Modify a "Talking House" part 15 AM transmitter

[wa2ise]

This is a small AM transmitter used by real estate agents to advertise a house to people in cars parked just outside of the house. With some mods, it can make a passable AM transmitter to feed our radios in your house.

Replace C301 with a 4.7uF cap, to get better audio bass frequency response (the existing cap was selected for human voice, like the phone line). And to make the audio input jack more usable (it accepts a 1/8 inch stereo jack and the stereo is mixed together thru a pair of 100K resistors), I replaced a 470 ohm resistor with a 1K trimpot as a rheostat, and in parallel with that a 150 ohm resistor. Then adjust the trimpot for best audio heard out of an AM radio, once you get rid of RF hum (which can be a PITA). One thing to help avoid that RF hum is to isolate the input jack's ground (cut the trace) and then connect a coil (1 to 5uH) across that cut trace (so the ground connection functions at audio frequencies, but becomes a high impedance at RF). The 100K resistors already create a high impedance to RF on the audio signal conductors. I also had to use a 3 to 2 pin power adapter plug on the wall wart to reduce RF hum.

This box has an autotuner to adjust itself to load the ten foot wire antenna, but this autotuner is not used for the "outdoor" antenna F connector output.
Loop antenna similar to mine.
I don't have their outdoor antenna, but I took a big tuned loop antenna I had (7 loops with tuning cap), added an extra turn of wire around the loop, and connected this turn of wire to the F connector output. Then I tuned this loop antenna to the transmitter frequency. You may have to rotate the loop (around a vertical axis) to null out RF hum).