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!

A Knack Victim's Midlife Crisis

Thanks to Steve WA0PWK for sending us this Jim Williams cartoon.  

Been there, done that. It doesn't mean you are a bad person.

German Mighty Mite works Venice on 40 (video)

In spite of being a bit off frequency, sTef,  DL1FDF (aka VY1QRP) has been inducted into the Color Burst Liberation Army.  Congratulations sTef!  Normally we would requite operation on 3.579 MHz, but sTef has been granted special dispensation because 1) he doesn't have a 3.579 MHz rock, 2) our stock of this crystal has been depleted, and 3) he actually made a contact with this rig, working II3ICZ in Venice.  FB sTef.  If anyone has a color burst crystal for sTef, please let us know.    

sTef writes:

I would like to say „Thanks" to both of you for your ongoing inspirations in soldering and homebrewing.  After 15 years out of ham radio it were you two guys who got me back into the world of -> SOLDERSMOKE. Thanks for that.And belive me been away for 15 years and now getting back into it feels a sometimes a little bit too "digital“ …. ARDUINO or NOT TO ARDUINO ? This is the question….

Anyway…

So what could be more sophisticating than having a MMM ready on the work bench and answering a CQ call on 40m with that thing and be heard. 

Yes, the first QSO today with my MMM was for you both.

I worked the Italian Radio Station II3ICZ. I was 559 into Venice with 0.5 watts from the MMM into my full-size triple leg for 40m.

Adafruit Profiled in "The New Yorker"

Congratulations to Limor Fried.  Her company got a very nice write up in "The New Yorker."

http://www.newyorker.com/tech/elements/limor-frieds-artful-electronics

"My Favorite Programming Language is Solder" -- Boldport Kits

Look closely at the inscription on that USB stick.   Obviously I sympathize.   The folks at Boldport have some very interesting ideas and projects.   And they operate from a very cool location, just south of the river Thames, not far from my old home in London. 

Here is their main site: http://www.boldport.com/blog/2016/2/21/boldport-club-project-1

Here is where you can subscribe to receive a monthly project (with parts!) from them:
https://boldport.cratejoy.com/

As for the solder quote from Bob Pease, this was discussed before on this blog, back in 2011.  We were talking about an intereview that had been done with Alan Wolke W2AEW:

I also liked Alan's response to the question about his favorite software tool: "Gee, solder is soft, can we consider that software? I use a lot of that!" This is very reminiscent of a quote from the legendary Bob Pease (colleague of Jim Williams): "My favorite programming language is solder." (That quote was sent to me by Steve WA0PWK. Thanks Steve.)

AA1TJ -- On the Air with a Tuning Fork Transmitter using the 2,212th Harmonic and Olive Oil Cooling

The saturable magnetic frequency septupler. The tiny computer memory core is submerged in olive oil (Italian...naturalmente).

Not a very good picture, but here's the 1600Hz tuning-fork, fork oscillator, SRD pulse generator, PLL S/H phase-detector (diode gate), differential amplifier D.C. amplifier, and part of the 500kHz VCO.

The Wizard (AA1TJ) reports from the Hobbit Hole:

February 26 at 10:55pm ·

I was pleased to have made the first contact with my tuning-fork transmitter this evening. My contact, N1QLL, runs a pretty B&B on the Maine seacoast, midway between Bar Harbor and Cutler. Jerry was operating a solar-powered QRP station.  I found a follow-up email from him when I came up to the house for dinner. He's asking for a better explanation of my set-up. I can't wait to tell him about the passive frequency septupler made from an East German computer memory core, heat-sinked in a thimble of olive oil. 

My signal was also logged by a number of automated "Reverse Beacon Network" receivers (image attached) located in Ohio, North and South Carolina, Virginia and Pennsylvania...not bad for 90mW on 80m. Please note that my operating frequencies, 3,528.0 and 3,539.2kHz, are the 2,205 and 2,212th harmonics, respectively, of my 1,600Hz tuning-fork frequency reference.
FYI: the third attached image illustrates the block-diagram and tuning-fork reference oscillator circuitry for three common-wavelength AM broadcast transmitters operating in Berlin, Stettin and Magdeburg, Germany from 1928 through the mid 30's. A central 2,000Hz tuning-fork generated reference carrier was transmitted by landline to transmitters in the aforementioned cities whereupon the 529th harmonic was generated, amplified and broadcast at 1,058kHz. The equipment was designed by the Berlin-based firm, C. Lorenz A.G.. The fourth image details Lorenz' technique of frequency multiplication via saturable magnetic iron-core inductors. My septupler operates in an identical fashion.
A very pleasant day...

Mike points out that this is a work in progress.  He hopes to cross the pond (the Atlantic!) soon. Here is a update from Mike:

A nasty cold has delayed work on the 20 meter implementation, although some of the time I've spent crashed on the sofa was put to use redesigning the loop filter network. I think yesterday might have been my "hump" day so I'm looking forward to getting in some quality bench-time over the weekend. 

By the way, my PLL-based transmitter frequency stabilizing circuit has much in common with a garden-variety frequency-synthesizer. Obviously, the tuning-fork frequency reference is the main point of departure. My sampling phase detector, for example, was old hat by the mid-1960's. Nevertheless, this has been a fun project.

That Time We Were Re-Transmitted on 487 THz On a Red Light over Salt Lake City....

Some of you may remember this from back in 2012:

http://soldersmoke.blogspot.com/2012/09/soldersmoke-in-red-light-zone.html

Fast forward to November of last year. By this time I'd forgotten about the Utah light beams.  Ron Jones, K7RJ, was kind enough to send me a wonder-filled bag of electronic parts.   I have been slowly sorting them.  All kinds of great stuff is in there, but I noticed a lot of stuff that you don't normally find in ham shacks -- lots of optical stuff, lots of LEDs and photo transistors, little transistors with lenses on the top.  Cool stuff all, but not the kind of parts you'd use for a 40 meter CW rig.  What the heck was Ron building?  I wrote and asked.  Here is his reply. 

I’m like you, Bill, I’m a jack of all trades and master of none. I dabble in this and that. I always have a hand full of half finished projects on the bench.

 The optical stuff probably fell on the floor when Clint (KA7OEI) and I were experimenting with “through the air light communication” a few years back. Clint in the real guru in that particular project. We made optical contacts over what we think is a world record – 173 miles! That meant packing in optical gear to the top of remote Utah mountains, but what a great time we had!  We used a high power LED – NOT a laser. Lasers really suck for super long range communications. They are great for wide band across a parking lot, but not for voice communication over tens of miles (in our cast 173 miles) over the  air. We did over 100 miles with a laser pointer – can you believe that? A $3.00 laser that you torture your dog with… 100 miles!  But, that is a different topic. If you do say anything about the optical stuff, be sure to mention Clint, he really engineered the optical communication project.

By far, most important thing that we did with optical communication was on one of our short tests (only about 50 miles) when we broadcast one of the Solder Smoke episodes for anyone who cared to “look in” on our red beacon.  I think Clint sent you a picture from his side of the path a few years ago.

 

If there are any parts in that pile of junk that you are particularly interested in, I may be able to find more data and/or circuit ideas I had. But, honestly, a lot of that is stuff that is as strange and wonderful to me as it is to you. Fun as heck to look at, but needs to be put in the “YAFP” pile (Yet another .. project). 

 

Thanks for doing the podcast. It is always an inspiration for me to keep my soldering hot. 

 

73

Ron K7RJ 

Very cool.  So Ron had been at the other end of Clint's Red Light beam, the light beam that was carrying a SolderSmoke podcast across Salt Lake City.   And it appears that some of the parts involved in that amazing project have ended up in my junk box.  The Radio Gods like this sort of thing and may have been at work here.   Thanks Ron. 

DD4WH's Fantastic Teensy SDR Receiver (Videos)

This is almost enough to make me abandon my analog, discrete component, HDR fundamentalism.  Check out that display.   And that StereoAM mode in which the upper and lower sidebands go to the left and right headphones "useful for CW"... Wow, that's seems like a step beyond binaural.

Don't miss Parts 2-4 --They are all on YouTube and will appear in the right hand column when you are watching Frank's videos.  But I couldn't resist embedding the video that shows the hardware.  Note:  the oscillator is an Si5351!   Yea!  And the LP filter board comes from Hans Summers.



Beautiful work Franz!   Thanks for making the videos.  73  Bill

From Paul Darlington M0XPD: A Book!

Our friend Paul Darlington M0XPD is a member in good standing of the International Brotherhood of Electronic Wizards. His AD9850 Arduino shield propelled me into the world of I and Q. His "Shack Nasties" blog is a valuable resource for all of us. And now he has written a book.  Paul was kind enough to let me read it before it was published -- I enjoyed it very much.  It is the story of a very personal journey. At one level it is about Paul's trip to the Dayton Hamvention.  But the trip goes much further than Dayton, both geographically and personally.  I especially enjoyed Paul's observations on the United States -- our British cousins often see things we ourselves overlook.   I'm really pleased that George Dobbs wrote the foreword -- he is the ideal person to do this for Paul's very philosophical book.

We give "Getting There" our highest review:  the coveted FIVE SOLDERING IRONS. And we are nominating Paul for a Brass Figlagee with Bronze Oak Leaf Palm.  

Read Paul's description of the book here:

http://m0xpd.blogspot.co.uk/2016/03/a-new-book.html

Buy the book here:

http://www.amazon.com/getting-there-Paul-Darlington/dp/1523452196

Congratulations Paul!

Radio Row, New York City, 1929

Check out this video:

https://vimeo.com/109197452

and more here:

http://www.radiodiaries.org/radio-row/

Antennas and National Monuments

We started SolderSmoke 185 with a brief description of my recent ascent to the top of the Washington Monument.  A few days later I was visiting George K9GDT's wonderful web site
http://www.qsl.net/k9gdt/radio/radio.htm  and in the humor section came across the above Gil cartoon from 1959.  That is the general idea. 

Pete then sent me this:

Pete originally had a three element Yagi coming out of Teddy Roosevelt's head, but that just wasn't right.  I asked that it be changed to a 17 meter Moxon.  Thanks Pete.

I would like to note for the record that I have no intention of using the Washington Monument, the Statue of Liberty, Mount Rushmore or any other national monuments as supports for any Yagis, Moxons, Cubical Quads, Ray Guns, Lazy H's, Inverted L's or any other type of electromagnetic wave launcher.

75 and 40 Meter AM on my HQ-100 (Videos) + Digital Display

And here is how I sample the oscillator frequency for the digital counter.  I use an old trick:  I wrap some wire around the oscillator or mixer tube.  I made the coil out of an old coil form. I had to play around with the number of turns to get suitable pickup on both 160 and 40 meters.  The San Jian board allows for IF freq offset.  I use a similar arrangement on the transmit side with the DX-100.  By the way, the box that houses the two displays is the carcass of one of the Heath QF-1 Q multipliers from which I heartlessly pulled the nice reduction drive variable caps for use in my BITX rigs.  

Add caption

Sputnik Replica Transmitter, an "Error" in the Sputnik Schematic, and Why 20.005 MHz?

Mark K6HX pointed me to very interesting Hackaday article on Frank PA3CNO's Sputnik transmitter replica.  As blog readers will recall, we went through a period of Sputnik-mania a few years ago:  http://soldersmoke.blogspot.com/search?q=sputnik  Chief Designer Comrade Mikhail Rainey AA1TJ sent me some of the Russian tubes (like those pictured above). 

The Hackaday article pointed to our post reporting that Oleg RV3GM had found the schematic:

http://soldersmoke.blogspot.com/2013/04/sputnik-schematic-found.html   Stefan reports that PA3CNO found "an error" in the original Soviet schematic:

http://www.radio.cc/post/Franks-power-supply-for-sputnik    A mistake you say?   HAH, I say!  Hah!  This must have been part of a sinister commie plot to prevent the capitalist imperialists from ever being able to reproduce the glorious transmitter of the Soviet people.  They almost succeeded. 

Just kidding.  

In the course of looking through our old Sputnik posts, I came across a question I posted:

I have a question: OK so the crafty Soviets picked 20.005 MHz for some good reasons: Being so close to the WWV freq, it would be easy for hams and SWLs to find it with precision. In the November/December 2007 issue of "Break In" (from NZ -- thanks Jonathan-san!) ZL3DW notes that this frequency selection would allow a receiver set to exactly 20 MHz to "produce an audio tone plus or minus the Doppler shift without ever going through zero beat." But zero beat with what? Most of the receivers out there would not have had BFOs, right? So the Soviets wouldn't have been using ordinary CW, right? Were they using AM, with the beeps produced by an audio oscillator modulating the carrier? 

Was their diabolical plan to use WWV as the BFO for those using ordinary AM SW receivers?   If so, a 5 kHz separation from WWV seems to be too much right?  Especially when the Doppler shift on approach would push the frequency up a bit. Maybe they just chose this freq to make it easy for listeners to find -- just a bit above WWV.  Comrade Rainey surmised that they were keying the PA stage -- the oscillator "backwave" was at times audible on the ground.

What do you think Comrades?

DSW and 73.

The Power and Potential of Small Computers (Quad Copter Videos)

Start by looking at this one: 

https://www.ted.com/talks/raffaello_d_andrea_meet_the_dazzling_flying_machines_of_the_future

Then, for more details, look at these:

"Hot Iron" New Issue, Great Articles

I was very pleased to find Tim Walford's "Hot Iron" journal in my e-mail this morning.  Lots of great articles in this edition, including one by a fellow we know:  Pete Juliano!  Pete writes about our esteemed dual gate MOSFETS.  All hail the 40673!  There is also a nice article about superhet receivers using a 6 MHz IF and a very convenient analog LC (yea!) oscillator arrangement.  Another discusses how to use Huff and Puff stabilizers to take care of VFO drift. N4HAY describes his initial foray into the world of homebrewing and how EMRFD helped him.

Hot Iron is free.  Tim writes:  

"Hot Iron is published by Tim Walford G3PCJ of Walford Electronics Ltd. for members of the Construction Club. It is a quarterly newsletter, distributed by e mail, and is free to those who have asked for it. Just let me know you would like it by e mailing me at electronics@walfords.net"

Thanks Tim!

SolderSmoke Podcast 185 -- SPECIAL FEBRUARY ANTENNA SHOW

SolderSmoke Podcast #185 is available

22 Feb 2016

http://soldersmoke.com/soldersmoke185.mp3

Travelogue:  550 feet above Washington DC

Bench reports
Pete:  Simpleceiver update.  Adventures in Raspberry Pi SDR.
Bill:  A daring but failed attempt at divide by 2 I&Q.
Audio Mods on the Hammarlund HQ-100.
Dual Digital Readout for the AM station.

SPECIAL FEBRUARY ANTENNA DISCUSSION
Why we build antennas in February.
Why hams should concentrate on antennas.
The importance of noodling.
Pete's beam project.
Pete's Lazy H.
The pernicious influence of automatic antenna tuners.
Bill's Ray Gun Antenna.
Bill's Moxon and his 160 inverted L.

MAILBAG
Tom Gallagher NY2RF (new ARRL Exec VP).
Mike Rainey AA1TJ on the air with a unijunction transistor.
Dale W9DKB sends me 160 meter book.
Alan Wolke W2AEW builds a Mighty Mite.
Daniel HK4DEI builds a DSB rig in Medellin.
Chris KD4PBJ modulates an AD9850.
Charlie ZL2CTM Builds a Teensy Superhet.
Jim W8NSA -- a Tek 465 goes toes up.
Thomas KK6AHT has roof, needs antenna!
Grayson TA2ZGE homebrewing crystal filters in Ankara.
Ian G3ROO and I had QRP QSO in 2001!
Steven G7VFy sent me a box of VALVES.
Frank KM4AXA repairs a rig and thus adds SOUL to the machine.

Design Wisdom from Allison, KB1GMX

Allison KB1GMX has helped me out of numerous battles with recalcitrant amplifiers.  She provided an interesting contribution on the r2pro mailing list thread that I referenced yesterday:  

Interesting thread...

 I see Rick as having provided the basis and tools and it up to the collective 'US" to use them to 

create that next generation radio.  All you have to do is decide the performance and 

then go about looking at the means to do so.  All the blocks are there.

Dynamic range, how much is enough?  When I'm portable or mobile raw sensitivity is 

more useful as the antenna is usually a compromise.  Overload is easy to handle with

switchable attenuator.  The exception to this was a radio designed for contesting in a 

hostile environment (a KW user 800ft away) if you burn power you get overload 

performance.  Its not a battery friendly radio (RX power is over 1A for headphone output).

Look at what you need and not what you want.

TX power is just adding stages.  I've worked MOSFETs, LDMOS, GaN FETS and there 

are some pretty cool devices out there and some not designated for RF are cheap.

If all else fails the IRF510 gets both raves and derision.  At 12V its a tepid device

but at over 20V and at 24V it starts to wake up and really perform. I've run The WA2EBY

design for a few years at 45W level using two of those push pull at 28V and its clean and 

solid and the original pair are now over 6 years old!  I also run 8 of them  (4x4push pull) 

at 32V at 6M for a cool 210W  with good IMD.  I'd add all the good (high gain, low IMD) 

power fets perform better at 28  or 50V.   For those into CW consider class E as I've 

worked with this and using GaN fets have generated 15W with 82% efficiency at 

13.56mhz (includes driver and osc) and using the lowly IRF510 at 12V a full 10W 

with 85% efficiency. Class E can be amplitude modulated.

As to the thermionic FETs, a 6AU6 crystal osc driving a 5763 for 10W  gets a lot of raves

on 40M from a buddy that runs CW.  The same deal plate modulated can sound good 

at 5-6W AM on 75M.  For those that want more a 6C4, 6aq5, 6146 will get you over 

50W on CW and 25W AM.  Change the bias a little and inject IQ SSB into the driver grid

and be running 50-80W PEP.  A 12BY7 or 6CL6 driving a pair of 6146 will get you into 

the 180-200W DC input range for about 100W.   Remember the hybrid radios solid state 

low level and rugged tubes for the heavy lifting.  The Pi network (or Pi-L) will load anything 

from about 28 to 100ohms more if you use enough taps and variable caps.  That and DC-DC

converter for the HV are not terrible at 80% or better (even the 1960s transistor designs 

were better than 75%).

In the end it all starts with the receiver.  For that you can always start with a 1T4 RF and 

a 1R4 converter and a 1T4 as regen driving a 3V4 audio.  Power it with 45V (five 9V battery)

and a C cell and go portable.  It should run for a very long while.  Hollow fets run well at low 

drain currents.  :)

Allison

Words of Wisdom from Rick Campbell, KK7B

Rick Campbell KK7B recently responded to a question on the r2pro mailing list.  His answer was so good, and so full of design wisdom that I asked Rick for his permission to post his message here.  Here it is:

I have designed and built several new single band HF rigs for my own use since the R2pro, but have not done any complete transceiver designs intended for others to duplicate.  The R2pro was specifically designed as a set of modules so that a designer can combine an assortment of those modules with others and come up with a transceiver optimized for a particular, personal application.  Much of my recent most design work has been for instrumentation at VHF and UHF, so it doesn't really lend itself to the "high performance at HF" realm.  The R2pro design still holds up well in 2016.

Regarding being inspired to design a new high performance transceiver, I find complete transceiver designs uninspiring, hi.  I personally enjoy coming up with a particular application that isn't well served by anything currently available, and working on some unique design for that particular niche.  Occasionally it has been a large enough niche that I've worked with someone like Bill Kelsey to come up with a commercially available kit of parts, but more often I just design and build a few to fill the immediate need in my lab.  Sometimes that "need" is just a whim, and some of my most enjoyable and technically rewarding work has been to satisfy some personal curiosity or other.

Regarding your wish list:

"Best Sounding Audio Possible" is still the same as it has been since my first receiver with diode ring mixers to do the frequency conversion before any gain, followed by a serious audio amplifier string drawn from the audio recording industry.  In most of my recent work, starting with the R2pro, the limitation on dynamic range inside the audio channel is set by the op-amps.  About 80 dB from the noise floor to non-harmonic artifacts is relatively easy, but you have to be careful.  If the noise floor at your receiver volume control is 80 dB below a volt, that's about 100uV, and well below what you can see on an oscilloscope.  These are very old principles.  Though they haven't been common in the communications receiver field, no breakthroughs are needed, just careful design.  The R2pro is better than it needs to be.

"Good Dynamic Range" is an interesting concept.  I like to design receivers that have good enough dynamic range, which is different for every application, on every band.  Unlike during the 1970s, today most of our receivers have enough dynamic range, in the same sense that cars have had enough wheels since designers figured out that 3 was not enough.  Once you have enough, adding more is not an improvement.

Some of my recent receivers have had a crystal filter between the antenna and first active stage.  Those are stellar, but that's not usually needed.  They do illustrate the point that if you find yourself operating in a hostile EM environment with many very strong nearby signals, there are other ways to address the problem besides in the receiver circuitry.  Ever since I achieved "good enough" for all my personal applications a while back, I've focused on other receiver performance measures.  In particular I try to avoid sacrificing something important to make an improvement in a specification that is already good enough.  I have never been on a hilltop with Wes Hayward when anyone missed a contact because of inadequate dynamic range, but I have been when we missed contacts because the batteries died.

"SCAF type filtering."  I've played with switched capacitor audio filters and other commutating signal processing since the mid 1970s.  Each time I've built one into a  receiver I've run into problems with that danged clock.  I tend to listen at and below the noise floor, and one of my pet peeves is when I can hear anything at all other than pure thermal noise when the receiver is terminated with a room temperature 50 ohm resistor.  Since I routinely record signals for post processing in a DSP system, it is disheartening to discover that some harmonic of the SCAF clock beat against the LO at a particular frequency, ten dB below the noise so you didn't hear it when you made the recording, but 10 dB above the noise floor in your FFT waterfall plot.  So I have avoided such things for my last few decades of instrumentation-grade receiver designs.  When I have a digital dial, I include a switch so it can be turned off when I'm recording weak signals.  None of this applies to you--please continue to experiment with SCAF filters, embedded processors and other generators of digital noise that may well be far beneath the threshold of signals and antenna noise for your particular application.

"Audio output power."  In my lab I generally find about a half watt is more than enough for a radio tuned to a ham band.  In other applications I go as high as 40 watts of audio at the threshold of detectable two-tone IM products.  All of that is nicely covered in the audio literature, and there are a number of good designs available on the web.  The R2pro audio amplifier in EMRFD works well driving a compact, efficient speaker in a quiet room.  For more power output, use bigger transistors and raise the supply voltage up to about 24.  Above that, you need to add Darlington drivers, as in the original R1 and R2 circuit, and you can then raise the voltage up to around 40v with NE5532 op-amps and get more than 20 watts of superb clean audio.  That R2pro audio output stage in EMRFD has been borrowed and modified for more than one very high end professional audio application.

"RF Power" For either audio or RF power, I encourage experimenters to use higher voltages than 12.  Within a few years we should have available some nice GaN transistors that will allow us to use supply voltages up around 80, which really makes it easy to generate many watts of power into either 50 ohm or 8 ohm loads.  If you don't want to wait for GaN, there are some huge N channel depletion mode FETs that run the electrons in vacuum and will easily handle many hundreds of volts on the drain.  They need a separate low voltage supply at an amp or so to generate the electron stream, but are capable of astounding performance, particularly in narrow band applications.  If they hadn't been invented 100 years ago, we'd be all excited about the possibilities now.  A 6146 would just idle along at 5-10w out and last forever.

For my most recent contacts on 40m CW, I used an R2pro and ran a very stable premixed JFET Hartley VFO driving a 6C4 and 6AQ5 output stage.

Enjoy the experiments.

Best Regards,

Rick KK7B

__._,_.___

Dr. Rufus Turner, W3LF. Homebrew Hero and Radio Pioneer

Thanks to Farhan for alerting me to this great Hackaday article about a homebrew hero who was -- sadly -- unknown to most of us.  He lived in Washington D.C.,  right down the road from where I live now.  The Hackaday article leaves no doubt about it -- Rufus Turner was one of us. He had THE KNACK.  He was a true radio pioneer and homebrew hero.  It is really a shame that we've known so little about him.  

http://hackaday.com/2016/02/15/do-you-know-rufus-turner/#comments

Inside the Hammarlund HQ-100

I continue to work on this old beast.  I picked it up in the Dominican Republic around 1994.  One of the IF transformers had gone open.  I fixed that.  Had to replace the AF output transformer too. And the variable cap that tunes the antenna.  Check out the flywheels!  And the rope and pulley thing.  You don't find those kinds of things in any of those fancy modern rigs. 

Earlier I had removed "the exclusive Auto-Response audio output circuit."  See:
http://soldersmoke.blogspot.com/2016/02/snowed-in-audio-mods-on-hammarlund-hq.html

Today I installed a simple feedback network in the AF amplifiers (as prescribed here:  
http://www.amwindow.org/tech/htm/hqaudiomods.htm

It sounds nice now.   The rest of the bands have been ravaged by some sort of solar event, but 160 seems to be benefiting -- signals last night and this morning were quite strong.  I was being heard by WA1HLR way up in Maine.

UPDATE 20 Feb 2016: After installing the feedback network mentioned above, I noticed a big increase in AC hum.   It was not the electrolytics.  I reversed the feedback mod and the hum went away.  But the receiver continues to sound a lot better with the removal of the Auto-Response output circuit.

Just Below 160 Meters -- "Travelers' Information Service"

In the course of working on my 160 meter AM station I came across a strong AM signal a bit below Top Band.  Turns out it is part of something called the "Travelers" Information Service."

The signal from this system on 1.670 MHz is very strong here.  A Shortwave (Midwave!) Listener in Austria heard it too.  Check out the confirmation letter from the Virginia Department of Transportation.  Nice of them to do this.
Here is the QSL letter sent to Austria:
https://remotedx.wordpress.com/2014/06/01/very-rare-reception-vdot-highway-advisory-radio-1680-khz/

They are running 10 watts into a 49 foot tall vertical with 40 radials. They have a text-to-speech system that is constantly describing weather conditions.  Quite useful actually.

I found a web site that lists all the stations of this kind in the US:

https://www.fcc.gov/media/radio/travelers-information-stations-search

I can see that the station I am hearing is just 2 miles from my location.


More information on this system:

https://en.wikipedia.org/wiki/Travelers%27_information_station

A Phasing Receiver from Montenegro (Video)

Thanks to Peter Parker VK3YE for alerting us to this beautiful receiver from Bore 4O6Z in Montenegro.  This may be our first ever report on a Montenegrin rig.  And it is a thing of beauty. Bore says it is based on a phasing circuit by homebrew legend V. Polyakov, RA3AAA.

Here is 4O6Z up on the tower:

Snowed In! Audio Mods on the Hammarlund HQ-100

It is snowing here today, so I am stuck in the hamshack.  YEA!

I've had the Hammarlund HQ-100 receiver on the bench because I am building an outboard digital frequency readout for it and for the DX-100.  More on this later.  But as long as I had it on the bench I decided to do a mod to the audio output that has LONG been needed.  

Here is a nice web page that describes the problem and the solution.  The problem is the "Auto Response audio output circuit" touted in the add up above.  Essentially I had to remove the touted circuitry.  The AutoResponseectomy only took me about 15 minutes and the results are quite noticeable.  The old receiver sounds a lot nicer.  I'm listening to 40 meter AM now.  FB.

Here is the page:

http://www.amwindow.org/tech/htm/hqaudiomods.htm

The HQ-100 does indeed have "three dimensional beauty."

"QSO Today" Podcast Interview with Michael Rainey AA1TJ

Eric 4Z1UG has a really great interview with Michael AA1TJ:

http://www.qsotoday.com/podcasts/aa1tj

I listened to it as I aligned my HQ-100 receiver and worked on a digital frequency readout for the old receiver.   The interview was the perfect accompaniment for such a project.  Inspirational stuff.  Lots of great info on QRPp and homebrewing.  Mike talks about some of his more famous rigs including the voice-powered New England Code Talker (pictured above).  

I loved the story of Michael carting his DX-100 home in a wagon.  And I really sympathized when he described the harsh reaction of the phone operator to his early efforts at voice modulation.

Strongly recommended!   You won't be disappointed.  Great interview.  Thanks to Eric and Mike.

http://www.qsotoday.com/podcasts/aa1tj 

ZL2CTM's Teensy SDR SSB Superhet -- Very Cool

Hi Bill

I thought I would drop you a quick line to show you something I have been playing around with for the past couple of weeks. It's a SSB superhet using a PJRC Teensy 3.1 microcontroller (YouTube link below), and a great audio library by Paul Stroffregen. Suffice to say I'm really happy with it.

There is a direct conversion front end, albeit using a VFO 15kHz down from the incoming RF. The 15kHz IF is then fed into the Teensy audio line in which can handle up to 22kHz. From there everything is in software. First is a 2.4kHz BPF tuned to the LSB, followed by mixer with a 15kHz BFO. Finally, there is a 2.4kHz LPF. Next step is to add both CW-wide and CW-narrow filters which can be selected during run time.

As you can tell from the video, my antenna is not the best and I have quite a bit of QRM in the shack. I really need to think about a better antenna, but that's another story.

https://youtu.be/9-rA-VAdrZA

I have been following your R2 endeavors with interest, and as I said to Pete I will attempt to replicate the R2 on a Teensy. I will try and use the divide by 2 arrangement you tried as the logic looks right.

I will also be adding in a transmitter. For that I'll use the microphone input and then take the audio from the line out straight to the RF pre/power amp. 

I must admit that I really enjoy homebrewing hardware/software hybrids as you get the best of both worlds. As i say that, I wonder how much ADCs cost these days to directly digitize RF...  Now that would be interesting.

I'll say again that I really enjoy following the podcast. I have loved electronics since I was a small boy when my parents bought me a battery, switch and light bulb. This age of cheap DDSs, microcontrollers and the like is amazing, and I get so much enjoyment putting them all together to make functioning ham radios. I hope more get into the homebrew field as the entry barrier is dropping fast.  

Keep up the good work.

73s

Charlie

ZL2CTM

A Snow Day Well-Spent: Chris Modulates an AD9850

Feb 10 at 7:40 AM
Hi Bill and Pete,
My work is closed today due to the snow so I wanted to show you what I've been up to.
I built sort of a test fixture a while back for those cheapie EBay AD9850 boards based on AD7C's DDS circuit using an Arduino Uno as a controller.
Last summer someone posted a link to Analog Devices App note AN-423 on QRP-Tech I think.
It was always on my list of things to try.
Armed with a schematic of the eBay DDS gleaned from Doug Pongrance's website, I got to work. It involved cutting a trace or two on the DDS board using an X-Acto knife.
Two outputs of the DDS chip are fed into a wideband transformer as in the app note's second page and I hung a scope probe off the secondary of the transformer.
Basically you are removing the Rset resistor on the DDS board (marked R6 on mine) and using a 2N7000 MOSFET as an electronic version variable resistor and modulating the MOSFET.
This lead to much frustration over the afternoon. No output on the scope!! Did I make an error or connect something up wrong? I was using the 600 ohm output of my HP652A audio generator. I thought about it during lunch and decided to try the 50 ohm output. Bingo!! At the 3V RMS range setting on the generator I now have some kind of signal. Not a nice sine wave shaped AM output but at least something resembling a clipped sine wave. The circuit is really touchy as far as needing a hefty audio signal in. The output of my iPhone at max volume doesn't turn on the DDS chip.
I set the DDS for 1200 kHz and can listen to it on a Radio Shack portable radio. Varying the audio generator varies the received tone on the radio just like I was expecting.
I just need to figure out what's up with the audio levels.
Chris
KD4PBJ

Feb 11 at 7:53 AM

I did manage to reduce the audio a little and get clipping to go away. I'll send another set of oscilloscope shots tonight. 

The only thing I don't get is why the audio level needs to be so high. The app note said 1 V peak to peak should be enough but I am having to drive it with 7 V p-p audio to get a decent waveform with 0.8 V p-p RF. 

I did cut the traces going to pins 12,20 and 21 to the DDS chip rather than pick up the signals elsewhere in the board. This was because once the traces go into vias down in the board, I'm not sure what else they connect to. 

Chris

Feb 11 at 1243 PM

Found the original email from May of last year about the app note. It was on the EMRFD list. After hearing you guys lately talking about AM it has me excited about an AM transmitter. 

I just got a thought over lunch that I'm going to try tonight and that is biasing the 2N7000 gate with a couple of volts to see if I can get the transistor on. Then maybe I don't need as much audio. I'll definitely put a series cap in though to my audio source so I don't fry my iPhone!!!

More to come this evening!

Chris

Feb 11 11:23 PM

I'm so excited!!

That's exactly what I needed to do-bias the gate of that 2N7000 so I'm not depending on the audio to turn it on, only to modulate it. 

I hooked up a 9v battery across a 10 k trim pot and connected the wiper to the gate of the fet. A 10 uF cap is in series with my audio line as not to feed DC back into my source. 

I have audio and now the output of a small radio or iPhone modulates it fine. 

So this is a great proof of concept! Those cheapie DDS modules from China can be AM modulated. 

I need a mic amp now, filter (surgery to the board disabled the on board LPF, but yes Steve I'll install one right away), buffer amp and some kind of linear RF amp to get a few watts. 

Chris 

Here's a video of Chris's project:

 

 

Gravitational Waves, A GREAT VIDEO, Phasing, and Joe Taylor K1JT

Wow, you really have to spend 20 minutes and watch the video (above).  It is really well done.  I loved it.  I give it FIVE SOLDERING IRONS!

And big news today!  They did it!  Gravitational waves finally detected.  Here is a good New York Times article that includes a recording of the signal, a nice NYT video that has a good explanation (with phasing!) of how lasers are used in the massive detectors, and mention of Joe Taylor, K1JT, whose Nobel Prize winning work contributed to this great discovery.

http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html?partner=rss&emc=rss&_r=0

Life in the Fast Lane: Potato Semiconductor Chips

Even I, with my luddite tendencies and analog preferences, have recently bumped up against the speed limit of 74 series logic chips.  The Si5351 chip in the I and Q VFO for my phasing receiver will run up to 160 MHz.   But the 74 series inverters and flip flops that I have attached to the output don't seem to want to go beyond about 120 MHz.   Our old friend Thomas LA3PNA tells us how to break this speed limit:

http://www.potatosemi.com/  

Be sure to go their "Milestones of 74 Series Logic" Page.

I like their explanation of the brand name: 

Single Sideband + Carrier -- The Collins KWS-1

Back on 2 February I was on 160 AM with the DX-100, talking to WA4PGI.  At the end of our QSO we got a call from a station.  I was at first confused -- was this station calling on SSB?  Or was he calling on AM?   Turns out that he was -- in a way -- on BOTH.  K4DBK was -- I think -- running an old Collins KWS-1, the transmit side of the famous Gold Dust Twins.  Aptly named:  It was built in 1955. 1000 watts output.  $2095.00 in 1955.  Gold dust indeed.  

The really interesting thing about this rig was that it put out CW, SSB and SSB plus the carrier.  I think that was what we were hearing from K4DBK.  FB.   

Does anyone have an e-mail address for K4DBK?  I'd like to drop him a line.

http://www.collinsradio.org/cca-collins-historical-archives/the-equipment-of-collins-radio/the-black-boxes/kws-1/