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Johnson Matchbox 160 Meter Mods - Experiences/Suggestions?




 
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Author Topic: Johnson Matchbox 160 Meter Mods - Experiences/Suggestions?  (Read 45882 times)
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W2DU
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Walt, at 90, Now 92 and licensed 78 years


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« Reply #25 on: September 08, 2008, 09:12:05 PM »

Hello All,

Son Rick, W8KHK (my original call in 1933), suggested that I make a comment here, though I don't believe anything I can say will add to the knowledge already presented. I'm sure it's common knowledge that any increase in L over what will provide a match will decrease the efficiency, thus you are going in the right direction by adding C instead of L to achieve a match on 160m.

However, IMO, the dual-differential C in the output of the Matchbox an unnecessary component, where a single variable C would suffice--I'll explain. Note that the inner sections of the C are shunted directly in parallel with the input to the feed line. The result is that, depending on the input Z of the feedline, the inner sections may assist in achieving the match, or it may detract from the match. If that section of the C were to be disconnected and only the outer sections left connected, the result will be a specific range of Z's that is matchable. Now if the inner sections are reconnected the amount of Z range will be the same, but the range will be shifted in frequency, because the inner C section is simply in parallel with the input Z of the feed line.

On the other hand, I believe the UnBal at the input of the Matchbox is the ideal way to achieve the balun function, rather than a ferrite-loaded balun at the output. However, I used a C in series with the input link to cancel the inductive reactance in the link.

As I was told many years ago, the dual-differential C performed as a voltage divider, and thus a Z divider, but IMO this is not true. The same condition appears in McCoy's 'Ultimate Transmatch', with the split-stator C at the input. The C portion in parallel with the output of the source is totally unnecessary, doing nothing to assist in achieving a match. I demonstrated this to Doug DeMaw and several other League Staffers in the ARRL lab in the 1970's, using a Dentron Supersuper tuner measured with a General Radio GR-1606A RF Impedance Bridge. Some years before that I notified Denny Had, the owner of Dentron. He checked it out and agreed. He was pleased, because he was just ready to order a new batch of split-stator caps, but changed the order to the less-expensive single-section caps, which was all Dentron ever used since then.

Incidentally, Sterba Curtain (oops, I mean Kurt Sterba) and Reflections are unrelated, except they are both involved with transmission lines. I'm associated in a way with Reflections, but I have no idea who Kurt is. Until a few short years ago it was Pete Onnigian, W6QEU, the owner of Jampro antennas, builder of FM BC antennas, but he give it up. I still have no idea who has taken his place. I believe Pete was somewhat better in explaining the details than whoever is now using Kurt as a pseudonym.

Walt, W2DU

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W2DU, ex W8KHK, W4GWZ, W8VJR, W2FCY, PJ7DU. Son Rick now W8KHK.
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« Reply #26 on: September 08, 2008, 09:19:31 PM »

Sorry, Pete 'gave' it up, not 'give' it up.

Walt, W2DU
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Ralph W3GL
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« Reply #27 on: September 08, 2008, 11:59:23 PM »

Sorry Pete...

I thought it was Demaw but Walt  kicked my memory, it was McCoy...

I stand/sit corrected.

Walt, you remember me now from my 1960's passport photo
(made in the RCA photo studio at Astro)?

Ralph, W3GL.
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73,  Ralph  W3GL 

"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow
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« Reply #28 on: September 09, 2008, 08:41:33 AM »

McCoy was my hero. He gave me a ferrite rod for my first linear a pair of 811As.
I called him one day looking for a place to purchase one and he told me to stop by the ARRL lab.
I thought Drentea designed the Dentron tuner?
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W1VD
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« Reply #29 on: September 09, 2008, 09:20:38 AM »

DeMaw did do a transmatch similar to McCoy's ultimate transmatch but with the split stator cap moved so that one section was in parallel with the shunt inductor and the other section was in series with the output. It's called the "SPC Transmatch" or "A Transmatch for Balanced or Unbalanced Lines" and appeared in the Handbook in the 80s...and maybe longer. It's in the 87 Handbook on page 34-17...the only year here at work. It uses the ferrite balun on the output like McCoy's.

Recall, on a number of occasions in the lab, McCoy and DeMaw having heated arguments and nearly coming to blows over which circuit was better...     
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'Tnx Fer the Dope OM'.
N3DRB The Derb
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« Reply #30 on: September 09, 2008, 08:14:51 PM »

Bruce,

I'm getting ready to put the screws back into mine ( KW matchbox) right now. I still think adding a ceramic wafer switch driven off the main band switch in the back  is the way to go. you could have 3 to 4 poles easy. lemme take a picture of what I meana b4 I lose it up for good.
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W2DU
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« Reply #31 on: September 09, 2008, 09:54:00 PM »

While speaking of Doug DeMaw, I was well acquainted with him personally. After writing the series of articles, "Another Look at Reflections" that was published in QST beginning in 1973 and ending in 1976, he asked me to write a paper on conjugate matching for the ARRL Handbook. He thought it would help hams better understand how transmatches work. My writing appeared there in every edition from 1986 to 1994, when Dean Straw deleted it, saying the conjugate match can exist in theory only, and therefore had no place in the Handbook. Doug appointed me ARRL Technical Advisor for antennas and transmission lines in 1980.

After Doug's death his widow, Jean, (W1CCK) invited me to give the eulogy at his funeral. She also gave me several of his engineering books that he used at the League, and one of the antenna tuners he built. All the components were mounted on plywood with no insulators. I measured the loss at 4.0 MHz--greater than 3 dB !!!

However, I did buy from her his Ameritron AL-80A linear amplifier, which is shown in one of the pics I posted earlier in the thread Bruce initiated concerning the National HRO receiver. It is shown along with my HRO. It also appears in the pic of my RF lab, shown on my web page at www.w2du.com.

Walt, W2DU
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WA1GFZ
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« Reply #32 on: September 09, 2008, 10:44:34 PM »

The old 4-1000A rig took out a tuner I built using a BB transformer at the high Z side. Fried it on the first key up. Bag that idea.  I wonder why McCoy and DeMaw never tested their units in a shoot out. Both were junk in my view.
I designed my tuner in '82 but never published it. balun on the 50 ohm side driving 2 L networks out of phase......Measures called it the balanced balanced tuner about 10 years later. I call it my fugly tuner.
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N3DRB The Derb
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« Reply #33 on: September 10, 2008, 01:02:08 AM »

 i know one thing - if a tuner has a ferrite balun it's going to blow up at some point. Period. I dont care how big it is, it's going to fail.
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ka3zlr
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« Reply #34 on: September 10, 2008, 05:44:12 AM »

Good Discussion here, But, with all do respect to the writers and engineers involved in this discussion, Both past and present...it has been my experience that Not necessarily the same antenna and or antenna coupler offers anything more than just average performance to the station, regardless of the design.

In the realm of Amateur HF it has always been my practice to use Two separate antenna,. ie, Receiving is one thing, Transmission is another...

73 jack.



 


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WA1GFZ
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« Reply #35 on: September 10, 2008, 08:23:13 AM »

Wrong Derb. I had a 1:2 in my fugly for 20 years and it took everything the 4X3 could give. When I moved my antenna I only needed 1:1 so converted to a RG393 airwound.
Does anyone know the value of the L in the Johnson KW match box?
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N3DRB The Derb
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« Reply #36 on: September 10, 2008, 08:26:36 AM »

how big was the thing?

i still think that statement is accurate for manufactured tunas. Homebrew you can pick and choose.
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K3ZS
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« Reply #37 on: September 10, 2008, 09:29:17 AM »

I put a huge DX Engineering balun on the output of my commercially made tuner.   Cured all balance and loss problems of the built-in balun.
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« Reply #38 on: September 10, 2008, 09:53:38 AM »

I think the KW "L" is around 33uh. I will re-measure when I get home again.  45uh would be a good number for 160. I debated about modifying one of my KW matchboxes for 160 but ended up building a balanced link coupled tuner. The classic "C" to ground unbalanced link input, with split stator cap/tapped coil secondary works FB. I used what was on the shelf. It is really easier to build a dedicated tuner for 160 than to tear up a matchbox. I do understand the compulsion to convert one though....just because we can!!!
Skip
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WA1GFZ
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« Reply #39 on: September 10, 2008, 11:53:47 AM »

Derb I used 6- 2 inch iron cores 3 beside 3 wound with #14 Teflon quadfilar.
Two in parallel for the primary and two in series secondary. Barely warm after an old buzzard. I need to build a tuner for beach QTH and have a nice 3/8 silver plated tubing inductor that would look nice. I'll have to measure it. My fugly is a pair of 22 uh 5 KW broadcash inductors. I agree 45 is a good value for 160. Higher may be even better if low resistance. 
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W1UJR
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« Reply #40 on: September 10, 2008, 01:02:26 PM »

I think the KW "L" is around 33uh. I will re-measure when I get home again.  45uh would be a good number for 160. I debated about modifying one of my KW matchboxes for 160 but ended up building a balanced link coupled tuner. The classic "C" to ground unbalanced link input, with split stator cap/tapped coil secondary works FB. I used what was on the shelf. It is really easier to build a dedicated tuner for 160 than to tear up a matchbox. I do understand the compulsion to convert one though....just because we can!!!
Skip



Righto Skip, nice to hear from you!
I'd rather have one tuner in the shack, than to wire in and allocate the space for two.
Rather keep that space for radios!

Do you have a photo of your creation which you might email over?
I'd be most interested in seeing what you built up.

The modified KW Matchbox works well, but as W1GFZ suggested, the voltage on the ends of the coils is rather high.
It will, on voice peaks, actually arc across the air variable, so I may try using some doorknob caps as Bowie Bill W3CK suggested.
Otherwise, the set up works very well, with no component heating.

I'll still not been able to track down the Matchbox efficiency article, referencing the 275 and KW units.
I assume it is in the Ham Radio magazine issues, I don't have them in my collection.
Perhaps some kind soul would be good enough to scan and email over my way?

I look forward to the return to 160 this winter!
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« Reply #41 on: September 10, 2008, 04:28:35 PM »

Bruce,
I think the Q is too high with a small coil and large cap value. This could be why you were flashing over last night. My fugly will do the same thing if the l is set too low and I have 1/4 inch spacing for the caps. Time to buy a roll of 1/4 inch tubing and roll your own coil. 
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W1UJR
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« Reply #42 on: September 10, 2008, 04:38:47 PM »

You're probaly right Frank, its just fun to try to make this work.

It sure was acting up last night, but had been fine further down the band eariler in the week.
Funny thing is that when I changed the value of the cap later, then retuned the Matchbox, I could bellow as loud as I wanted and it would not flash over, even at 1KW.
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Ralph W3GL
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« Reply #43 on: September 10, 2008, 07:25:22 PM »

Bruce,

I just checked my H.R. reference and that article is not the one you are looking for...

I think I saw it in QST but the Dec. 63 note in QST is only a Hints & Kinks thing about adding two coils in series with the balanced output terminals to make up for lack of output Z matching... Personally, when I ran into that problem I used coil stock as a balanced auto-transformer across the output.

Take care...





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73,  Ralph  W3GL 

"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow
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« Reply #44 on: September 11, 2008, 06:29:37 PM »

I hope this little smattering of history, appearing in the attachment, will not be too boring for your reading.

Walt, W2DU

* History.doc (26.5 KB - downloaded 278 times.)
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ka3zlr
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« Reply #45 on: September 11, 2008, 07:28:27 PM »

Hmmm, Interesting Article....
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Ralph W3GL
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« Reply #46 on: September 11, 2008, 09:44:08 PM »

Hey Walt...

Did all the BIRDS work?

Nuf said...
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73,  Ralph  W3GL 

"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow
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