QRSS LED FSK Experiments: More Blue vs. Red

On my little Colpitts/DaVinci/G0UPL less-than-10 mW QRSS rig, I started out with a forward biased (downward pointing) Superbright Blue LED (from AL7RV). (Refer to Hans' schematic, above.) You can see the resulting pattern below. That is my signal above that of Alan, VK2ZAY. At first I thought the diode was just switching in the 5 pf cap, but Hans (who knows this turf far better than I) thinks it is more of a varactor action. I now think it is a little of both: When that + 2.5 volts from the multivibrator hits the diode, it goes partially on (it even glows a bit). This puts the 5 pf cap into the circuit (through the resistance of the diode). The diode itself increases in capacitance because of the increased forward bias. As a result, the total capacitance increases, and the frequency drops a bit. Thus, forward-biased diodes result in upside down FSK. You can see a bit of the varactor action in the curve on the trailing edge of my not-so square waves -- I think that marks the period in which the voltage from the multivibrator is slowly rising:

Just to make Hans happy, I switched from a forward biased blue to a reverse biased (upward pointing) red diode. The resulting pattern (below) looks a lot like the pattern shown in the picture in Hans' excellent SPRAT article. This is clearly FSK. The positive voltage from the multivibrator increases revers bias on the LED, DECREASING capacitance and RAISING the oscillator frequency. In the curve of the leading endge of the pattern you can see the voltage from the multivibrator slowly rising. FSK here is "right side up."

Finally I tired a little 1N914 diode forward biased. I was hoping to see some cleaner switching action, but even with this little diode you can see quite a bit of varactor action at work:

I think the switiching would be a lot cleaner and more complete if the voltage from the multivibrator wasn't coming through a 1 meg resistor. But when you put a lower resistance in place of the 1 meg ohm part, you start to mess up the frequency of the multivibrator.

I have to say, my favorite pattern is that from the Blue diode forward biased. Sorry Hans. To each his own...

I'm guessing that AL7RV went to Michigan...

Thanks to Johan for the ON5EXcellent grabber which is visible over here>>>>>>>>>>>>>>>>>>>

Altoids to the Max!

Rogier, KJ6ETL, sent an interesting link to some inspirational projects involving Altoids tins:
http://blog.makezine.com/archive/altoids_and_tin_cases/ The first one that appears seems to belong somewhere else -- just scroll down to find the tins.

Wiki provides background info:

Altoids are a brand of breath mints that have existed since the turn of the 19th century. Altoids are less widely available in Britain—their country of origin—than in the regions to which they are exported, the standard peppermint mints being the only flavour available and only stocked in relatively few stores. Callard & Bowser-Suchard manufacture and produce Altoids at a plant in Bridgend, Wales, although Wrigley, the brand's owner, announced in mid 2005 they planned to move Altoids' production to an existing plant in Chattanooga, Tennessee, in order to manufacture its products closer to where they are sold.

The history of Altoids dates back to the reign of King George III. The brand was created by a London-based Smith & Company in the 1780s but eventually became part of the Callard & Bowser company in the 1800s. Their advertising slogan has been "The Original Celebrated Curiously Strong (insert flavour here) Mints" for a number of years, referring to the high concentration of peppermint oil used in the original flavour lozenge. The "Story of Altoids" text is printed on the paper liner inside certain tins.

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One cautionary note: Apparently Altoids mints played a minor role in the Bill Clinton-Monica Lewinsky mess. We won't go into the technical details here, but suffice it to say that a collection of Altoids tins on your desk at work may raise some eyebrows among some of your colleagues.

Soldersmoke Podcast #124

That's Billy on the right

http://soldersmoke.com

May 3, 2010
Oprah follow-up: On to Martha Stewart and Dr. Phil?
Fencing on a Roman piazza
Breaking an important cable
My WSPR Direct Conversion receiver
Roger Hayward's wonderful ugly AF amp circuit
The beauty of SBL mixers
My DaVinci Code Oscillator goes on the air!
Making my own 555 timer chip (sort of)
LEDs as varactors (or are they colorful switches?)
Black Holes in workshops -- is the LHC to blame?
Altoids: now made in TENNESSEE!
G3RJV's wonderful video
MAILBAG

Down For Maintenance

Not the radio gear, not the blog, not the podcast. ME! All that running around in the fields of the Sabine Hills finally caught up with me. Last Sunday, while chasing a kite, I tripped and my foot moved in way that nature never intended it to. I popped (quite audibly!) my Achilles tendon. No big deal, but it did require some minor surgery and now I have a big cast on my foot that may cause me to spend additional time in the shack.

I hope to get the next podcast out as soon as I can. Maybe tomorrow. I will try to spare you all the gory details. Back to the radios! I've had a very interesting e-mail exchanges with Hans Summers G0UPL about LEDs as varactor diodes and their use in QRSS FSK systems. I'll talk about this in the next podcast.

Red vs. Blue. (Diodes)

Hans: Live and let live OM! Some people like their diodes up and red, others down and blue!

Any little diode would, of course, work as a switch, regardless of its possible varactor properties. When the diode is not conducting, that 5 pf cap in your SPRAT 134 circuit has one end floating. When the +2 volts comes in from the multivibrator, that little cap is fully across your 22 pf trimmer, and the frequency shifts.

I did some additional Googling this morning and found that Alan, VK2ZAY used this diode as a switch scheme in his early QRSS design. See:
http://www.vk2zay.net/article/180 Alan wrote "A small trimmer in the oscillator circuit is diode switched by the beacon controller to pull the oscillator an adjustable amount." (He later went RED on us with upward pointing varactors!)

I did the test you asked for (shorting out the diode). Before I shorted it out, my freq counter shows the transmitter shifting from 10140020 to around 10140030. Shorting out the diode with a bit of wire puts the freq at 10140010, and it stays there.

The switching scheme has a side benefit: You get a cool-looking LED that turns on and off with your keying.

73 Bill

--- On Mon, 4/26/10, Hans Summers wrote:

From: Hans Summers
Subject: Re: [Knightsqrss] FSK LEDs: Red or Blue, Switches or Varicaps?
To: "Bill Meara"
Cc: knightsqrss@cnts.be, "g3zjo"
Date: Monday, April 26, 2010, 1:18 PM
Hi Bill

Currently it's still offending my sense of correctness, having that
diode upside-down!

And also I'm still not convinced it's behaving as a switch.
Even when reversed (i.e. Forward biased), the diode can still show a
variable capacitance effect, seemingly.

Please can you try shorting the LED and tell me what FSK
that produced? 73 Hans

On 4/26/10, Bill Meara
wrote:
I'm thinking that both configurations might work:
Perhaps with Red LED working in reverse bias mode, the diode serves as a
varicap, with the voltage from the multivibrator varying the capacity
and causing the FSK. I guess we'd call this the "diode as varicap" mode.

In the configuration that I am using, (which I guess we could call the
"diode as a switch" mode) the diode is FORWARD biased
by the voltage from the multivibrator. Then that output terminal goes
positive (mine goes up to about 2.35 Volts), the diode conducts, and the 5 pf
cap is effectively added to the circuitry between the crystal and ground. And
the LED glows (even with current severely constrained by the 1 Meg
resistor between the multivibrator and the diode. When the voltage from
the multivibrator goes below around .6 volts, the diode stops conducting, and
that 5 pf cap is in effect taken out of the circuit.

You can see what I'm talking about in the hand-drawn
schematic here:
http://soldersmoke.blogspot.com/2008/10/i-shift-to-fsk-on-30-meter-qrss.html
This is from the QRSS rig I built back in 2008. You can see in this circuit
I use only 220 ohms between the keyer and the switiching cap.
I plan on putting a 220 ohm resistor in this latest rig (just to make the
blue diode glow brighter!)

One bit of kind of strange electronic serendipity: I turned Hans's diode
upside down, and used it as a switch. But the 5 pf cap that he had in his
original circuit was just right to produce an 8 Hz freq shift.

73 Bill
> >
On 4/25/10, Bill Meara
wrote:

Eddy: But Hans's circuit has it fed through
a 1 Meg resistor. So even if
it glows, that diode is QRP! 73 Bill

--- On Sun, 4/25/10, g3zjo
wrote:

From: g3zjo
Subject: [Knightsqrss] FW: New beacon
To: knightsqrss@cnts.be
Date: Sunday, April 25, 2010, 2:59 AM

Hi Hans, Bill/Group

Its funny how this simple subject can get confusing, brought about
sometimes by people (me) not caring which way up the LED is sketched in
a circuit, because when it comes to building we know what
to do. However sometimes I have seen the LED
deliberate forward biased for a 2
level code and used as a switch to merely
add the extra capacitance in
circuit.


For the QRPp purist though, you could get
around the world on the current that is flowing in the LED :-)

Eddie G3ZJO


-----Original Message-----
From: knightsqrss-bounces@cnts.be

[mailto:knightsqrss-bounces@cnts.be]
On Behalf Of Hans Summers
Sent: 24 April 2010 22:52
To: Bill Meara
Cc: Knightsqrss@cnts.be
Subject: Re: [Knightsqrss] New beacon

Hi Bill
Congrats on getting your multivibrator
working and the success on air!
One thing interested me particularly: not
the use of a blue LED
specifically, but that you mentioned
you'd seen actual light come out
of it? Really? That isn't supposed to
happen! Are you sure you have
the LED connected correctly? It is
supposed to be reverse biased.
Which would mean it shouldn't light up.
See my varicap diodes page
http://www.hanssummers.com/varicap .
On the other hand: there's a good
argument which I refer to daily,
which says: if it ain't broke don't fix
it. Diodes do seem to exhibit
a variable capacitance even when forward
biased, though this probably
has other undesirable side effects such
as lowering the Q.But that
won't matter much in this non-critical
application anyway.

73 de Hans G0UPL


On Thu, Apr 22, 2010 at 7:06 PM, Bill
Meara
wrote:

I just finished my version of Hans
Summers' ultra
simple QRSS beacon (I mean, uh, MEPT). I've been
discussing it on http://soldersmoke.blogspot.com

I got some instant gratification. My QRO
20mw rig was still making it
into Johan's grabber at around 1840
tonight. So I figured the new 10 mW
rig would also be visible. Sure enough --
there it was, rocking along at
10140030. Square wave FSK from an
astable multivibrator.
I confirmed it was me by turning it off at 1850. Right
on cue, it disappeared from the
ON5EX screen. Very cool.
I'll leave it on for awhile tonight,
but the band seems to be shutting
down. Please keep an eye out for it
tomorrow.

73 Bill I0/N2CQR

Running into Alan, VK2ZAY, in Belgium

I first met Alan, VK2ZAY, years ago when his web site alerted Billy and me to the fascinating world of trivial electric motors. Over the years we seem to have bounced around in similar kinds of projects. Yesterday morning, our two QRSS signals sort of crashed into each other in Belgium, on the "grabber" of Johan, ON5EX. Alan was making the LONG trip on about 1.5 watts, with all kinds of cool and sophisticated modulation (including HELL). My sig was, in comparison, a local, and a crude local at that: just 10 mW with nothing but an FSK pattern. For few minutes there we were on exactly the same freq, so I shifted up by about 20 hertz (amazing how quickly we get used to making such TINY frequency changes!). The screen shot above shows the results.

Here is a shot of one version of Alan's constantly evolving QRSS rig.

Conditions aren't quite so good this morning. Alan's signal is visible on the ON5EX grabber, but mine is only very faintly and intermittently in there.

I included the photo from Alan's Twitter page, because I felt a bit guilty about the last picture we ran of him -- he was wearing a hat made of LED's!

HOMEBREW HERO: George Dobbs, G3RJV

This morning the mailing lists alerted me to a video of a recent talk by George Dobbs, G3RJV, of the G-QRP club. As I sat here in Rome and tinkered with my QRPp QRSS beacon, I went to the site, plugged in my earphones and was presented with a really wonderful, inspirational program. George has a truly unique way of combining the technical and the spiritual. (A while back he declared that my London shack had an element of "Wabi-Sabi" too it -- my wife heard this, did some research on Wabi Sabi, and found it very helpful in her garden design work.) In this talk, George reviews QRP construction techniques -- I learned about additional uses for garden slug tape, and heard for the first time of the new "Limmerick" PC board technique. George talks about the history and the evolution of some of the most well known QRP rigs (I builtone of those Sudden receivers!). And he talks about books for the QRPer (like me, he has a special fondness for SSDRA). Most important, I think, are George's comments about the spiritual, philosphical aspects of what we do, about why this hobby makes us happy.

So... run, don't walk to the British Amateur Television Site. Have a cup of coffee (or tea!) at hand. Have some rig to tinker with while you listen. You'll like it. How to get there:

Video of G3RJV QRP Talk

The talk given by Rev. George Dobbs, G3RJV, at the Lough Erne ARC Rally titled 'QRP Why and How' can now be watched on the BATC video site

To watch the video follow these steps:
Go to http://www.batc.tv/
Click on the 'Film Archive' icon at the top-left
Select G3RJV QRP Lecture from the drop-down list
Click on the > icon to start the player and click on the icon to the left of the volume control to display the picture full screen.

There is a link just under the player to save the video to your computer.

Videos such as this are examples of the wide variety of services offered by BATC to the amateur radio community. These include an excellent magazine. New members are very welcome.

Cyber membership, magazine by email, costs as little as £4.00 on-line. Membership gives individuals and clubs access to the BATC streamer allowing live webcasts from your shack or from a radio club display, talk or meeting.

British Amateur Television Club (BATC)
http://www.batc. org.uk/

QRSSuccess!

There it is. That's the rig we've been talking about. The astable multi-vibrator sits in the upper right. The Colpitts oscillator takes up most of the rest of the 9 square inch board. You can see the LED for the FSK circuit in the lower right. (I went with blue -- Jim, Al7RV, sent me that part.) (See that space on the lower left? I'm thinking that I could put in an SBL mixer and one stage of audio amplification to give this thing receive capability.)

After a bit of frustration during the building of the multi-vibrator, the initial on-the-air testing of this rig went amazingly well. I got home from work yesterday and finished wiring up the LED and a 5 pF cap for the FSK circuit. My frequency counter showed a nice 5 hz shift. Perfect. And the LED does flash a bit of blue light!

The sun was going down at this point, and I knew that 30 meters would soon be closed. But a quick check showed that the Belgian Grabber of Johan, ON5EX, was still picking up my QRO (20mW) rig. So I figured that this new rig (with around 10 mW) had a good chance of being received in Belgium. It took me a few minutes to spot it, but then I saw it. It was beautiful. Kind of a square wave with skirts, if you know what I mean. About 4 cycles per minute, and right on the freq shown by my counter. Here is a screen shot of the initial reception:

Nice, don't you think? One transistor, modulated by two others, making the trip over the Alps from Rome to Belgium. Here is a larger view of Johan's grabber screen. Time is marked along the bottom.
This rig will be on the air today. You can see Johan's grabber in the right hand column of this blog. Or here: http://www.on5ex.be/grabber/grabber.html
When the sun is up over Europe you probably should be able to see my signal.

Amazing: On the receive portion of this system we have billions of transistors (certainly millions in Johan's computer, and countless millions more in the internet). But on the transmit side we have only three.

Good Vibrations!

Somehow this goofy circuit diagram (sent to me by Mike, KC7IT) seems appropriate this morning. That is because, gentlemen, this diagram represents the kind of homebrewer I've been this week. After far too much struggle, and with the kind assistance of wizards from around the globe, I succeeded this morning in making an astable multi-vibrator do its thing. Not exactly a momentous achievement, I know. What you may ask, was the problem? Simple: Hans Summer's diagram called for 680K resistors from the power supply to base. But I somehow managed to put in two 68K resistors. This apparently results in an entirely different RC time constant!

Anyway, it is now percolating along nicely. The 2N2222s work fine, as do the two 10 uF electrolytics in parallel. It seems to produce a frequency of around one cycle every 15 seconds. That should be just about right for the QRSS FSK.

Thanks to all for the help and assistance provided. And thanks to xkcd for the cartoon!

Bad Vibes (No Vibes) :-(

Thanks for all the advice. I especially liked the LTSpice model -- it was good to get back to that great program. I plugged in the values that I am using (from Hans' circuit) and the 2N2222 transistors -- Spice says it should work. But no joy in the real world. I tried it with .1 uF caps -- nothing. I tried it with two fairly big 15 uF electolytics (as always, with the positive terminals to the collectors). No luck. Both collectors are just sitting there at .015 volts, both of the bases are at .6 volts. Sounds like both transistors are constantly at saturation, right?
Any other ideas? (I know I could do this with an IC, but I want to try to make it work with the simple two transistor circuit.)

Astable Multi-NON-Vibrator (Help!)

Having made good progress on my Ugly, Discrete Component, DC recever for 30 meters, this week I turned my attention to the little QRSS transmitter that I mentioned last week. The idea is to run this thing out at the country house. The inspiration here comes from Hans Summer's ultra-simple QRSS transmitter:

I ran into trouble this morning. The oscillator is running fine. But the little two transistor astable multivibator that is there to put some FSK on the signal is not vibrating. What am I doing wrong here? Instead of the BC-107s or 108s used by Hans, I'm using 2N2222s. Hans used 22uF caps. I didn't have any, so I just put two 10uF electrolytic caps in parallel. But nothing happens. It just sits there. Any ideas? Hans was running his rig off bleach batteries and was struggling to keep current low -- I don't have this constraint, so maybe by using lower value resistors to the collectors and bases?

Help me! Help me!

(I apologize in advance if this posting results in ads for other kinds of vibrators!)

Space Shuttle Over U.S. on Approach to Landing

This is an early Monday morning event. Lots of SolderSmoke fans within visual range of this flight path. (Somebody please alert Jerry, NR5A!) Spaceweather.com reports:

"Landing is scheduled for 8:48 am EDT, and it takes the shuttle about 35 minutes to traverse the path shown above. Observers in the northwestern USA will see the shuttle shortly after 5 am PDT blazing like a meteoritic fireball through the dawn sky. As Discovery makes its way east, it will enter daylight and fade into the bright blue background. If you can't see the shuttle, however, you might be able to hear it. The shuttle produces a sonic double-boom that reaches the ground about a minute and a half after passing overhead."

Please let us know if you see or hear it.