Three Blind Mice 3 Band QRPp CW Transmitter

 Three Blind Mice 3 Band QRPp CW Transmitter 

BY KN2A

The Scoop!

While doing research on QRPp Transmitters, Bob (AK4JA) pointed me to

Steve McDonald's (VE7SL)  Radio Notebook.

Steve incorporated  The MICRONUAT CW TRANSMITTER by Dave Ingram - W4TWJ (CQ Magazine - April 1996 issue , pages 48-51), into a Tuna Can and called it MINI-TUNA.



I decided to build the circuit however I did not have any PCB or breadboards  to build it on. Desperately I ran to the hardware store and purchased a few wooden moustraps and small nails.

I used the wooden board of the Mouse Trap and used Steve's (VE7SL) schematic as a template to build the circuit. I used small nails and soldered all the components. A 7.040 Mhz xtal was used.

I emailed Steve and he was very pleased with my tinkering!

He suggested I call my version of the transmitter

The Mouser-40!

because it was built on a mousetrap... hi hi!

Well I liked the idea of using a board and nails even though its a bit old school I found it to be so much fun!

I looked at the values of the caps and inductors for the output filters of the original Micronaut and incorporated the output pi filters for 20 , 30 and 40 meters in the schematic and  built a three band version in one "Mousetrap" wooden board.



I Named It:

Three Blind Mice 3 Band QRPp CW Transmitter

-  Or just "Three Blind Mice"



The bands will be changed by means of three jumpers and changing the xtal for the desired band.

1 jumper from emitter to respective band emitter capacitor

1 jumper from C4 Q1 output to respective band filter input

1 jumper from respective band filter output to output connector (antenna out)



My brother Jose Luis (Cartoonist and Artist) did the artwork for the mousetrap board.

I added a small meter to see a indication of output power. The schematic for the meter is not in the original design. It is basically a diode, capacitor and a variable resistor.
It rectifies the output and takes a small sample of the rectified voltage to deflect the meters needle. It can be turned on or off by means of just a alligator clip.
A variable capacitor was also added to the circuit in series with the XTAL. It fine tunes the output frequency + or - 500 Hz.

POWER OUTPUT TESTS WITH ELECRAFT DL-1 DUMMY LOAD

MAY 5th , 2015

Elecraft DL-1 Dummy Load formula:
P(watts) = (V + 0.25)2 /25 where V= volts and 0.25 is the RF voltage drop across the diode

The following tests were done with the following QRP frequency XTALs:

- 7.030 MHz

- 10.114 MHz

- 14.060 MHz

The variable tuning cap was tuned to obtain minimum , midrange and maximum frequencies

Emitter Resistor at minimum - 39 Ohms  (maximum collector current)

SUPPLY VOLTAGE	FREQUENCY MHz	OUTPUT POWER WITH (50 Ohm Load)
13.8 V	7.02847	256 mW
13.8 V	7.02974	232 mW
13.8 V	7.031015	226 mW
9.3 V	7.02847	113 mW
9.3 V	7.02974	106 mW
9.3 V	7.031015	99.4 mW
13.8 V	10.113850	211 mW

http://qrz.com/hampages/kn2a/KIMG0173.jpg

In the photo above you can see 1 jumper from the emitter to the 40m band emitter capacitor, 1 jumper from C4 Q1 output to 40m band filter input and 1 jumper from 40m band filter output to output connector - (antenna out).

I made my first contact on 40m with THREE BLIND MICE on 5/12/15 to VA

Station N7DC @ 20:45 UTC  on 7.113 MHz with 123 milliwatts using a Endfed Antenna


QRPp is lots of fun!