DSB – Page 4 – SolderSmoke Daily News

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

SolderSmoke Podcast #148

SolderSmoke Podcast #148 is available:
http://soldersmoke.com/soldersmoke148.mp3
December 30, 2012

SPONSORED BY usedradiomall.com

— Hurricane Follow-up
— Subliminal Mind Control to Encourage Homebrewing (beep-beep)
— The Shortcomings of the All American Five Receiver
— Solid-Stating a Heath SG-6 (with Farhan’s circuit)
— VK3YE’s Beach DSB Rig
— Tek ‘scope connection to frequency counter
— Mod to W7ZOI/W7PUA power meter
— JBOTing my 20 meter DSB Rig — A Tale of Woe
— LU1AR “The Most Interesting Ham in the World”
— Billy’s Raspberry Pi
— Latest QST, SPRAT, Hot Iron
— Videos: Landfillharmonica, Knack in Sierra Leone
— Santa delivered a Soldering Station
— MAILBAG

A Christmas Present from Argentina

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

Woe is me! Why Podcast is Late: Parasitic Oscillations!

I’m building my FOURTH JBOT and this one is giving me more trouble than all the others combined.
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!
\

Another VK3YE DSB Rig

Hi Bill

A short e-mail from across the pond. Thanks for sharing the VK3YE link, so impressed I was that I have built one.

It receives great and puts out a nice looking dsb signal, looking forward to some good qso’s, ready to improve on it as we speak and looking to make a top band and 18m version also, love the site and keep up the good work…Ian

Ian Miller

G7FFV

Schematic of the VK3YE “DSB-On-The-Beach” Rig

Peter Parker’s amazing 8 transistor DSB rig (featured in an equally amazing YouTube video — see earlier blog post) has sparked a worldwide resurgence of QRP minimalism. There is now a lot more activity on the “Minimalist QRP Transceivers” Yahoo group (be there or be square). Steve “Snort Rosin” Smith WB6TNL is minimalist mentoring to the max — with his help it looks like more VK3YE transceivers will soon be on the air. Steve was kind enough to take the info from Peter’s video and turn it into a .pdf schematic (see above). It is in the file section at the Minimalist QRP Transceivers group. I was, of course, pleased to see the inclusion of a robust 7 element low pass filter.

Michigan Mighty Mites are also tickling the ether. I may pull out my single MPF-102 Yingling 80 meter rig. You can join the Minimalist group here: http://groups.yahoo.com/group/Minimalist_QRP_Transceivers/

8 Transistors = 40M DSB XCVR (on an Australian Beach)

Another brilliant rig from DSB guru Peter Parker, VK3YE. I really liked this one.
I loved his drawing of the circuit diagram — right there on the beach! Lots to be learned from this video. Thanks Peter!

Homebrew QRP Fun on 75 Phone

OK, I take back all of the bad things I said about the 75 meter phone band. I recently finished work on my Kick Panel 75 meter DSB rig. Last week I took portions of the multiband antenna that Solder-Lexicographer Steve Silverman sent me and turned it into a 75 meter dipole. It is now suspended in the trees above my house. With some trepidation I ventured out into the 75 meter ether. And, to my surprise I found friendly hams willing to give my 3 watt DSB signal a chance. The first contact was with K2WS. I had called Billy into the shack, thinking that I was just going to show him the beauty of a Direct Conversion receiver. To my astonishment I found K2WS calling CQ! On 75! Who knew? I gave him a call and — BINGO — we had a wonderful QSO. Alan is at the other end of the tech spectrum — he was running a Flex Radio. With that rig’s panoramic display he was able to SEE that I was running DSB. Very cool. Billy was duly impressed.

Yesterday morning I ran into a very congenial bunch of guys from the Gallups Island Radio Club. They welcomed me into the group and allowed me to join in the roundtable. Thanks guys!

Then came the icing on the cake. This morning I heard a familiar voice calling together the Mid Atlantic chapter of the Quarter Century Wireless Association. Could it be? Yes indeed, it as an old friend, Ray, a guy who had brought me into the QCWA group during our previous stint in Northern Virginia. I checked into the net and had a great time.

Above you can see the latest version of this long-evolving rig. It has a built-in speaker. Below you can see it with the top off.

Three cheers for 75!

Kick Panel Progress; Podcast Delay

I’m kind of behind on podcast production, but once again I have a good excuse: I’ve been melting solder. I decided to finally finish the Kick Panel DSB rig that I started building back in London. It is built on a kitchen cutting board purchased in a Dyas store in Windsor. The cabinet is fashioned from an aluminum kick panel for a door (a pub door!).

I originally intended this to be just a transmitter (for use with my trusty Drake 2-B) but it is so easy to add a direct conversion receiver to a DSB rig that I just threw together a version of the NE-602 LM386 Neophyte receiver and hooked it up to the 75 meter VFO. It sounds great. I love DC receivers. They seem to connect you directly to the ether. And now I’ll have a complete 75 meter DSB station in one box.

This morning I tested the balanced modulator (singly balanced with two diodes). DSB is being generated. All I have to do now is put a little 6 db pad between the modulator and the amplifier chain, then work on the antenna a bit and I should be on 75. The amplifier chain dates back to the period when Mike, KL7R, and I were using LTSpice to design amps….

I was very pleased to include in this rig a part that Michael, AA1TJ, sent me: I have a little 10.7 MHz IF can in the front end of the RX. A cap allows it to tune in 75 meters. Thanks Mike!

I hope to get a podcast out this weekend (if the computers cooperate — the Sony Vaios “light bulb-repaired” laptop finally gave up the ghost last weekend.)

The ZL2BMI DSB Transceiver

Oh man, I’ve been a fan of this rig for many years. I first read about it in the pages of SPRAT. Today I stumbled across what appears to be an on-line version of the instruction booklet prepared by Eric Sears, ZL2BMI. Lots of lore in there. Lots of soul in this rig.

This site has three documents describing the rig. All three are a lot of fun: http://www.mightymessage.com/

Three cheers for Eric Sears! Hip-hip…

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

Kick Panel Rig: EXPOSED!

There it is, sans kick panel. You can see the breadboard (a real one!) on which it is built. The box in the center has the oscillator circuitry (currently on 75 meters, but subject to change); the box is elevated a few inches by two pieces of wood — I do this so that the frequency control will be a comfortable distance from the table! HB-ergonomics! The AF (mic) amp is in the lower left (just a 741 op amp). You can see the adjustment pot of the balanced modulator behind the mic amp. The low pass filter of the PA is visible on the right (rest easy Steve Smith!). The switch on the right is T/R. The red switch is “spot” (or in the UK “net”).

I thought I was having some trouble with RF getting into the mic amp. The audio out from the mic amp looks a bit distored when I have the oscillator and PA circuits fired up. I worked on it for a while, beefing up the decoupling on the 12 volt lines, but that didn’t change things. I’ve decided not to worry about it, because the output signal from the final looks clean, and the signal sounds good on my trusty Drake 2-B. It may have been a test gear problem — the ‘scope probe may have been picking up some RF and may have been uglying up the AF wave form.

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

Kickin’ the Kick Panel to 40?

Thanks for all the suggestions re what to do with the kick panel rig. Steve “Snort Rosin” Smith (pictured above) suggested getting a 9 Mhz crystal filter and building an SSB rig for 75 and 20 meters. I was tempted Steve, but remember, simplicity is a virtue, and DSB makes a transceiver REAL simple.

Craig and OM KWJ suggested 10 meters. I hear you, but I’m looking for a rig that I can use for pre-dawn rag chews, and at that hour 10 is often a white noise generator.

Bruce wants me to put it on 475 KILO hertz. I dunno about that one Bruce — sounds kind of lonely!

As I thought this over, I remembered a comment from the true guru of DSB: Peter, VK3YE. In one of his inspiring videos, he mentioned that 40 meters is his favorite band for DSB rigs. It is 0545 local and I am hearing a lot of activity on 40. It all sounds very friendly. Some DX coming through… I could make a stable VFO for 40. Then I add a little DC receiver and I’m in business. So I’m leaning towards 40 meters at this point.

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

Back to the “Kick Panel” DSB Rig

OK, so now that the 17 meter rigs are fully operational, I am turning my attention to another homebrew rig from days gone by: This is what I call my “kick panel” DSB transmitter. You see, the metal cabinet is made from a piece of metal intended for placement on the bottom part of a door — so that people (in a pub, I suppose) won’t wear out the door with their feet. I built this rig in my attic shack in London. The breadboard on which it is built is from a Dyas store in Windsor, England. The top of the box comes from a computer I found discarded on the mean streets of South Kensington. I think I originally built this thing for 40 meters, but later switched the VFO and the low pass filter to 80 meters. This rig is discussed in the opening pages of the London chapter of “SolderSmoke — Global Adventures in Wireless Electronics.”

The oscillator is running as it should and the RF amplifier chain (my design) is amplifying (and not oscillating!). The balanced modulator is doing its balancing act quite nicely. The only problem seems to be with the the little op-amp that have in there for the AF — it seems to be distorting the audio quite a bit. That shouldn’t be hard to fix.

There is room in the box for a simple Direct Conversion receiver, so this box will become a DSB/DC transceiver.

But here is my problem: I find myself unenthusiastic about working on a rig for 75 or 80 meters. On the one hand those frequencies are good for me — I’m an early riser and I need a rig that I can use in the hours before sunrise. But 75/80 always seems to be an unfriendly place — lots of frequencies that seem to be “claimed” by groups who don’ t seem interested in meeting newcomers, not a lot of people calling CQ…

I can put this rig on another HF band. 40 seems nice, but I have plenty of old boatanchor stuff that covers 40. I don’t need another 17 meter rig. I already have a homebrew 20 meter DSB rig. How about 12 meters? Or 10? I know they are both dead in the early morning, but better times are coming, right? What do you guys think? To what band should I kick the kick panel rig?

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

The New 17 Meter Phone Station

There it is. The SSB station has moved from the workbench to the operating position. I have it situated above the DSB rig, but both of them are hooked up and ready to go. My crystals (and the FCC) allow me to go from 18.110 to 18.128 with the DSB rig. The SSB rig goes from 18.128 t0 18.168 Mhz.

I’ve been having a blast with this setup. I’m running into old friends who I haven’t talked to in one (or in some cases two!) solar cycles. I talked to Lee, G0DBE this morning — our last contact was June 2000 (just before our departure from the U.S.) Yesterday I talked to Jorge, HK4CZE — I hadn’t spoken to him since 1995! Lots of U.S. contacts too. People really like it when I turn off my linear and go to 1 watt; they can almost always hear me with the 1 watt.

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

SolderSmoke Podcast #140

Universal VXO

A new episode of the SolderSmoke podcast is now available:

http://soldersmoke.com/soldersmoke140.mp3

January 9, 2012

— Santa Claus: Ice Skates, Brownie Box Cameras, and Piper Cubs
— On the air with 17 Meter Azores DSB rig
— Seeking balance (with antennas)

— 23/24 recycling of Azores SSB Rig: Adding Soul to the Old Machine!
— Attacked by my own soldering iron!

— RG-174, swarf, and other insidious threats to the homebrewer
— Inspiration from QRP Quarterly
— G3RJV validates the D-104
— T/R admonition from the 1973 Handbook (words to live by)
— The Woz on electronics and teenage social isolation
— BANDSWEEP: Straight Key Night at WA6ARA
— MAILBAG
Our book: “SolderSmoke — Global Adventures in Wireless Electronics”http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmokeOur Book Store: http://astore.amazon.com/contracross-20

SolderSmoke Podcast #139

December 3, 2011

http://soldersmoke.com/soldersmoke139.mp3

Halloween, Thanksgiving, and Billy’s Birthday (on the range!)

Astro-Knack: CCD camera in the telescope. Solar astronomy.

Winter approaches: Shack heating by Heath, Halli, Hammarlund and Drake.

2B troubles on 17 meters.

Rig Re-Cycling: Rebuilding 17 meter rigs from the last solar cycle.

Azores DSB re-build: Oscillator troubles then adding a JBOT.

Manhattan style construction and the need for urban renewal.

Book Review: Steve Jobs. (Woz has the Knack!)

MAILBAG

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

Secret Listeners — The Voluntary Interceptors

Jim, AL7RV, and several others sent me the link to this really interesting video about the British radio amateurs in WWII. Real “stiff upper lip” spirit in this video. Musn’t grumble! Great stuff from Great Britain: http://www.eafa.org.uk/catalogue/5108

That regen receiver they showed looks a lot like the beast that I brought back from the UK with me. Once again, I am hearing the siren song of the diabolical regens….

Progress continues on my Indian-ized Azorean DSB transceiver (with JBOT amp). I now have the amp nicely stabilized (thank God!). Now I just need to get the output from the balanced mod close to the 1 mW PEP level needed by the amp. Should be done soon. And my cold seems to be going away, so maybe I’ll be able to share my tales of JBOT derring-do in a podcast this weekend.

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

A Re-balanced Modulator for my Re-cycled Rig

My effort to bring my Azorean 17 meter DSB rig back to life continues. This is proving to be harder than I thought. I’m still taming my version the JBOT amp. It still seems to break into oscillation — I think the oscillation freq is around 1 MHz. But I am making progress.

I had to go back and work on the balance modulator circuit. I really like the simple two diode singly balanced mixer circuit. But my original Azorean board had, like the oscillator board, been through a few too many rounds of modification and repair. I decided to start over. See above. I even came up with my own little innovation on this circuit. Doug DeMaw’s original design called for a 100 ohm pot at the junction of the two diodes, with the signal coming off the tap. You adjust the pot to balance the circuit and null out the carrier. But I didn’t have a 100 ohm pot. Lots of 1K controls were available, so I put in two 50 ohm resistors in place of the pot, then put the 1k pot between the diodes, with the tap to ground. This balances things out nicely. See below.

I hope to get a podcast out next week, but I’ve been suffering from a nasty headcold that would have introduced all kinds of weird audio effects.

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

Sunspots! QRP DSB contacts on 17 meters

You can see here why I had so much fun in the summer of 2001 with my Azorean Homebrew QRP DSB rig. And why I am now re-CYCLING (get it?) and refurbishing the 17 meter gear that I built last cycle.

I’ve had the DSB rig on the air yesterday and have worked seven stations (2 watts peak DSB to a dipole).

Back to the Future! Someone on QRP-L said the SFI was recently at 180! Go Sol!

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