Squawk Box" ..for fun Field Day listening
When I have operated on Field Day, I like to turn the audio gain up loud to hear the weak ones. The result is that everyone near the station starts complaining that they can't hear themselves think.
One solution was to put headphones on but that meant the logger and the observers couldn't hear what was going on. So, I decided to throw this circuit together to satisfy everyone.
The Squawk Box is plugged into the 8-ohm audio output of your radio. RV2 and RV3 control the volume of headphone jacks JK I and JK2 respectively. The speaker volume is controlled by the 8-ohm L-Pad RVL 1.
PLI is a 3.5 mm mono phone plug. This is a typical size for most modem rigs. You might need something different to suit your rig. JK I and JK2 are 6 mm stereo phone jacks. The left and right contacts are strapped together for stereo headphones.
If you have a mono plug on your headphones, do not use the straps or the mono plug will short out the output to the headphones. This won't hurt the radio output as RI or R2 will be in series with the audio output - you just won't hear anything in the headphones.
With mono headphones, wire RI and R2 to the tip only of the stereo jack. Resistors RI and R2 might need to be changed, depending on the impedance of your headphones.
For newer headphones that are between 39 and 100 ohms, try the 1.8k ohm value. For older headphones that are 4 or 8 ohms, try 1000 ohms.
I built this project for last years Field Day. Nothing is worse when working with headphones and having visitors. Now the visitors have total independent control over the external speaker volume with no effect on your earphone volume. I use the box full time in my shack at home which allows me to use my boom headset and still allow independent external speaker level adjustment. I did not find that I required the 1.8K (R1&2) resistor in my box. I also only made provisions for a single headset. Between field days I use the interface in my shack so I can still use my headset