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Wednesday, March 12, 2014

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:


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Sunday, March 9, 2014

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!





Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Saturday, March 8, 2014

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/


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Friday, March 7, 2014

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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Wednesday, March 5, 2014

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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Tuesday, March 4, 2014

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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Saturday, March 1, 2014

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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Thursday, February 27, 2014

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

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Wednesday, February 26, 2014

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. 


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Tuesday, February 25, 2014

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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Sunday, February 23, 2014

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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Saturday, February 22, 2014

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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Wednesday, February 19, 2014

Taking the Knack a Bit Too Far



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Monday, February 17, 2014

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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Sunday, February 16, 2014

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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Saturday, February 15, 2014

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/

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Thursday, February 13, 2014

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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Wednesday, February 12, 2014

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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Tuesday, February 11, 2014

Mars Star Party from La Palma (video)



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Monday, February 10, 2014

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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Wednesday, February 5, 2014

Coils, Magnets, and Special Relativity (video)



Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Tuesday, February 4, 2014

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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Sunday, February 2, 2014

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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Friday, January 31, 2014

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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Thursday, January 30, 2014

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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Monday, January 27, 2014

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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Thursday, January 23, 2014

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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Wednesday, January 22, 2014

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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Monday, January 20, 2014

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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Thursday, January 16, 2014

Farhan's New Design: A General Coverage Transceiver: The Minima!


The homebrew phone QRP community has been waiting anxiously for the unveiling of Farhan's new design:  The Minima.  It is a general coverage transceiver with many innovative circuit features.  It has an Arduino in it and an Si570. Farhan's write up of the design process and the construction of the prototypes is really interesting.

http://www.phonestack.com/farhan/minima.html

I've built FOUR JBOTs and TWO BITXs.  I even built Farhan's Subway Sandwich Straw signal generator.   So even though I've been trying to keep my rigs all discrete,  I know I will build this one too. 

Three cheers for Ashhar Farhan!  Viva La Minima!

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Sunday, January 12, 2014

Words to Live By...





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Saturday, January 11, 2014

Bert's Blog and BITX


Our friend Bert is once again melting solder.  And he has launched a blog.  (SolderSmoke listeners will remember Bert as the advisor to the University of Virginia radio club.   That was the club that had its HQ in some sort of nuclear reactor building.  They put up a huge wire antenna, but then took it down when they realized bike riders could possibly, uh, run into it.)    Bert has some interesting stuff on his blog, including an article on conductive paint and one on the use of mail boxes as antenna tuner enclosures.  And he reports that he has dusted off a BITX 20 kit.  Welcome back Bert! 

Check out his blog:
http://wf7ihomebrew.wordpress.com/ 

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Wednesday, January 8, 2014

First Light


Preston:  Your use of the term "First Light" is especially appropriate.  I got the concept from a wonderful book of that title by the author Richard PRESTON.  I pulled it off the shelf this morning, and, as my coffee was brewing, read this on the dust cover:

"First Light won the American Institute of Physics award in science writing. An asteroid has been named "Preston" in honor of First Light. It is likely someday to collide with Mars or the earth."

The book's glossary defines first light as: "A technical term from astronomy signifying the moment when starlight is allowed to fall on a new mirror for the first time."  The first light experience must, I think, be similar to the feelings we get when we first allow RF to fall on the front end of a new homebrew receiver.

Congrats on the S-107 OM.

73  Bill N2CQR
------------------------------------------

From Preston Douglas WJ2V:

I am happy to report that my little novice rig (well it's not so little if you weigh it) consisting of my restored circa 1960 Hallicrafters S-107 and circa 1959 KnightKit T-50 (with V-44) made our first QSO with a guy 20 miles away on Staten Island.  This was Saturday afternoon, in full daylight, on 40 meters.  He was also running vintage equipment (Heath) but running an SB-200 Heath linear.  I have no idea why he needed a linear on 40 meter CW, but he seemed happy with it.  I could easily hear his signal via leakage through my Daiwa cavity switch, so it was a pretty powerful signal.  The T-50 puts out maybe 20-25 watts full bore, but it certainly works fine, and got a 569 signal report.  The 9 part was obviously the important one.
 
I had just turned on the equipment, so the S-107 needed to be adjusted a bit during the QSO to allow for a bit of warm up drift.  It stabilizes ten or fifteen minutes after warmup.  I had to use a straight key as I have not yet built the little kit that interfaces solid state keyers with old rigs.  I'll get to it on a slow afternoon this winter perhaps.  But for now, a straight key is about the right speed for this setup.  T/R requires switching the antenna, the VFO to transmit, and the receiver to standby for transmitting.  Not exactly QSK. Since there are so many switches, it may not pay to add an antenna relay switch to this setup.  Besides, switching is part of the fun.  

I did not get set up in time for New Years, so missed the chance to operate SKN.

I learned about first light from Bill Meara's podcasts.  It refers to the first time a telescope is used, but, as he says, it applies just as well to a new (old) rig.

All of this was caused by a local ham offering a Hallicrafters S-107 for ten bucks. Even with the few bucks needed to put it right, I sure got my money's worth.  

Regards guys and Happy New Year,

Preston WJ2V
----------------------------------------
 
Earlier from Preston:
 
I am pleased to report my S-107 is restored to full function.  Based on the build up of filth on it before cleaning, it is also cleaner than it has been for many years.  The greasy dirt (I shudder to think what it was made of) in between the flutes of the control knobs has succumbed to a toothbrush and detergent.  Who'd have thought what a difference clean controls would make in the overall appeal of a radio?

The S-107 was purchased without negotiation from a local and fellow member of the Long Island Mobile Radio Club for ten bucks.  I cheerfully handed over a ten spot and drove home with this rig.  

On the bench, the tubes lit, and I could hear a couple of AM stations, but it made an awful racket with 60/120 cycle hum.  New electrolytic caps cured that.  The chassis felt "hot" to the touch.  Resistance checks on the HV-to-AC sides of the transformer confirmed that, thankfully, there were no shorts.  On advice of some pros on this list and elsewhere, I removed a cap and resistor from the AC line to the chassis that Hallicrafters thought was a good idea.  With a new three wire grounded plug, the chassis was now cold.  

Alignment was done with an old Conar signal generator (my $1 victory from an old hamfest) and trusty Tek 465 with frequency counter connected to its rear connector.  The double IF transformers peaked up, and so did the front end compression caps on all bands.  And now, the radio really receives CW and SSB!  With a simple dipole (my beam seems to have gotten sick from Irene and Sandy) I get good signals on 80, 40, and 20.  Maybe next weekend I will have time to try the upper bands during daylight hours.  But, the signal generator suggests they should be fine.

The ten buck receiver needed ten bucks worth of electrolytics.  And I needed to buy a little 20 buck kit of Bristol Splined wrenches.  (Nobody I thought to ask had a set to lend.)  They were needed because: Another Hallicrafters bit of wonderment is that the setscrews in the control knobs need to be turned with these unusual wrenches that look like, but aren't, hex keys.  Well, I suppose I can say I have the wrenches if I decide to restore another Hallicrafters.  I hear Collins has them too.

I think I mentioned that I had to restring both the band spread and main tuning with real dial cord.  Another three bucks, perhaps.  So, my ten buck receiver is still a bargain at around 40 bucks in all.  And, I had a lot more than 40 bucks worth of fun.  I spent part of the afternoon just listening to the receiver, it sounded so good.  You know how it is when you first listen to a new receiver.

Now, next thing will be to see how it does making contacts with a Knight T-50.  I know the T-50 is not quite QRP.  I probably puts out about 25 or 30 watts.  

This will be about as close to my novice station as I am willing to fall.  The original station had the T-50, but no VFO (which came with the T-50 I have now); but the receiver was an S-38E, which was, (collectors notwithstanding) a piece of crap.  And it's dangerous since it is really one of those transformerless AM radios in shortwave clothing.  No wonder I only made a handful of contacts with it as a novice.  I have no nostalgia for my old Hallicrafters S-38E.  I hear folks recommend operating it with an isolation transformer.  I have a better idea.  Don't plug it in.

I had so much fun with the S-107, though, I am starting to think about restoring an S-108 or an SX-110.

Preston Douglas WJ2V

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Sunday, January 5, 2014

BITX 20/40 BUILD UPDATE #4: 11MHz SSB Ladder Filter


As reported yesterday I have the 20 meter receiver portion of my BITX 20/40 rig up and running.  I decided to take a closer look at the crystal filter I built.  

Here is my method:  

1) Using an Arduino/DDS sig generator, I put 11 Mhz energy into the base of Q2 (the stage immediately prior to the crystal filter).   

2) Using my Rigol 1052E oscilloscope, I measured RMS voltage at the output of Q3/Q3A (the stage immediately following the filter).   

3) I looked at Vrms as I MANUALLY varied the input frequency in 100 Hz increments.

4) I took the results and plugged them into a spreadsheet.  I then used the spreadsheet to calculate the db drop from the peak Vrms value (So I wasn't looking at insertion loss, just the filter shape).  
I used 20*LOG(Vrms/276)

5)  I ended up with the chart displayed above. 

I have a few questions: 
1) What do you folks think about my methodology for evaluating the filter? 
2)  Where would you guys put the BFO frequency? 
3)  I know the ripple looks ugly, but the receiver sounds great.  Should I attempt to get rid of the ripple? 

Here is the filter I used (as prescribed by the AADE software):  I estimated Q at 10000 and used LM and CM values derived by the G3UUR method, and made no effort to match impedances going into the filter:   



Here is what GPLA predicted.  I estimated Rin and Rout values.  That probably accounts for the difference between the GPLA prediction and what I measured. 
  




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Saturday, January 4, 2014

BITX 2040 Build Update #3 Receiver Sounds Great!


There it is,  my second BITX transceiver, this one for 20 and 40.   Once I got the VFO sorted out, this one went together very quickly.  Obviously experienced gained on the first project was a big help.

I followed Farhan's advice and characterized the 11 MHz crystals in the filter.  Then I used the AADE filter design software to build a 3 KHz filter.  Using my Arduino DDS signal generator and the new Rigol 'scope, I was able to do a manual sweep across the passband -- it looked very close to what was predicted by the software. 

This morning I built the bandpass filter for 20. As soon as that was done, I fired up the receiver.  This was an amazing experience for me: a homebrew receiver that worked right away!  That never happened before.   I'm listening to 20 meters now.  It sounds great.  I even managed to demodulate and display some SSTV.  The VFO seems very stable.

I still have to build the RF amplifier stages, the bandpass filter for 40 and low pass filters for 20 and 40 (I know Steve Smith is watching!).  Then it will be time for cabinetry.   I guess I should put some paint or varnish on that walnut box.   Any recommendations?   I'll line it (on the inside) with copper flashing material.     

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Wednesday, January 1, 2014

Happy New Year! Straight Key Night

 
For the first time in years I got on the air on New Year's eve.  I fired up the HT-37 and Drake 2-B on 20 meters last night right at 0001 UTC  (well, with these rigs I should say GMT!).  There was a moment of stress when, as I was trying to adjust the key, the whole thing fell apart and the little ball bearings spilled out.  Yikes!  It was as if the radio gods were trying to tell me something.  It took me a few minutes to re-assemble my straight key, then I called CQ.  The HT-37 puts out a lot more power than I normally emit,  and it caused the Carbon Monoxide detector to go off, sparking a minor panic among family members.  (See, this never happens with QRP!)  With that resolved I had nice QSOs with K5KFK in Texas, W6VNR in California, and N1WPU in Maine.  This morning I worked WA0ZDE in Missouri.  The old HT-37 was drifting a bit, but Rick said he kind of liked that.  (I put a muffin fan on top of the transmitter -- that should settle it down a bit).   By the way, my key is a bit unusual: it is just a cheapo key, but I have it mounted on the base from a Vibroplex bug.  I never mastered the Vibroplex, and ended up giving the bug parts to HI8G in Santo Domingo -- Gustavo planned on using them to fix another bug that had been given to him years before by Fred Laun (K3ZO). 
 
Rick, WA0ZDE ( who I talked to on 20 this morning) sent me a VERY SKN photo collage (see below).  I see that Rick also tends to hold onto his gear for a long time. 
 
HNY to all!   GL in 14.  73! 
 



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Designer: Douglas Bowman | Dimodifikasi oleh Abdul Munir Original Posting Rounders 3 Column