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Tuesday, April 27, 2010

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
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:
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

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

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

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

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

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

73 Bill I0/N2CQR

Sunday, April 25, 2010

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!

Saturday, April 24, 2010


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/

Thursday, April 22, 2010


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!

Wednesday, April 21, 2010

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.)

Tuesday, April 20, 2010

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!)

Sunday, April 18, 2010

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.

Saturday, April 17, 2010

Colin's Power Meter

Hi Bill,

Thought you would be interested in the attached pics, one shows a power meter that a colleague made for me. I had mentioned to my colleague about the W7ZOI power meter after listening to SolderSmoke at work. A couple of days later I was presented with a power meter constructed from scrap parts! We work for a company that repairs cell 'phone base station equipment and the power meter was made from some scrap VSWR monitor circuits. My favourite part of the device is the heatsink fins on the 30dB attenuator along the top, which can be taken out of circuit by removing the SMA link. To use the meter, the 8V regulator is powered up and if any RF is present at the RF in, a voltage, which can be read by an external Volt meter, is output via the multiway connector. I use a ribbon cable, which has three connections used, DC (+&-) and meter test point. A graph plotting RF in against Volts out can then be used to determine measured RF.

The second pic shows a QSL card for a 17m CW contact I received for my contact with Ronny SM4RRF. I was using a low dipole and 500mW from an FT817! This was my 2nd ever CW contact.

73 and keep up the good work at SolderSmoke.

Colin M0CGH

Friday, April 16, 2010

Moonbounce Day!

Rafael in Mexico sent me some very interesting info about World Moonbounce Day. Today!

From: "MM"
Sent: Wednesday, April 07, 2010 3:06 PM
Subject: [amsat-bb] Arecibo on 432 MHz Moon Bounce

> Hi all:
> Here is a EME event you cant miss.
> Dust off your CW key, its time for Satellite, QRP EME.
> The 1,000 foot dish has 60 dBi on 432 mc and 400 watts.
> That comes out to be approximately 243,902,443 Million Watts ERP.
> enjoy
> wf1f
> www.marexgm.org
> (thanks to KB1MGI for passing on this data)
> Arecibo on 432 MHz Moon Bounce
> The Arecibo Observatory Amateur Radio Club will be putting the
> 1000-foot radio telescope on the air for 432 MHz EME from April 16-18.
> It can be heard with a small hand-held yagi pointed at the moon
> The scheduled times of operation are:
> April 16: 1645 - 1930 UTC
> April 17: 1740 - 2020 UTC
> April 18: 1840 - 2125 UTC
> Callsign: KP4AO
> Tx Frequency: 432.045 MHz
> Rx Frequency: 432.050 to 432.060+
> Tx power: 400 W
> Antenna gain: 60 dBi
> System noise temp: 120 K (cold sky)
> System noise temp: 330 K (when pointed at moon)
> KP4AO can be heard with a small hand-held yagi pointed at the moon and a
> good receiver. A 15 dBi antenna and 100 W will be enough to work us on
> CW.
> Operators at KP4AO will do their best to work as many stations as
> possible. Each session will start with a brief announcement and CQ in
> SSB. SSB QSOs may continue for 30 minutes to an hour, if the QSO rate
> remains high.
> The mode will be shifted to CW as soon as it is judged that higher QSO
> rates would result.
> We will listen for calls at frequencies 5-15 kHz higher than our own,
> and even higher if QRM warrants. Callers who s-p-r-e-a-d o-u-t are more
> likely to be copied.
> If you've already worked us in any mode, please do not call again --
> give others a chance.
> If we call "CQ QRP", we will listen for stations running 100 W or less
> to a single yagi. Please do not answer such a CQ if you are running more
> power or have a larger antenna.
> On April 18, if we reach a condition where most calling stations have
> been worked, and we judge that operating in the digital mode JT65B would
> produce a higher QSO rate, we will switch to JT65B.
> Note that any of these planned operating strategies may be changed as
> circumstances dictate.
> We are extremely fortunate to have been granted access to the world's
> largest radio telescope for this amateur radio good-will event. We look
> forward to working as many stations as possible in the alloted time!
> >From QRZ.COM

Thursday, April 15, 2010

Homebrew Hero: Ed Roberts (RIP)

The Maker blog has a really great 20 minute podcast interview with Forrest Mims. He talks about his recently deceased friend Ed Roberts, founder of MITS and creator of the Altair 8800. The interview is really great. You guys will like it. Look for the little audio bar just underneath the article on this page:

Tuesday, April 13, 2010

Receiver Success! Combining Computers and Homebrew Radio

Well, it turns out that yesterday was a GREAT day for a new receiver. When I got home from work 30 meters was open. I fired up the new receiver and the FLDIGI program. Immediately I started to see and decode PSK-31 signals. I quickly switched over to the WSPR program and right away I could see the little two minute WSPR sigs. Here is what my screen looked like:

The program also began to automatically upload reports to WSPR HQ. Here is the report I found on the WSPR web site this morning:

I know all this WSPR and digi stuff often seems to be very computer-centric, and very "appliance radio," but I think this little project shows how we can have the best of both worlds: This rig combines a laptop computer and some pretty sophisticated software with a VERY simple, discrete component, homebrew direct-conversion receiver.

OK. So you see that I left a lot of space on the PC board. That's where the DSB transmitter (for WSPR and possibly PSK-31) will go.

BTW: You can keep an eye on my reception reports by going to the Database section of the WSPRnet site and plugging my call (I0/N2CQR) into the "reporting station" block. I'll leave the receiver on today.

A Bad Day for a New Receiver

Here is the latest picture of my version of the W3PM WSPR receiver. You can see the Ugly Weekender AF amp in the upper left. No front end of any kind yet -- the sig goes right from the antenna jack into the RF pin on the SBL-3 diode ring mixer.
Turns out that this morning was a bad time to test a new receiver. Spaceweather.com reports that a big coronal mass ejection hit earth today, causing havoc in the ionosphere. I'll try it again later today.

Monday, April 12, 2010

G0UPL's Ingenious QRSS Circuit

Just look at that circuit! That's a complete QRSS beacon transmitter, including a multivibrator (the two transistors on the left) to generate a recognizable pattern on the grabber screens. This diagram appears in SPRAT 134. Hans Summers ran this rig with just a couple of volts from his homebrew bleach-based battery system back in 2008. I plan on putting a version of this rig into the solar powered lawn lamp I showed you two posts ago (scroll down).

In other news, I finished building the Ugly Weekender AF amp this morning, and it passed the smoke test. My WSPR system went toes up this morning, so today I am QRSSing on 30 meters. I'm running my usual upside down FSK. Please let me know if you see me.

Friday, April 9, 2010

Colpitts Mania! Two Rigs Under Construction

I'm really into Colpitts oscillators lately. I blame Gene, W3PM. He reminded me of the fact that these little one transistor stages can pump out the 7 dbm needed to drive a diode ring mixer. Gene sent me a note warning that I'd have to take special precautions to ensure stability, but I found that this circuit never strayed more than 20 hertz in the course of a full day of oscillating.

Above you can see my version of the Colpitts circuit that Gene has in his very nice WSPR transceiver. You can see the SBL-3 diode ring mixer above the oscillator in this picture. I still haven't decided on the audio amplifiers.

I'm working on a second Colpitts circuit. This one is for a QRSS transmitter, also for 30 meters. Here I took my inspiration from Michael, AA1TJ, who has been working DX with power levels similar to that of this little oscillator. Long-time blog fans might recognize this board, or at least the device that it was used in. This is the board from my "DaVinci Code" 30 meter frequency standard, so called because I used a paperback copy of the Dan Brown novel as insulation for this weird piece of test gear. With my Kempton Park Frequency counter working, I had no need for the DaVinci device. But the oscillator was a Colpitts, capable of pumping out 10 mW all by itself... I plan on building a Hans Summers-style multivibrator circuit to put a distinctive pattern on my QRSS sig. It should fit nicely on the same board. I have a case and a power source in mind: see below. See if you can figure out where I'm going with this.

Thursday, April 8, 2010

Workbench/P! Taking Solder on the Road!

Sure, lots of guys carry rigs with them to the field, on vacations, etc. But how about taking your WORKBENCH with you on trips? Perhaps only truly hardcore homebrewers reach this extreme.

It may be that with summer approaching, guys are getting nervous about being away from their beloved workbenches... This week I got three e-mails related to portable workbench operations:

Jim, AL7RV, sent in a nice shot (above) of his most recent workbench location. Jim says while he does not have racks and racks of sophisticated test gear, he does have lots of fresh air (and a nice view) while working on his projects.

Nicholas, M1HOG, sent me a web page describing the portable bench he put together for use at his country cottage. While out there, he said he had "started to miss the delights of melting solder." We hear you Nicholas! Nice solution:

Finally, Rogier, PA1ZZ & KJ6ETL, reports on some very nice cabinets that seem ideally suited to this kind of work: http://www.gerstnerusa.com/

This is all great, but I think we have to draw the line somewhere. How about this: No soldering while driving!
No soldering while in flight on an airliner!

Soldering Irons to the Field! EXCELSIOR!

Wednesday, April 7, 2010

Success! Uganda WSPR Station On The Air!

Isn't it beautiful? Like an RF palm tree rising out of Uganda. That's a map display of the stations that have received the WSPR signals of 5X7JD in the last 24 hours. Not bad considering that Jack's rig is running one watt and that we are in the midst of a pretty massive geomagnetic storm.
This is a beautiful story for several reasons: Technically, the rig is very elegant. But even more appealing is the human aspect of this operation: This is a real "International Brotherhood of Electronic Wizards" story. First, Jack Dunigan goes to Kampala to help kids who are struggling with AIDS. Then Gernot, OE1FM, jumps in and designs and builds an ingenious rig that will allow Jack to run a WSPR beacon from Uganda. For more details, check out Jack's web site: http://hamradiosafari.com/ I got a kick out of his mention of a certain station in Rome that is running a 200 mW WSPR beacon. (And I'm looking forward to Jack's article on Kampala's "Radio Row" -- I suspect it will be a lot like Santo Domingo's.) Three cheers for Jack! Three cheers for Gernot! Three cheers for Joe Taylor! Three cheers for the International Brotherhood of Electronic Wizards!

Tuesday, April 6, 2010

SolderSmoke Book Helps With License Upgrade SAVE 10%!

Thanks to all those who are helping to get the word out about "SolderSmoke -- The Book." I put together a web page about the book:
http://soldersmoke.com/book.htm Lulu is running a sale: 10% off during April. Coupon Code: SHOWERS

I got a very gratifying e-mail from OM Walter. I was very pleased to hear that the technical portions of the book helped him in his license upgrade efforts:

Just thought I would drop you a note to let you how much your podcasts and book have influenced my life (for better or worse). I have been listening to you podcast since last summer and have all of them on CD and have listened to them all. Living in Florida for the past 10 years I have not been active because I thought I could not get a proper station and antenna setup here (HOA restrictions). Boy was I wrong. Late last year I bit the bullet and bought a Icom 703+ QRP rig and hooked it to my computer for digital modes. Antenna of choice? A PAC12 vertical antenna kit. The antenna is indoors sitting on a small photo tripod.
With this setup using PSK and RTTY I have over 1/2 of the US confirmed and 8 countries including England and Germany. I am having a ball. My wife calls it "Playing with Radio's". At least she knows where I am...
Next steps is to get my code speed up and I have a couple of kits on order (QRP of course).
Your book was instrumental in me ugrading from General (N2LTB) to Extra (AJ4UM) in Dec 2009. Read your book and used the ARRL study guide. Your explanations hit home and I believe made studing for the test easier. Also very entertaining.
Thanks again for all you do for the Ham community and keep it up.

Geo-Magnetic Storm! Aurora as seen from orbit

Batten down the hatches my friends. The solar wind is blowing, and we're in a geo-magnetic storm. Well, we were anyway, yesterday. Astronaut Soichi took this amazing picture of the resulting aurora.
No WSPR spots of my little signal this morning -- I blame it on the storm.
You can see some interesting discussion of the storm conditions on the WSPR live-chat system. Here is a sample of last night's commentary:

Monday, April 5, 2010

How much AF amplification needed between diode ring and a sound card?

Progress continues on my WSPR direct conversion receiver. The Colpitts oscillator is working nicely and is very stable. Yesterday I glued an SBL-3 diode ring to the board and hooked it up. With my 'scope and sig generator I can see it turning 30 meter RF into audio. So far so good.

Now it is time to build the AF amp. Here's my question: How many db do I need? The standard 100 db DC RX AF Amp seems like a bit of overkill -- this thing won't drive a speaker or a headphone, but instead, a computer soundcard. What do you guys think? How many db?
Designer: Douglas Bowman | Dimodifikasi oleh Abdul Munir Original Posting Rounders 3 Column