The Sporadic-E is the strongest available propagation mode. An ionized „cloud” acts like a metal reflector, that allows signal to skip over a huge distance. It is possible to receive many stations with just a small portable radio and a telescopic antenna. With better equipment, when the frequency is clear, it is also possible to receive stations that transmit at extremely low power, like 50W, with full RDS and stereo! So, the signal level must be really strong, but how strong?
Today during a massive Sporadic-E opening BBC Radio 2 peaked once to 72dBf signal on Körner 19.3 (114m asl + 10m agl).
Körner 19.3 has 9dBd gain on 89 MHz. Assuming that BBC Radio 2 came from the Holme Moss TX with 250kW ERP, we can calculate the following values:
|ERP||Signal (Körner 19.3)||Signal (dipole)|
|250 kW||72 dBf||63 dBf|
|100 kW||68 dBf||59 dBf|
|10 kW||58 dBf||49 dBf|
|1 kW||48 dBf||39 dBf|
|100 W||38 dBf||29 dBf|
|10 W||28 dBf||19 dBf|
|1 W||18 dBf||9 dBf|
|100 mW||8 dBf||-1 dBf|
Yup. With high gain antenna, like Körner 19.3, 1W can still produce RDS level via Sporadic-E propagation, depending on the subcarrier injection level. 100mW ERP at 8dBf is audible quite well above the noise floor at peak!