Been There, Done That: "...he begged his oscillator to osc and his amplifiers to amp."

This ad is from the December 1931 issue of QST.   This copy has a LOT of mileage on it.   In 1993 or 1994, David Cowhig (now WA1LBP) was living in Okinawa Japan and was operating as 7J6CBQ.   I was living in the Dominican Republic and operating as N2CQR/HI8.   We were both contributing to a 73 magazine column (as "Hambassadors"!) and we were both in the Foreign Service.   I wrote to David -- he wrote back, sending me some old QSTs, including the one from which the above ad is taken.

This ad shows that many of the homebrew/troubleshooting woes that we face today are very old.  And that having access to good technical books is very important when you are trying to overcome these difficulties.  

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Peter Parker Reviews a DSB Kit and Presents Cool Mods (3 Videos). Also: Why DC Receivers Don't Work with DSB sigs. (It doesn't seem fair!)

I found Peter's recording of the DSB signal being received by a DC receiver to be very interesting.  We've long been warned about the very ironic incompatibility of DSB rigs and DC receivers. 

In "W1FB's Design Notebook," Doug DeMaw wrote (p 171):  It is important to be aware that two DSSC (DSB) transmitters and two DC receivers in a single communication channel are unsatisfactory.  Either one is suitable, however, when used with a station that is equipped for SSB transmissions or reception. The lack of compatibility between two DSSC (DSB) transmitters and two DC receivers results from the transmitter producing both USB and LSB energy while the DC receiver responds to or copies both sidebands at the same time."     Bummer.

In essence, we've been warned that the simple DSB/DC rigs we've put on the air cannot communicate satisfactorily with similar rigs.  We are, it seems, doomed to only speak with SSB/Superhet rigs.

The later portion of Peter's second video allows us to hear just what happens when we try to listen to a DSB signal with a DC receiver:  It sounds, well, unsatisfactory.   I was trying to figure out why.  Here are some ideas:

Simplify things by assuming we are transmitting only a single audio tone of 1000 Hz through our DSB transmitter.  The rig's VFO  is at 7100 kHz.  The 1 kHz tone results in signals at 7101 and 7099 kHz.  Along comes somebody with a Direct Conversion receiver. If he were able to put (and keep) his receiver oscillator on EXACTLY 7100 kHz,  he would end up (by taking the difference products from the product detector) with  a 1 kHz tone resulting from the 7099 kHz signal AND a 1 kHz tone from the 7100 kHz signal.  But there would be phase differences between these two signals, so you would end up with a less than pure 1kHz tone. (Did I get that right?)  And if -- as is likely -- your local oscillator is a bit off frequency you'd get a real mess.  If for example the local oscillator was at 7100.1 kHz, you'd have tones at   900 Hz (7100.1 - 7101) and 1.1 kHz (7100.1 - 7099).      Yuck.  

You might think you could just use the local oscillator in your DC receiver to replace the carrier in the DC receiver, turning it into an AM signal, then use an envelope detector as you would with any AM signal.  But not so fast!  For this to work your local oscillator would have to be not only at the same frequency as the original carrier, but also in the same phase.  That is hard to do. (Hard, but possible -- that is what they do with synchronous detectors using phase locked loops.)

I think you can actually hear many of the DC-DSB problems as Peter tries to tune in the DSB signal of VK7HKN using the DC receiver in the MDT transceiver.  It is indeed unsatisfactory.    But don't worry.  It is highly unlikely that when using a DSB rig you will encounter another DSB rig.  I speak from experience on this.  Pity.



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

Tonight is the "Night of Nights"

 

 

From "The SWLing Post" we learn that tonight may be the last opportunity for us to listen to CW from U.S. Coast Guard stations:

 

http://swling.com/blog/2015/07/night-of-nights-xvi-july-12-2015/  

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

Interview in China with Arduino's Massimo Banzi: "Be nice!"

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

KC2THY's Mighty Mite - A Thing of Beauty

Bill,

I have been a listener of the Soldersmoke Podcasts for several years now and I have worked my way through most of the back episodes of the podcast. It is terrific production and has taught me so much about radio electronics. I have also read all of your books. Thanks for what you do for this hobby.

Attached is a photo of my recently completed Michigan Mighty Mite.  The FFT function in my scope confirms a good clean signal and it sounds great when I listen to it on another radio. I am sure that the photo depicts one of the worst looking MMMs to date. I built it on a solderless breadboard as I have never built anything using Manhattan or ugly construction techniques. It was a great introduction to very basic homebrew electronics.

Thanks again,

John Stockman, KC2THY

Morristown, NJ

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SolderSmoke Dreams (and Nightmares)

 

 

 

Bill,

I've just listened to Solder Smoke episodes 168-170 and I'm following your advice.  My Michigan Mighty Mite sits on my desk only lacking the variable capacitor.  I was amazed that I had everything needed in my junk box!  Including a 3.575611 crystal.  

Last night I dreamt that the incomplete breadboarded Mighty Mite was beckoning me.  I walked over to the desk and I had the palpable sense that the Mighty Mite itself wanted to oscillate, as if by arranging the components in this way I created something alive.  I touched the tank and it began oscillating by itself without the variable cap.  The universe seemed complete in that sweet moment.  

When I awoke I attempted to replicate the event unsuccessfully.  haha.  I definitely need a variable capacitor....  

Regards,

Bryan 

KV4ZS

 

 

Bryan:   You might be able to make your dream come true with a fixed value cap.  Do you have something of about 150 picofards?    Try that.   It might work.   Or do you have an old transistor radio that could sacrifice its tuning cap?   
 

I have had similar homebrew dreams.   Well, nightmares mostly.   I dreamed that in a fit of frustration I took ALL the parts off the BITX 17 board.   That was a scary one.   I'll cc Steve Silverman to see if he could help with the variable cap.  

73  Bill

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The Wizard of Warrenton: Jerry KI4IO

 

That's Jerry KI4IO of Warrenton Virginia sitting in front of truly impressive collection of homebrew gear.  The cream-colored box above the Vibroplex is Jerry's new 7 MHz phasing transceiver.   He has a wonderful write-up of this rig in the qrp-tech group files section:

https://groups.yahoo.com/neo/groups/qrp-tech/files/KI4IO/

You may have to join the yahoo group to access it, but believe me, it is worth it.  Jerry took a very eclectic approach to circuit selection and came up with a very cool rig.  Lots of soul in that new machine!  Here it is in breadboard form:

 

 

Jerry worked in U.S. Embassies as a communications officer and is obviously a member of the International Brotherhood of Electronic Wizards.  From his QRZ page:

 

While in India I was licensed at VU2LHO and worked a lot of US hams with a 135' flat-top and open-wire feed. I had the antenna strung between two bamboo towers atop the embassy housing 2ND-story roof-top. I also put up a 3/8 wave vertical on the roof for 10 meters. That little antenna had 110 radials stapled into the roof scree and worked very well! The rig was a HW-101. I was in Kathmandu, Nepal from early 1980 to late 1982. I could not obtain a license there, but became good friends with Father Moran, 9N1MM, and would often spend time up at his place putting his Drake station on CW. Pretty cool being real DX!

 

Warrenton, Virginia is not far from my QTH (it is the birthplace of Cappuccio the wonder-dog). 

 

FB Jerry. 

 

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