QRP - Low Power

The term QRP derives from the standard Q code used in radio communications, where "QRP?" are used to request, "Reduce power", and ask "Should I reduce power?" respectively. The opposite of QRP is QRO, or high-power operation.


Essentially QRP can be defined as operating with low power under 5 watts. Many amateur's still build their own equipment. And like myself, some just love building transmitters and transceivers using bare minimum of components as possible, this gives a real sense of achievement when contacts are made, especially if they are made over long distances. In view of the fact that signal strengths can sometimes be lower than those of stations using higher powers (QRO) most QRP operation uses Morse, although this is not always the case. Using Morse transmissions enables contacts to be made when it would not be possible using other modes. SSB and other modes are used for QRP operation.

 

 

A very quick and easy way to get on the air is to build a "Michigan Mighty Mite" CW transmitter for 160, 80, 40 or 30 meters. I have just built one for the 40m band, it uses only 7 components including the homebrew coil. And I must say it works really well indeed. On the first test transmission (day time) it was heard in Twente in the Netherlands which is about 290 Miles at RST 589 with an output of around 100 milliwatts. Band conditions were not that good at the time, so more testing needs to be done.

 

 

Circuit

 

Circuit of the Michigan Mighty Mite



Q1

 

2N3053, 2N2222 or similar inexpensive general-purpose NPN transistor. I used a plastic-case 2N3904 TO-92 transistor which works really well, I did have to use a heat sink which was just a alligator clip as the transistor did get hot.

 

 

TANK COIL:


Use a 1.25" diameter form (35mm film canister, pill bottle, etc.) and #20 - #22 SWG enameled wire. To make tap, wind L1 to the "tapped at" number of turns (see table below). Make a loop about 1 inch long, twist it a few times and finish winding. Sand the insulation off the end of the loop. This is your tap. After winding L1, wrap it with a thin layer of masking tape and wind L2 on top of the tape in the same direction as L1. Secure L2 with more tape and finish by sanding insulation off remaining leads.


 

Tank Coil Windings

 

L1 - Primary/Collector WindingsL2 - Secondary/Antenna Windings
160m -- 60 turns, tapped at 20 160m --- 8 turns
80m -- 45 turns, tapped at 15 80m --- 6 turns
40m -- 21 turns, tapped at 7 40m --- 4 turns
30m -- 15 turns, tapped at 6 30m --- 4 turns


XTAL:


Fundamental crystal for desired frequency.



As for the 365pf variable capacitor. I found a 20 - 320pf on ebay but it wasn't cheap. You could salvage one from an old MW/LW transistor radio.



Pictures to follow

 

 

Popular QRP Frequencies.

 

CW. 1.836, 1.843, 3.560, 7.030, (The USA also use 7.040), 10.106, 10.116, 14.060, 18.086, 18.096, 18.106, 21.060, 24.906, 28.060.

SSB QRP Frequencies. 3.690, 7.090, 14.285, 18.130, 21.285, 24.950, 28.365.



Much More Coming Soon ......