Jeff Logullo N0̸MII
 

Dave,

Glad you have solved the mystery of your tuner's behavior!

Here's an article that you -- and others -- might enjoy: 

   Getting the Most Out of Your T-Network Antenna Tuner, by Andrew Griffith W4ULD (from QST January 1995)

"To achieve the highest possible efficiency at a given impedance transformation, tune the network with the highest output capacitance that allows a match."

The section on the last page, "For Tapped-Inductor Tuners" summarizes the process to follow to accomplish the above.

Jeff N0MII

On Jun 6, 2020, at 5:19 PM, Dave W0DCX <cwqrp73@...> wrote:

Well well well.  This has been pretty interesting, somewhat humiliating, and rather humorous.  I followed Jim's directive and, at least with the dummy load in place, the Tuner at last seems to be behaving as one might expect. So maybe I did assemble it correctly!  Who would have thought!  In the final step, as per Jim's advice, I replaced my NanoVNA with my transceiver set on 40-meters at 1 watt and obtained the same LED pattern on the Tuner.  Interestingly, when I switched to 20-meters at first it seemed not to work well.  But I was assuming there was an incremental pattern of tuning to be expected when adjusting the inductor.  I had previously assumed that I could "bracket" the inductor settings to more quickly figure out the best tuning, but I guess not.  I think one has to try each and every inductor setting more methodically.  Lo and behold I found that 20-meters gave me the green light when I had the inductor at the B position, Cap-L at 10 and Cap-R at 0.  B is the next to highest setting of A which worked well for 40-meters.  Lesson learned is that I need to be completely empirical when trying to adjust the tuner for the best match and not assume any patterns will emerge.  But the big question now is how will this all work with an actual antenna instead of a dummy load?  I was flummoxed when I first tried it on my AX1 vertical whip, but maybe now that I understand the tuning process better I can get it to work with that and other antennas too.
Thanks!
Dave W0DCX


--
Jeff N0̷MII

Dave W0DCX
 

Thank you, Jeff, for that link.  I think I have become spoiled with the marvelous internal tuner in my KX2 that will tune just about anything including the proverbial rain gutter.
Dave

Frank Perkins
 

Hi Dave, good thinking on the rain gutter antenna. Have scraped off a little paint and clipped to a downspout on one in the past.
After all, anything metal is an antenna.
An old couch spring could become a circular polerised yagi for 3 GigaHertz!!
Frank N6CES
After


On Fri, Jun 12, 2020, 1:14 PM Dave W0DCX <cwqrp73@...> wrote:
Thank you, Jeff, for that link.  I think I have become spoiled with the marvelous internal tuner in my KX2 that will tune just about anything including the proverbial rain gutter.
Dave

David Wilcox
 

Don’t forget the screen door of your slider out to the deck.  Make sure the screen is metal, but then again the metal frame itself will work fine too.  You get a higher score if the slider looks out on a golf course.

David J. Wilcox K8WPE’s iPad

On Jun 12, 2020, at 4:55 PM, Frank Perkins <N6CES.r@...> wrote:


Hi Dave, good thinking on the rain gutter antenna. Have scraped off a little paint and clipped to a downspout on one in the past.
After all, anything metal is an antenna.
An old couch spring could become a circular polerised yagi for 3 GigaHertz!!
Frank N6CES
After

On Fri, Jun 12, 2020, 1:14 PM Dave W0DCX <cwqrp73@...> wrote:
Thank you, Jeff, for that link.  I think I have become spoiled with the marvelous internal tuner in my KX2 that will tune just about anything including the proverbial rain gutter.
Dave