TALKING PIXIE2 TRANSMITTER PROJECT

Carl Blare, Updated 6-5-11
6-1-11 Modified AM Pixie2 Version 1.0.8

NEWS 6-4-11  A new 3-transistor SW Transmitter Project

F.C.C. Part 15.225  Operation within the band 13.553-13.567mHz.
United States Only
15.225   Operation within the band 13.110-14.010 MHz.

(a) The field strength of any emissions within the band 13.553-13.567
MHz shall not exceed 15,848 microvolts/meter at 30 meters.

ATTENTION SHORTWAVE HOBBYISTS:  This project has been re-activated (5-11-11) and we are planning Version 1.1 which should fix a few bugs in V 1.0
All communications regarding this project should be posted at http://www.part15.us/node/2856  --  Do not write to this website.

Previous Versions - Figures 1 - 8
Version 1.0
Version 1.0.1
Version 1.0.2
Version 1.0.3
Version 1.0.4
Version 1.0.5
Version 1.0.6
Version 1.0.7

Figure 9 - Version 1.0.8 - Status:  Most Recent Version in Progress

V_1.0.8
Notes:  Based on The "Talking" Pixie2 QRPp AM Transmitter  QRPp-I  http://www.indianapolis.net/QRPp-I/talking_pixie2.html
Earliest known version  http://www.qsl.net/we6w/projects/pixie2.gif

Brief Project Commentary:  Upon finding that the source diagram, once built, suffered from modulation failure. Experimental changes were made, documented in this thread http://www.part15.us/node/2065
Version 1.0.8 features collector feedback bias to Q2 (R3)
Version 1.0.7 built by Radio Bon Esprit in Paris, France features Class C output stage (Q2)

Parts List:  Parts numbering from the Original Diagram, QRPp-I, is maintained.

Capacitors:
C1  100 pF
C2  220 pF
C3  82 pF
C4  .01 uF
C5  .01 uF
C6  omitted
C7  omitted
C8  270 pF
C9  270 pF
C10  .01uF

Diodes:
n.a.

Crystal:
13.56 mHz

Inductors:
L1  omitted
L2  22 uH
L3  replaced by 13 mHz 5-pole Lowpass Filter 50-ohms in/out

Submitted by scwis on September 18, 2009 - 19:46.

In the document linked in the Talking Pixie post above the output filter is shown in the XMTR schematic and the component values are supposed to be shown using the fliter page link. That link is dead but even if it wasn't it's no help - I checked it on the Internet Archive and none of the values specified were for 13.5x anyway. John Smick suggests a better design and calculated the proper values, shown below.  Figure 10 - 13.560 LP Filter
13mHz_LP_Filter

L4  1 uH
L5  1.5 uH
L6  1 uH

Resistors:
R1  47k
R2  1.2k
R3  22k
R4  0-ohms
R5  omitted

Transformer:
273-1380 Radio Shack Audio 1k/8-ohm
Audio Input low-impedance/ B+ high-impedance; RF path

Transistors:
Q1  2N2222
Q2  2N2222A (metal can type) with KH3412 Hat-Type heat spreader TO-18
Two other options are specified in the Pixie2 document: 2N3866 or FET 2N7000
Used GE-20 / ECG-123A as temporary substitute

Addenda:

12/7/09        Voltage DC = 9 VDC
Velleman P1823 Power Supply 1 Amp

Audio Amplifier Velleman K4001
Audio Modulation Schematic

AC Output Readings:
pending

Power Output Measurement:
Submitted by Ermi Roos on September 15, 2009 - 14:36.

The cost of a field strength meter that allows the legal verification of a 13.56 MHz installation is out of the range of just about every experimenter; but WILCOM LABS, a contributor to this web site, has come up with a practical solution. He sets the output power of the transmitter to a 50 or 75 ohm resistive load (depending on the coax to the antenna) to 0.5 mW. This works out to a maximum of about half of the allowed field strength, using a monopole or a dipole. This should be enough of a safety margin to avoid trouble with the FCC.

Please contact WILCOM LABS for any further information about his installation.



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