An SSB kit from Spain

The ILER-20 and ILER-40 SSB transceiver kits of Javier Solans,
EA3GCY, look very interesting.

For more info: http://www.qsl.net/ea3gcy/


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DSB Audio -- Why Worry?

In a recent post I mentioned my concern about shaping the audio frequency response of my DSB transmitters.   This concern was sparked by an article in the May 1993 issue of "Electric Radio" magazine.   John Staples, W6BM,  had an article (the first in a three part series) entitled "Good Audio." The article (like most of ER) was focused on AM rigs and, it seems to me, contains a lot of technical wisdom.  Here is the part I found most relevant: 

"Good hamband AM audio is not the same as hi-fi audio. A broadcast-quality transmitter fed with a broadcast quality mike would sound flabby and under modulated. The highs would be lost in the narrow bandwidth of the receiver. The low frequency component would dominate the modulation power, but would be lost to the low frequency roll-off in the receiver.  What's left of the mid-range would sound weak, and the signal would lack punch.  Proper response shaping results in audio that sounds powerful, natural and undistorted." 

This seems to apply to DSB (suppressed carrier) audio just as well. 

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How to shape audio in simple DSB gear?

How should we handle the need for frequency response shaping in simple DSB transmitters?  If we don't roll off the lows and the highs, we risk wasting a lot of energy on RF that will be outside the passband of the SSB rigs on the other end.  This is especially worrisome if we use those cheap electret mic's that seem to have response curves from DC to daylight (well, maybe not that high, but you know what I mean). 

This is not a real concern with SSB rigs, because that crystal filter keeps our signals on the straight and narrow (!) but with DSB rigs, what is the best SIMPLE way to keep the audio between 300 and 2500 hz?    Is there an alternative to the 741 op amp configured as an audio bandpass filter?  

73  Bill N2CQROur book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Il Fido -- A Simple Receiver from Italy

As part of a refresher course in Italian, I am reading a bunch of old radio magazines from Italy sent to me by Stephen.   There are some really wonderful projects in these magazines and I feel compelled to share them with the SolderSmoke community.  No full translations yet, but perhaps that would provide a good language learning opportunity.  For now, just schematics and drawings (aren't they beautiful?).   

This one is a simple crystal receiver with one stage of AF amplification.  It covers the AM broadcast band, the HF bands, and (apparently) VHF using a switch and three different coil/capacitor combinations.  You could make it a lot simpler by just building it for one band.  Looks to me like a nice rig for an Altoid tin. 

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C.F. Rockey, W9SCH, Homebrew Hero, SK

In podcast # 148 I recounted how I had turned to one of his articles, "Prolegomena for QRP Transmitters" for inspiration.   Just Monday Brian,  N1FIY,  e-mailed asking for info on how to find the article.  Today, Mikey,  WB8ICN,  let me know that on December 23, 2012,  QRP Hall of Famer C.F. Rockey,  W9SCH, had become a Silent Key.  

I've been a big fan of Rockey's writing and projects for a long time.  I was sad to hear that he had passed away, but I know that through his writing his influence will be felt in workshops and on the airwaves for a long time to come.  

Here's a sample of Rockey's writing:  http://n4trb.com/AmateurRadio/QRPp_Vol01_No03.pdf

Here's Rockey's obit:


Charles Franklin "Rock" Rockey, Jr.,
Whitewater, WI (1918 - 2012)
June 21, 1918 - December 23,2012
Charles Franklin Rockey, Jr., known as "Rock", age 94, of Whitewater, died on Sunday,
Dec. 23, 2012, at Fairhaven in Whitewater. Rock was born in Oak Park, IL, on June 21,
1918, the son of Dr. Charles F. and Ada (Nichols) Rockey. At an early age, he became
interested in ham radio, earning his amateur radio license at age 16. Operating as W9SCH
for more than seventy years, he made contact with ham radio operators all around the world. In 1996, he
was inducted into the QRP Hall of Fame. Rock graduated from Oak Park-River Forest High School in
1937. He enrolled in Elmhurst College, but interrupted his studies in 1942 by enlisting in the U. S.
Navy. He served as an aviation electronic technician in Port Lyautey, French Morocco, and in Naples,
Italy. After World War II, he returned to Elmhurst College, graduating in 1947.
Rock worked at Walhenius Institute instructing brew masters, then in the early 1950's, taught at
Milwaukee School of Engineering. From 1955-1979, he taught chemistry, physics and electronics at
New Trier High School in Wilmette, IL. He was also the faculty sponsor of the student radio station
WNTH.
On retirement, Rock and his wife (the late Frances) moved from Deerfield, IL, to Albany WI. Rock
became friends with the local farmers in Green County as a milk tester for the Wisconsin Dairy Herd
Improvement Association. In addition to contributing many articles to radio and scientific magazines,
Rock wrote two books: "Electrons, Atoms, and the World: Chemistry for the Young in Heart" and
"Secrets of Homebuilt Regenerative Receivers." He greatly enjoyed playing polkas on the accordion.
Rock is survived by his son, Joseph (Jane) of Highwood, IL; and two grandsons, Jonathan (Meghan) of
New York City, and William (Alexandria) of Esparto, CA.
A Memorial Service was held at Fairhaven in Whitewater. Memorial contributions are requested to
Fairhaven Senior Community, 435 Starin Road, Whitewater, WI 53190.



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Knack Story: Ryan's Rig

Bill,
      
... [I know] a young ham locally who suffers terribly from the
affliction of the "knack". Ryan, KJ6HBY, is 17, and an Extra class,
who earned his DXCC in a year. He is a great builder, starting out
building his first antenna a couple years ago by breaking apart an old
washing machine motor and unwinding it for the wire. Along the way he
has restored various rigs, i.e. HR10, S-38, IC707, etc and built a
BTX17 (17 meter version of the BTX20). Enclosed is a couple photos of
his latest creations. First, he hand carved a wood morse code key. It
actually feels and works well. Now he has build a single tube xmtr,
and after fussing with it, is pumping out 4 watts. Both of the kid's
folks are hams as well as his sister. I had an opportunity to visit
his shack the other day. It's a teenage ham's dream and a mother's
nightmare. Racks floor to ceiling with radios! If anybody has the
knack, Ryan does. Makes me think there is a future, we can sleep well
tonight.
73
Mike Herr
WA6ARA
DM-15dp
Home of The QRP Ranch

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

But Why Did Swamping Resistors Cure JBOT Oscillations?

OK,  so as I mentioned in SolderSmoke 148 (apprently with screeching in the background -- sorry) I managed to tame a bad JBOT oscillation problem by placing 680 ohm resistors across the primaries of the broadband transfomers in the JBOT.  Now I'm wondering how/why this worked, and what we could do to make this kludge unnecessary.  

Am I correct in suspecting that at the problematic frequency of 250 kHz, the one or more of the tranformers are self resonant, and that the resistors just bring down the Q of the -- in effect -- tuned circuit?  This lowering of Q makes feedback and oscillation more difficult, right?  

Here is the background.   Read from the bottom up.   

There is an old saying in Spanish:  "No hay mal que por bien no venga."   More or less this is the same idea as: "Every dark cloud has a silver lining."  Well, the dark cloud was my techno-agony with the parasitic oscillations (see my plea for h elp from yesterday).  The silver lining was the e-mail from Edgardo, LU1AR, in Buenos Aires that helped me get rid of them.    Edgardo advised putting a resistor across the primaries of the JBOT amplifier stages.  This is an old "lower the Q" trick, the idea being that lowering the Q might help prevent the amp from self-oscillating.     I used 680 ohm resistors.   First I put one across the primary of Q1.  No joy. Then Q2.  No luck.  Then I put one right across the primary of that big output transformer.  That did it!  The parasitics disappeared.   And I still get a nice 4 watts of output.  Thanks Edgardo.  I hope to make a contact with this rig today. 

The real silver lining in this story comes, however, in the form of Edgardo's blog site.  Wow, what an inspiring example of Argentinian Knack.  Radios, telescopes, auto-giros.  This guy is also into homebrew DSB rigs.  Wonderful stuff.  Check it out.  (Google will translate it for you, if necessary, but even if you don't read Spanish, the pictures tell most of the story.) 

http://www.lu1ar.blogspot.com.ar/

I put this URL blog up on the SolderSmoke blog.  

Thanks to all who sent advice and encouragement.  Merry Christmas! 

--- On Sun, 12/23/12, lu1ar  wrote:

From: lu1ar
Subject: [BITX20] Re: JBOT taking off at 250 kHz
To: BITX20@yahoogroups.com
Date: Sunday, December 23, 2012, 9:56 PM

First. You must secure the RF decoupling of +B line. Use a bunch of small capacitors in paralell 1n and 100 nF with 22 uF electrolitic.
Second: Use 1Kohm resistor in paralell with primary of the transformers. Begin with the driver, then the 1st amplifier and then the output transformer.
Let us know results.
Regards.
Edgardo Maffia LU1AR
Buenos Aires - Argentina

--- In BITX20@yahoogroups.com, "iam74@..." wrote:
>
> 
> 
> --- In BITX20@yahoogroups.com, Bill Meara wrote:
> >
> > I'm building my FOURTH JBOT and this one is giving me more trouble than all the others combined.   I seek the help of the group. 
> > Here are the details of my tale of woe:
> > 20 meter rig.  Double Sideband.   The JBOT is fed by a simple two-diode, trifilar toroid singly balanced modulator.  NO DIPLEXER TO SPEAK OF.  At the output of the balanced modulator there is a 1000 uH choke to ground and a .001 uF cap to the input of the JBOT.  AF amp is an LM-386.  VXO is a very simple MPF-102 one stage ceramic resonator VXO with no buffer stage.  7 element low pass filter (three coils, four caps). 
> > All the transformers are wound on FT-37-43 cores.  T3 is four such cores stacked 2X2.
> >  
> > The arrangement works beautifully into a 50 ohm dummy load.  But as soon as I connect it to an antenna (a dipole out in the yard, fed with 50 ohm coax) the output signal gets ugly.  
> > Looking at it on the scope, instead of the nice figure eight pattern (similar to the two tone test pattern of SSB) I get ugly fuzzy outcroppings from the peaks.  Looking at the signal more closely I can see that in addition to the 14.2 Mhz signal, there is another LF oscillation at around 250 kHz. 
> > I've been struggling with this.  I can't get rid of the LF oscillations. The leads are all short and the inputs are far from the outputs.   I've beefed up shielding, and decoupling.  I've sacrificed a chicken to Papa Legba. Nothing seems to help.  
> > I THINK the feedback/oscillation is taking place in the JBOT itself -- not through the
> > audio amp or the balanced modulator or the VXO.
> > I watch the RF and the AF inputs to the balanced modulator to see if there is any difference between the stable situation (with the 50 ohm dummy load) and the unstable situation (with the antenna),  I don't see any differences. 
> > I even put an antenna tuner between the final and the antenna anb made sure that the antenna looks like 50 ohms non reactive.  This seems to help a bit, but the ugly instability is still there. 
> > Help me! 
> > 73  Bill N2CQR    
> >
> 

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