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/

KiwiSDR

https://www.kickstarter.com/projects/1575992013/kiwisdr-beaglebone-software-defined-radio-sdr-with?ref=video

QRPi WSPR with a Raspberry Pi Shield from Hungary via Tuscon

VA2NM's Michigan Mighty Mite (with Tuna Tin LPF!) (video)

Bill,

  Here is my contribution... After managing to somehow get my hand wound transformer to melt a pill container, I used my Dad's hand made, circa 1950 transformer and got it working on a 1.4 MHz xtal and also on 3.58 MHz with a colour burst xtal.  A re wound coil on the remaining unmelted pill container worked on 40 meters. I succeeded in getting my Mighty Mite working on three bands.  My father would have been pleased, as this was kept aside all this time and now has been put to use. He had built the coil while working part time in post World War II England at the GEC labs in U.K.

Thanks for the motivation! I'm going to move forward and clean up the 80 meter signal and see how far it goes on the reverse beacon website.

The coil form was about 80 turns on a 1 inch diameter with a 20 turn secondary that I used for the center tap portion by joining both bottom ends.  Then I wound an 10 trim secondary, loaded up with a 50 ohm resistor to tune up (capacitor fully opened up) on 3.58 MHz in the video, and the audio coming from my receiver tuned to the 3.58 MHz signal.

Regards,
Nigel Maund

A Great Knack Story: Peter Parker Interviewed on "QSO TODAY" by 4Z1UG

I really liked Eric's interview with the Peter "The Wizard of Melbourne Beach" Parker aka VK3YE. What a great Knack story!  There he was, trolling the garbage dumps of Western Australia, looking for discarded electronics.  Using the LO of one broadcast receiver to demodulate SSB signals coming in on another... Great stuff!  Check it out:

http://www.qsotoday.com/podcasts/vk3ye

HEAVY METAL! How to Handle HEAVY Boatanchors -- And Which is Heavier: R390 or DX-100?

Grayson: 

I was on 40 AM today and I mentioned to the guys your thoughts about the possible need for a block and tackle and a metal beam in your shack roof to help you deal with your R-390A.  They sympathized completely.  One fellow claimed he knows hams who are working out with weights just so they can handle their boatanchors.  Another guy said he is thinking of building a small crane, perhaps powered by his chain saw (yikes!).  A third fellow said he actually bought a thing called a "lifting table" from Harbor Freight.  

This got me to thinking:  How much do those R-390s really weigh? 

A MERE 85 pounds!  That's it?  Holy cow, the DX-100 has a listed shipping weight of 120 pounds!

73  Bill  

Bill:

Nice thing about a “regular” boat anchor (DX100, HT37, SX101, etc.) is that you can put it on its side and get fairly easy access to both sides, and all the components at once.  The problem with the R390 (and a lot of Collins military gear) is Collins worked hard to cram so much in a “small” space that you have to take whole sections apart to get at anything.  So you have to “flip” the chassis over, side, over, on its back, etc.  UGH.  To get at the RF front end components, you gotta take the front panel off before you can remove the RF chassis.  UGH

I know about the lifting table from harbor freight.  A really nice shack accessory.  Puts the rig at a better height to work on.  With a “lazy susan” thing on top, a nice arrangement!   Maybe next Christmas.

73, TA2ZGE

Grayson

TA2ZGE - Ankara, Turkey

KJ7UM

Follow the Hollow-State Design Blog

hollowstatedesign.tumblr.com

Another Lightwave Communication Knack Story from the UK

Hi Bill,

I've been following your podcast since you started and enjoy every episode. I've been licensed here in Scotland since 1970 as GM8EUG.

I thought you/others might be interested in how I got into radio/electronics and how I feel I may have the 'Knack'. 

The above reference reminded me of some experiments I carried out in 1967 as a schoolboy. There were no ready sources of parts locally for me.. I lived  in a rural area so the nearest electronics parts shop was 50 miles away so it was all done by letter and mail order.

My first audio link was driven by a tube broadcast receiver with a 3 volt torch bulb connected instead of the loudspeaker. (I hadn't heard of impedance matching!)  This flickered nicely on speech/music peaks. The bulb was positioned at the focal point of a parabolic car headlamp reflector from a scrap car.  I now had a beam of light with audio on it.
Next step was the receive side...I didnt have access to a photo cell but had a Cadmium Sulphide photo resistor. Connecting a pair of low impedance headphone in series with this cell and a 1.5 volt battery gave me recognisable audio when the cell was in the beam...no amplifier needed!

Next step was greater range...this was achieved with a 6 inch shaving mirror to focus the beam onto the photo resistor. This gave me the length of the street (100 yards when it was dark outside )with the flickering beam shone out of my schoolboy bedroom window resulting in puzzled  looks from passers by.

Next problem was the frequency response.. all bass and no treble. Some research indicated that the photo resistor had a slow response so that was part of the problem but I had a hunch... How fast does a filament bulb react to audio? Biasing the bulb with a 1.5 volt cell so that it glowed  dimly with no audio improved the audio response greatly.

So what got me into radio...my father was a Chief Radio Officer in the Merchant Navy during WWII and my schoolboy bedtime reading (the only technical stuff I could find ) was his textbook ...the 1939 edition of the Admiralty Handbook of Wireless Telegraphy. Capacitors  were called condensers and they were measured in 'jars'!

That was the start of a career. I've now moved through testing international telephone exchanges, installing 2 way radio for the whole of Scotland for British Rail (paid for my hobby!) and finally 32 years in IBM writing manufacturing test software from the original IBM PC to Thinkpads.
Now retired I am active on WSPR and am writing Android apps to keep my brain in gear.

I just can't leave this stuff alone!

Hope this of interest/amusement.

73s

Neil Roberson GM8EUG

EMRFD Joy of Oscillation (Part 1)

Guys:

I have been catching up on the last few SolderSmoke podcasts after
that little QSO Today diversion.  I wonder how many others did the
same thing?  I have really enjoyed these recent 'casts.  Lots of
fantastic HB content.  Funniest moment was when Bill described his
post-project workshop as looking like the aftermath from an electronic
barfight.

I took a new ham up on a SOTA activation last year.  Then about a
month ago, he said that he wanted to do HF HB.  He said he had been
googling and found so much that he didn't know where to start.  I told
him that I'd be interesting in doing a beginner HF HB project with
him.

I could have pointed him to LBS, et al.  I could have pointed him to
the Michigan Mighty Mite.  I did neither.  I pointed him to:http://web.cecs.pdx.edu/~campbell/EMRFD1dot34.pdf  Note the name of
the document.  I pointed him also to:http://www.arrl.org/files/file/Product%20Notes/chapter_1.pdf 
(Did you guys know that chapter was online and free?)  We scaled to 20m and
kitted parts for this.  And parts for a 4th transistor PA for serious
QRO.  :-)

Two others joined us building for 40m.  Check out the attached photos
of the first 3.  The joy of oscillation was experienced by all.

After testing each oscillator, and borrowing from an article KK7B ran
in CQ VHF, I told each that he had to ID every 10 minutes.  Even
though nobody was going to hear these signals a few hundred yards
away.  (But it sounds loud on a shortwave portable a few inches away!)
 I even wrote out the dots and dashes for a couple of them.

Next stop:  to have everyone find a curbside TV discard, rip out some
parts, and get on 5 meters!  Haven't we gotten it back now, after the
transition to digital TV?   :-)

OK, maybe the next stop is to add some gain stages and experience the
joy of communication.  The joy of QSO-ification?  The joy of
EM-radiation?  :-)

Best regards,

Drew
kb9fko

2 Attachments

OzarkCon is Coming Up -- April 1-2

http://www.ozarkcon.com/index.php

Elser-Mathes Cup Opportunity!

I'm sure he'll be on the air.  With a homebrew rig.

Stay thirsty my friends!