Find the fox or test your antenna with sound instead of a meter.

 Beside being a help in finding a Fox, an audio FS Meter is the perfect tool to gain confidence in the pattern of your antenna.

This FS Meter is derived from a schematic suplied by Joe Leggio WB2HOL.

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DETAILS of the design:

View the schematic V1.1
PLEASE NOTE THESES CHANGES:
.1 uF cap added across the gain pot, the 10K res. coulping the AMP to the PIC is replaced by a short, the 4.7 uF cap on pin 7 of the PIC is removed a .01 uF cap added at the supply input.

View the parts list

Parts location and PCB
The PCB is also availlable in the EASYTRAX format, just ask.

OPERATION:

When the Field Strength input is near nothing, there is no sound comming out of the FS Meter.
As the input signal increases above the threshold, the sound will vary from 300 to 3000 Hz.
If the input goes to Full Scale, the 3000 Hz will be chopped to indicate the need to reduce
the gain of the FS Meter.

When working near a multi-Watts TX, activate the numb switch to reduce the gain.

CONSTRUCTION:

This PIC is programmed as a specialized VCO for fox hunting. Its cost is about the
same as the cost of the discontinued LM566. DK price is 4.96 $Can or 3.18 $US.
The MAX495 AMP is a rail to rail single supply OP Amp, it provides a larger range of output voltage than an ordinary OP Amp.

Adjust RV2 for no sound with no signal at the input. Adjust RV3 for a confortable sound at the earphone.

Mount the batteries outside of the case, you then save the ON/OFF SW and the replacement is made easy.
Remove one battery to turn off the FS-Meter.

Free use for Ham radio operators is granted. The software is available for the asking.

My stripboard prototype

A PCB version from VE2JX

June 1999