iPhone Direct Conversion Receiver with Variable Ceramic Oscillator

A while back Bob N7SUR got us talking about winter projects.  Receivers.  Of course, Pete and I quickly went down different paths.  Pete is making great progress with lots of interesting digital circuitry.  He is going over to the dark side. Check it out here: 

http://n6qw.blogspot.com/2017/11/21st-century-homebrew-sdr-ssb.html

I went with simplicity.  Extreme simplicity.  Direct Conversion (thanks Wes!).  Discrete components.  No chips.  Analog Oscillator.  40 meters -- monoband.   

Schematic updated 29 November 2017

There it is.  You can click on the picture to make it larger. Here is an outline of the circuitry: 

-- Single tuned circuit bandpass filter preceded by a simple pot that serves as a gain control. 

-- JFET RF amp

-- Singly balanced passive mixer inspired by F5LVG's RX-20 in SPRAT 100.  For the coil I used one of the many trifilar toroids that Farhan gave me. 

-- The local oscillator is the coolest stage.  I used a 7.37 MHz ceramic resonator and a circuit inspired by Miguel PY2OHH. With a polivaricon I can tune the entire 40 meter band. I put a reduction drive int here to make tuning easier. 

-- The AF amp is an op-amp free design.  It works well into ear buds or into a computer speaker. 

-- Perhaps in an effort to catch the attention of the younger generation, I built it into an iPhone box.  

Please let me know if you spot any flaws in the circuit, or see any places where it might be improved. 

More to follow.   This prototype is now in the mail, en route to my nephew John Henry who will be testing it for me. 

China and SETI: What Happens if China Makes First Contact?

Here is a really amazing article from The Atlantic.  It is very thought provoking.  Mind blowing.  Strongly recommended. 

You can read it here: 

https://www.theatlantic.com/magazine/archive/2017/12/what-happens-if-china-makes-first-contact/544131/

Or you can listen to a reading of it (like a podcast) here: 

https://soundcloud.com/user-154380542/what-happens-if-china-makes-first-contact-the-atlantic-ross-andersen

Thanks to Mike Rainey AA1TJ for alerting us to this. 

Jeff Murray's Grumpy Audio Guy from 40 meters

I've talked to this guy several times.  He usually waits until I'm testing a new rig.  

https://www.facebook.com/6sj7jeff/videos/10208309648978285/

I'm sure Pete has worked him too.  

Amazing Homebrew/Boatanchors QSOs on 40 --Six solder melters in a row!

Al W8VR

After a day of happy tinkering with the Direct Conversion receiver I've been working on, I turned off the soldering iron and got on 40 meter SSB with my BITX Digi-Tia. 

First -- Steve W4IJ came back to my CQ.  Steve is a boatanchor enthusiast and has written for Electric Radio magazine.  FB. 

W4IJ Boatanchors

When Steve signed off, I got into a contact with Pete W8NBO.  We had spoken before and he had told me of a homebrew transmitter he'd built as a kid.  This time I asked for details: It was a 6AG7 oscillator to a 6L6 amplifier.  He ran it with an S38 (brave man!).  He described what must have been a very painful effort to hack (literally) the needed holes in the transmitter chassis using just a spike, a hammer and a file.  I told him this brought back my memories of similarly painful chassis work (mine was for a power supply for a Heath HW-32A).

At this point we were joined by Arnie, W2HDI.   Arnie's rig is in Stowe Vermont, but he was running it remote from the South of France where he and his wife were celebrating their 50th wedding anniversary.  Arnie shared with us memories of similar chassis pain -- his were related to an external modulator that he built for a DX-40. I think he said that all he had was a hole punch and a file.  Oh, the humanity! 

Then Al W8VR joined the conversation.  Al said that he's been in the game so long that his early rigs were built using cigar boxes as chassis.  I pointed to a connection:  I noted that my BITX rigs are enclosed in what could be considered cigar boxes.  Al's QRZ page picture has a magnificent AM rack rig that he said was actually built twice.  There is also an HRO-60 in the picture.  FB. Check it all out at Al's web site.  Click on the mic for the write ups, the key for the pictures.  http://www.w8vr.org/

Then Dennis K0EOO called in.  Holy Cow!   Dennis and I spoke not long ago.  You may recall my enthusiastic write up of his beautiful 1974 SSB rig: 

http://soldersmoke.blogspot.com/2017/08/k0eoo-homebrew-ssb-in-1974.html

and

http://soldersmoke.blogspot.com/2017/08/more-on-k0eoos-amazing-homebrew-ssb-rig.html

This was almost too much.  Rarely will you spontaneously come across so many hams who have melted so much solder.  FB. 

Icing on the cake:   When I returned to the bench, I fired up the DC receiver and heard Mike KN4EAR talking about his BITX40.  I switched to the Digi-Tia and gave Mike a call.  He reports making many contacts with his rig. FB. 

TRGHS. 

Beautiful QSL by Jeff Murray K1NSS

Here's a reminder of the amazing art work of Jeff Murray K1NSS. 
You can have him draw a QSL for you:   Go here:
https://www.jeffk1nss.com/hamgraphics/

Jeff writes: 

Well, I got as far as high school intermediate algebra and then I saw a squirrel.

Thank goodness others like Ken N2WWD were paying attention and went on to surf gravity's rainbow of flight dynamics, all in a day's work and play for rocket scientists. Tandem surfing and professional activities somewhat aside, Ken is also actively involved with ARISS, i.e. Amateur Radio on the International Space Station, the group guiding ham radio operations aboard ISS. So Kelvin cool to work with Ken on this New One, with Ken cooking up a special Easter Egg for all you galactic hitchhikers!

What might I draw with you?https://www.jeffk1nss.com/hamgraphics/

Jan's FB Slovakian SMD TIA Boards

Hello,

I have put up my SMD version of the TIA amplifier boards online, in case

someone wants it. The files are here:

http://janoc.rd-h.com/archives/574

and direct OSHPark order link:

https://oshpark.com/shared_projects/2V9cuV1M

73!, Jan

Peter Sripol Takes Off In His Homebrew Airplane

Termination Insensitive Amp Boards from VU3ZMV -- Eagle Files

Bill: 

Here are the eagle file data for the TIA, that I love to use as incorporated in Farhan's ubitx.

The TIA , I tried to realise two such on a double sided pcb measuring less than an inch.

 It mounts one TIA on each side.  I suppose one could simply homebrew.

It has provision for 5 pin berg (male right angle) and would be easy to plug into the main board. We may not need PTH except the connector. We can use bare pins soldering on either side.

Here are the eagle files I created.

Sarma's TIA Board

Sarma's TIA schematic

regards
Sarma

 vu3zmv

The Ham-Radio Thermatron Roots of Silicon Valley

Hack-A-Day had an excellent piece on tubes and Silicon Valley this week.  Makes me want to get the book "Secret History of Silicon Valley." 

https://hackaday.com/2017/11/02/silicon-valley-was-built-on-tubes-of-glass/ 

Note above the Klystron prototype mounted on a wooden board.   These guys clearly had THE KNACK. 

Another Source for BITX Amp Boards - AG4ZP

Thanks for sharing (the infor on the modular BITX boards). I actually had a similar idea a number of years ago and designed a small PCB for the ubiquitous BITX amplifier design. I have the project shared on OSH Park and you can get three of them shipped for $5.

The project is shared here.
73,
Ryan AG4ZP

https://oshpark.com/shared_projects/6mnfQQ6e

Cliff Stoll on Software, Snake Oil, and the Creation of Real Things

"I guess today's experimenters build things in software, without ever touching a soldering iron. The hocus pocus is inside the program.  It's cleaner this way -- nothing to burn or zap, and you don't need a voltmeter... What happened to home-brewed and breadboarded circuitry? Where's the joy of mechanics and electricity, the creation of real things?  Who are the tinkerers with a lust for electronics?"   

From "Silicon Snake Oil"  1995 by Cliff Stoll  

Modular BITX Boards

https://hackaday.io/project/20067-puzzle-radio-building-blocks

From Mike W0MNE to the BITX20 group: 

Good afternoon,

I've had a few emails regarding the modular BiTX build and I probably should clarify a few things.  First, ON6RF has posted his gerber files on the link at Hackaday.com that I originally posted - just scroll down to around the middle of page to the 'Files' section.  Since he has placed these in the public domain they are available to anyone that cares to download them.  But, because it is HIS work, I'm not comfortable forwarding the files myself.  I don't know if he follows it but I'm sure that he can keep track of how many downloads have occurred and I'm certain he would be gratified to know that his work is appreciated.  What I have offered is to make my gerber file for the motherboard available and, if I can manage it, I will post it here in the files section in the Modular BiTX folder.  I will also include the pdf files that I created for each of the module showing component placement and values.

As for acquiring the circuit boards, as I stated earlier, I use PCBWAY.com for production.  Their prices are excellent and the turn-around time is hard to beat.  The cost of the panelized pc board for me was $5.00 for 10 boards with DHL shipping costs of $22.00 for a total of $27.00.  I ordered the boards late on a Monday and DHL delivered the finished boards the following Monday morning.  Their website says boards that measure 100X100 mm or smaller cost $5.00 for 10 boards so whether you order 1 or 10, the cost is the same.  To complete the build you will need 3 boards to have enough bi-directional amp modules so, if you're interested in following thru with building a modular version, you could perhaps join with two other interested parties and split the cost between you.  With 3 boards you will be able to build a complete transceiver and have 2 extra modules for experimentation for every section except the bi-directional amps.  As an example, on my first prototype I built the double balanced mixer as designed and a second one using an ADE-1 to compare the results.  For the record, there was absolutely no noticeable difference between the two.  I also built a 4-crystal filter as designed and an 8-crystal QER filter on a second board for comparison.  There was a definite difference between these two modules.  

I hope this clears up some of the questions and I'm still available via direct email to answer questions specific to my build or class presentation.  I'm currently working on the assembly manual for my class and when finished I will post it also in the files section.
--73-- Mike  --  W0MNE

https://hackaday.io/project/20067-puzzle-radio-building-blocks