Category: Summers-Hans

Hey, check out the Altoids heat sink for the PA in my little 30 meter MEPT rig. Is this a new use for our beloved Altoids tins? I like the smoke-stack look.

This rig has evolved quite a bit. It started out as a frequency standard for QRSS and was mounted inside a paperback copy of Dan Brown’s book. Then I matched the oscillator up with the multi-vibrator pattern generator from one of Hans Summers’ rigs. This week I decided that I really needed a buffer and a PA — I needed a bit more stability. I’ll try to post a schematic tomorrow. In the meantime, watch for my little signal on the ON5EX grabber (off to the right). The pattern is small (3 Hz) bumps, about 4-5 per minute.

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>>>>>>>>>>>>>>>>>>>

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

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!

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!)