Pixie2 - Gesammeltes aus dem Internet von DF2OK, 9/98

One Ham Asked:

> 
> Well, I would love to add some of the things you mentioned but don't
> have a schemo or any other info than your printed post from QRP-L.  If
> you get a chance, could you explain the 60pF cap in the RIT switch area
> and also the blocking out of the AM junk.  I was about to build the W1FB
> version with the audio filter and the auto-switching offset, but maybe I
> should continue to experiment with my old faithful some more.  You've
> introduced some fresh ideas for me to try.
I have the UPDATED/CORRECTED W1FB schematic on my web page.  (See sig.
below)
OK.  You've got a XTAL.  For a NO-RIT rig, just ground one end of the
crystal, the other end to transistor Base input as shown on the
original Pixie2 schematic.  (also on my web page.)

Instead of directly grounding the crystal, you can ground it THROUGH
a .001 capacitor.  .001 uF is a low impedance at the RF frequency, and
you still get a single freq., no-Rit pixie2.

RIT:  Permanently ground the crystal through a smaller capacitor,
say 50 to 60 pF.  This raises the xtal frequency about 600 hertz.
So a 7040 xtal == 7040.6 KHz.  Connect a SPST switch such that allows
you to parallel a .001 uF cap across the 60 pF, thereby totally
providing an excellent ground to the xtal.  The crystal now operates
at it's proper (Lowest) possible frequency.  There you have it.

A smaller, say 30 pF cap will provide 1Khz offset or so.  Just remember,
the well grounded crystal operates on the lowest frequency it was
designed for.

AM BC BAND:  Get Ferrite Chokes.  They are the size of 1/4 watt
Resistors.
Do NOT use wirewound molded inductors, they are miniature antennas!
The ferrite chokes I use are 5 millihenrys and have a green paint drop
supposedly revealing their value in millihenrys. Green=5.

Looking at the schematic you see the KEYING LINE and Ground; SPEAKER
LINE and Ground, POWER Positive Line and GROUND, a 1 Kohm resistor
feeding reduced current/voltage to the LM386.  Also, the Detected
Audio from Q2 line goes to the audio input pin 2 or 3 of LM386.

OK.  Place a RF CHOKE: Audio Output; Key Jack; Detected audio to
LM386 Pin 2; Power Supply Positive line.  Next; add small Ferrite
bead to Positive Voltage line going to each Transistor.  

The Following is probably Optional:
This next part is Tricky!  I wanted a stable 5.62 volts to the LM386
and decouple it from the power supply (Car Battery).  On the Pin 6 side
of the 1 Kohm resistor (R5), put a 5.62 Volt Zener Diode.  Change R5 to
500 ohms, or parallel another 1 Kohm as I did.  Put in 250 uf to 470 uF
electrolytic capacitor from pin 6 to ground of the LM386.  YOU WILL
GET IMMEDIATE IMPROVEMENT IN AUDIO AND BC INTERFERENCE REDUCTION!!!

Add 100 ohm resistor from D1 switching diode Cathode to Keying line.
This suppresses the now SURGING current from 470 uF powersupply capacitor.
Without the 100 ohm resistor, the keying device has to pass too much
current to be reliable.  My keying relay contacts stuck sometimes...
Also, some current flow is possible thru D1 and the 10KOhm emitter resistor
and the Q2 amp gets stuck in Self-Transmit mode!

OK!  Mine works FB and althoug I still get a small amount of BC
interference from the AM station about 2 miles away, I find it
disappears when I touch the enclosure.  So it is just stray capacitance
and when I put the lid on my PC BOard constructed/soldered enclosure,
I expect all BC qrm to be gone. 


> 
> My Pixie is a 40/80 dual band switchable and I beefed up the 2
> transisters to a 2222 and a 2219 can type for the amp.  I get about 1
> watt out on a 12vdc battery.  I'm very happy with the output and I do
> make some contacts but copy is very rough.  I've checked into the Klites
> net on Sunday eves but that's a tough one and usually rely on my Icom
> for that.

I tried the 2219 and it is FB.  Currently using a 2n5109.  But the
2n2222A works well too.  But I put in a bigger socket that fits
the 2n2219 and 2n5109 so I'll keep those.

> 
> Thanks for the post,

Thanks for your input.

I hope I have helped!
Vy 73/72 -- Ed Loranger, we6w

What?  You didn't see the updated W1FB version on my webpage?
Hi, Hi.

FB on the pixie2 project Bill.  But what ever happened with that
little firecracker rig you were running at the end of November/Beg
December?  Really sounded nice, even though Stan liked the Chirp
at 1/2 watt.  I'm like you, don't need that.

I found most chirp due to inadequate power supply current.

I am pasting some text regarding the pixie2 that I've written today.

I don't recommend the W1FB rit mod.  Manual rit gives you 2 freqs to
work from.  Then toggle to the other side to receive.
At least put in the RF Chokes and the 5.62 Volt zener to pin 6 of
the LM386 if you use that audio circuit, cuz if you go to 12 volts
from a car battery, the LM386 no-workey!  (Or you could increase
the 1 KOhm resistor to compensate....)

------------------------ Begin Paste of Prior Responses ---------------
To another Ham I wrote:


For rit I prefer the manual switch!  I have the xtal
permanently grounded with the 60 pF cap.  Then switch
in a .001 uF in parallel which puts the rig exactly at
the xtal freq.

I don't like the automatic xmt offset of w1fb for fixed 
freq. rigs.  Great if you have vfo's, but for a xtal
rig, you'll get TWO sending freqs if you switch manually
for RIT.

Too bad my neighbor ham lives so close, (300 feet by antenna).
The approx, 1 milliwatt Local Oscillator feedthru of the
pixie during receive bothers him.
-Ed
--------------------------------------------
To another Ham, I wrote:

OK.  I would love to share what I have learned, and fixed!

First a summary:  I used pin 3 for audio input to the LM386.
It seemed more stable than pin2.  I orginally used pin2.
If you touch pin 2 (or 3) you provide HUGE BC signal and it
gets detected.

If you Touch the PA transistor CASE, Same affect and it feeds 
directly into the LM386.

If you Touch you straight key hot-lead -- SAME Affect.
If you use a speaker near another rig powered by AC line -- HUM and BC.

SO. I proceeded to clean it up. 

I used these broadband ferrites having 5 separate holes drilled
in the body.  These are commonly available RF chokes.  Look like
3/8 inch section of a pencil.  It comes pre-wound with solid
wire strung in/out of the holes and finishes as an axially mountable
part.   I have lots of these.  But I figure any RF choke in the
millihenry range will work, but have more ohmic loss.

Even better and cheaper ferrites are probably available cheaply.
I also used ferrite beads where the power is applied to the oscillator,
and also where the bypass capacitor is attached to the collector
load inductor of the power amp.


I found that the LM386 preferes NOT to run at 10 Volts.  I put in
a 5.62 Volt on the Pin 6 of LM386 just after the 1 Kohm resistor
comes from the main battery supply.  No more problem there.  Now if
I load it with a speaker, the LM386 doesn't squeal.

Also, I added a 100 ohm resistor 1/16 watt thing, to the pin 1/8
feedback
loop of the 386 to tame the gain a bit.

Another Ham wrote:
> 
> Ed,
> 
> You are addressing a basic fault of the Pixie design.  My project
> is a Pixie derivative and also suffers from BCI at night.  I fought it the
> whole contest, and probably made less than half the contacts I could have
> if I could have heard past the BCI which was overloading the LM386.  As it
> was I made my contacts when QSB dropped the BCI to a mere S9 +20db :-)
> ----------
> > I also added RF chokes to all extenal wiring locations and RF
> > beads on the supply wires to the OScillator, and the PA/Mixer/Detector
> > blocks.
> 
> I think your mods will be among the first to be applied to Our Project.  Can
> you be more specific?  Size of choke, etc. 

I'm not certain. 5.5 millihenry?  These were in my junk box.  Size of
1/2 watt resistor.
 Also, can you define which of
> your mods had the greatest effect? 

NOTE: BC station is about 4 miles away, and very easy to 
detect.  You can turn off the pixie2, touch the LM386 at
audio input and hear on your headphones!

In order of importance.
1)  Definately the RF choke going to the audio input of LM386.
2)  RF Choke on headphone/spkr jack center lead.
3)  RF Choke to keyed line.
4)  RF Beads on each line to oscillator/PA resistors.
5)  Shielding between stages.

> I'd been thinking about putting a
> 3.5MHz series resonant circuit on mine to see if I could cut down on the
> BCI, but you seem to have minimized the problem another way. 

I built a HI-Pass, 3 MHz filter the second day of the Pixie/49r contest
and improvement was good.  But have since put that circuit on the
shelf.  The ferrites have CURED the problem!  Check out my log
on the last day of the contest!

If you send me Your Project, I can build, troubleshoot and optimize
it.  I can send it back for you when I'm done, if you wish.

-Ed

Have fun Buddy!  Hope to see the transceiver you were using
earlier in December.
-Ed
------------------------------------------------------------------------
> Ed, I want to get the Pixie II going here soon as you have but have a
> couple of questions:
> 
> 1. where did you get the Pixie II unit?  Homebrew?

I bought my first one.  I homebrewed a second for a friend.
And have now homebrewed a third one, that is the best!!!

Only buy the kit if you don't have much of a junk box.

> 2. what were your mods.
> 

Mods....  Well, I prefer manual rit.  So get a switch and
permanently ground the xtal thru a 60 pF cap.  Switch in
the .001 cap for RIT.  The beauty of manual rit is you can use
either switch position to transmit and receive at the other spot!
Basically extends you frequency coverage.  It is nice to note
the xtal is on its base frequency when grounded thru the .001 cap,
for FREQ spotting purposes.

I added 5 milliHenry Ferrite chokes to any jacks (Except the antenna :)
Do NOT use regular wirewound inductors, they pick up the Broadcast band
QRM by induction.

ADD a 250-470 uF bypass electrolytic for pin 6 of the LM386.  Otherwise
you'll get audio problems.  OH, make sure the LM386 is getting
sufficient
current, a current starved LM386 will otherwise be a great detector
for your local AM Radio station -- :)

I built mine using PC Board stock and built the circuit compactly using
"ugly construction" or "Dead Bug" construction techniques.  Also
shielded
the oscillator and RF amp sections.

I later decided to run at 12.7 or so volts from a car battery and
the LM386 had trouble.  I've sinced changed R5 to 500 ohms, put in a
5.62 Volt zener at pin 6 of the LM386.  MUCH BETTER!

ONE PROBLEM with HAVING a 470 uF cap on pin 6 -- The audio muting diode
passes the current thru your keying circuit to ground.  So I added a 
100 ohm resistor in series with the muting diode and that keeps my
keying relay from arcing.   I'm planning to drive a sidetone with the
voltage developed across the 100 ohm resistor during key down.  We'll
see...

Use a .1 uF capacitor at LM386 pin 6 too.  I also added the little
preamp on page 30 in the new QRPp.  But you need to put a 1 Kohm
resistor in the emitter leg.  I put a 100 ohm resistor in series with
the 10 uF cap between pis 1/8 of the LM386 to tame any overdrive
problems
too.

I removed the 33 kOhm bleeder bias resistor in the power amp.

Ferrite beads and .1 bypass caps in the supply lines to both
transistors.

Remember:  The current starved LM386 causes many BC interference
problems.
Be sure to put that 250 uF or so electrolytic at PIN 6.  And if this
doesnt help your audio, lower R5 a bit.  Heck, just experiment!

> Many thanks, I can't wait to get mine!
It's fun.

Hope this is useful. 
72/Ed Loranger, we6w 

More info...


Ok, the stock pixie2 uses about 20 to 25 milliamps and is capable
of running off of a 9 Volt transistor battery.  I'm not sure, but
another problem develops with the 741 in this circuit due to the
additional current demands.  Try the thing on a pair of 9 Volt batteries
in parallel to check that.

Explanation of what I did and why I changed the 1 Kohm.

This is a bit complicated, but when I hooked the stock pixie to the
9 volt battery I noticed a few things.

  1)  The LM386 Motorboated as the battery voltage got to about
      7 volts.  The spec sheet on the LM386-N1 recommends it run
      between 5 and 12 volts.  

      1A)  7 volts should have been fine, I deduced the LM386 was
           being starved for current.

  2)  The LM386 is a good detector for AM BC band.  I decided to 
      further decouple the LM386 from the power supply by putting
      a 5.62 volt zener to ground on the LM386 side of the 1 Kohm.
     
      2A)  I lowered the 1 KOhm to 500 ohms by parallelling another
           1K.  This allowed me to stabalize the LM386, decouple the
           Battery and Leads from RF, and supply more current as 
           needed.

  3)  The LM386 had problem with strong signals and I observed problems
      with audio on CW peaks.
      
      3A)  I added a 470 uF electrolytic to pin 6 of the LM386 to serve
           as a current reserve for those peaks.  This also improved
           audio response SIGNIFICANTLY, and eliminated more BC
           interference.

  4)  The mods ran too much current through the diode on key down.  Also
      the idle current through the 10 Kohm resistor - Diode - to power
      supply was too much and this turned on the power transistor as
      if you were keying.  (BAD PROBLEM!)

      4A)  I put a 100 Ohm resistor on the Kathode (Key) side of
           the diode.  This reduced the current through the key
           contacts during key down, also kept the output transistor
           from turning on.

  There you go Friend.  I hope this helps.  It was a lot of work,
  but very worth it!  I have a very quiet pixie2 and works FB.  The
  audio is strong enough to drive a speaker and the key clicks are
  virtually non-existant.  The 470 uF bypass cap on the LM386 was
  totally amazing.  Really helped the circuit in three ways: Audio
  quality, LM386 stability, Reduced BC interference to to RF detection
  of the current starved LM386.

Let me know how it works as you go.

Best of luck.
-Ed
-- 
Recipient of coveted Samuel F. B. Morse Award, NTTC Pensacola, FL 1977.
72/73 de we6w qrp es CW ONLY; Member: QRP-L/ARCI/Norcal/ARS/AR
http://www.qsl.net/we6w (From Non-Ham to Extra in one Day.)

*****************************************************************************

I've got great news regarding my Pixie2!  I have now
reached 330 mW at 7.04 MHz and a little more than 
400 mW at 3.579 MHz!

First I'd like to say that this is an excellent
transceiver project.  Very simple and a tremendous
learning experience for those who will go all the way
and insist on extracting the last bit of performance 
out of the rig.

What I did:  Swapped out the Q2 Final 2n3904 transistor
with a 2n2222A.  It immediately went from 2.X volts on the 
detector to 5 Volts.  I was so excited I immediately called
back a CQ-er and got a QRZ? de ....  I called 2 more times
and got a WE6? de ....  Never QSO'd with the Pixie2 but did
get a SRI QRN too Weak etc...

Hooked up the HW-8 and after biding my time while he qso'd
a third party, finally connected and had an excellent
rag chew.  He was in Tacoma Washington.  My QTH Santa Rosa,
CA.  I think that's about 900 miles north of me.  Don't
remember the Call so no QRZ database check on the miles yet.

I also added a .01 uF cap from the + supply line to ensure
adequate RF bypass.  Currently the XTAL provides this function
but I decided to go the extra mile.

Also changed the PI output netowork to 390pf-1uH-560 uF
per w1fb mods.  (Didn't change the 1uH to 1.5uH yet.)
This added another 15 mW or so to my 100 mW of yesterday.
The transistor change was afterward.

Still Way too much BC coming in so will attempt to solve
this problem someday.  The BC station is about 4 miles away
and you can pick them up with rig off (Almost).

On Diode Detector Power Measurement conversions:
Unless you've got an exceptionally accurate power meter
to calibrate you xtal detector, I've determined that
significant non-linearity exists as to make the detector
useless.

I have computed a 'K' factor for my detector where
Voltage * 'K'=Vrms
Power=(Vrms)^2/50

The 'k' factor ranges from 2.147 at 100 uW to .812 at 330 mW.
A .85 'k' factor gives less than 10 % error at power levels
between 10 mW and 300 mW.

To compute your detector 'K' factor:
K=sqrt(Pwr*50 Ohms)/Volts ; where Pwr is Lab-Quality measured.

NOTE:No need to do a Peak*.707 for rms, 'K' factor only needed.


I'm putting this note on my pixie2 web page section for
reference.

Happy QRPp operation to all!

-Ed Loranger, mailto:we6w@qsl.net
(Unlimited Distribution of unedited document allowed)

*******************************************************************************

Much thanks to Doug Hendricks, KI6DS, and QRPp for allowing this posting.
Originally Published:QRPp June 1995 pp. 45-48
  
           The Great Dayton Building Contest 1995
                 Sponsored by NorCal QRP Club


This building contest is an endeavor to have fun, promote fellowship, and
provide a learning atmosphere.  Chuck Adams, K5FO, came up with the idea
and gave me (Doug Hendricks, KI6DS) the job of finding a suitable project.
The project had to be one that could easily be completed in less than an
hour, have readily available parts, and preferably a circuit board.  The
project that I came up with is the Pixie 2, which is a transceiver that can
be put on 40 or 80 meters, determined by the crystal frequency chosen and
changing one coil.  Here are the rules of the contest.

  1.  Obtain the information sheet and circuit board from Doug Hendricks
      Thursday or Friday night at the hospitality suite of ARCI for $3.
  2.  Buy the necessary parts at the swap meet.
  3.  Bring the parts to the Hospitality Suite after the QRP ARCI Banquet
      on Saturday night.  Show the parts and the board to one of the
      judges, (Doug Hendricks, Jim Cates, or Chuck Adams).
  4.  We will all start building at the same time.  The objective is to build
      a finished transceiver with all parts in the schematic and all connectors
      attached.  (Clip leads are not legal).  The transceiver must be finished
      to qualify for prizes.
  5.  The prizes are:
      A.  First working rig finished.  Prize: 1 Year extension to QRPp 
          subscription from NorCal.
      B.  First QSO, must get signal report and calls exchanged both ways.
          Prize: 1 Year extension to QRPp subscription from NorCal.
      C.  Greatest DX worked by 12:00 midnight, local Ohio time.
          Prize: 1 Year extension to QRPp subscription from NorCal.
      D.  Best looking construction.  Prize: 1 Year extension to QRPp.
  6.  Modifications are legal.  You don't have to use the exact parts.
      The objective is to build a working transceiver.
  7.  Builders are responsible for supplying their own tools.
  8.  The judges decision pertaining to all matters in this contest are final.

     
The Pixie 2: An Update  by Dave Joseph, WA6BOY, 1873 Harris Ave, San Jose, CA

Builders NOTE: The trace between the pins on C11 must be cut! Murphy lives.
(K5FO Note.  This applies only to boards at Dayton.)

The Pixie 2 first appeared in the third issue of the NorCal QRPp Journal.
Doug, KI6DS, recently asked me if I would write another article updating
it, since the membership has grown so much and many of the new members have
not seen the article.

The circuit first appeared in an issue of the G-QRP Club's "SPRAT" and the
first issue of QRPp.  It was designed by RV3GM.  I've modified the circuit's
output and audio amplifier.

Although most of the QRP circuits today have evolved into using superhet
receivers, a diversion back to direct conversion is not unusual...since
QRP, after all, is a unique part of amateur radio and simplicity is certainly
a part of it.

The Pixie 2 is a tiny rig, with a standard two transistor transmitter.  It's
a Colpitts oscillator, left running, and a keyed power amplifier.  There is no 
external mixer used to feed the audio amplifier.  Instead, the mixing is done 
at the final amplifier itself with the resulting audio taken off the emitter.

As you look at the audio amplifier you will certainly notice D1.  It is an
unorthodox approach, but it works.  The diode can be left out but it helped 
to keep down the "crashes" during keying by shutting down the 386 chip.  I'm
no wizard at this... I just tried it and it seemed to work.  I'm sure there's
lots of you that have much better ways.

There's no RIT, a simple switch and cap in parallel, between the crystal will
work as an offset though.  You'll lose QSK but, here again lies the call
for enhancement.  The whole idea here was to make a tiny rig that worked,
with LOTS of room for improvements, using a minimum of parts.

Contacts spanning hundreds of miles are routine with this rig on 80 meters.
Band changing is simply a matter of pi-network and crystal changing.  If
you build one, I'm sure you'll have fun with it.  Construction can be by
any method, perfboard, "ugly" and pc board.  Complete parts kits are
available for those of you who are interested.

           CONSTRUCTION:

You will need a low wattage soldering iron with a small tip, some rosin
core solder, solder wick (for removing parts when you make mistakes), small
wire cutters, needle nose pliars plus any additional tools you may wish to use.

PLEASE PROTECT YOUR EYES WHILE CUTTING LEADS AND SOLDERING COMPONENTS!
WARN OTHERS CLOSE BY.

Since all the components, except for U1 the LM386, are mounted vertically,
it's best to start at one end of the board and work to the other.  No 
particular starting point is necessary.  Take your time, enjoy the assembly.
Your transceiver will be finished sooner than you think.  There are no coils to
wind, no alignment either.  This is definitely a FUN project.

Note:  There is one component that will be mounted on the underside of the
board if you build it with the PC board.  This is the 1K resistor in the kit.
Refer to the drawing on the parts layout for it's location.

Before you get started, note the following parts MUST be installed only
one say:  the 10uF electrolytic caps, D1 diode, the two transistors, and
finally the audio amp chip, U1, a LM386.  Make sure you mount these
components exacly as the parts layout shows you to.  If you mount any of these
the wrong way, your transceiver will not work and you may destroy the part.
The only exception is C11, but it is best to install it as shown.

Mount all the parts, again, starting from one end of the board.  Carefully
check to see you have the correct part before installing it in it's
location.  Refer to the parts layout drawing.  Double check before inserting
the part.  This will avoid problems in getting your rig on the air.  Install
the 1K resistor last.  This resistor is R5, and it is tack soldered between
the 9 Volt pad and the POSITIVE terminal of C10.  Dress the leads of this
resistor so that they don't touch the board.  You might want to put some
sleeving over the leads, or, some electrical tape underneath to be sure
they don't short to the board.  R5 is shown in dotted lines on the layout.

This transceiver does not have RIT (receiver offset).  It is possible to
work other stations, if you are close to their frequency.  Even if the
received signal is off frequency, give them a call.  A simple RIT circuit
using a mini-toggle switch and capacitor, hooked up in parallel, and
placed in the line between the crystal and ground works well.  You won't
have full break-in, but it works.

Remember, all that's needed to change bands on this rig is change L3 and
the crystal, and you have a rig for another band!!  You can use "walkman"
style headphone, with a mono adapter.  There is even enough audio power to
drive a speaker.  It's not very loud but you can hear easily in a quiet
room... neat!!

This rig has been packaged in a 35mm film can, a Tic-Tac box, Sucrets
box (easy), just to name a few.  The enclosure is up to you.  One just big
enough to hold the rig and the 9 Volt battery will give you a tiny self
contained unit.

Many contacts using a simple end fed quarter wave wire, worked against
a good ground, have been made with this rig.  Most of them have been
over hundreds of miles away.  The transmit signal is very clean, with no key
clicks since the oscillator is always running.  Just listen to it!!  Power
output is in the 200 to 300 milliwatt range.  You'll be amazed what happens
at this power level with a decent antenna.

This is a "bare-bones" rig.  User your ingenuity or enlist the help of an
experienced ham to help enhance the operation of your rig.  Refer to QRP articles, like those in QRPp, SPRAT, ARCI and others devoted to QRP operating.  If you're not an experienced builder, this kit was designed especially for you.  If you've been building circuits, it's hoped you'll have fun with this little rig and/or help a beginner get started in the wonderful world of QRP.
If you come up with mods for the rig, publish them in QRPp.  Send Doug reports on your experience building and operating it.  There are surplus crystals available for less than a dollar for 3.579MHz and 3.686MHz.  For that price, buy one, solder it in and don't worry about changing frequencies.
Enjoy, 72, Dave WA6BOY
Parts kits for the Pixie 2 are available from 
HSC Electronics, 3500 Ryder St., Santa Clara, CA  95051.  The cost is $9.95 + $2.00 shipping and handling for the PC board and all board mounted components except the crystal.  Chokes will be provided for both 40 and 80 meters.  Phone 1-800-4HALTED.
You will need the following additional items (not supplied in the kit):
2-RCA jacks, or 3.5mm jacks for key and antenna
1-3.5 mm mono or stereo jack, depending upon your headphones
1-short piece of RG-174 for antenna connection
1-crystal socket or pair of mini-alligator clips, you may solder in the
crystal for the contest.
L3 is 1uH for 40M version and Crystal is in the 40M band.
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Copyrighted Material, please obtain permission from the author and QRPp to reproduce in any form.
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