Standard Computer Crystals for 17 Meter SSB VXO and IF Filter

Pete Juliano, N6QW, is an electronic  genius.  The ideas in his SPRAT article will be of great use to all those who share in Doug DeMaw's devotion to VXOs and reluctance to spend money.  I'm really tempted to go back and re-do my BITX using Pete's 11.52 MHz computer crystal super-VXO and 4.9152 IF (I could then take my expensive 23.1 MHz crystals and put them back in my Doug DeMaw Barebones Superhet).  I also like Pete's DPDT reed relay crystal switcher too.  Three cheers for Pete Juliano, Doug DeMaw, and SPRAT!  And thanks to WB9FLW for reminding us of Pete's articles.

Hi Bill,

 

Your BITX17 really has me fired up! I came across an interested Super VXO by Pete N6QW for use on 17 Meters.

He uses standard computer xtals (4.9152 MHz for the IF) and (3 - 11.520 MHz freq doubled in the VXO)

This gets you on 18.120 to 18.150 using these two standard xtals.

See Link Below:

 

http://www.jessystems.com/SPRAT%20Article.pdf

http://www.jessystems.com/Images/23%20MHz%20VXO.jpg

http://www.jessystems.com/vxo2.html

http://www.jessystems.com/switchedxtalvxo.html

Thanks for all your efforts they are much appreciated!!

Best Wishes,

Pete WB9FLW
 

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Beautiful French Aerial Photography Project. UPstagram! (Video)

We've put cameras in kites and rockets, but I think this is much cooler.

More details (and pictures) here: http://hackerloop.com/upstagram/

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BITX Build Update #19 Layout, VXO, Bal Mod, Filter, PA

The files of the BITX20 Yahoo group were very useful to me during my BITX build.  So I have decided to make a contribution myself.  I uploaded a few drawings today.  Here is how I laid out the circuitry on my 8 inch by 11 inch copper clad board.  I included the isolation (Manhattan) pads for one of the bidirectional amps.   

Here is the VXO.   I built is on a separate board, but I could have put it on the main board. 

Here is the balanced modulator and crystal filter. 

 

Here is the power amplifier circuitry.  Amazingly easy to stabilize. 


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BITX (and W2AEW) on Hack-A-Day

The guys over on Hack-A-Day ran a little follow-up article on the BITX-17.  Check it out:
http://hackaday.com/2013/11/13/bitx-a-return-to-hackers-paradise/#comments

They also had an article about Tek-Wizard Alan Wolke earlier in the week:
http://hackaday.com/2013/11/11/diagnose-and-repair-a-yaesu-ft-7800-ham-radio/

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New Book About Heathkit Gear

Jeff Tranter, VE3ICH, has a new book out -- it is about Heathkit Test Gear.  (Hey, I had that VTVM on the cover!)  This book looks like it deserves a place under the Christmas trees of SolderSmoke fans.   The book is available from Lulu.com, and Santa (or Mrs. Claus) can use the discount coupon below (Coupon code: CORNUCOPIA.)

http://www.lulu.com/shop/jeff-tranter/classic-heathkit-electronic-test-equipment/paperback/product-21272772.html

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Save 20% on SolderSmoke and other Lulu books (through Nov 15)

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That wonderful first contact, when the new HB rig is still on the workbench...

In this video, YC0AFF in Indonesia seems to be having as much fun with his new BITX as I've been having with mine.  I think there is something special about those early contacts, when the newly finished (or not quite finished!) rig is still on the workbench.  Designed in India and built by radio amateurs all around the world, the BITX has become a global ham radio phenomenon, reminding us that we form an International Brotherhood of Electronic Wizards.

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An Amazing French Workshop (Video)

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Knack-to-the-Max! Early Moonbounce

The link below will take you to an amazing collection of QST articles describing the early days of EME or "moonbounce."  Very interesting.   I was really blown away when I found out that Ross Bateman, W4AO, (pictured above, on the left) did the very first amateur moonbounce work from the small suburban Washington town that I live in now -- Falls Church, Virginia!

I am trying to find OM Ross's old address or more info about him.  If anyone has an old callbook, could you please look up Ross Bateman, W4AO, aka W4XNB?   He worked at the National Bureau of Standards. 

The moonbounce story is filled with interesting technology and characters and clubs.  Sam Harris and his Rhododendron Swamp VHF Society sounds like our kind of group!  Scroll through the OK2KKW web site and you will come across our esteemed Doug DeMaw and Bill Orr. 

http://www.ok2kkw.com/eme1960/eme1960eng.htm

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Zoltan Bay and his Chemical Moonbounce Detector

In March 1944, Bay recommended using the radar for scientific experimentation, including the detection of radar waves bounced off the Moon. The scientific interest in the experiment arose from the opportunity to test the theoretical notion that short wavelength radio waves could pass through the ionosphere without considerable absorption or reflection. Bay's calculations, however, showed that the equipment would be incapable of detecting the signals, since they would be significantly below the receiver's noise level.

The critical difference between the American and Hungarian apparatus was frequency stability, which DeWitt achieved through crystal control in both the transmitter and receiver. Without frequency stability, Bay had to find a means of accommodating the frequency drifts of the transmitter and receiver and the resulting inferior signal-to-noise ratio. He chose to boost the signal-to-noise ratio. His solution was both ingenious and far-reaching in its impact.

Bay devised a process he called cumulation, which is known today as integration. His integrating device consisted of ten coulometers, in which electric currents broke down a watery solution and released hydrogen gas. The amount of gas released was directly proportional to the quantity of electric current. The coulometers were connected to the output of the radar receiver through a rotating switch. The radar echoes were expected [11] to return from the Moon in less than three seconds, so the rotating switch made a sweep of the ten coulometers every three seconds. The release of hydrogen gas left a record of both the echo signal and the receiver noise. As the number of signal echoes and sweeps of the coulometers added up, the signal-to-noise ratio improved. By increasing the total number of signal echoes, Bay believed that any signal could be raised above noise level and made observable, regardless of its amplitude and the value of the signal-to-noise ratio.²⁶ Because the signal echoes have a more-or-less fixed structure, and the noise varies from pulse to pulse, echoes add up faster than noise.  From: http://history.nasa.gov/SP-4218/ch1.htm

During the war, Zoltán Bay protected Jewish colleagues from Nazi persecution. In 1998, the State of Israel honored him as Righteous Among the Nations for his actions and listed his name at Yad Vashem.


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SolderSmoke Podcast #156 -- Special Echolink Interview

 

Podcast #156 is available: 
http://soldersmoke.com/soldersmoke156.mp3

Special hour-long interview with Peter Parker, VK3YE
-- Early experiences with radio
-- CW
-- DSB Gear
-- Simple gear, and gear that is TOO simple
-- VXOs, Super VXOs and Ceramic Resonators
-- Building receivers
-- Chips vs. Discrete
-- Making the leap to SSB
-- The Knob-less wonder and the BITX
-- No need for a sophisticated workshop
-- Advice for new phone QRPers


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BITX Build Update #18 -- BITX in a Box?

I've really been enjoying using my BITX17 without an enclosure.  Having all the electronics exposed on the workbench really accentuated the homebrew nature of this rig.  But obviously it was time to box this thing up.  At a local craft store, I found a wooden box that is exactly the right size for my BITX copper clad board.  I put the BITX in the box yesterday.  I kind of miss the exposed electronics.  

The far left control is AF gain.  The need for a few inches of wire to the pot has introduced a bit of AC hum.  I'll try to knock this down with better shielding on the lead to the pot.

But this gets brings us too a bigger question: the need for a cabinet that shields.  Obviously the wood shields it only from dust.  I know there are some benefits to putting this thing in a proper metal box.  The AC hum would be less of a problem.  Also -- listen to this -- in the morning, before 17 opens, I can hear -- faintly -- the WWV transmission on 5 MHz (recall that the IF in this rig is 5 MHz).  And if I ever build an external linear amp for this rig (I might), I guess a proper metal box would help prevent the kind of oscillation that often drives me crazy on these kinds of projects.

So, what do you guys think?   Stick with the wood, or put it in a metal box?   Any thoughts on putting metal shielding material around the inside of the box (thick aluminum of tin foil)?    

(The other black control knob is for a rotary switch that will allow me to select among two or three crystals for the VXO. )

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40% Off SolderSmoke Book!!! Through 4 November

And on all Lulu books.

Just use the coupon code FALLSALE40 at checkout.

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Arecibo Birthday

Thanks to Bob Crane for this birthday alert:

The Arecibo Observatory opened on this date in 1963. At a diameter of a thousand feet, it's the largest single-aperture telescope ever built. It's also got the largest focusing dish in the world, which gathers electromagnetic waves from space. Located near the city of Arecibo in Puerto Rico, it's close to the equator, which enables it to "see" (via radio waves) all the planets in the solar system; within six months of its opening, it enabled scientists to study the rotation rate of Mercury and determine that it rotated every 59 days, rather than 88 as was previously thought. It's also been used for military purposes like locating Soviet radar installations by tracking their signals as they were reflected off the moon. It's provided the first full imaging of an asteroid and also led to the first discovery of planets outside our solar system.

In 1999, it began collecting data for the SETI Institute; SETI stands for "search for extraterrestrial intelligence," and the organization looks for deliberate radio or optical signals from other planets. The Arecibo Observatory also sends data over broadband to the home and office computers of 250,000 volunteers, who, through the Einstein@Home program, donate their computers to be used for data analysis during periods when they would otherwise be idle. A year ago, three such volunteers in Iowa and Germany discovered a previously unknown pulsar, 17,000 light years from Earth.

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Brooklyn Bike Generator -- Want one!

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The New "Gold Standard" in QRSS Grabbers

Bill 

I just discovered Scott Harden's "QRSS Plus" grabber aggregator...

http://swharden.com/qrss/plus/

Check it out - it is the new "Gold Standard".

73, Paul

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An Interesting Idea for Checking Crystal Filter Passbands

Today at 9:37 AM

Hi Bill,

Just listened to your last soldersmoke blog with reference to xtal filter checking using a DDS and scope. What do think of this idea to check filter performance?

http://www.qsl.net/7n3wvm/Fil_Meas.html

 Logical, relatively easy to build and NO digital electronics to deal with. 

Best 73

Rick G6AKG

PS keep up the great work, love the Blogs.

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Slide Show of BITX 17 Build

As I was building this rig, I periodically stopped and took a picture of the board.  I think the resulting slide show is kind of fun.  Check it out:  There is a button to launch the slide show.

http://www.flickr.com/photos/106886073@N04/sets/72157637045750216/

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Book Review: "Bunch of Amateurs" by Jack Hitt

The title held a lot of promise, but the subtitle ("A Search for the American Character") hinted at the main problem that I had with the book:  the author (perhaps driven by his editor) seemed to be struggling to prove that there is some uniquely American elements to amateur science and technology.  Early on, Mr. Hitt, makes the preposterous claim that "the rest of the world doesn't have amateurs."  He goes on to write that "In Europe and on other continents, the word hints at class warfare... Amateurs may be taken seriously, but, almost by the power of the word, are kept in their place: isolated outside some pre-existing professional class, some long-standing nobility.  In America, amateurs don't stay in their place or keep to themselves."   

What a load of rubbish!  This claim directly contradicts what many of us have been finding out in the quintessentially amateur world of amateur radio:  as we travel around the world (in person, or via the ionosphere) we find, all around the globe,  guys who have followed shockingly similar paths to ham radio.  From Sudan to Switzerland, from India to Indiana, the story is much the same.  And I'll bet you'll find similar similarities in just about every serious sci-tech hobby (astronomy, photography, etc.).  To claim that there is something fundamentally exceptional about amateurism in the U.S. is, I think, ridiculous.  Mr. Hitt should have spent some time looking at the amazingly diverse and vibrant world of British amateur science and technology.  That alone would have prevented him from straying into these silly claims of American amateur exceptionalism. 

But, all that aside, there is a lot of interesting material in the book.  I liked his description of John Dobson and the amateur telescope builders.  And, somewhat surprisingly, Hitt's description of the DIY Biology movement (these guys are playing with genetics and cooking up new organisms) seemed to capture very well the creative joy and satisfaction that amateurs find when working (just for fun) on their projects.  I was kind of surprised when I found myself identifying with the DIY Biology folks. Their basement labs sounded a lot like our radio shacks.   

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BITX BUILD UPDATE #17 Arv's Discrete AF AMP

I've been kind of cheating with the audio output from my BITX17:  I've been using one of those little battery-powered computer speakers.   It sounded fine, but hey, this is supposed to be a homebrew project right?  I've already noted my ideological objections to the use of the LM386 CHIP.  The files of the BITX20 yahoo group provided a very promising and completely discrete AF amp circuit by Arv Evans, K7HKL.  I used a 2N3906 and a 2N3904, with a 2N2222 driving them. It works like a charm.    Not a bit of feedback or motor-boating.  It sounds great.  I've already had a contact with it:  Jack, W7YUM is a builder of big amplifiers out in Salt Lake City.  He seemed very impressed with the BITX concept so we may have a Utah BITX in the works. 

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Words of Wisdom (on Amplifier Stability)

From "A Simple SSB Transceiver"  by Ashhar Farhan:

"What if your transmitter is unstable?  Don't curse your fate.  All transmitters start out as unstable beasts. Relax."   Farhan goes on to provide some good pointers on how to tame the beast.  

I've had very good luck with the PA in the BITX  -- very little cursing of fate on this project. 

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BITX BUILD UPDATE #16 -- FIRST QSO!!!!!!!!!!!

 

Wow, it is very clear that the radio gods are pleased with my BITX efforts!  I had my first QSO on the new rig today.  And it was with a station in my old home, the place where I got my start in 17 meter homebrew phone:  THE AZORES!  CU7MD.  Very cool.

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BITX Build Update #15 -- Necessary Mic Amp Mod

I was having trouble with the mic amp on my new Manhattan Discrete BITX 17.  I had it wired as per the schematic, but it just wasn't working right -- I was getting very little DSB out of the balanced nodulator, but everything worked fine if I 1) unbalanced the bal mod or 2) injected audio (from a sig generator) directly into the audio in port of the balancec modulator.  Clearly something was wrong in the mic amp circuit.  I noticed the collector voltage seemed quite low.

Some quick Googling revealed that others had struggled a bit with this problem also.  Nicolae's note was especially illuminating and useful: 
http://users.tpg.com.au/nfieraru/Electronics/BitX20_Mic_Preamp.htm

As Nicolae noted, the 10K value may have worked with lower gain transistors.  We must remember that BITX was (very admirably) designed for minimal cost and maximum use of scrounged parts.

I swapped the 10K resistor for a 39K and all is right with the world.  The band is not yet open here, but I bravely called a European aeronautical mobile station, hoping that he would be my first QSO on this rig.  I think he heard me, but no QSO (yet!).

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BITX Build Update #14 -- STABILITY!

Good news on the BITX.  I think I have solved the low frequency oscillation problem in the power amplifier.  I tried running the PA off a separate power supply -- the oscillations disappeared leading me to conclude that the feedback was taking place via the power supply lines.   I put a 22 uF cap to ground from the top of the PA's RF choke.  With this cap in place I can dispense with the separate supply kludge. The amp is stable.

This morning I also resolved a different stability problem.  I'm using a relay for T/R switching.  One set of contacts controls the DC power, the other set was supposed to disconnect the receiver input from the antenna/lowpass filter when on receive.  But I had positioned the relay too far from the LP filter and RX input, so I ended up with this long piece of coax that was hanging off the PA output terminal and carrying lots of RF on transmit.  Yes, this led to oscillations.  I thought about repositioning the relay, but I think part of the problem is that even if optimally positioned, the long unshielded contact levers inside this relay would be radiating a lot of RF and causing stability problems.   So instead I put a small reed relay very close to the PA out and RX in connections.  It carries the signal to the receiver when in R mode, and disconnects the RX when in T mode, without any long coax lines or unshielded relay levers.   It works.

I still have a few things to do:
-- I need to build a proper speaker amplifier so that I can dispense with the amplified computer speakers KLUDGE.
-- I need to get a 3 pole double throw switch and some crystal sockets so that I can switch crystals from the front panel.  Three rocks will cover all of 17 meter phone.
-- I have to build a case for this rig.  I'm thinking wood, with tin or aluminum sheeting glued to the inside (for shielding).  


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From Bits to Atoms -- Software vs. Hardware

I thought this was pretty good.  On Hack-A-Day.

http://hackaday.com/2013/10/18/guest-rant-from-bits-to-atoms/#more-105097

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Feynman at G-QRP Convention!

What do Richard Feynman and the G-QRP club have in common?

The answer is an annual pilgrimage to Ripponden in Yorkshire, England. The G-QRP club have their convention in a local school and Feynman went there every summer to visit his wife's family. Here's an interview with Feynman filmed at the Old Bridge Inn which is about a mile from where the G-QRP club gather:

http://www.openculture.com/2012/11/richard_feynman_talks_physics_in_take_the_world_from_another_point_of_view.html

Is this enough to make Ripponden the Knack Centre of England?

Regards,  Alan G0RWB

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Yikes! Screeching Transistors Throwing off Blue Light!

I found a quote from Doug DeMaw that I wanted to share.  This one seems appropriate as I struggle with unwanted oscillation (and as Halloween approaches). From the January 1986 QST:

"Self -oscillation occurs not only in the low-frequency and high-frequency spectrum, but it often takes place at audio frequencies!  I have actually heard the transistors "screeching" when strong audio oscillations were taking place in a homebrew transistor power amplifier. On one occasion I could see a bluish glow coming from within the transistors (visible through the ceramic heads of the devices) during a period of instability.  Needless to say, the transistors self-destructed."

I've been having some instability problems with my BITX 17 IRF510 final.  But I think I have the problem identified.  I was getting low frequency oscillations (around 100 KHz).  Tonight  tried putting the IRF510 on a separate power supply.  The oscillations ceased and I am getting a nice clean 3 watts out.   So I'll go back and beef up the decoupling on the power supply lines.


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20% off on SolderSmoke Book

Just use the coupon code PUMPKINS at checkout:

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(You can also use this coupon to buy Grayson's "Hollow-State Design" :
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SolderSmoke Podcast #155 BITX17, TEK465

Podcast # 155 is available for download (or you can listen by clicking on the button above):
http://soldersmoke.com/soldersmoke155.mp3

October 14, 2013  (Delayed Back-to-School edition)

Topics covered:

-- BITX Beauty -- Building a BITX17

-- VFO woes, and the wisdom of Doug DeMaw's love for crystals

-- Why does a 55 year old man NEED clear nail polish varnish?

-- How the VFO KILLED the Tek 465

-- Trying to fix the Tek 465 (not for the faint of heart)
 
-- New products:  Justin Beiber Duct Tape, bifocal safety glasses,
magnetic reading glasses, Ward Silver's new book

-- Backwards British Bike Brakes

-- MAILBAG 

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"Robert Ford -- A British Radio Operator in Free Tibet..."

http://www.economist.com/news/obituary/21587201-robert-ford-british-radio-operator-free-tibet-died-september-20th-aged-90-robert-ford

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Nice Slide Show on BITX

https://sites.google.com/site/arvidevans/BITX_QRPacificon..pdf?attredirects=0


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BITX BUILD UPDATE #13 -- VIDEO TOUR

I hope to get the next podcast out within a week or so.  The BITX has been keeping me busy!


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BITX BUILD UPDATE #12 -- Relay and PA, BITX 17/10?

As you can see, the board is starting to fill up.  I really like it.  It seems (to me) like the canvas of a painting approaching completion. This morning I put in the T/R relay.  That space in the upper left is reserved for the driver and the IRF510 Power Amplifier.

I got some help from the Chief Designer this week.  As noted in an earlier post, Farhan  advised me to check the mixers.  I knew that I had them wired correctly and that they were in fact mixing, but when Farhan advises you to check something, YOU CHECK IT.  Farhan was right (see earlier post).

It really sounds great.  I know that the filter still has significant ripple in it, but the receiver sounds so good I'm reluctant to mess with it.  Should I de-ripple it?

On the train yesterday I was thinking about this rig, and it occurred to me that my 23.1 MHz VXO/ 5  MHz IF arrangement means that this 17 meter transceiver could also generate signals on the 10 meter band.  Of course, I'd have to build a second bandpass filter, but the radio gods guided my hand and caused me to leave space on the board for just such a filter (see above).  I realize the IRF510 PA wouldn't be too good up at those frequencies,  but when the radio gods speak, you have to listen.   

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Tek Troubleshooting Triumph

Thanks to the manual provided by Jim and the HV test gear provided by Alan Wolke, I was able to finish the troubleshoot on the broken Tek 465.   It is the HV multiplier, U1432.   The cathode voltage is supposed to be -2450.   It initially tested at -1000.    The manual calls for a jumper to be removed to take the HV Multiplier out of the circuit.  As soon as I did that, the cathode voltage went to -2500.   Bingo.

 

Now I have to get a replacement for U1432.    Any carcasses laying around?

 

Thanks guys. 

 

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BITX Build Update #11 -- Peakin' and Tweakin'

Oh how I love the sound of a newly built receiver!  I'm sitting here listening to G0MJS on 17 meters.  Lots of other stations from across the pond coming in very nicely. 

Earlier in the week I had some sensitivity problems.  I could hear the noise floor, but just barely.  And the receiver just seemed to have trouble inhaling.  So I started poking around.  It seemed that each poke improved things a bit.  I had used Farhan's original schematic (mostly).   Later versions put an additional transistor in the IF amp.  So I went ahead and added that mod.  That helped a bit.  Then I noticed that BFO energy was getting into the AF amp.   So I put a .1uF cap to ground at the input to the AF preamp.  That took care of the RF and did no damage to the AF.  

But the rig still seemed a bit hard of hearing.  This morning Farhan advised me to take a look at the mixers.  I used some junk-box diodes that I didn't know too much about...  I measured the forward resistance and found it to be quite a bit higher than the usual 1N914s.  So I switched all 6 mixer diodes.  That helped noticeably.

I also checked the input bandpass filter.   It seems OK.   In the process I learned to use the EMRFD filter programs (thanks Wes) and the ELSIE filter program (also very nice).

Anyway, the rig sounds great now.   On to the transmitter.  

Farhan advises building the power amplifier on a separate copper clad board.  But I have room for it on my main board.  Should I live dangerously?   


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Occam's Microcontroller

Paul, M0XPD, has what I'm sure is a wonderful article on a simple microcontroller-based rig in the current issue of our beloved SPRAT.   I look forward to seeing it.  And I really like the logo with William of Occam (of razor fame). I have encouraged Paul to take a break from the microcontrollers and build something discrete and analog... like a BITX!  

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BITX Build Update #10 -- Darling(ton)

Having concluded that I was significantly short on overall receiver gain, I went in yesterday and changed my AF amp from a 40db direct-coupled circuit to a 100db Darlington pair.  I immediately noticed a big increase in audio output. 

I did a quick receiver alignment using my Arduino/AD9860 sig generator.  First I determined the actual bandpass of the crystal filter: 4.998170 MHz -- 5.000960 MHz.   Using a freq counter, I set the BFO at 5.00126.   I immediately started hearing 17 meter SSB signals from the West Coast.  That's always a nice moment:  first signals through a new receiver.  Kind of like "first light" in a new telescope.  Even with the filter ripple, it sounds great.

I think I'm still significantly short of gain.  Audio is still faint. I notice that in the BITX17A they have added a second transistor (Q17) in the second RX receive amp.  Maybe I should try something similar.   Or should I add some gain in the audio chain?

I'm really enjoying this BITX project. 


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Hackers' Paradise

http://hackaday.com/2013/09/23/guest-rant-ham-radio-hackers-paradise/

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BITX Build Update #9 -- Discretion

With the exception of the PA, all of the stages of my BITX 17 are built.  Over the weekend I put in the DC wiring for the receiver and the inter-stage connections (using the Belden coax with the exposed shield and Teflon di-electric).  It looks nice. 

In my experience, almost all new superhet receivers require a certain amount of debugging and coaxing before they will work.  This one is no exception.  The VFO and the BFO work fine, and all three RF and IF amp stages are also good.  The bandpass filter  that I built passes the desired band and tunes up nicely on the right frequency.  The product detector was acting weird and wasn't balancing out properly, but I got that all sorted.  

I can put an 18.110 MHz signal at the antenna connection and see the signal go through the bandpass filter (with loss), on to the RF amp stage, to the first mixer where it meets the 23 MHz energy from the VFO.  A very messy mixture goes from the mixer to the first IF amp which sends it to the 5 MHz Cohn filter.  The filter works, but it has a lot of ripple, so I need to work on the termination impedances.  Second IF works fine, then the signal goes to the product detector.  AF comes out.  

Here's where the discretion comes in.  Instead of the LM386 chip, I built a 40db two transistor direct coupled AF amplifier. 

So it all works, but the receiver is quite deaf.  I think I just don't have enough gain in the whole system.  I looked at the schematic for the BITX-17 kit.  It very helpfully has total (net) gain figures for the RX.  I can see that my current configuration comes up short.   

Here is what I'm thinking of doing:  I might replace the 40db direct-coupled AF amp with a 100 db Darlington pair.   I really like the discrete Darlington AF amp that KD1JV has in his "all discrete" transceiver:
http://kd1jv.qrpradio.com/ADC/ADC-40.htm  Nice.  3 2N3904's driving a speaker.  I may use that.  
 
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BITX Build Update #8

Big progress on the BITX:  All the bidirectional amp stages are done.   A bag of 20 5 MHz crystals arrived from Mouser today.  I put one in the BFO/Carrier oscillator and it fired right up.  I'll soon be checking frequencies on these crystals, looking for four that are closest in frequency for use in the filter. 

While waiting for the mail I built the audio amplifier for the receiver (lower left corner in the picture above).   Here I need some advice/encouragement:  In an effort to keep this rig "all discrete" I decided to dispense with the LM386, and replace it with an AF amp using individual transistors.  I found a circuit in the 1980 ARRL Handbook that I liked.   It has two direct coupled transistors, one NPN, the other PNP.  I went with a 2N3904 and a 2N3906.   The Handbook said it would yield 40 db gain.  I figured this was a close enough replacement for the 46 db gain of the LM386.  

As usual, I'm not sure of the impedance matching.  I built the first AF stage from the BITX schematic (the stage that precedes the LM386).  It goes to a 10K pot.  The wiper of the pot would normally go into pin 3 of the LM386.   I have the wiper going through a 4.7 uF electrolytic into base of the first transistor.  The Handbook says the circuit has an input impedance of 1000 ohms.  Does my arrangement sound OK? 

Output impedance from this Handbook circuit is also 1000 ohms.  I tried it with some HI-Z headphones that I have, putting AF in from my Maplin AF sig generator.   It sounds OK.   Not a LOT of audio available.  But OK.  I may need one more stage to drive a speaker.     

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Inside a Tek 465

The TEK 465 'scope is as they'd say back in the Bronx "a piece of work."  It has real character.  Perhaps a bit too much.  If you look closely, you'll see transistors in sockets.   I had kind of gotten my head around that, when I noticed that many of the transistors were not in sockets.  They looked like they had been soldered to into the holes in the PC boards.  But NOOOOO!  They are snugly in the holes, but they are NOT soldered in!  You can pull them out, then (if you are lucky!) slide them back in.  There is even quite a bit of "ugly construction." with connections floating in the air.  You can really see the influence of tube era thinking in this instrument.

I think I have narrowed the problem down to the HV supply.  Alan Wolke is lending me a high voltage probe.  I hope to be able to get it fixed this weekend.  I need to get it working because my BITX 17 is nearing completion and I'll need the 'scope for the lineup and de-bugging.

The picture above is from:  http://www.eevblog.com/forum/projects/tektronix-465-repair-and-restoration/   More pictures of the scope are available there.  Also see http://www.spurtikus.de/basteln/repair/tek465/index.html for more scenic views of this instrument.


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Battushig has The Knack (Mongolia and the MOOCs)

"How does a student from a country in which a third of the population is nomadic, living in round white felt tents called gers on the vast steppe, ace an M.I.T. course even though nothing like this is typically taught in Mongolian schools?"

"Most homes in Ulan Bator have Internet connections, and almost everyone, including nomads, has at least one cellphone. Even on the steppe, with only sheep in sight, you can get a signal."

http://www.nytimes.com/2013/09/15/magazine/the-boy-genius-of-ulan-bator.html?pagewanted=all&_r=0

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BITX Build Update # 7

As you can see (above) I've made lots of progress on the BITX-17.  Going counter-clockwise from the lower right, you can see the mic amp, the BFO/carrier oscillator, the first mixer, the first and second bi-directional amplifiers, the diode ring VXO mixer and the VXO.

I plan on building the whole rig (including the power amplifier stages) on this wonderful piece of PC board (thanks to Jim, W8NSA).

I had what I thought was the brilliant idea of using LEDs for  all the T/R switching diodes.  I thought I'd use red for receive and blue for transmit.  I consulted with the BITX yahoo group and cooler heads prevailed.

The design has an LM-386 as the speaker amp.  I'm kind of bothered by this -- I'd prefer an all-discrete component rig, so I am thinking of building an AF amp with discrete transistors instead, perhaps the circuit from Roger Hayward's RX for the Ugly Weekender.  What do you all think about this? 

I'm having a lot of fun building this rig.  If anyone out there is looking for a fall/winter project, build one of these.

I have to order some 5 MHz crystals for the filter and oscillator.  Mouser has them at about 70 cents each.   


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BITX Build Update #6: Rock Steady

So, having given up on the VFO,  this week I built a VXO.  The IF in my W4OP-built Barbones Superhet is at 5 MHz.   That receiver has a VXO running at 23.133-23.168 MHz with two crystals switchable from the front panel.  My plan is to build a 5 MHz filter for the BITX 17.  So I just plucked one of the crystals in the Barebones RX and used it to test and tweak the VXO.  Trying different values for the series inductor, I got wide variations in freq swing.  With .7uH I could only pull the rock 9 kHz (too little).  With 5.6 uH, it was pulling 434 KHz (way too much -- it was acting like a VFO). 3.213 uH was just right:  With my 19-148 pF variable cap (with 53pF in series) I got a swing of 22 kHz, with crystal-oscillator stability.

I know, I know:  I could have done this with a DDS chip, or with an SI570.  But simplicity is a virtue, and the BITX is all about simplicity, right?  Having recently built a DDS RF generator, and now this simple three transistor device, I must say that I like the simple analog circuit better.   But hey, that's just me.  I'll talk about this in the next podcast.

Today I built the mic amp circuit.  You can see it off to the right of the VXO.

One of these days I'm going to have to actually troubleshoot and fix my Tek 465.  But I'm
afraid of that thing!  The voltages in there are HIGH, and so is the circuit complexity.  

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Moon Launch from Virginia (video)

NASA launched a mission to the moon last night.  The rocket went out of Wallops Island, Virginia and was visible from Washington D.C.   I forgot about it, so we missed seeing it ourselves, but this fellow got a nice view from the balcony of his Washington apartment. 


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Burning Man: Probably more Fun than a Hamfest!

Check out this report from the Burning Man event.  Two intrepid nerds head out to the dessert  (with ham radio gear) and appear to have an amazing time. 

http://blog.thelifeofkenneth.com/2013/09/my-first-burn.html


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NASA needs Ham Help! Say HI to Juno (on its way to Jupiter) on 10 meter CW!

This is really interesting:

http://www.jpl.nasa.gov/hijuno/

Thanks to Richard, KK4JDO, for the heads-up.

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BITX Build UPDATE # 5: ADRIFT!

Sometimes it is better to have LESS test gear.  Watching my 5 MHz VFO on the frequency counter was driving me nuts.  If I hadn't had the counter, I might have been satisfied with the VFO.  Ignorance is bliss!   It did settle down a bit.  But then it would wander off.  I hated watching it drift around.  I have been spoiled by Doug DeMaw's VXOs.   So, I went for the VXO.   It will run around 23 MHz.  I'll build the filter at 5 MHz.  That's definitely the plan.  For now. 

I intend to go back and build a real VFO someday.    There seems to be a lot of magic and lore involved.  Bees Wax!  Hot Glue!  Nail Polish!  Q-Dope!  Air-wound coils!   

TEK 465 is still broke.   I think it is the high voltage supply or (less likely) the CRT. 

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Fixing TEK 465 Oscilloscopes

I'm having TeKnical difficulties.  My beloved Tek 465 'scope quit on me.  I'd been running it continuously for a day or so, watching the output on my BITX VFO.  Then, suddenly, it blew the 1.5 amp fuse.  I replaced the  fuse, but afterwards the trace was gone and the "Low Line" light was acting weird -- on when it should have been off, then flickering.   I consulted with Alan Wolke.  He happened to be out at TEX HQ in Beaverton, Ore.  He provided some good suggestions, but before I had a chance to try them, the trace came back.  I attributed this good luck to the Radio Gods being pleased with Alan's presence in Beaverton... but my reprieve was short-lived.  Trace went out again today. 

I found this video of the legendary Jim Williams (RIP) fixing a Tek 465.  (Check out Jim's junk box!)
I'll start by checking the Tantalums.  I may get lucky. 

If anyone has any other suggestions, send them this way.  The Tek scope may be old, but it is a COMPLICATED piece of gear... 

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BITX Build Updat #4 VFO Stability

I wasn't quite satisfied with the long-term stability of my VFO.  It seemed like it was drifting about 70 Hz per hour, even after the initial warm-up period.   So, all out of Q-Dope, I went to the local pharmacy in search of clear nail-polish.  (My family was making fun of me.)   I got home and applied several coats of "Sally Hansen No Chip Top Coat Vernis de Protection."   I let it dry a bit, then started watching the frequency counter.  At first results were disappointing.   Drift continued.  Now it seemed to be drifting up!   I cracked the books.  EMRFD has a good chapter on temperature compensation of VFOs, but the process seemed painful.    I wasn't looking forward to it.

I left the VFO on when I went to work, noting the freq as I departed.   Ten hours later I returned, and was delighted to find the frequency almost exactly where I left it!  It may have taken a while for the nail polish to completely dry.    I'll leave it running again today to see how it does.


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