All the talk about Part 15 FM, 15.239, and experienced signal distance have inspired me to conduct semi-professional experiments for purposes of comparison.
I have already compared three "certified" FM transmitters and found they all produce the same field readings in "dBu" on a spectrum analyzer at 14'7" from the transmitters, using the 14" telescoping input antenna that came with the analyzer.
Those transmitters are C.Crane FM Transmitter 1, Wholehouse 2.0 and Scosche FMT4R.
Setting aside the fact that all three transmitters produce the same field levels when set for U.S. compliance, today's experiment will be made using the Wholehouse 2.0.
At the moment I have these readings.
Wholehouse 2.0 with 3" wire antenna = 31dBu.
How much signal increase occurs by adding an additional 4.5' vertical transmit antenna wire? Answer: 2 dBu for a total field reading of 33 dBu.
What are some comparative analyzer readings for full power local stations?
88.1 MHz 42 kW located approx. 30-miles south = 26 dBu;
90.7 MHz 100 kW located approx. 6-miles south = 62 dBu;
92.3 MHz 99 kW located approx. 20-miles south = 46 dBu.