From Wayne and Garth in San Diego: EMRFD Joy of Oscillation Part 2

Oh great and mighty masters of the SolderSmoke:

We've continued on with this project and it has been a lot of fun.

Sure, there's

THE JOY OF OSCILLATION

but we've progressed to

THE JOY OF MODULATION (added a keyed buffer)

THE JOY OF AMPLIFICATION (added driver and PA, not threatening QRO, yet)

THE JOY OF RADIATION (perhaps my favorite)
THE JOY OF RECEPTION (picked up by RBN, yeah!)
last on the list is to experience
THE JOY OF COMMUNICATION

for that, we'll try out a number of different receivers.  Cheap SW
portable.  Softrock Lite.  websdr.org.

Does one try to count all the joys?  :-)

Here's a few snaps:

0.jpg - RBN evidence
1.jpg - lashup on the lid of a tupperware container
This worked great for throwing the work in progress in a backback for
our build session meetups.
2.jpg - Fig 1.34 less output LPF.
3.jpg - The missing LPF.  THE JOY OF FILTRATION  (OK, that's taking it too far.)


4.jpg - Fig 1.35 amp with BD139 transistor.
5.jpg - "breadboard" and a front panel to hold the T/R switch.  Key
and cheap SW portable for RX.  Waiting for DX contest to end, so I
have a chance.  :-)

6.jpg - simple breadboard chassis

Our fun has certainly been cheap.  The parts cost, including PCB and 1
BNC jack, was about $13 in low quantity from Mouser (and Diz) for all
but the amp.  The amp portion was $4 in low quantity from Mouser (and
Diz), and most of that was the expensive heatsink.  The "chassis" was
just a piece of cheap 3/4" hardwood and lexan from home depot.  I
drilled and tapped the holes in the wood for the #4 screws.  (Seems to
hold quite nicely.  I thought I might have to harden the threads with
CA adhesive as is done sometimes with balsa.)

If there are any of those air variable caps left that you are meting
out to the worthy, well, like Wayne and Garth, "we are not worthy."
If you do have between 1 and 4 and find it in your heart, we'd be very
grateful.

Best regards,

Drew
kb9fko
San Diego

Renewed Hope for Divide by 2 I and Q

An anonymous reader posted this interesting message in the comments section yesterday.  Very interesting.   A potentially important tip that may help in the quest for 90 degree phase shift with divide by 2 Flip Flop circuits.  What do you guys think?   And who is that masked man?

I wanted to make a comment regarding your Frankenstein R2 Clock divider, but did not come around to do it until now and fear if I were to put it below the appropriate post, it would be so many pages away nobody sees it. Please forgive me for posting this here if my assumption is wrong. I had a play with two edge-triggered JK - Flip Flops (74HC109 & HC107) and tied the J and K to the appropriate rails to use them as T- Flip Flops. Because of one being positive, the other one being negative edge triggered, this behaves as a divide by 2 IQ clock generator. The HC107 has an inverting clock input, so as with the other design, some kind of inverter is involved. And as Bill has reported, I initially measured the Phase shift on the scope to be off. But while playing around, I realized this was a function of the signal level. I could tune the phase shift by adjusting the signal level of the driving clock! When the clock and power supply levels were almost equal, the phase shift was very close to 90° and pretty stable with frequency (tested with 1-10Mhz). Later I thought about it some more and suspect it might have to do with the exact time the inverter "flips" on different signal levels in relation to supply voltage level. Aside from the exact cause, I believe one could vary the supply voltage of the gates with the same effect on the phase shift as with varying the signal level. I hope my observation helps to somewhat make the advantages of divide by 2 IQ clock generators more accessible.  

Grayson Evans TA2ZGE on "QSO Today"

Eric 4Z1UG has a really great interview with Grayson Evans TA2ZGE.  I'm writing this as I listen.

My reactions:

I sympathized completely with his reaction to EE professors who insisted that current flows from positive to negative.  Indeed.  Let's turn those arrows in the diode and transistor symbols around!

I too stripped down a Heathkit VFO and rebuilt it from scratch.

I share Grayson's aversion to metal work.  Viva Manhattan!  

Here is the interview:

http://www.qsotoday.com/podcasts/ta2zge

Switching to a Resistive Splitter on the Frankenstein R2

I did a little work on the Frankenstein R2 phasing receiver.  I noticed that I had a lot more noise and hum on 30 meters and above than I did on 40 and below.  I don't think it was common mode hum -- switching to a battery supply didn't help much.  But when I took a look at what happened to RF signals between the antenna connector and the input to the DC receiver mixers,  I noticed that the signal level seemed to vary quite a bit with frequency. 

There were only two circuits in there:  a 1.7 MHz high pass filter (to knock down AM broadcast interference) followed by a simple bifilar toroidal transformer signal splitter.   My guess is that the 1.7 MHz high pass filter's response was being messed up by the bifilar toroid transformer that I was using as a signal splitter. There might have been some unplanned-for resonances between them. This might have had the effect of knocking down the higher freq signals, making any noise in the receiver (probably from the digital VFO) more apparent.  Also, I noticed that I had this toroid too close to the digital VFO box and to the DC power plug for the Arduino/Si5351 combo -- that might have been sending some noise into the DC receiver input. 

To make a long story short, I took out the toroidal signal splitter and went with a resistive splitter like the one above.  This seems to have helped quite a bit.   I know it adds some additional loss -- about 3 db over the toroidal transformer, right? 

Another possibility:  While rummaging around I found a little 3-terminal TV signal splitter.  It is marked "5-900 MHz" but I'm guessing it would be fine down to 1.8 MHz.  Any thoughts on trying that?  

KK7B's Thoughts on Notebooks, Experiments, and Building

From the r2pro yahoo mailing list:

Hi All,

Some interesting posts lately, with notes or links on "to build or not to build," new H-Mode mixers for HF, and front-end filter intermod.  A recurring thought is that I do lots of projects and each of my projects is a separate design, starting with a bunch of sketches.  I didn't invent this approach--think of DaVinci, for example.  I don't count my sketches, but probably make ten or twenty for every one that progresses to a design of something that would actually work, and maybe only one in ten of those makes it to prototype hardware.  I do a lot of sketches--hundreds for every working radio, and maybe finish a dozen working radios for every one that I write up, either as a good or bad example.

But my sketches all seem to have something in common--they are sketched to do one particular thing well.  They tend to be for one band, one mode, and are designed with particular power supply limitations and the antenna I'm going to use known ahead of time.  They often include at least one but no more than two experiments--something new and risky enough that it might not work.  More than two experiments almost always end up interacting in some unpredicted and dysfunctional way, so I try to limit risky new brilliant ideas to no more than one or two per project.  The key is to do lots of projects, and lots and lots of sketches.

I don't normally operate in brutally strong signal environments, so my dynamic range/IIP requirement is already satisfied with techniques that have been standard since all the excellent work by Wes Hayward, Ulrich Rohde et al. in the 1970s and 80s.  The problem has been solved, like the appropriate number of wheels on a bicycle.  Sure, there are extreme enthusiasts who limit themselves to one wheel and play the bagpipes while riding...  My risky new front-end sketches are often aimed at meeting those acceptable prior benchmarks in some clever and different way, rather than adding a few dB on top of already good dynamic range.  ...Yes, that works well, but I think I'll try doing it this way instead...

Similarly, my input filters aren't the limitation on my intermod performance.  PIM is a big deal in some contexts, and the latest research is fascinating.  Do a google search on Passive Intermodulation PIM to get started on some interesting reading on that topic.

Regarding the question "to build or not to build," I believe that comes down to something very basic: are you a builder?  If yes, then you have no choice.  I can look around my radio room and see a hundred different radios that I've designed and built, and a few more in progress.  If you do the math in my first paragraph above, that's around ten thousand sketches.  My lab notebooks have 200 pages, and I've filled up 140 notebooks since 1975, so that figure is reasonable.  It's just something I do, like some guys go fishing.  Sketches don't take long.  I can do two or three on a half-hour train ride on the way to work.  A complete design to where I start cutting metal and gathering parts might be a few hours a day for a week.  Then another month, maybe a few hours at a time on weekends to finish up a nice project.  There have been more than 2000 weekends since 1975, so even 100 completed radios has left most of my time for other things.

I am very close to folks who are the same way writing code.  They've been filling notebooks with it since grade school, and doing Software Defined Radio since long before they ever encountered the abbreviation "SDR."

If your personal sketches are full of code or CMOS logic, I expect your radios to look and work differently from mine.  If you operate 6m weak signal modes a half mile from a hilltop kilowatt contest station, you have a fascinating set of dynamic range problems to solve.  Years ago, my 11 year old daughter and her best friend thought the absolute best radio ever was the morse code transmitter that Wes Hayward and Bob Culter worked across town using a couple pieces of metal stuck in a lemon for power.  Neither Wes nor Bob would embrace the limitations of that rig for all their amateur radio contacts, but at the time it was a really cool project.

These are just some rambling, Saturday night thoughts, but if you read between the lines you can maybe understand a bit more of why I tend to do things some interesting way that might not apply to your particular application.  One time I accidentally left one of my notebooks at a close friend's house, and he took the liberty of making copies of a bunch of the pages.  I'm not sure it did him any good, but he sure found it entertaining.  There is great freedom in sketching things that have a small probability of actually having to work well in practice.

Enjoy the experiments, and if you have self-identified as a builder, as have many of the denizens of this site, then enjoy making sketches, developing designs, and taking risks that either pay off or end up as learning experiences.

Best Regards,

Rick

Be afraid! Be VERY afraid! Digital Audio on 20 Meters (video)

Here is a very interesting comparison between digital audio, and plain old SSB audio (from a Collins rig!).

I don't know.  I may be prejudiced here, but that digi audio just doesn't sound too good to me.  And I ask myself: "How could it?"  They are restricting the transmit bandwidth to 1.2 kHz.  Can the error correcting elements of the software help them get around the bandwidth limits of Shannon's communications theory?  

The digi audio sounds quite robotic to me. Even Siri sounds better.  Is this because -- as the receiving station noted -- they were only getting "80 percent decode"?   Would the digi audio have sounded better if signal strength had been better? 

Again, I don't know.  But remember. I am a Ludite (with a single d -- the ORIGINAL spelling!).

W6JL's Amazing Phasing Station

Eric 4Z1UG interviewed Don Huff W6JL a few months back.   I really like Don's approach to homebrewing.   I recently came across his QRZ.com page -- I was lured in by the phasing receiver with the Tayloe detector.  And of course I like the modules spread out in the desk.  FB Don.  

Here are the details on Don's rig:

https://drive.google.com/file/d/0B7YOOrbLoXkvbHkwWDRnV1JFVHc/view

Here is Eric's interview on QSO Today:

http://www.qsotoday.com/podcasts/w6jl

Could Grayson's Arduino Thermatron Shield Protect Us From Digi Domination?

Something old, something new, eh Grayson?   The author of "Hollow State Design" is engaged in an (I suppose) admirable effort to bridge the gap between our beloved Thermatrons and those new-fangled Arduinos.  Here Grayson tries to explain and justify his flirtation with the dark side:

I want to do some experimenting with Thermatrons and Arduino.  Sound weird?  Maybe not.

I really like playing around with the Arduino even though it violates my ban on digital technology in my shop. (My excuse is I am trying to use it teach my son something he can use to get a job someday.)

Sure Grayson.  That's what they all say.  "I was doing it for the kid..." 

Kidding aside, that tube shield looks pretty cool.  And I like the MeTubes base for the Thermatron.

Winterfest Hamfest with Armand WA1UQO

 I had a great time at the Vienna Wireless Society's  Winterfest Hamfest.  As I have done for several years now, I joined forces with Armand, WA1UQO. A prediction of cold rain caused many of the tailgaters to stay home, but there was still a lot of good stuff to be found at the 'fest.  I came home with a large stock of potentiometers, a 130 foot doublet with open wire line, TWO copies of SSDRA (one given to me by Armand) and various other bits and bobs (including some Cadmium Sulphide light sensitive resistors....)   I successfully resisted the siren calls of several old Hallicrafters receivers.  After the 'fest Armand came with me for a visit to SolderSmoke HQ.   Armand always brings along some part to be used to help members of the International Brotherhood in their radio endeavors.  This year, that included several 80 meter crystals suitable for Michigan Mighty Mites and the ColorBurst Liberation Army.  Thanks Armand!  And thanks to the Vienna Wireless Society.  

Great Video on Mixers

You know that you are sinking deep into The Knack when you watch a video like this one and find yourself thinking: "FANTASTIC!  WOW!  Now I know why square waves are better!" I really liked this one.  In the beginning I was kind of concerned about his refusal to explain how non-linear, non-switching mixers work.  He actually used the dismissive non-explanation that I've always found so disappointing:  "Blah, blah, blah... it's in the trig."   And he actually said, "Blah, blah, blah." But he more than made up for it when he got into the switching mixers.   Note that his drawing (at the start) of "Mixing by Switching"  attempts to show the waveform that results from an LO "chopping up" an incoming RF signal.  I always find that picture worth a thousand trig equations.

I also really liked his explanation of the benefits of rapid rise time in switching mixers, and how slow switching causes the diodes to spend some time in the non-linear part of their curves, giving rise (!) to IMD products (I'm paraphrasing).  You can really see why they say it is better to drive diode rings with square waves.  So stop trying to put low pass filters between your LO and the diode ring.  Square waves are your friends here. 

Mr. Marki seems to be one very cool EE.   And I'd like to hear more about his dad.  Here is some more about the Marki engineers:

http://mwexpert.typepad.com/markimicrowave/