Locate a QRP RF power source of 0.5W to 5W power level. Connect this to the TX connector, J1. Flip both
switches into the up positions, so that the meter is ON and measuring VSWR. Apply 0.5W to 5W of RF
power to the TX connector, and adjust the calibration pot on the back of the LCD meter until the display
reads “1.00”. It is
IMPORTANT
to unkey the transmitter before turning off the QRPometer! The
QRPometer is now calibrated!
Remove the 9v battery. Snip off the test jumper on the back of the board between the two switches.
Install R11, R36 and R40:
( ) R11 49.9k Yellow-White-White-Red ( ) R36
100k Brown-Black-Black-Orange ( ) R40 1.0M
Brown-Black-Black-Yellow
Step 9 – Final Assembly
Install the hardware in each corner of the board. A screw is inserted into each corner through the top of the
meter board. On the back, a spacer is placed over each screw. The screws are then inserted through the
mounting holes in the corners of the bottom board, over which lock washers and nuts installed.
Adhesive rubber feet are supplied with the kit, which are then attached to the bottom of the
QRPometer, near the mounting screw holes. You are done!
How to use the QRPometer The QRPometer is inserted between the QRP rig and the tuner or antenna. In
the OFF condition, the QRPometer is bypassed, and may be left in-line without signal loss.
When the QRPometer is switched ON, it may be operated either as a Power meter or VSWR meter. In
the PWR mode, a 50 ohm, 16 watt dummy load is switched in, and the connection to the Antenna
disconnected. This permits testing of a QRP transmitter without radiating QRM. The accuracy of the
power meter is typically 2% or better from 100 mW to over 10W.
In the VSWR mode, a resistor bridge type circuit is switched in. This inserts 6 dB of attenuation between
the QRP rig and antenna, which limits the VSWR presented to the rig to less than 2:1 during tune-up into
an unknown antenna. This is a valuable feature for use with QRP transmitters that lack any VSWR
protection. Once the VSWR of the antenna circuit has been nulled, the QRPometer should be switched out
to remove this attenuation.
If the QRPometer is operated in the VSWR mode with no applied power, you will notice the display will
slowly increment up or down. This is due to the analog mathematics of the board attempting to calculate
the ratio of forward and reflected power, which are both zero.
The accuracy of the VSWR meter is typically 5%, so that at minimum VSWR, the meter may read
something other than 1.00. Tuning for the smallest number will, nonetheless provide a 50 ohm match.
