Digitizing the Barebones Superhet

I did this for Pete.  And I did it to start out the new year with something different.  And because I needed the crystal for my beloved BITX and didn't want to buy more crystals. 

After successfully broadening the filter in my Barebones Barbados Superhet (originally built by Dale Parfiit W4OP) I decided to replace the VXO with an outboard Arduino/DDS device. Nothing new in that  (I was playing with this back in October), but in what I think is a symbolically significant twist, I pulled out the tuning cap for the VXO and, in the hole left by the tuning control, replaced the knob with a BNC connector.  That connector now carries DDS signals into the receiver.  The crystal was at around 23.125 MHz -- that's why the LCD display is showing 23 MHz.  

It works great.   I was listening to the DX station in Iran this morning.  

Here is a video of the October 2014 experiments: 


   

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Colin Finishes His BITX

Wow, that is one beautiful BITX.  Nicely done Colin.  But I must say that you are exhibiting an almost inhuman degree of patience!  Who needs a case?  Fire that thing up and make the traditional "still-on-the-workbench" initial contact. 

Hi Guys,

I loved the last SolderSmoke, it was another great episode. It really does amaze me, that a few years ago, hams were saying that it was too difficult to build your own gear that would be anywhere near to the commercial stuff, but here we are with Arduinos etc bringing powerful functionality to the masses. I couldn't have imagined building an SSB rig with a pretty and functional LCD screen when I started in ham radio.

Bill, first regens, now SDRs? Amazing! I exchanged a few words with George Dobbs about your change of heart towards regenerative receivers, he seemed genuinely pleased. :)

Pete, your Si5351 work with the pretty displays is cool, I can see me getting pretty hooked! I have the Si5351 board, Paul M0XPD advised me to buy it. I'd love to build another SSB rig in a smaller box for regular SOTA activating. I must look into the pretty little displays and have a play with the Si5351. I notice that Hans Summers has now put out a cheap Si5351 based kit, handy for us guys in Eu. http://www.hanssummers.com/synth.html

I finished building my BITX board yesterday but wanted to have a sleep before applying power! Today I carefully checked the circuit for errors and found none, phew! I fired the rig up gently, watching the current carefully. I wound up the TX bias to 50mA as stated in the MKARS80 instructions, all went well. I plugged in the mic and spoke - BANG! - Everything went off. Oops - I had used a 500mA fuse for initial safety and forgot to swap it for the bigger one! I fitted a 1.6A fuse and hey presto, all was fine. I was absolutely amazed and to be honest, rather proud of myself. I think the TX is a little bit too hot, my meter is showing about 6W on voice peaks- eek! The rig seems to be perfectly behaved though, no wierd effects seem to be happening. I can just turn the bias down a bit, right?

Anyway, I was happy with my progress so I finished for the day. I still need to investigate and probably tweak the carrier suppression.

I spent a short while talking into a dummy load, using my FT817 to monitor the transmission. My 2yr old son was interested in my voice coming out of the 817'sspeaker!

Thanks for all the guidance and help along the way, I'm elated that I've built a voice rig that works! I've attached a pic of my finished board, I only just squeezed the circuit on, but isn't she pretty? :-)

Can't wait to get the rig built into it's case and score that first QSO.

73, Colin, M1BUU

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Kansas Mighty Mite

Greetings Bill

I have been a bit ill,  but finally found some time to work on my Meara Mighty Mite, which i wish to call it as it was by the grace of Bill Meara that I am able to play a part in the Colorburst Revolution could begin.

I just wanted to share some pictures from the bench of my progress, which is not yet fit for the ether.

I originally wanted to build a really unique design. I have a tendency to complicate things. The more simple it is, the more complicated I tend to make it. After a lot ambitious failed starts, I decided that the best thing to do is to keep it simple. In fact, I would say that I was "over-noodling" this one. So I just started building.

I use copper clad PCB, which I get for very cheap from an ebay seller named abcfab. I use a tool I made to cut islands by hand. Information can be found about this method on my blog.

I am almost embarrassed to share photos of my build, especially after seeing such wonderful designs as you have featured on the webpage. But the excitement is just to great, so here it goes:

I build ugly circuits and I'm proud of it.

I haven't build the LPF yet and wouldn't put it on the air without one. 

Thanks for all the great inspiration and for inspiring a revolution of colorburst liberation!

I want to share something from Solid State Design for the Radio Amateur, W7ZOI & W1FB, page 19

"All of the circuits shown are aimed at reasonable stability, but have relatively low output power. It is possible to bias many of these circuits higher to obtain outputs of up to perhaps 1/4 watt. However, thermal stability is often severely degraded, chirp is introduced if the oscillator is keyed, and the user stands a chance of damaging the crystal from excessive rf current. It is not recommended that a single oscillator stage be used as a simple transmitter. The addition of an amplifier is so straightforward, and the system efficiency is so much better, that the minimal simplicity is not of value."

That may be true, but the Mighty Mite is for learning and getting our feet wet. Still it may be interesting to point the above out or talk about it.

Also, I'm curious to know which schematics everyone is using. The famous Easy QRP transmitter on the QSL page, perhaps DeMaw's from QRP notebook (available on archive.org in pdf form for free).

73, keep your iron hot and stay fluxy,

-KE0BFF, Lawrence KS.

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Pete's Beautiful Tiny Color Display

Oh man, this is the kind of thing that lures me ever deeper into the digital morass.  That would be hard to do with my beloved discrete analog circuits!    Be sure to note the size (it is sitting on the top from a pill bottle -- you can also look at the pen for a size reference). It is 1.25 inches by 1.25 inches.  Pete has it working with the Si5351 software.  As you can see there is still room at the bottom of the display.  Pete notes that an SWR readout is possible.  And Pete got this device for FIVE BUCKS! 

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

Broadening the Barebones Barbados Receiver

I've been working on the crystal filter of the Barbados Barebones Superhet receiver.  This was designed by Doug DeMaw in 1982.  This one was built by Dale Parfitt W4OP and then repeatedly modified by me.  It is now on 17 meters with a crystal-switchable VXO.    Earlier I had made a very crude attempt to broaden the filter from its original very narrow CW configuration.    This week I did this again, but this time I actually characterized the crystals and used Wes's LDA and GPLA software (from EMRFD) to design the filter.  

I played with the capacitor values and finally got the 3 kc bandwidth I wanted, but I'm having trouble getting rid of the ripple.   I know this is dependent on the impedances at the two ends.  The programs say I need 2000 ohms.   

I'm kind of puzzled about how Doug DeMaw did this with his original design.  For his crystals and his 250 Hz (!) bandwidth he said he needed 450 ohms.   He used 4.7:1 turns ratio transformers at either end and said that by putting 10k resistors across these transformers he got the needed impedance.  I can see how this would work looking into the gate of the 40673 IF amp, but looking back at the drain of the 40673 mixer, I'm not so sure that that would yield 10k. (See schematic below.)

But who am I to doubt Doug?   So I assumed he was correct about the 10K and I re-wound the transformers with a 2:1 turns ratio, thinking that would get me closer to the needed 2k.   But the ripple is still there.  I guess I could use a return loss bridge at this point... 

I don't know whether this is worth messing with anymore.  The receiver sounds nice.  The 3kHz bandwidth gives it a nice sound, and the ripple doesn't seem to be noticeable  That FAR circuits board is tightly packed and difficult to work with.  So, should I leave good enough alone, or should I proceed with fanatical ripple eradication.  Any advice?

BTW:  Why is it that receivers always seem to sound better when opened up (as above) on the workbench?  

 

 


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

Kai's Redwood Mighty Mite with Poker-Chip Hacksaw Key

And Check out Kai's homebrew key:

Hi Pete,

 

  Thanks for your kind words.  I really enjoyed the MMM project, first analog oscillation .  Your right about the homebrew key being a hacksaw blade and a few pieces of plywood.  The knob is an old poker chip.  You can adjust the spring tention by moving the blade in and out of the plywood.  Travel can be adjusted by raising and lowering the bolt under the blade.  I needed something for CW and wanted to stick to the ham maker thing.  As for me sending lefty, I do that so I can switch when the right gets tired or I need to hold ipod for video.  Thanks for what you add to soldersmoke.  73.

 

Kai

Ps I will send picture of key.

On Monday, January 12, 2015, Pete Juliano <jessystems@verizon.net> wrote:

Hi Bill,

 

Wow –so cool! I was impressed with not only his M^3 but the homebrew key and sending with his left hand.

 

It would be nice for Kai to send us his details for the key.  It looked like a hacksaw blade sandwiched between some plywood blocks of wood and some sort of plastic tuning knob from a defunct transistor radio as the key knob. Now that is what I call homebrew –elegant and it works well!

 

73’s

Pete N6QW

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

SolderSmoke Podcast #170 Double A DX-pedition, SI5351, Mighty Mites, Phasing Dreams

SolderSmoke Podcast #170 is available: 

http://soldersmoke.com/soldersmoke170.mp3

Bill's Double A, DSB, Dipole, Dominican DX-pedition.  
             Living the "How's DX?" Dream
Seeing the Southern Cross with Soviet Binoculars
Pete goes remote 
SI5351 a chip with a lot of potential
Pete's experiments with Nokia LCD displays 
Michigan Mighty Mites around the world
               The Postal Stream Roller
Steve Silverman's very kind variable cap offer
MOXON modeling with EZNEC
Aspirations for 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