QRPworks
Stay Tuned
Manual rev 1.0 Page 7 of 8
Use as a VSWR Meter
Switch Positions:
o
ON - METER
o
VSWR - ANT
With the On/Off switch in the
ON
position and the Mode switch in the in
the
VSWR
position, 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 minimized,
Stay Tuned
should be switched
OFF
to remove this attenuation.
If
Stay Tuned
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 device 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.
Tuning by Audio
In addition to the VSWR meter,
Stay Tuned
adds a unique audio tone
that adds to its usability. In the VSWR mode, when forward power
exceeds about 150mW, it generates a steady tone whose pitch is
proportional to VSWR. This makes tuning for minimum VSWR an easy
and intuitive process if you aren't able to watch the display while you
tune - you just tune for the lowest pitch, and you are there. This is
helpful when adjusting any antenna, and especially helpful when tuning
magnetic loops.
