I'd call information and ask for the number to the FCC Field office for whatever state you are in...
I got lucky and had a friend who knew one of the agents.
The 5watt was a custom build.. I needed something, and Jack had spare bits lying around and cobbled a (REALLY) nice tx together for me.
AFAIK, the 100mW is not being produced any longer.. and I personally do not have plans for either tx.. 🙁
by MRAM 1500 kHz
I have Metzo and Wild Planet Radio DJ transmitters and for now the antennas are the 8 foot wires that came with them hanging from the basement ceiling.
I hear both about .3 miles down the road on a good day.
I also have a 1962 Remco Caravelle part 15 transmitter. It has a 3 foot rod antenna attached to it. From my 2nd floor it can be heard about the same distance.
All of them require some type of ground to transmit that far. I connect them to the AC neutral which seems to work better than the AC ground even though they are bonded at the breaker box.
When the weather breaks the Metzo will go outside to a ground mount vertical.
I'm in NE Ohio where average ground conductivity is rated "8". The neighborhood is residential and there is a wooded park across from my house.