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Sunday, December 17, 2017

Building the Ceramic Direct Conversion Receiver Part 2 -- Building the VFO -- Our Goal is JOVO!

DC RX VFO and Buffer

I'll put the full schematic at the bottom of each of the posts so that you can easily refer to the big picture. Above you see the schematic of the VFO circuit. 

OK, here we go. Let's build the oscillator.  Our goal is JOVO -- the Joy Of Variable Oscillations. 

At this point you should have a big-enough copper clad board, and you should have given at least some thought to what kind of enclosure you are going to put the board in when you are done.  It pays to think ahead at least a bit, but don't get so carried away with planning that you never get around to building. 

You should plan the allocation of the space on the board.  Think about where you are going to place each stage.  You can mark out the spaces with a pencil or a Sharpie marker.  You might want to look at my board for ideas:     

In the picture above you can see the four stages.   On the left side of the copper-clad board you can see the Front end: the input filter and the RF amplifier (transistor near the top).  Moving toward the center you can see the mixer stage (around the circular 1k trimmer potentiometer).  Below the mixer (near the big round hole in the Bud Chassis) is the Variable Ceramic Oscillator stage and its buffer amplifier. The right 1/3 of the board is taken up by the audio amplifiers.  Note the use of Manhattan pads throughout.    Click on the picture for a closer look. 

Once you know where you will put the VFO, eyeball the schematic and think about where you will need Manhattan pads.  I often start by thinking of three rectangular pads for each transistor, one for each lead.  You can see that there are a lot of parts hanging off each of the terminals.  I sometimes put a long strip across the top or the middle of the board to carry the DC voltage.  

Since this is an oscillator, you don't have to worry too much about keeping the outputs away from the inputs.  You want this one to take of on you. 

For the feedback capacitors (C16 and C17) and the output capacitor (C19)  , get some ceramic disc NPO caps.  I put a 180 pf cap at C17 only becasue I didn't have a second 150 pf cap in the junkbox.  Either value will probably work. 

You will need a ceramic resonator.  I recommend this one from Mouser.  Again, buy a bunch.  They are cheap:

You can, to start,  build this circuit WITHOUT the two components that allow you to vary the frequency: without L4 and C5.  Just run the left end of the ceramic resonator to ground. See below.  

Connect a 9V battery to the top of C24.  Without L4 and C5 (with one end of the resonator to ground)  you should be oscillating at around 7.168 MHz (the capacitors in the oscillator circuit are pulling the frequency down from 7.37 MHz).

You need some way to find out if it is oscillating.  If you have an oscilloscope, great.  Put the probe at the output and take a look.  But perhaps a simpler and more satisfying way to do this test is with a radio receiver.  Tune the receiver around 7.168 MHz.  You do not need to connect your receiver to the oscillator.  You should be able to hear it.  If you do, congratulations.  If not, check your work.  Be patient.  This is not plug and play radio! 

Once you get the thing oscillating, it is time to make it variable.  Here is an opportunity for variety and experimentation.  Here are some of the options you have: 

Here is what I found.   The frequency stability of these circuits vary.  But all of them are stable enough.  They might drift a bit so that you have to retune the dial every few minutes.  If that realy bothers you you can upgrade to the air core coil with air variable cap arrangement.  

When I put just a variable capacitor that goes from 17 pf to 159 pf between the ceraamic resonator and ground, I was able to tune the oscillator from 7.220 MHz to 7.420 MHz. 

If I put a fixed 8.18 uH coil between the ceramic resonator to ground that moved the frequency to 7.010 MHz.  You could use a toridal core coil for this, but I had best results with an air core coil.  By putting the 17-159 pf variable cap between the coil and ground (similar to the arrangement shown above) I could tune from 7.010 MHz up to 7.367 MHz. 

You could also replace the variable capacitor with a voltage variable capacitnce diode (aka a varactor or a varicap diode).    I had good results with an MV2301.   

You could try using a cheap little polyvaricon capacitor for C5, but my best results came with an air variable. Walter KA4KXX points out that nice variable capacitors are available here:  If you can, get one with a reduction drive to slow the rate of tuning as you turn the shaft.  If you can't get one of these, try to get find a reduction drive to slow down the tuning. 

I ended up using a 3 uH air core coil with a variable cap of around 365 pf this allows me to tune from 7.115 MHz to 7.300 MHz (all of the phone portion of the band) with very good stability -- Juliano Criteria levels of Stability.  

One more idea:   As you build this stage, or right after you finish it, go ahead and build a dulicate circuit, perhaps without the variation components.  Why?  Well that second oscillator might be useful when it comes time to peak and tweak the front end input filter of your receiver.  And that second oscillator can become the start of a second version of this project. 

We talked about this project in SolderSmoke Podcasts #199 #200 and #201

Now I'm going to the beach.  I hope the holiday season bring you all joy -- especially the Joy of Variable Oscillations. Send us reports on your progress, your joy, or your tales of woe. 

The Big Picture

Saturday, December 16, 2017

Building the Ceramic Direct Conversion Receiver -- Part 1 Introduction, Stages, Parts.

I hope many of you decide to build this little receiver.  With it, you can break into the ranks of those intrepid ham homebrewers who have actually built a receiver.  Today I'll begin a series of blog posts on how you might do this.  Of course, there are many ways of proceeding.  I will describe my method.

FIRST:  ALWAYS look at this receiver as a collection of stages. Understand what each stage does and how they all work together.   Build it stage-by-stage.  Proceed to the next stage only after you confirm that the stage you just built actually works.

I see this receiver as having four stages:

1.  Front end  (RF gain control, input filter, first RF amplifier).

2.  Mixer

3.  Ceramic resonator variable frequency oscillator (and buffer)

4.  Audio amplifier (consisting of four transistors and associated parts).

In the picture above you can see the four stages.   On the left side of the copper-clad board you can see the Front end: the input filter and the RF amplifier (transistor near the top).  Moving toward the center you can see the mixer stage (around the circular 1k trimmer potentiometer).  Below the mixer (near the big round hole in the Bud Chassis) is the Variable Ceramic Oscillator stage and its buffer amplifier. The right 1/3 of the board is taken up by the audio amplifiers.  Note the use of Manhattan pads throughout.    Click on the picture for a closer look. 

I think you should build the oscillator stage first. 

What you will need:   In most cases, you shouldn't buy individual parts for this receiver.  I won't be providing a BOM.  Here is what I think you should do.  If you do not already have a good stock of electronic parts, start developing one.  Buy assortments of parts, or at least several of each part that you will need.  I use e-bay, amazon, mouser, digikey.   The parts are out there.

-- Get an assortment of resistors.  1/4 watt resistors will do.
-- Get a bunch of .1uF capacitors.  You will use a lot of these as bypass caps.
-- Get a bunch of 2N3904 and 2N3906 transistors. 
-- Get a bunch of 2N2222 transistors
-- Get a bunch of MPF102 and/or 2n2819 FET transistors.
-- Get an assortment of small electrolytic capacitors.
-- Get some Zener diodes in the 6-8 volt range. 
You will need some trimmer caps (8-80pf work fine).  Some 1K trimmer pots.  and some other stuff.

Get some copper clad board.  Pete suggest this, or something like it.

Try to avoid the cheap fiber glass boards.   I prefer single-sided, but double sided is OK too. 

You will need to cut the board.  Get some tin shears.  Mine look like big strong scissors.  Use them to cut your boards to size AND to cut the little isolation pads for Manhattan construction.

Crazy glue.  I kind of like Gorilla Glue liquid (not gel).

Small wattage soldering iron.  35 W or so.   Get a small fan to keep the smoke and glue fumes out of your respiratory system.

   I used a piece of scrap wood to get the variable cap into position. 

Here it is with my fancy Archer Dial.  I used a bit of copper clad board to finish the front panel 
and to support the audio gain control. 

Next time I'll write about how you might build the Variable Ceramic Oscillator stage. 

Saturday, December 9, 2017

SolderSmoke Podcast #201 Santa, Storms, BUILDING A DC RX, SDR, uBITX

SolderSmoke Podcast #201 is available:

9 December 2017

Santa Juliano

Forest fires, snow storms, and an earthquake. 

Santa arrives from Hyderabad -- uBITX in the house. 

Radio history.  First transtalantic amateur contacts. 

Bill's International Brotherhood Ceramic Discrete Direct Conversion Receiver Project. 
-- Goals -- Build your own receiver.  Really.  From scratch.  No cheating. 
-- How to get started.  Get parts and tools. 
-- Stage by stage. 
-- VFO first -- maybe build two. 
Bill built two already
-- Nephew is testing the first one. 
-- Polyvaricon limitations. 
-- Varactor limitations
-- Variable cap limitation.  

Understanding the F5LVG mixer

Pete goes to the dark side with an SDR receiver. 
Pete's 800 Watt Amplifier gives him trouble. TRGHS. 

People in the News
Cliff Stoll -- Still Passionate about Electronics
Peter Parker -- VHF/UHF  By the Bay
Yardley Beers -- Early SSB with "The Black Rose"
John Kraus -- Moonbounce without the Moon. 


Sunday, December 3, 2017

Discrete Ceramic 40 Meter Direct Conversion Receiver in Action (Video) -- BUILD THIS THING!

I've been holding off on making this video until I improved the stability.  N6QW is vigilent!  I only did this video after certifying that it meets the Juliano Stability Criteria.  I had to dispense with the polyvaricon and go with an air variable. 

We will be talking about this on the SolderSmoke podcast next weekend.  I hope to put on the blog  a stage-by-stage discussion of how to build this receiver.  

The dial from HI8P and the knob from a SW receiver that Elisa gave me definitely add soul to this new machine.  


Saturday, December 2, 2017

Cliff Stoll -- Still Passionate About Electronics (Video)

I open Chapter 3 of my book "SolderSmoke -- Global Adventures in Wireless Electronics" with some quotes from Cliff Stoll:  "Where's the joy of mechanics and electricity, the creation of real things?  Who are the tinkerers with a lust for electronics?"  Well Cliff, that would be us! 

I'm glad to see in the (obviously) recent video that OM Still has not lost his passion for electronics. You guys will like this one.  Keep 'em comin' Cliff!

Friday, December 1, 2017

"The Black Rose" -- Yardley Beers' 1955 HB SSB Transceiver

I've been a fan of Homebrew Hero Yardley Beers W0JF for a long time.   Here is a link to previous posts on him: 
Yesterday I got a nice e-mail from Boulder Colorado about Yardley's very early SSB rig.  I'm guessing that the 4.7 MHz is a typo -- it might have been 3.7 and 14 MHz.   FB.  Thanks Mike

Yardley Beers W0JF moved to Boulder in the early 1950's to work at the National Bureau of Standards (now NIST) laboratory.  There he headed the Time and Frequency Division, which maintains the atomic clock.  He later taught at the University of Colorado and Denver University.
About 1955 he homebrewed what, at the time, may have been the only SSB transceiver in the world.  It was built with individual transistors (no IC's in those days) and Yardley had to grind the crystals himself for the filter.  He enjoyed naming his radios and this one was "The Black Rose."
The transceiver ran at 4.7 and 14 MHz.  Its 1/2 watt output was fed to a home built amplifier.  The transceiver demonstrated the practicality and benefits of SSB in a world where AM was the voice mode.
In the year 2000 Yardley demonstrated this original, old SSB transceiver to the Boulder Amateur Radio Club by using it to make contacts with two club members.  Attached to this e-mail are a couple of photos.
Mike W3DIF
Treasurer, Boulder Amateur Radio Club (BARC)

Thursday, November 30, 2017

VK3YE QRP by the Bay Goes VHF/UHF

Peter Parker again hosted the VK3 radio amateurs.  This time the event fell on VHF/UHF Field Day weekend.   So Peter and his friends went up in frequency and up into SPACE!  

VK3HN has a nice blog post here:

Be sure to read about Peter's ankle manacles -- he apparently uses them to get a good ground (sea) plane while running pedestrian mobile on the sea shore. Peter is DEDICATED! 
Designer: Douglas Bowman | Dimodifikasi oleh Abdul Munir Original Posting Rounders 3 Column