So went googling. There are several good YouTube presentations:
But both refer to an older version with a "black box" that controls the signal strength. My unit is Model #F8V3080eaBLKP. The videos show how to open the unit correctly, but when it came to finding the black box it is now completely gone!
But all is not lost: In its place there is a pad of some six test points in a rectangular grid:
I energized the unit as shown in the first video and started touching things with a stretch of 20 gauge wire. On touching the second pad in the first row the signal jumped up. I checked out the rest, but this seems to be the best.
So with some very delicate soldering, tacked a stretch of 20 gauge to that pad:
Then put the unit back together, and all is well.
• Next: Antenna length.
wavelength (in meters) = 300 / Frequency in MHz
There is some farkling about required:
• Experiment with different frequencies. I started out mid range at 92.5 MHz, but for the length that I had cut the reception was noisy. Moving down to 80.1 MHz solved that.
• Experiment with various volume levels. A level of 20 worked for me.
• Experiment with antenna placement. Laying it out flat on the table worked for me.
So here is what you do:
1. Buy the transmitter somewhere.
2. Open up the case and solder one meter of wire to the second pad in the first row.
3. Close up the case.
4. Turn on the unit, to say 88.1 MHz.
5. Turn on and tune the FM receiver to the frequency you have chosen.