AA1TJ's 150 Microwatts Heard at 112 Kilometers -- "To Boldly Go Where no Unijunction Has Gone Before."

AA1TJ reports: 

Breaking news from W1PID... "Mike! I just copied the beacon. I got 'VVV de AA1TJ 150 uw' and it faded out. 2146Z on 3551.95MHz" That's it! Jim copied a message produced by a lowly unijunction at a distance of 112km. How's that for cool! In a nutshell... the unijunction runs as an R-C relaxation oscillator at ~500kHz. A quartz crystal at the emitter frequency-locks the sawtooth waveform to 507kHz. The 7th harmonic is admitted to the antenna via a bandpass filter. The RF output to DC input conversion efficiency is all of 0.1%. Heat-sink? Check! Mission statement:
"...to boldly go where no unijunction has gone before." Cheers,
Mike, AA1TJ

I think the really cool thing is that EM waves are once again flying out of the Vermont Hobbit Hole, propelled into space by the poet laureate of QRP.

QST de AA1TJ -- Please listen for Mike's Microwatts!

QST de AA1TJ...

I've a 150uW transmitter built from a single unijunction transistor currently running as a beacon on 3552kHz. If my New England amateur radio pals would be so kind as take a listen for it I'd be most appreciative!

Alan Wolke W2AEW Builds a Michigan Mighty Mite (Video)

We are honored to induct Alan Wolke W2AEW into the Colorburst Liberation Army.  And for his valiant effort to build and explain a MMM Low-Pass filter, he is immediately promoted to the rank of CBLA Two Star General.  Congratulations General Wolke.

As is the case with all of  his videos, this one has already had an impact far and wide.  Ian writes from far-off Western Australia:

Jan 27 at 6:19 PM

G'day Bill,Just in case none of your other correspondents have brought it to your attention, here is a great video W2AEW has put up showing really clearly the positive effect of a low pass filter on the output of the Michigan Mighty-Mite.

It made me appreciate the benefits of an LPF more fully. It's always been clear to me that the harmonics would get rolled off, but in my head I hadn't made the connection between that and the improvement to the beautiful smooth sine wave that we are working towards.

Anyway, I thought you, and your mate Steve "Snort Rosin" Smith may be interested.

Thanks to you and Pete for Soldersmoke, I'm sure you're responsible for keeping the flame alight in many a ham.

73,Ian VK6MIB

And Steve "Snort Rosin" Smith, the guru of low pass filters, observes:

Of course, to work properly in the land down under, the inductors must be wound in the opposite  direction as those in the Northern Hemisphere :-P .

Seriously, there is a lot to be learned from the lowly Mighty Mite especially regarding impedance matching; not to mention LC circuits, link coupling, amplifiers, oscillators, etc. .  What fun!

73.......SR

Humidity Data and the Zapping of my LCD Display

Sometimes the Radio Gods conspire against you.   Check out the chart above.  It shows relative humidity at my location.   I zapped my LCD display right around 2000 UTC on January 25, 2016.  That poor little LCD didn't stand a chance :-(

Right now relative humidity here is 79%.  No sparks now! 

I like the solution (!) proposed by Brendan, EI6IZ:

You can get an anti-static spray designed to treat carpet, upholstered furniture etc. This is a sensible thing to do if one tinkers with electronics and for the average hamshack a bottle will last for many years as it only needs to be applied lightly and infrequently.
For example http://ie.rs-online.com/web/p/esd-safe-clean-room-treatments-lotions-dispensers/0182893/ For cheapskates however, diluted fabric softener sprayed on the carpet and chair will work well for at least a few months but will require much more frequent application than the 'proper stuff'.

I give my car seat an occasional squirt in dry summers to stop the 'zap' when getting out on a dry day.

73
Brendan EI6IZ

An Electro-Static Bandaid to Protect Sensitive LCD Displays

After the big East Coast blizzard,  the atmosphere in my ham shack became very dry.  I sit in one of those desk chairs with little plastic wheels.  The shack is carpeted.  So when I roll from operating bench to workbench,  the chair, the carpet, the dry air and I all become a kind of Van de Graaff generator.  Yesterday, my hand brushed against the 16X2 LCD display on my new R2 phasing receiver.  The pretty glowing numerals in that display disappeared in a small spark, never to return.

I swapped out another display I had, so all is well.  But the repair was a pain in the neck, involving the soldering of some 16 LCD pins, so I don't want to do it again.  I consulted with Pete Juliano N6QW who told me that this kind of LCD carnage is quite common in dry environments.  He said he had cured the problem by placing a small piece of Plexiglas in front of his displays. 

This got me thinking about those static protective bags that Digikey uses when shipping many of its components.  Might the material from these bags prevent the loss of another display? 

I retrieved a couple of these bags from the garbage and did a little test:

First, I rolled across the shack in the chair with a small screw-driver in hand.   At the other end of the shack lies my well-grounded DX-100 transmitter.  I moved the screwdriver close to the metal on-off switch.  SPARK!  It was visible, and quite audible in the AM broadcast receiver nearby. 

Next I taped a small piece of this material over the switch and repeated the ride in the chair.  No spark. Nada.  I repeated this several times and always got the same result.

It appears that the material in the bag helps dissipated the static discharge over a wider area, preventing the spark.  I quickly taped a piece of this material over the two LCD screens in my shack.  It's not pretty, but it is temporary, and cheaper than a humidifier.

I'm not going to try this on the actual screens, but I do think these small pieces of material will help prevent another accidental frying of an LCD display.

Here is the Wiki on anti-static bags: https://en.wikipedia.org/wiki/Antistatic_bag

And here is the data sheet on the bags that I am using:
http://documents.staticcontrol.com/PDF/Static_Shielding_Bag_1000_Series.pdf

1936 Shortwave Listener QSL card

I found this today while rummaging around in the shack.  It is starting to fall apart so I figured I better digitize it before it turns into dust.

July 24, 1936.  7 am in Central Germany.  29.0 degrees Centigrade.  Clear skies?  German Shortwave Receiving Station DE 2518/F monitored W5AIR's contact with Irish station EI7F on 20 meter CW. The receiver was an OV2 Schnell tube (almost certainly a regen) fed by a 38.5 meter long antenna.  

Conditions must have been pretty good -- they were approaching the peak of sunspot cycle 17.

In 1954 W5AIR was assigned to Garold D. Sears.  He was probably the operator.

Listen to My R2 Phasing Receiver (formerly known as "The Frankenstein" )

I really like this receiver.  Thanks to all who helped. 

Blizzard Prep Priorities: Protecting the 160 meter L network!

I'd been meaning to build a proper cover for my improvised 160 meter L network. The approach of Winter Storm Jonas pushed me into action yesterday afternoon. 

First I mounted the variable cap (from an old Johnson rig) and the roller inductor on a suitably sized piece of wood:

Then I put the tuner inside an old cooler.  I drilled holes in the bottom for the coax and the antenna wire and the ground.

Here it is at the feed point.  Pretty cool, don't you think?

And here it is 24 hours later:

The blizzard has been quite impressive.  Early this morning it featured lightning and thunder!

Some Inspiring Phasing Philosophy from KK7B

KK7B holding his original Mini-R2

Rick Campbell KK7B concludes Chapter 9 of "Experimental Methods in RF Design" with these inspiring words:

"An amateur who has built up a phasing receiver, looked at the I and Q channels on a dual trace oscilloscope, and tweaked the phase and amplitude adjustments while listening to an opposite sideband signal drop into the noise acquires a depth of understanding far beyond that of most wireless graduate students and many of their professors. The best part is that understanding of phasing systems comes from experimenting with simple circuits and thinking -- the tinkering comes first -- then the understanding. In this area the amateur with his simple workbench; primitive test equipment; and time to contemplate, has a profound advantage over the engineering student with a computerized bench and exam next week, and the professional engineer with a million-dollar lab and a technician to run it."

N2CQR Frankenstein R2 showing I and Q audio outputs

(No exam next week for me!)

Lee Snook W1DN's Amazing New Rig

Wow, I feel myself being pulled into the digital vortex.  What a cool combination of digital and analog construction!   I love that small spectrum 'scope.

Lee's rigs and his workshop have been discussed on this blog before:

http://soldersmoke.blogspot.com/2014/11/the-amazing-rigs-of-lee-snook-w1dn.html
http://soldersmoke.blogspot.com/2014/11/the-amazing-rigs-of-lee-snook-w1dn.html

High-Pass Filter Knocks Down AM Broadcast Interference

WFAX 1220 AM was starting to bother me.  Each morning, I'd be drinking my coffee, listening to nice roundtables on 160 meters, when, right at 6 AM, WFAX would fire up its 5 kW AM transmitter, 1.5 miles from my location.  And they would crush the "front end" of my R2 phasing receiver.  It doesn't take much to do that, since the only thing between the SBL-1 mixers in the R2 and the antenna is a signal splitter.  Obviously I needed some filtering. 

I turned to the free program called Elsie (L-C, get it?) and quickly whipped up a design for a seven element, capacitive input high-pass filter that promised to take about 45 db out of WFAX's sails, without attenuating even the lowest end of Top Band. 

Last night I scrounged through the junk boxes and found suitable capacitors.  A visit to an on-line toroid calculator showed that around 35 turns on a T-50-2 (red) iron powder core would yield the needed 6 uH coils.   I built the filter  this morning -- picture below. 

It works very well.  You can see the results in the picture above.  The yellow trace on the 'scope shows the signal at the antenna terminal.  Yikes, it shows around 4 volts rms at 1.220 MHz (the scale is 5 volts/div).  The blue trace below is on the same scale -- this is the signal coming out of the filter.  Not enough to really measure on the 5 volts/division scale.  

This was a very satisfying "quick and easy" build.   I really like the sound of the R2, so much so that I'm not firing up the DX-100 as much as I had been.  Instead I find myself just listening to the R2.

Another AM Broadcast Interference Story

Bill,Pete

Another great solder smoke podcast today.  I especially liked the detail
of you using the S-meter to check on the local broadcast station, and
the better reception you had on 160 with a resonant antenna.  Before I
retired I had spent over 25 years as a field service tech working on
neurological instrumentation.  One of the test our instruments performed
was called an Electro-Myography. Part of this test involved a needle
electrode being inserted into a muscle.  This was fed to an
instrumentation amplifier connected to a computer that processed the
output of the amplifier.  The signal from the amplifier was also fed to
a speaker so you could also hear the response of the muscle fibers
activating as you flexed the muscle.  One of my customers called and
said that quite often when he inserted the needle electrode, he heard
music  instead.
I made a trip to his office and  using a field strength meter, I could
see the modulation peaks on the FSM.  But only in one location against
the wall in the exam room.  I at first thought it might be from a
speaker cable for their intercom / background music system in the wall. 
But there was no wires near that location , and it was an outside
wall.  I went outside with the FSM and found that the signal was coming
from the down-spout for the rain gutter. Apparently the gutter was
resonant at the frequency of the local AM station and the received
signal was being radiated through the wall and picked up by the amplifier.
I quickly got the set of jumper cables out of my van and connected the
down-spout to a near by water faucet, the signal went away. After a
quick trip to the local Home-Despot and picking up some heavy copper
wire and a ground clamp for the water pipe I was able to fix this
problem.  It is amazing how broadcast interference can show up in so
many places.

DuWayne