First Contact with Herring Aid 5 AND Tuna Tin 2

Ah, it was a good morning in the N2CQR shack!  Last week I ran into fellow ham David Cowhig at work.   I was regaling him with tales of Herring Aid and Tuna Tin derring-do.  Oh the stations I had heard with the receiver!  And the stations that I'd worked with the transmitter!   Then David asked the question: "Yea, but have you worked anybody with the receiver paired up with the transmitter?"  Uh, no.  Not yet. 

 

Well this morning I took care of that.  7040 kc.   1115 UTC.  W4ELP was calling CQ.  He wasn't too strong, and I wasn't sure if we were on the same side of zero beat (that's what happens with direct conversion -- you get all the sigs in two places on the dial) but I took a shot at it.  And he heard me! 

 

Here's the icing on the cake:  This was his SECOND QSO with my Tuna Tin 2!  Ed had been contact #4 when I was running the TT2 with the Drake 2B.   After exchanging reports he asked "Bill ARE YOU STILL ON THE TUNA TIN?" 

 

The rig (TX AND RX) is pictured above.   Close-up of the receiver appears below.  And below that is a picture of Ed, W4ELP, in his Georgia shack.  Note the HW-8.

 

Thanks Ed! Thanks David!

 



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Harv's DDS Function Generator

Nice looking DDS function generator Harv!  Glad to see the HT-37 in the background. (And it appears well protected -- is that some sort of digital shielding to protect it from the bits and bytes?) The eraser buttons are a nice touch. Good luck with the Minima!

Hi Bill,

 

Well I have nearly completed my DDS Function Generator as I prepare to construct the Minima.

 

The Function Generator was a necessity for the bench so I can tackle Tweaking and Troubleshooting my work.

It is housed an aluminum box and completely self-contained.

My objective was to have the choice, to either lay the unit flat on the work surface or stand it on a shelf for easy reading while seated.

The Generator has both a  DDS and HF-ECG output.

The buttons are fashioned from White Pencil Erasers since finding proper buttons for the membrane keypad beneath was difficult.

 

I have obtained a set of Farhan’s Boards for the Minima but will begin my effort with a Manhattan Style Construction so I can perfect my choice of parts.

The soldering iron is heating and I’m ready for a new and exciting challenge.

 

Happy Solder Melting Everyone!

 

Harv -=WA3EIB=-

Albq., NM.

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Remotely Controlled Stations on the Internet

Now for something completely different!  

I  find myself talking fairly often to hams who are using remote transceivers.  The operator will be in say, Michigan, with the rig in Florida.  Some of them are using the online system:

http://www.remotehams.com/

I signed up and downloaded the software.   It works very well.  Many of the stations are closed to outsiders, and some of them don't let you transmit, but it is fun to listen from remote locations.

This morning I hooked up the Tuna Tin 2 and was able to hear my 200 mW signal through AI4W's receiver in Kentucky. 

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Hackaday Goes to Shanghai

http://hackaday.com/2014/03/24/the-gathering-shanghais-hackaday-community/


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VU2JN's "Transistor Transmitter from India"

VU2JN

VU2INJ's very interesting blog led me to a wonderful 1967 QST article by VU2JN.  Check it out.  Necessity truly is the mother of invention and -- as is the case with our beloved BITX -- we see that in the design of this transmitter.  I love how the speaker was left in the cabinet and used as the microphone.  Check it out:

http://vu3inj.blogspot.in/2014/01/tribute-to-vu2jn.html

More on VU2JN (who very clearly merits "Homebrew Hero" status):

http://shipwreck1.hopto.org:8080/projects/hamprojects/VU2JNArchive/

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The Really BIG Discovery (Cosmology, Gravity Waves, Inflation)

The signals that were announced this week are a bit outside our normal frequency range, but this is a REALLY BIG discovery so of course, it needs to be covered by SolderSmoke Daily News. I liked this info-graphic from space.com. It is worth looking at. Note the line "The universe continues infinitely outside Earth's Hubble volume."

http://www.space.com/25075-cosmic-inflation-universe-expansion-big-bang-infographic.html

Source SPACE.com: All about our solar system, outer space and exploration.
Source SPACE.com: All about our solar system, outer space and exploration.

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A Short Video on my Herring Aid 5

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The Ladybird TRF (Regen!) Receiver

http://www.mds975.co.uk/Content/trfradios02.html

My feelings about regenerative receivers and their possible connections to the nether-world are well known.  But the receiver described on this beautiful British web site is almost enough to make me change my mind.  Thanks to Stephen, G7VFY, for alerting me to this (and to so many other great sites!)   I also find myself forced to give regens another chance because George Dobbs, G3RJV, was the original source of this design.  It comes from a book he wrote in 1972.    I love the wooden bread-board construction.  Thanks Stephen!  Thanks George!



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The Wizard of Sao Paulo

It has been about 4 years since Miguel, PY2OHH, has been mentioned in this blog.  That's too long!  Miguel has churned out an impressive series of homebrew rigs, the latest of which he calls the Baita Tche.  Does that name look familiar?  It is a play on words using slang from Southern Brazil.  "Baita"  means big or enormous.  "Tche" means "you."  Together they sound sort of like BITX!  Miguel has been building BITX rigs and rigs (like Baita Tche)  similar to Farhan's rig.  Here is his page on Baita Tche:
http://py2ohh.w2c.com.br/trx/baitatche/baitatche.html

Here is his home page with a LONG (almost JF1OZL-ish!) list of projects:
http://py2ohh.w2c.com.br/

Here's his YouTube channel:
http://www.youtube.com/user/py2ohh

Here's a Photostream of some excellent Brazilian homebrew:
 http://www.flickr.com/photos/py2jcm/2066764415/in/photostream/

Muito obrigado Miguel!

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Farhan's RM386 RF Amplifier

An RF amplifier inspired by a quest for an AF replacement for the LM386.  I like it!  Check it out:

http://www.hfsignals.org/index.php/RF386


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Herring Aid Motorboating STOPPED!

FIXED!   Following up on suggestions from Tony Fishpool and from Roy Morgan, I put a 10 ohm resistor between the two supply lines and put 100 uF caps to ground at either end of the resistor.   I can now operate the receiver at high AF gain (no problem running a speaker) without the KLUDGE of two power supplies.  The RX sounds great.    I will soon match it up with the equally awesome Tuna Tin 2 for 1976 QRP EXTRAVAGANZA. 

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Stopping the AF oscillations in the Herring Aid 5

Thanks to all who responded.   This morning I got a significant clue:  Following up on Tony Fishpool's suggestion, I separated the power supplies:  I ran the RF amp, oscillator and mixer base bias off a small 12 V battery, with the mixer collector circuit and the AF amps running of the bench 12V supply.   The AF oscillations completely stop under these conditions.  So the feedback is probably taking place via the 12 V supply lines.  73


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Direct Conversion Receivers, AF Transformers, and Motorboating

The Herring Aid 5 is a direct conversion receiver (scroll down for details).  It is a minimalist design from 1976 using parts available at Radio Shack stores.    One of the parts no longer carried by Radio Shack is a 10K-2K ohm audio transformer.  Following NORCAL's 1998 design update I ordered an equivalent Mouser part (Xicon 42TU002-RC).   I had been running the receiver with simple RC coupling instead of the transformer.

Yesterday the Mouser part arrived and I put it into the circuit.  An increase in AF gain was immediately apparent, but the thing went into AF oscillation as soon as I turned up the AF gain. 

I tried beefing up the AF decoupling.   But I think the real problem is just the presence in the middle of the board of a rather large (1 inch x 1 inch) audio transformer.    I moved it around a bit to get it away from the toroid of the preceding stage.  This helped a bit, but it still breaks into oscillation if I turn up the AF gain.

Any suggestions?  Or is this just part of  the minimalist 1976 lifestyle?  


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German Radio Amateurs Receive Signals from ICE Spacecraft

The wizards at AMSAT-DL have done it again!  Their latest feat of outer space derring-do is the reception of the 5 watt (QRP!) signal from the lost (now found) ICE spacecraft.  Details here:
http://amsat-uk.org/2014/03/09/radio-amateurs-receive-nasa-isee-3ice-spacecraft/

Here is their facility:

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I Too Built a Tuna Tin 2

I didn't plan on doing this.  I didn't even really want to do this.   I've become a phone guy -- I'm not into CW anymore.  I figured I'd just finish the Herring Aid 5 receiver and settle the score from 1976 and that would be it.  But everything I read about the Herring Aid 5 included references to the iconic Tuna Tin 2.  Obviously I was also under the strong influence of my late February encounter with the original TT2 at the Vienna Wireless Winterfest.  That Mojo is powerful stuff!   Then my wife brought home this can of Russian tuna.  The dimensions were perfect.  Then I looked in my junkbox and found 40 meter CW crystals.  That was it. I had to do it. 

I built mine Manhattan style, using several of W1REX's fantastic Me-pads.   I also used as the final a transistor that Rex gave me at Winterfest. Thanks Rex.  Soul in the New Machine. 

I'm getting about 200 mW out.  I;m on 7030 kHz and 7040 kHz and 7110 kHz.   I have the TT2 up with my Drake 2-B (Herring Aid 5 integration will come later).  I can feel the Mojo. 

I just had my first contact with the TT2:  I called CQ on 7110 and AB2RA came back.  Jan was running 20 watts from an old 807 rig, listening with an old Hammarlund.  So it was HB transmitter and vintage receivers on both ends!  FB!





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Lulu Book Sale, Job Openings

Lulu is running a 20% off sale on books.   You can pick up SolderSmoke -- The Book at a discount.  Just use the coupon code SUPER20  :
http://www.lulu.com/spotlight/soldersmoke

And as long as we are talking about money, I spotted some job openings that might be of interest to readers of this blog: 

http://makezine.com/2014/03/06/wanna-work-for-us/

http://hackaday.com/2014/03/06/were-hiring-2/


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Some notes on the Herring Aid 5

Sure, this receiver is not "state of the art."  But that's the whole point.  I wanted to finish the receiver project that I couldn't finish back in 1976. 

I tried to stick as close as  possible to the original design and parts.  NORCAL came up with an updated schematic in 1998 with parts that are more readily available.  But Designer Jay Rusgrove was shooting for something that could be built with all the parts coming from Radio Shack.   I think that is probably one of the factors that attracted me to the project way back when.  That's why Jay went with varactor tuning (no hard-to-get variable caps!).  And that's why he used coils that were wound  on Radio Shack 10uH RF chokes (no need for hard-to-find toroidal cores).  In this sense there is some common ground between the BITX rigs and the Herring Aid 5.

I stuck with the RF-choke as a coil idea for the VFO, but went with the NORCAL-prescribed toroids for the front end and mixer coils.  (I may go back and try to use chokes in these circuits, but I'm not sure my junk-box will yield the kind of RF chokes that Jay used).

I wish I had known a few things when I was building this back in 1976: More knowledge about how to wind the coils would have been a big help.  I wish I had realized that I could use a SW receiver to get the oscillator on the right frequency. I guess this was in the days before Ugly and Manhattan building techniques, but it would have been nice to know that there was no need to actually etch a board for this project (I did!).

The coils really are a bit tricky.  Jay didn't use any trimmer caps, so I guess you had to just hope that the front end coil and cap resonated somewhere near 40 meters.   As for tuning the oscillator, Jay recommended scrunching and un-scrunching the turns on the RF choke.  Yikes!  Give me some trimmer caps! 

I also found that you have to watch the level of the RF going from the oscillator to the mixer.   Too much, and the receiver is deaf.  Too little, same result.    You need to experiment a bit with the number of turns on the pick-up coil from the oscillator.   

The warnings about the pitfalls of that single BJT mixer were right on the mark:  Lots of AM SW breakthrough.  But I kind of like the background music.   Strong RFI from local FM broadcast stations was another story (WMZQ is a country music station!).  I reached into my junkbox and found a low-pass filter from a Heathkit DX-60.    I just put that between the antenna and the receiver and the country music was GONE! 

I really love this little receiver.  I have it playing 40 meter CW as I type.  It sounds great.   I feel the urge to built a Tuna Tin 2 and put both of them on 40. 

In the original Tuna Tin 2 article, Doug DeMaw notes that Jay Rusgrove was thinking of doing a companion receiver and says that he was thinking of calling it the "Clam Can 5" !  There were jokes about receivers for hams with "tin ears" and about there being "something fishy" about these rigs.

Thanks to Doug DeMaw and Jay Rusgrove and QST for bringing us these little circuits. 


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Herring Aid 5: Working after 38 years!

I know, it is just a little Direct Conversion receiver.  Getting it going is no great technical achievement.  But this little receiver gave me such trouble as a teenager, it has been in the back of my mind for a long time.  Finally, yesterday afternoon it started picking up signals. 

I felt a bit bad about insinuating (a few days ago -- see below) that QST may have made an error in the 1976 schematic.  They didn't.   So it was kind of spooky when I heard that first call-sign coming through the speaker:  It was W1AW!  It was as if they were saying:  "See, the schematic was correct!"

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Herring Aid: It was NOT the dots! Rotational Sense and Phasing

Opposite "sense" winding and resulting phase shift

My second attempt at building a Herring Aid 5 (the first was 1976) continues. 

I thought I had discovered an error in the schematic that (I hoped) explained my failure to get this simple receiver running (scroll down for details).  But Dex, ZL2DEX,  in New Zealand spotted something that got QST off the hook and put all the blame back on me:

I had failed to check the rotational sense of the windings.  The schematic called for 4 turns over the Radio Shack choke.  So I just went ahead and wound them.  I didn't pay any attention to the direction of the winding.  I then hooked it up in accordance with the phasing dots in the diagram.  And it didn't work.  So I switched the coil connections around.  And it worked.  Aha! I thought! QST messed up!  It wasn't my fault. 

Dex brought me back to reality.  He noted that I probably wound the coils with the wrong rotational sense.   I confirmed this.  I rewound the coil following the rotational sense of the choke.  I hooked it up following the phasing dots of the schematic.  This time the oscillator started right up.  So the problem wasn't an incorrect drawing of the phasing dots.  Instead it was my failure to remember that phasing is more than just the top or the bottom of a transformer's winding.  Rotational sense is also important.  That's why "phasing dots" are sometimes referred to as "sense dots."

This doesn't come up very often, because most of the toroidal transformers we make are bifilar or trifilar -- the windings are always in the correct sense because we twist the wires together before putting them on the coil.  When we look at those phasing dots, we are focused on getting the proper tops of coils connected to the appropriate bottoms of other windings.  We don't pay any attention to the sense of the windings.  Thanks to Dex for bringing me back to my senses :-o

Grob's Basic Electronics has this definition for those phasing dots:

"	Used on transformer windings to identify those leads having the same instantaneous polarity."

This morning I did a little experiment to confirm all this:  I took a toroidal core and wound a little transformer.  Using a dual trace scope, I looked at the input and output wave forms.  Sure enough, when the windings are in the same rotational sense, there is no phase shift.   But when that secondary is wound in the opposite sense, you get a 180 degree phase shift.  I know this is very basic, but it was fun to re-learn it and to confirm is.

But I still don't have the little receiver running.  I think there are a few problems.  That single BJT mixer stage needs a lot of RF (2.5 volts p-p) from the oscillator.   Also, I think the 10 uH chokes that I am using are not the same as the chokes used in the original Herring Aid design.  So when I build transformers on these chokes, they don't work very well.

But I will keep at it.  It has been 38 years... I can wait another week or two.   

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38 Year HB Mystery Solved? Was it the phasing dots?

 During the summer of 1976, at the age of 18, I made an audacious attempt to join the ranks of the true homebrewers.  I tried to build a receiver.  It was the Herring Aid 5 from the July 1976 issue of QST, a 40 meter Direct Conversion receiver intended for use with the famed Tuna Tin 2. As I have recounted (perhaps ad nauseum), I never got it to work.   My recent encounter with the ORIGINAL Tuna Tin 2 (Mojo was transferred to my BITX17, and it definitely works better now) got me thinking about this painful experience.   I decided to try again.

There is an updated NORCAL schematic for this rig.  I found it (and some good articles) on the NJQRP club page.   In the original, designer Jay Rusgrove, WA1LNQ, used only parts that could be found at Radio Shack stores.  In the days before the internet and Mouser, this was a good idea.  Instead of toroidal ferrite and iron powder coils,  Jay built his coils around Radio Shack solonoidal 10 uH chokes. 

The NORCAL version dispensed with the Radio Shack chokes, and used toroids.  But I wanted to try to find out what went wrong 38 years ago.  So I dug up some 10uH chokes. 

I know that my problem was that I never got the oscillator working.  I remember being able to hear signals with my "almost" receiver when I put my HT-37 in "CAL" mode and tuned through 40.  I was so close!  The Herring Aid was picking up RF from the HT-37 and using that in lieu of the LO energy that obviously wasn't coming from my Herring Aid VFO.  But WHY didn't that oscillator work?

Today I started with the VFO.   Again, it didn't work!   But now I have decades of troubleshooting experience under my belt.  So I poked around a bit.  Then I decided to look closely at the phasing.

Take a look at the schematic(above) and the picture (below).  L7 is the 10uH choke.  L6 is 4 turns wound over it (or adjacent to it).  Now, here is the key question:  Look at the phasing dots.  How would you guys connect those coils?   For me, the schematic indicates that the TOP of L6 should go to the Zener and the BOTTOM of L6 should go to the drain of the JFET.   The TOP of the choke should go over to C5, and BOTTOM of L6 should go to ground.  Right?  Or am I reading the phasing dots wrong?

Well, the oscillator was not oscillating in this configuration.  Then I did something that I might not have known to try back in 1976:  I reversed the phase of L6:  I put the top of the coil to the Drain of the JFET and the bottom of the coil to the Zener.  Bingo.  The joy of oscillation.  Now it works.  (The picture below shows it as it is when the oscillator is working well.)

So,  is there an error in that diagram?  Was this not all my fault?   

Aha! I just looked at the schematic of the NORCAL version.  Check out the dots!   I think that was the problem!

 

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Links Fixed, Podcast Version of Hamfest Presentation

Armand, WA1UQO, with BITX 17

 

Using Dropbox to post the video of my BITX presentation at the hamfest didn't work out too well, so I put it on Vimeo:

 https://vimeo.com/87725154

The slideshow is here: http://soldersmoke.com/winterfest.pptx

I stripped out the audio for those who would like to dispense with the video.

Audio only is here: 

http://soldersmoke.com/soldersmokewinterfest.mp3

73

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Hamfest Presentation on SolderSmoke and BITX (Video)

The Vienna Wireless Society of Northern Virginia asked me to give a talk at their 23 Feb 2014 hamfest.  I spoke about homebrewing and the BITX transceivers.  Click on the link below to watch the video.  (Special thanks to Elisa for doing the video.)

https://vimeo.com/87725154

The Powerpoint slides are here:

http://soldersmoke.com/winterfest.pptx

For those who just want to listen podcast style,  I will try to turn the audio into a podcast and will post it via the normal channels. 


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HB Chips! Discrete Component Version of 555 Timer

The world would be a better place if we could do more of this...  Thanks to David Cowhig for alerting me to this wonderful development. Details here:

http://spectrum.ieee.org/geek-life/hands-on/build-your-own-giant-555-timer-chip


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Tuna Tin Mojo Transferred to BITX17!!!!!!

It happened at the Vienna Wireless Society's Winterfest Hamfest today in Northern Virginia.
That is Doug DeMaw's original Tuna Tin. 
This may be the first time TT Mojo has been given to a phone rig. 
Doug DeMaw would, I'm sure, approve.

Thanks Rex!


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Brilliant! New "TX Factor" Ham Radio TV Show from the UK

I really enjoyed this.  It is the first episode of what I hope will be a long-running series.
These guys did a great job.  Excellent quality video production and very interesting subject matter. A LOT of work went into this.  I liked the PSK from a smart phone on a foggy hillside (with Moroccan soup!).  The Marconi stuff was wonderful.  Beer barrels as 2 meter cavity resonators! Excellent Knackish-ness!  And a two meter repeater in an astronomical observatory.  Well done! 

Thanks to Nigel and Dino for alerting me to the TX Factor.

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Taking the Knack a Bit Too Far

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BITX 17 Build Update: More Filter Maintenance

 

 

 

Having had great success in straightening out the 11 MHz filter in my BITX 2040 (scroll down for details),  today I decided to see what I could do with the filter in my 17 meter BITX (four 5 MHz crystals in Cohn MIN LOSS configuration, with 40 pf caps all around).  The key to my success in all this has been the filter programs that came with EMRFD.  After characterizing my crystals with the G3UUR method, I plugged the values into LADBUILD 8, then took a look at the expected results.  As you can see from the image above the predictions were not pretty.  Yuck.  Lots of ripple and lots of insertion loss.

I went into the rig and using my DDS sig generator and my RIGOL 'scope, measured actual performance.  It looked worse than the prediction (part of the worsening is a difference in vertical scale):

LADBUILD lets you play around with the values of the components in the filters.  I know that ripple is usually related to an impedance mismatch.  So in LADBUILD I experimented (virtually) with different impedance values at the end.   I noticed that at about 1000 ohms, the ripple and insertion loss got better:

So I went and built two broadband toroidal transformers.   4 turns primary with 12 turns secondary (1:9 Z).  I'm assuming that the BITX has around 150 ohms at either end of the filter.  That would put about 1350 ohms at the ends of the filter.

Here are the results:

Much better.



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ISEE-3 Spacecraft Returns after Being Forgotten

Hack-A-Day has issued a challenge to hams and hackers:

http://hackaday.com/2014/02/14/call-for-hams-and-hackers-welcome-iceisee-3-home/#more-114769

If a BITX 20/40 would help, I stand ready to assist!  


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Homebrew Junkbox Machine Tools

In the book "The Ugly American"  the hero (the ugly guy!) come up with a way to use old engine blocks to build water pumps to help farmers in South East Asia. Now, Mr. Delany is putting them to similar good use.  Homebrew junkbox machine tools!  Yea!

http://makezine.com/magazine/make-37/patdelany/

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BITX 2040 Build Update #10 : Fixing my Filter

That dip on the high side of the passband was bothering me.  The GPLA crystal design program predicted it, and indeed, when I measured the performance of the actual filter, there it was.   The rig was working fine -- the receiver sounded fine and everyone tells me that it sounds great on transmit.  But still, it bothered me.

So I started working out with the various crystal filter software packages.  

This filter was -- sort of -- a Cohn Min-loss filter, but I had built it with four crystals and three shunt caps (80 pf each) and no series caps at the input/output.  This morning I decided to see what would happen if I put the series caps in there.  Here is what Wes's GPLA predicted:

Wow, that looked a lot nicer.  And the 150 ohm terminations seemed to be just about perfect for the BITX design -- no need for impedance transformation.  I heated up the soldering iron and searched the junkbox for suitable caps (I found 2 82 pf caps -- close enough).

Here is what the results looked like (I didn't measure insertion loss so the top of the curve is just the peak of the response curve).

Exactly as predicted!  Thanks Wes! And thanks to Farhan for encouraging me to characterize my crystals and to use the available software

Now I have to go back and de-ripple the 5 MHz filter in my BITX 17.

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Back to the W7ZOI/W7PUA Power Meter

Recent e-mails and Facebook postings from Jim (W8NSA) and Michael (AA1TJ) got me thinking about my old W7ZOI/W7PUA power meter.  The 15 inches (38 centimeters) of snow that fell last night gave me the day off -- and time to play with this very useful and interesting piece of gear. 

The last time I used it I remember thinking that a digital readout would be nice.  But I didn't feel like going back into the world of Arduinos and LCD screens.  So I came up with a real Kludge solution:  I had cheap little DVM that I wasn't using, so I just velcroed it to the side of the power meter.  That little connector above the BNC is the output for a DVM.  I might work on calibration later today.

Wes has some very interesting info follow-up info on the meter on his site: http://w7zoi.net/qststuff.html
I really like the part about how the meter is so sensitive that you can see the thermal noise in the input circuit and can actually measure the strength of signals from your antenna. 

I think I might need a low pass filter at the input of the meter.  There are strong FM broadcast transmitters in this area (some of you may have listened to them in the background of early episode of the SolderSmoke podcast!). I notice that just bringing my fingers close to the input causes the meter and the DVM readout to swing up.  That's not good.

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A Very Simple SSB Transmitter

 

 

I found this in the files section of the BITX20 Yahoo Group.  There is no information on the source.  I see two balanced modulators and two very simple phase shift networks. 

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Mars Star Party from La Palma (video)

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BITX 2040 Build Update #9: On-the-air Observations

The BITX 2040 has moved from the bench to the operating position and is producing a steady stream of contacts on 20 and 40 meters.  In the picture above it is the rig with the copper-clad front panel (the BITX 17 is below it).  It has already crossed the pond on both bands.

Some observations:

I get significantly more power out on 40 than on 20:  about 7.2 watts PEP on 40 and about 4.4 watts PEP on 20.  I saw a QST article that showed similar frequency/power out variations from IRF510 amps.   But I notice I get more power out from my 17 meter rig.  On that rig I am using trifilar (9:1 Z) transformer instead of the standard BITX bifilars. 

My 40 meter receiver is LOUD.   Too much AF out.  I am not used to having this problem!  On this rig I am using the same discrete component 2n3904 2n3906 transformer-less circuit that I used in the BITX 17.  But AF out on 40 was so loud that I had to go back and add 20 k ohms to the top of the volume control pot.   I didn't have this problem with the 17 meter rig, and I didn't have it on 20 with this rig.  Any ideas why this rig would be so loud on 40?

I still want to go in and fine tune the crystal filters in both rigs.  I am studying the various software packages out there (especially Wes's LADPAC).  I hope to get rid of the ripple.   

In most of my contacts with these rigs, I end up describing the circuit and its Indian origins.  Most people are really fascinated.  Yesterday W1IDL in Michigan suggested that I contact my Indian friends and get some assistance in making some Hindi or Urdu labels for the rig and the controls.   I think that is a very cool idea. 

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Coils, Magnets, and Special Relativity (video)

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Inductive Reactance and Special Relativity

Bill,

I'd been meaning to share these stories with you after I read your book a couple years ago but I never got to it.  I thought you might enjoy them, from an "engineering perspective", I guess.

One of the courses I had to take for my undergrad was an engineering physics type class.  I loved it.  I think a lot of hams seem to have more curiosity about the physics of electronics than regular non-ham engineers, at least that's how it's always seemed to me.  Anyway, I'm sending you a snapshot of the relativistic length contraction figure in the book "Concepts of Modern Physics", 4th Ed by Arthur Beiser.  I thought you'd enjoy it as it is almost identical to what you mentioned in Soldersmoke (from your "Atoms to Amperes" book I think).

Hopefully there's enough resolution there to make it out.  Basically, when you flow current in the same direction in both wires, they attract.  That's because the electrons see effectively many more positively charged nuclei from the other wire than they do other electrons due to the nuclei distances being compressed by the Lorentz-Fitzgerald contraction (later refined by Einstein). 

When I first saw this, in my early 20s, I was completely floored!  Nowhere had I ever learned anything like this from the ham license manuals or even my basic physics course.  The implications were also very profound -- magnetism was nothing more than electrostatic attraction, the attraction between charges.  The "electromagnetic" force was really just an electric force.  Relative motion between charges gives the illusion of "magnetism". 

Much later, I listened to some of the old Feynmann lectures.  In them at one point he adamantly proclaimed that there's only the electric force between charges, and there is no magnetic force!  I still find this confusing.  Recently I brought this up to a university RF engineering professor.  I wondered why we dealt with Maxwell's equations when in reality the magnetic field is an illusion.  The "real" formulas come from Feynmann's theory of quantum electrodynamics!  His reply was something along the lines of Maxwell's equations being a solution of quantum theory that worked well for our purposes.  To be honest, I didn't really understand his reply and I'm still skeptical!  I think his point was that the QED calculations are overly complicated and unnecessary for most problems we deal with, things like patterns from an antenna.  I don't think Maxwell's equations appropriately describe things like lasers though, which are more quantum in nature with the coherent beam.

FYI, most engineering students I ran across had only passing curiosity for these things.  Only in graduate school did I start to find people curious enough to really try to understand "what lies beneath" some of this stuff, mainly this physics.  Honestly not even everyone in grad school was all that captivated.  As you've said before, there's a lot of "turn the crank" mentality in engineering where you wade through mathematics to get answers, not always thinking about the physics.  It's even worse in the digital world, where everything gets boiled down to computer code! 

One more quick thing.  I talked to a physics prof once, asking him if there was any research happening in his department focused on electromagnetics and radio waves, etc.  His reply: "radio waves are nothing more than the result of accelerating electrons".  Period!  Discussion over.  In other words, that's ancient history.  Engineers are still very much involved with new technologies involving antennas and amplifiers, etc.  But as far as the physicists are concerned, I get the impression that our whole field is pretty ho-hum.  But he was right about accelerating electrons, I also found out later.  And it doesn't have to be electrons.  Anything carrying charge undergoing acceleration will emit photons.  That's another crazy situation that I only more recently learned.

Hope that was entertaining!

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BITX 2040 Build Update #8: All Boxed Up and Ready to Go!

Its kind of scary:  my BITX 20/40 is starting to look vaguely appliance-like!   Once again I find myself missing having the rig exposed -- sans-cabinet -- on the bench.  For me, the contacts made under those conditions, with solder smoke still in the air, are the most satisfying and memorable.  

But anyway, it is in the box now.  I think it looks pretty good.  I enjoyed working with the copper foil.  I did some trial and error testing and found that ordinary Krazy Glue is the best adhesive for joining the plastic material on the back of the foil to the wood of the box.  I like the look of the foil -- it reminds me of the copper (or gold?)  foil covering that they put on some spacecraft. 

There is always the danger that a rig that works well on the bench will go into rebellious oscillation when confined to a metallic box.   That didn't happen with mine. 

We discovered that the wood in the box is not actually walnut.  But I'm not complaining because whatever it is, it is very easy to work with.  BITX or Minima builders should consider these boxes (available via Amazon). 

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G0MGX's Minima

Wow, Mark didn't waste any time in building his Minima. FB OM.   His web site has a lot of good info on this project:  http://g0mgx.blogspot.co.uk/


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BITX 20/40 Update #7: Cabinetry and Socketry

With the 20 Meter Oscillation Exorcism behind me, I have decided to take a break from electronics and do bit of woodwork.   I took the walnut (I think) box that I bought via Amazon and cut out a big piece of the wood on the front.  That's where the rectangular piece of copper clad board will go -- it will be the front panel, supporting the AF gain control, the bandswitch, the main tuning control, and the mic jack.   A similar copper clad board will be on the back, this one supporting the antenna jack,  speaker jack and 12V input jack (with space for a linear amplifier T/R control jack).  (George Dobbs, G3RJV, calls this the "socketry.")

That beautiful copper sheeting will line the inside of the box.

I found the soft wood on this box to be very easy to work with.  The little saw pictured above made the woodwork easy.

I have boiled linseed oil and clear polyurethane for the finish. 

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BITX20/40 Update #6: 20 Meter Exorcism

The transmitter was working fine on 40, but was horribly unstable on 20. In the past, this kind of thing would really drive me nuts, but experience has made me more patient. I know that "taming the beast" is part of the homebrew process. 

I knew that layout was part of the problem:  I had significantly less room on the board with this rig than I'd had with the BITX17:  the additional bandpass filter and low pass filter, and the associated relays, used up a lot of copper clad real estate. So by the time I built the PA chain, the inputs were too close to the outputs.

The fact that the rig was stable on 40 but not on 20 led me to believe that this was not a problem of insufficient decoupling.  Instead, I thought that I was getting additional inductive feedback at the higher frequency.

I noticed that the instability disappeared when I put the 1X scope probe on the input to the first amp in the RF chain (Q14). That was an important clue.  Looking closely at the circuit, I realized that the base of Q14 had a long lead (several inches) up to the low pass filter.  I had experienced problems with this lead on the BITX 17 project and had cured it with a relay at the low pass filter -- this relay took one end of the lead out of the circuit on transmit, preventing it from becoming a little radiator.  I used that mod in this rig, and figured that that cured the trouble.  Wrong.   The other end of that lead was still connected to the input to the RF power chain.  It was picking up enough RF to send the PA chain into oscillation.

I put a SECOND relay at the other end of the line.  That took it completely out of the circuit.  And the instability disappeared.  I fired up the rig and worked California on 20.  Very satisfying.   

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BITX 20/40 Build Update #5: It is ALIVE!

I got the BITX 20/40 on the air this morning.  The receiver has been working for a week or so, but as usual it was a bit of a struggle to tame the transmitter.  I got up early this morning and started poking and probing.  I played with the driver and final coils a bit.  I had used the same trifilar toroids that I'd used in the BITX 17, but this rig didn't seem to like them. So I went with FT-50-37 bifilars -- that seemed to work better.  That IRF-510 seems to put out about seven watts on 40.  (I still need to tame the transmitter on 20).  The 40 meter signal looked great on the 'scopes (RIGOL and Tek!).  Shortly before 8 am I worked AD4SY who reported that I was filling his shack with booming audio.  Life is good.  

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Digi 'scope, Analog 'scope

Carl (M0ICR ex 2E0TEC) saved the day with my Tek 465 -- he sent the replacement HV multiplier that put the 'scope back in action.  (Ace Tek repairman Tad WA1FQO made the repair.  Tad sells Tek scopes on E-bay -- check out his products: Search for fqo63 on ebay.)

Carl notes a number of similarities between our workbenches and recent projects.  All he needs now is a Drake 2-B!

Alan Wolke said he'd be interested in my reactions to having both a digi scope and an analog scope on the bench.  I can already see areas where one might be a bit better than the other.  The Tek is better at watching a fast moving audio or SSB waveform.  But the Rigol doea all kinds of math tricks.  Check out the FFT function shown on Carl's page:  http://iqrp.net/

Bill,

I am very pleased that you finally got it working with the help of brothers from the fraternity.  Having listened to your latest Podcast I think that must be your alter ego!  I have A Tek 465, Rigol 100MHz DS1102E and have built 2 Bitx, one for 20m and the other for right bands- using a DDS VFO  (3 if you include the 80m version by Steve Drury G6ALU - look up MKARS80) ...I also have 2 copies of SSD!

My website is here:  www.iqrp.net  where you can see both scopes in my shack and images of my Bitx and my Hans Summers WSPR beacon!

I have just returned from my local radio club social meeting (the Radio Society of Harrow) and took great pleasure in listening to Soldersmoke 158 whilst driving there ... half on the way there and the other half on the way back.

Very best wishes from London (where it is cold, wet and miserable !)

72/73 de Carl M0ICR (ex 2E0TEC from Nov 13)
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SolderSmoke Podcast #158: BITX 20/40, Farhan's "Minima", BITX Bandsweep

SolderSmoke Podcast #158 is available:

http://soldersmoke.com/soldersmoke158.mp3

January 20, 2014
MLK Day. Tough winter.  Shack heated by Heathkit.
BITX 20/40 Almost done:
Bandswitching arrangement.
VFO construction using spreadsheets.
2N2222s wired in backwards! (CBE not EBC! Who knew?)
Other amusing building errors.
Crystal filter evaluation -- the G3UUR method.
Sweeping a filter with an Arduino DDS.
Building a BITX in LTSpice.
New Rigol 'scope (now 100 MHz).
Tek 465 REBORN!
QRP HATERS -- They are out there!
MAILBAG.
BITX 20/40 dual band bandsweep

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John Dobson (Sidewalk Astronomer, Telescope Maker) RIP

http://www.skyandtelescope.com/news/home/John-Dobson-1915ndash2014-240456881.html

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