One of the major unkowns in transmitting on long wave band, is the real radiated power from the antenna. This information can be optained only by appropriately performed measurements. According to my very modest working conditions at a frequency of 137 kHz me this information is particulary interesting:

- Antenna: inv. "U" 7 and 6 m. vertical, 27m. horisontal
- Measure with W&G SPM 3 (thanks S52AS)
- Measuring antena is 1m. diameter, non-resonant loop
- Distance from transmitting antenna is approximate 400m. The accuracy of the reading of each location is + - 5m.
- Foressen ERP before the measurement is about 15 - 20 mW ERP. I suppose that is shown to increase at the expense of second    vertical part of the antenna
- Heigh of the measure loop antenna above the ground (from 30 cm to 2m.), does not effect the measurements. The measured signal    level is the same irrespective of the heigh of the antenna above

So, the existing modest antenna, is the effective radiated power of 30 mW at 100 W tranmitting output . 30 mW ERP - this is probably the real value.