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Monday, February 26, 2018

Dragnet Goes After TV Repairmen in 1951

Detective Friday goes after a vicious new kind of crime:  Crooked TV repairmen who overcharge their customers.  These monsters unnecessarily replace (or say they do!) transformers, when all that is needed is a new 5U4 tube.  Oh, the humanity!   

And the reporter they were working with pretended to be a salesman for a new company dealing in rosin-core solder!   

No kidding.  I really thought this was a joke.  They were serious.  Just click on the video above to listen.  

Or scroll forward to the 1:32:59 point on this link.  Lots of tube talk.  This one's for you Grayson!  https://wamu.org/story/18/02/20/big-broadcast-feb-25-2018/

Sunday, February 25, 2018

Soldering Fingers (and SWR Bridges) in Norway

Tore Bonderudt√•jet LB4RG tells us that he is a SolderSmoke listener, and that the old tradition of hams soldering their fingers together continues to be practiced in Norway.   Here are some pictures of his latest efforts.  This is an SWR bridge project.  Thanks Tore!  Careful with the fingers OM! 

Tuesday, February 20, 2018

N8NM's "20 Dollar Bill" DC Receiver

Steve N8NM wrote: 

I call it "The $20 Bill" because it contains about $20 in junkbox parts and complies with Bill's discreet component, hardware defined radio ethos.
73 - Steve N8NM

I replied:  

Excellent Steve.   Very nice.   

Your post caused me to fire up my DC RX -- I was listening on 40 earlier today.  I think the world needs MORE 40 meter direct conversion receivers.  

Too bad about the regulator IC chip.  We need to get you an 8 volt Zener so that you can bring that receiver into a state of discrete component purity.  


73  Bill N2CQR 

Monday, February 19, 2018

A Wonderful Troubleshooting Story -- Thailand, Mixers, a Simpson 260, Microwaves, and some Black Tape

My old friend was really fortunate to have had such a good Staff Sergeant instructor at Signal School, someone for whom the mixer trig was obviously not enough.  And our old friend obviously also benefitted greatly from having had a dad who set him up with a Simpson 260 and some handmade experimental glass diodes. Wow.  It all came together with some black tape in Thailand... 


Enjoyed your latest blog. I remember your asking about mixers years 
ago.  I received much the same explanation from a Staff Sergeant 
instructor at Ft. Monmouth in 1967.  His example was a mixer with 
diodes, noting the need to have them forward biased by the LO supply.  
We worked out much the same waveforms as shown in your Blog and 
the concept became part of my 'intuitive' knowledge.

A few years later I was fighting 120hz hum on the baseband of an IWCS 
microwave system feeding USAF command at the Korat Air Base in
Thailand. The hum was pretty high level and causing inter-modulation 
problems on the 60 channels of signal sideband suppressed carrier 
being applied to the microwave system.

We ended up with a couple of DCA DoD employees being flown in to help, 
to their credit they were prior service and darn good at what they did.  
After three days of testing all parts of the microwave system with a 
very long distance and long duration phone call to the manufacture in 
Calif, they still had not found the trouble.

I had stayed working with the DCA guys all of the time, during the 
testing I noted the hum seem to lessen in strength with someone standing 
directly behind the radio bay.

I went around to the back and took a close look, Yep! the mixer diodes 
for the baseband order-wire were glass and exposed.

Put a length of black tape over them and the hum went away.  Not the 
power supply problem everyone was fixated on, it was diode photo 
sensitivity.  I guess we could have just turned off the florescent 
lights too.

When I was 10 years old my father showed me how to use a Simpson
260 to check diodes and early transistors*. We were on the floor of the 
living room with sunlight streaming in.  I saw the forward resistance change
a lot when the glass diode was in sun light vs shade. It was this memory 
that prompted me to try the black tape.

All the MW systems in SEA later received a MWO to change out the 
order-wire board and I found that the assembly was a non-standard part 
of the microwave system just for military use.  Civilian deployment of 
that microwave system had no need for the order-wire.

Thanks for the quick trip, for me anyway, down memory lane and the 
memory of being an electronics tech hero for all of two minutes. The DCA 
guys made me buy the first round at the club.

73  from an old friend....

Sunday, February 18, 2018

HB2HB QSO with KC1FSZ and his Al Fresco Scratch-built BITX

I had some good luck on the ham bands last weekend.  First, I was called by Bruce KC1FSZ -- this time he was on his Al Fresco scratch-built BITX-on-a-board.  FB.  The next day, I called CQ on what seemed like an empty 17 meter band.  I heard someone come back -- it sounded like DX.  I had to swing the Moxon a bit -- oddly, I thought, to the south-east.  FR5FC was calling me from Reunion Island.   TRGHS. 

Here's a follow-up message from Bruce: 

Hi Bill:

Great to catch up with you on 40m yesterday.  I was using the Peppermint II which is a scratch-build of the BITX-40 for the most part, although I did my own digital VFO/BFO and made a few other modifications in order to be able to use it on 80m.  It took about 8 months of noodling to get the thing to work, but it was a great learning experience. 

As discussed, I’m working on a 24V power supply (LM723 + 2N3055) and a push-pull IRF510 final so that I can get some more power.  

I got a few more Williams-Sonoma Peppermint Bark tins off of EBay so I’m ready to start boxing things up as soon as the linear is working. 


Bruce KC1FSZ

Saturday, February 17, 2018

KD4PBJ's Acorn AM Broadcast Band Regen

From Chris, KD4PBJ: 

This is my AM band regen I built during December and early January. 

It uses a 955 acorn tube and is a really hot performer! I can pick up dozens of stations with only a 20 ft piece of wire thrown out my shop window and tied to a nearby tree limb 5 ft off the ground. This is from rural Tennessee where we have no local AM’s. 

It uses a velvet vernier I bought off eBay back around 1999 or 2000 and had saved for a special project like this. 

I’m running filaments off a 6V lantern battery and plates off a type 415 45V battery. 

A nice ham/machinist I met on the Time Nuts list who lives in San Francisco made my insulated shaft couplings. I got the Delrin rod cheap off eBay. He cut them to length, center drilled for 1/4 inch and drilled each end for 2 setscrews.

Wednesday, February 7, 2018

Understanding Switching Mixers (as in the Ceramic DC RX)

W3JDR's Comment on my post about the DC RX mixer got me thinking.   He was right -- my explanation of the mixer action wasn't quite complete, especially as far as switching mixers are concerned.  I remembered that I had written about this in the SolderSmoke book.  Below you can see the part of the book in which I discuss switching mixers.  Realize that the two diodes in F5LVG's mixer play the same role as the two gates in Leon's circuit.  It will be worth your while to sit down with Leon's circuit diagram, his frequency chart,  and a ruler and really go through this so you can SEE and really understand how the two gates (or switching diodes) generate sum and difference frequencies.  


I guess I still yearned for clarity and intuitive understanding...  Time and time again, as I dug into old textbooks and ARRL Handbooks and promising web sites served up by Google, I was disappointed. 
Then I found it.
It was in the Summer 1999 issue of SPRAT, the quarterly journal of the G-QRP Club.  Leon Williams, VK2DOB, of Australia had written an article entitled “CMOS Mixer Experiments.”  In it he wrote, “Generally, mixer theory is explained with the use of complicated maths, but with switching type mixers it can be very intuitive to study them with simple waveform diagrams.” 
Eureka!  Finally I had found someone else who was dissatisfied with trigonometry, someone else who yearned for the clarity of diagrams.  Leon’s article had waveform diagrams that showed, clearly, BOTH sum and difference output frequencies.

Switching mixers apply the same principles used in other kinds of mixers. As the name implies, they switch the mixing device on and off.  This is non-linearity in the extreme.
Not all mixers operate this way.  In non-switching mixers the device is not switched on and off, instead one of the signals varies the amount of gain or attenuation that the other signal will face. And (as we will see) it does this in a non-linear way.  But the basic principles are the same in both switching and non-switching mixers, and as Leon points out, the switching circuits provide an opportunity for an intuitive understanding of how mixers work. 

Let’s take a look at Leon’s circuit.  On the left we have a signal coming in from the antenna.  It goes through a transformer and is then applied to two gate devices.  Pins 5 and 13 of these gates determine whether the signals at pins 4 and 1 will be passed on to pins 3 and 2 respectively. Whenever there is a positive signal on gate 5 or on gate 13, signals on those gaps can pass through the device.  If there is no positive signal on these gates, no signals pass.  Don’t worry about pins 6-12.

RF A is the signal going to pin 4, RF B is the “flip side” of the same signal going to pin 1.  VFO A is a square wave Variable Frequency Oscillator signal at Pin 5. It is going from zero to some positive voltage.  VFO B is the flip side.  It too goes from zero to some positive voltage. 
Look at the schematic.  Imagine pins 5 and 13 descending to bridge the gaps whenever they are given a positive voltage.  That square wave signal from the VFO is going to chop up that signal coming in from the antenna.  It is the result of this chopping that gives us the sum and difference frequencies.  Take a ruler, place it vertically across the waveforms, and follow the progress of the VFO and RF signals as they mix in the gates.  You will see that whenever pin 5 is positive, the RF signal that is on pin 4 at that moment will be passed to the output.  The same process takes place on the lower gate.  The results show up on the bottom “AUDIO OUTPUT” curve. 
Now, count up the number of cycles in the RF, and the number of cycles in the VFO.  Take a look at the output. You will find that that long lazy curve traces the overall rise and fall of the output signal.  You will notice that its frequency equals RF frequency minus VFO frequency.  Count up the number of peaks in the choppy wave form contained within that lazy curve.  You will find that that equals RF frequency plus VFO frequency. 

Thanks Leon!  

F5LVG's Glue-Built Mixer Transformer

One thing I forgot to mention:  In Olivier F5LVG's DC receiver article back in SPRAT 100, he casually mentioned building a transformer for his mixer by taking two inductors of the appropriate values and GLUING THEM TOGETHER.   What a great idea!  I had to try it.  I did.  Picture above.  It worked in my Ceramic DC receiver, but the trifilar transformer from Farhan in India worked better.  Perhaps the coupling was tighter.  But hey, it worked.  Three cheers for Olivier.    

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