Swamping or Q-Killing

Sounds like some new TV series on the Discover Channel, doesn't it? Actually it refers to efforts to stabilize oscillators by reducing the Q of components that may be helping to turn the amplifier into an oscillator.   A 300 ohm resistor across the primary of the output transformer on my most recent version of the JBOT amplifier recently solved my instability problem.  As part of an effort to understand how and why I came across a CQ magazine article by Doug DeMaw.  The relevant passage appears above.  

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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/


 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

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