Very Cool Vosworx AZ-EL Satellite Tracker

When I was in the Dominican Republic working the RS satellites, MIR and the Space Shuttle, I didn't have an elevation rotator.  I could only move the antenna in the azimuth plane.  So I just aimed it about 45 degrees above the horizon, spun it around, and hoped for the best.  I also had no computer control of the azimuth heading -- I'd just watch the location of the satellite on my computer screen and operate the rotator control manually.  

This device is a big improvement. 

The Original Tuna Tin 2 (and the Mojo Transfer Ceremony with W1REX)

From the Amateur QRP Radio group on Facebook:‎

Brian Murrey‎to

 Amateur QRP Radio

The Original Tuna Tin II built by Doug DeMaw W1FB (SK)...Ed Hare W1RFI of the ARRL Lab, brought this to FDIM in 2001 and allowed us to borrow it for a night. It was so cool. The little guy was found at a hamfest somewhere on the east coast, and brought back to the ARRL. Bruce Muscolino W6TOY (SK) recieved it from the ARRL and he replaced missing parts and got the thing working again. It's in the museum at the ARRL HQ today. I think we made like 16 contacts using that for the transmitter, and a homebrew receiver from Diz W8DIZ that was part of the MultiPig Rig. Antenna was a dipole we had strung up out the window of the Ramada Inn (FDIM Central).
-----------------------------------
Here is my only encounter with the original Tuna Tin 2 -- In 2014 Rex W1REX conducted this solemn ceremony in which some of the TTT mojo was transferred to my homebrew BITX 17. 

The South Atlantic Anomaly in Earth's Magnetic Field

In case you've grown tired of worrying about infectious disease, here's another scientific problem for you to worry about:

https://www.youtube.com/watch?v=qpdQcw_52iM

SolderSmoke Lexicographer Worked on Earth-Moon-Earth Laser

Hi Bill

A ham, well known to us, actually me, was very involved in the very first laser reflector experiment.  I was a new EE graduate and was hired by the University of Maryland Physics department to design and build the control system for the laser experiment.

The first reflector was placed on the moon immediately after Apollo 11 landed.  And the equipment on Earth to use it was in place and ready to go to work.

Here is how it worked.  A very powerful laser was installed at the McDonald Observatory in west Texas.  It pointed into the viewing end of the telescope and had 5 Joules of energy.  When it was fired, a control system made from discrete logic chips was used to control an electronic shutter in front of a very sensitive photomultiplier tube.

In order to prevent stray photons from impacting the photomultiplier tube, the shutter was opened just microseconds before the reflected photons were expected to arrive from the moon, a round trip of about 2.5 seconds.  Then the photons were collected from the laser's pulse.  Only between 1 and 10 photons were collected from each shot and were statistically analyzed to get the best transit time to determine the distance to the moon.

Similar systems were set up on other continents in order to triangulate the distances between the telescopes to determine continental drift.  In addition, the outward shift of the lunar orbit was also determined.

Because the moon's orbit varies by about 10% and is easily predicted, the control system used thumbwheel switches to set the time of transit to open the shutter at the right time to keep out photons that were not from the laser.

The control system also sent the trigger pulse to the laser's gigantic capacitor bank to send trillions upon trillions of photons to the moon. So a 5 volt pulse triggered this massive release of stored energy into the lens of the telescope.

And here is the coolest part,  the astronauts could see the laser pulses from the telescopes when they were fired.

I had no idea that these reflectors were still in use and that their efficiency has degraded likely due to lunar dust. 

73

Steve

KB3SII ... .. ..

------------------------

See also: http://soldersmoke.blogspot.com/2020/08/earth-moon-earth-with-lasers.html
and
https://www.smithsonianmag.com/smart-news/scientists-shot-lasers-moon-decade-then-one-bounced-back-180975585/

WU2D's TR-3 -- Mike Refurbishes a Nice Old Drake Transceiver (PART 1) (Video)

There is a lot of Tribal Knowledge in this video.  And good discussion of the many moral issues faced by those of us who work on old gear. 

-- Mike seems apologetic about his blatant and blasphemous spray painting of the Drake copper chassis.  As well he should be. 

-- His stubborn replacement of the tube socket (to allow for shielding) seems wildly reckless to me.  The Radio Gods may retaliate with some unexpected instability in that circuit. 

-- He CORRECTLY refers to the rewiring of the final circuity (to accomodate 6146s) as "the evil thing."  Indeed. 

-- I love in the beginning how he is listening to some ham radio chatter and the guy is talking about the selection of COM PORTS. With old radios "we don't have COM PORTS -- we have an antenna connector."  Well put Mike. 

-- I was struck by how much the TR-3 innards look like my 2-B receiver.  But the TR-3 has no dial strings.  That is a major technological improvement. And it has a PTO.  Was this a case of Collins envy?

-- Mike adds a useful word to the lexicon:  "shotgunning" -- the indiscriminate replacement of entire categories of parts in old radios.    Now I don't mind shotgunning the electrolytics (some people bitterly oppose this).  But I agree with Mike on the wisdom of keeping the paper caps in there.    

I am looking forward to Part II.  These videos are like "This Old House"  but instead "This Old Rig." And I will go back and look at Mike's video on the Power Supply refurb.  Thanks Mike. 

Earth-Moon-Earth -- With Lasers

https://www.nytimes.com/2020/08/15/science/moon-lasers-dust.html

Thanks to Chuck KE5HPY for alerting us to this very interesting article. 

Fixing up a Radio Shack DX-390 (AKA Sangean ATS-818) While Suffering from Fat Finger Syndrome

I've had this Radio Shack DX-390 portable receiver since the early 1990s.  I bought it when I was in the Dominican Republic.  It accompanied me on some interesting trips to the Haitian border, and on one very memorable 1994 trip to the Haitian capital.  I have made some CW contacts with it serving at the inhaler.  

Click on the diagram for a better view. It is a dual conversion superhet.  First IF is at 55.845 MHz.  There is a big 90's era IC-based PLL oscillator that runs from 55.995 to 118.7 MHz -- The main tuning dial moves this oscillator.  Second IF is at 450 kHz.  There is an oscillator at 55.395 that takes the signal down to 450 kHz. Selectivity (not a lot) is provided by ceramic filters.  Finally there is a product detector and a 450 kHz  oscillator that produces the audio.   While there are many mystery chips in this receiver, there is also a lot of discrete-component analog circuitry in there -- it is kind of a pleasing mix. 

DX-390 Main Board.  Note kludged toroidal replacment for L10 (just above ferrite antenna) 

The old DX-390 suffered a lot of wear and tear.  The case is very beat up.  The most serious problem was that at some point, probably on a cold, dry, winter day in Virginia, static electricity took out the FET in the receiver's front end.  I made a half-hearted effort to fix it, but it never really worked properly.  

I occasionally found myself thinking of this receiver.   I spotted one on e-bay not long ago, and bought it.  This newer one was in very nice shape.  

But that old one was kind of staring at me from the corner of the shack.  "C'mon radio man," it seemed to say, "can't you fix a shortwave receiver?" So this week I took up the challenge.  

First the FET.  I had kludged an MPF102 in there, but that didn't seem to work well.  Internet fora seemed to think that a J310 would do better, so I installed one of them -- it did seem to work better.  (Note:  Pete Juliano likes J310s -- TRGHS.) 

Kludged in J310. And two sets of back to back diodes

During my earlier repair effort I had apparently destroyed the front end output transformer (L10) but I discovered that I had replaced this with a toroidal transformer.  It still worked, so I left well-enough alone. 

I was pleased that the old receiver was receiving OK, but there was a problem:   The "BFO" control wasn't working.  The BFO would come on, but turning the BFO control did not vary its frequency.  

At this point I discovered that while there are many copies of the DX-390 service manual and schematic on the internet, all of them have seriously degraded copy quality right around the parts of the circuitry that I needed to study.  Sometimes Murphy overpowers the Radio Gods. It took me a while to get a useful schematic of the BFO control mechanism. 

BFO is a bit of a misnomer here:  the control actually shifts the frequency of the 55.395 MHz oscillator that drives the second mixer.  See Block diagram above).   There is a varactor diode in the base circuit of a BLT oscillator circuit.  Turning the BFO control varies the voltage going to the varactor thus causing the oscillator frequency to slide up and down.  But mine wasn't moving.  And that was a problem. 

So I dove right in, trying to figure out why it was oscillating, but not shifting in frequency.  At this point I discovered that I too am afflicted with the disease that Pete Juliano suffers from: Fat Finger Syndrome.  That BFO control circuit has a nice big 100k pot, but all the fixed resistors and caps were surface mount and SMALL.  As I poked around trying to troubleshoot, I managed to make things worse.  It turned out that the lead carrying 6 volts to the BFO control circuitry had broken.  But before I discovered this, I managed to do all kinds of damage to the board.  I lifted two PC board  pads (I should have turned down the temperature on my soldering iron).  Then, when I tried to fix this, I managed to put a solder bridge across two parts of the circuit that definitely should not have been connected.  

This resulted in a bizarre BFO situation.  From the center position, turning the BFO to the left OR TO THE RIGHT would move the BFO in the same direction.  So I could tune in an SSB station by turning to the right, or by turning to the left.  That was just not right. 

Lifted solder pads.  And small wires that now bridge the gaps 

Uffff.  It took me a while to find that fault.  While trying to figure this out, I built the circuit in LTSpice just to see what it was SUPPOSED to be doing.   This helped.  Eventually, through careful inspection with magnifying goggles, I found a solder blob, and removed it.  Now all was right with the universe.  Even though I had caused most of the trouble, it was still quite satisfying to fix it. 

Some additional observations on the DX-390. 

-- It really is a Sangean ATS-818 in disguise.   Just look at the marking on the PLL board.  If you can't find a decent DX-390 schematic, just use an ATS-818 schematic. 

ATS 818 marking along the bottom (green) part of the PLL board

-- The service manuals on these receivers are quite good: the include bloc diagrams, detailed alignment instructions, and even voltage charts for all the chips and transistors.  Impressive and useful. 

-- The static discharge vulnerability is hard to understand.  There is so much cool circuitry in these receivers, why not add four simple diodes?   Not wanting to repeat this saga, I went in and put two sets of back-to-back small signal diodes in each receiver: one set on the telescoping antenna, and other at the input for the external antenna.  Curiously, on the newer receiver, it looks like a previous owner had gone in and tried to address this vulnerability -- but he did a very incomplete job.  He just put ONE diode between the external antenna input and ground.  I had always thought that two diodes back to back would give you good protection from static discharge.  And I don't think that single diode protects the front end in any way from discharge coming in from the telescoping antenna.  

This was a good project.  I got more familiar with general coverage dual-conversion receivers.  And I got reacquainted with an old receiver that I liked a lot.   Both receivers could probably use some alignment.  I'll take that up next. 

Tor LB4RG Builds an IRF-510 Amplifier

Click on the link to check out Tor's very FB and artistic video about his homebrew IRF-510 amplifier. 

Very Nice.   Also, check out Tor's FB SolderSmoke hat.  

https://gopro.com/v/bQ1JGOXRrRqrQ

And here is an update from Tor" 

https://gopro.com/v/gv19pDDqQnO1a

Arecibo Dish Antenna Seriously Damaged

https://www.sciencealert.com/a-broken-cable-smashed-a-huge-hole-in-the-arecibo-observatory

Teddy Roosevelt on Homebrewing: "The Ham in the Arena"

"It is not the critic who counts; not the sharp-tongued appliance operator who points out how the homebrewer stumbles, or where the builder of rigs could have built them better. The credit belongs to the ham who is actually melting solder, whose fingers are marked by burns and glue and blood; who strives valiantly; who errs, who splatters and distorts again and again, because there is no homebrewing without error and shortcoming; but who does actually strive to build and improve his rigs; who knows great enthusiasms, the great devotions; who spends himself in a worthy project; who at the best knows in the end the triumph of saying “rig here is homebrew,” and who at the worst, if he fails, at least fails while daring to try, so that his place shall never be with those cold and timid amateurs who never try to build anything, but who only stare at their waterfalls, ready to pounce on those who do."

See also: 

https://en.wikipedia.org/wiki/Citizenship_in_a_Republic#:~:text=It%20is%20not%20the%20critic,could%20have%20done%20them%20better.

Using SDR without SDR Hardware -- N2CQR Adjusts Analog BITX20 using Web SDR

I know what you are thinking:  Software Defined radio with the TOTAL elimination of hardware? WHERE IS BILL AND WHAT HAVE THEY DONE WITH HIM?  

Relax my friends.  All is well at SolderSmoke's East Coast HQ.  In fact, just yesterday I was making use of one of the systems described in this video.  Here's how: 

I was on 20 meters with my BITX 20 Hardware Defined (HDR) homebrew transceiver. Everything was going smoothly.  We have some sunspots now, so DX is once again possible.  I heard a loud U.S. station (that will remain anonymous) calling CQ, so I gave him a call.  

The trouble started right after he looked at my QRZ page. You see,  I have pictures of my homebrew rigs there.  These images sometimes trigger hostile reactions, especially from guys who have almost their entire stations INSIDE their computer boxes.  I also admit to occasionally making things worse by pointing out that it is possible to build a BITX20 for about five dollars U.S.   Some guys apparently don't like hearing about this. 

Anyway, the fellow I was talking to proceeded to give me a very blunt and harsh signal report:  "Well, I suppose your signal is strong enough, but your audio is TERRIBLE!"  Interpersonal relations pointer:  This is NOT a good way to alert a fellow ham to possible technical problems in the rig that he has built by hand, from scratch, in his home workshop.  Especially when the person delivering the harsh signal report is using a "rig" that was built by credit card in a robotic factory on the other side of the planet. 

So that QSO ended rather quickly. But I did want to follow-up in the comment about the audio.  And here is where I turned to Web SDR.   Mehmet NA5B has a really nice WEB SDR receive system in Washington DC, just about 8 miles east of me.  Before 20 meters opened, I called up Mehmet's SDR on my computer, tuned it to the frequency of my transceiver and watched the screen as I asked if the frequency was in use.  I then issued a couple of hopeless CQs, again watching the screen.    I could see in NA5B's waterfall that my signal was indeed seriously lacking in low frequency audio. 

Now it was time to turn to hardware.  Rig on the bench, 'scope and sig generators fired up,   I quickly determined that the problem most likely resulted from my placement of the  carrier oscillator frequency in relation to the homebrew USB crystal filter.  I had placed it about 300 Hz too low.  This resulted in a low AF frequency roll off not at the desired 300 HZ, but instead at around 600 Hz.  That would make the audio sound "tinny." So I moved the carrier oscillator up 300 Hz and went back to Mehmet's SDR receiver.  I could see that the lows were now at the right level.  Thanks Mehmet. 

One note about the audio coming out of the many SDR radios on the air:  When you look at the passbands in the Web SDR receivers you can see audio going almost all the way down to the frequency of the suppressed carrier.  With non-SDR rigs  you usually see a gap of around  300 Hz between the carrier freq and the start of the SSB signal.  This is often the result of our filter rigs having IF filter skirts -- you would place the carrier oscillator frequency a bit down the skirt -- this would help with opposite sideband suppression and all you would be losing would be the lows below 300 cycles, which weren't really necessary anyway.  I had placed the carrier oscillator too far down on the skirt.  

Of course, sometimes SDR rigs will also have a gap between the carrier freq an the start of the audio if the operator has set the passband this way, or if the microphone attenuates below 300 Hz.  But you see a lot of signals with audio filling almost the entire passband --some of the "Enhanced SSB" guys are running audio passbands that go as low as 50 Hz.  

Has anyone else noticed this "full passband" effect when looking at the waterfalls?  
Any other tips for using Web SDR for troubleshooting?  

Presence (Absence?) and Direct Conversion Receivers (with wise comments from Farhan)

Hello Bill,

    I was reading an online article by Wes Hayward, W7ZO  from 1968  about the history of direct conversion receivers (http://w7zoi.net/dcrx68a.pdf)  .  It was linked in an email in qrptech.    It recounts how he had first build a dc receiver with a single diode for the detector, and how microphonic it was, and dissatisfying an experience.   This was in the early days of solid state devices, and so they were hard to come by.   He describes meeting another ham engineer at work Dick Bingham, W7WKR who immediately recognized that what he needed was a diode ring mixer.    The story goes on to describe their experiments, and success at this design.   

  They decided to write up the design for QST.   I won't bore you with the details...the article is well worth reading about how Wes mailed the radio and the design to ARRL, and how it ended up in the hands of a new person on their staff there, Doug DeMaw, W1CER (later W1FB.).  Here is an excerpt from the article describing Doug's reaction to the receiver:

"This was the epiphany, the moment when Doug realized that solid-state technology had produce a new way to build a simple receiver. Doug tuned the receiver higher in the band and found some SSB. Again it was like nothing he had ever heard. It was as if the voice came from the same room. Doug used the term presence in his description."

Here I present the earliest use, that I know of, of presence being used to describe a receiver.    I have to say when I read it, I immediately thought of you guys, and decided to share.

Thanks for all you guys do.

   dave    /nt1u

----------------------------------------------------------

Bill replied:

Thanks Dave.   Yea, that's the 1968 article that launched the use of DC receivers.  I had forgotten about DeMaw's early use of "presence." 

Just to cause trouble, perhaps we should start commenting on "absence"  i.e.  "I dunno OM, I think your rig lacks a bit of absence in the mid-range... turn menu item 63b to ELEVEN!"  

:-)

73 Bill 

----------------------------------------------------------

 

Farhan wrote: 

Mon, Aug 3 at 3:22 PM

When I got my license, my friend Anil SM0MFC was living in Hyderabad. He lent me his HW-8.  I stringed up a 40 meter dipole with a lamp cord and worked with it. Somehow, the combination of the lamp cord length and the 40 meter inverted V made it resonate on 20 m as well. The HW-8 had a nominal antenna tuner and I worked pretty good DX.

Till date, it remains the best receiver that I have used for regular contacts. The only trouble it had was the the MC1496 was a nominal detector, it overloaded heavily with shortwave broadcast stations. There was an unnecessary RF amplifier in the front-end that they could have done without.

I made several direct conversion receivers, but never managed to hang on to any. This makes me want to build one, one of these evenings. I even have a KK7B R1 kit. but real men solder on without any PCBs or even circuit diagram!

A 7/14/21 direct conversion radio that puts out 3 watts of power is what my ideal setup would be. I am not too bothered with the images on CW. I just tune them out in my head. Real soon now, at the moment, i am trying to finish a radio that has been in the works for years.  Finally, I am making some headway.

-f

---------------------------------------------

Farhan of course is no slouch in the DC receiver area.  Years ago he wrote a wonderful post about building a DC receiver with his cousin for her class project: 

 https://web.archive.org/web/20171109081542/http://www.phonestack.com/farhan/dc40.html

Included in this post was a passage that I included in my book  SolderSmoke -- Global Adventures in Wireless Electonics: 

--------------------------

Why build a receiver?

    Why do you want to build it? These are available at the Dubai Duty Free asked Harish, an old friend, when he spotted us struggling over the DC40 one evening. I didn't have an answer to this question and considering the amount of work piled this quarter, it appeared to be a sensible thing to ask.

    I think this question is answered by us all in different ways. My personal answer would be because we human beings are fundamentally tool builders. We have an opposable thumb that allows us to grip the soldering iron.

    For an engineer (by the word ‘engineer', I don't just mean those who have a degree, but anyone who applies technical knowledge to build things) the act of building a receiver is a fundamental proof of her competence and capability. It is much easier to put out 1 watt signal than it is to receive a 1 watt signal.

    A simple definition of a good receiver is that a good receiver consistently, clearly receives only the intended signal, such a definition hides a wide range of requirements. The receiver has to be sensitive enough to pick up the weakest signal imaginable (note: clearly), it has to be selective enough to eliminate other signals (only), it has to be stable enough (consistently).

    For a ham or an engineer, building a usable receiver is a personal landmark. It establishes a personal competency to be able to understand the very fundamental operation of the radio and mastery over it.

--------------------

Bill:  OM Ryan Flowers did a 5 part series on building the DC40.  If you are want to build one, I suggest you use the schematics on Ryan's site.  There was an error in Farhan's original schematic -- Farhan corrected it but some of the incorrect schematics are still floating around the internet.  Here is part one of Ryan's series: 

 https://miscdotgeek.com/building-direct-conversion-receiver-part-1/ 

Farhan's DC40