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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Amazingly Cool MONTV Video on Direct Conversion Receivers with Glue Stick PTOs

I think this is one of Nick's best videos. And he has made a lot of good ones. 

https://www.youtube.com/watch?v=xl9dnajkYO0

This is a really excellent description of how a Direct Conversion receiver works. But more importantly Nick really captures the joy of building one of these receivers using discrete, analog components, including a Permeability Tuned Oscillator made from our beloved Glue Sticks.  

Extra mojo comes in the form of a mixer designed by Pete Juliano using J310s to simulate a 40673 dual gate MOSFET.  Fantastic.  Icing on the cake comes from a W8DIZ AF amp out of SPRAT magazine. 

There is a grand finale.  I won't spoil it.  Watch the video. Suffice it to say that Farhan would be pleased with this.  

Great stuff.  Thanks Nick!  

HOMEBREW HERO: REX HARPER W1REX AND THE WORLD'S BIGGEST BUILD-A-THON

Rex, shortly before questioning by authorities

Wow, Rex Harper W1REX deserves some sort of big award.  I hereby grant him the coveted Brass Figlagee with Bronze Oak Leaf Palm, but that is clearly not enough.  Rex spent a month of 20 hour days putting together kits for the Four Days in May QRP event at the Dayton Hamvention.   The results were spectacular:  246 hams succeeded in building QRP transmitters, and they all did it in under 70 minutes.   

Just as impressive as the results were the ways in which Rex overcame the technical and organizational hurdles prior to the event.  You can read all about this in Rex's excellent write up:
http://www.qrpme.com/docs/FDIM%202016%20Report.pdf

The OFFICIAL SolderSmoke Correspondent at Dayton was once again our friend Bob Crane, W8SX.  Bob caught up with Rex and somehow managed to get him to stand still long enough to do this interview:

http://soldersmoke.com/W1REXDaytonInterview.mp3

And it was very nice that Rex did this as a tribute to Dave Ingram K4WTJ whose magazine articles about simple QRP rigs inspired many of us.  Years ago, right after completing a homebrew QRP transceiver, I talked to Dave on 30 meter CW and told him that his articles had helped motivate me to build. 

Finally, no SolderSmoke post about Rex would be complete without a repetition of the video showing him transferring the prodigious mojo of the original Tuna Tin Two into my BITX-17 transceiver.

The QRP Mojo Ceremony

More from Lobstercon (from N2HTT): 
 http://n2htt.net/2013/11/24/there-are-lobsters-in-the-woods/
And thanks to Pete, VE2XPL, for alerting me to all this. 

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

N3FJZ's New Blog and Impressive Rigs (and a Bandscan!)

Rick N3FJZ and his Lakeside direct conversion receiver bolstered my spirits when I was getting some harshly critical reviews of my signal on 40 meters a while back.  Rick happened to pick me up with his homebrew receiver. The Radio Gods seemed to be trying to balance things out.  There is a LOT of radio mojo in Rick's Lakeside receiver.  Not only does it eschew digital synthesis of the VFO signal, it goes a step further and uses a permeability tuned oscillator -- very cool.  The component and material sourcing adds more luster to the rig.  Rick writes: "A lot of the components used to construct the LS-40 were harvested from discarded consumer electronics I collected back in the 1980's. The base substrate material for the Manhattan style construction, as well as the RF tight enclosure for the PTO, is made from a flattened out tin plated food can. All components are discrete; i.e. no IC's or CPU's."

Rick has launched a blog.  He has some amazing stuff on it.  Be sure to check out his ZX-SSB rig.  Amazingly detailed documentation Rick!  Thanks. 

Find Rick's Blog here:
http://www.remmepark.com/circuit6040/