Questions For rfry Regarding Harmonics Of AM BCB Facilities

[Schroedingers Cat]

Here's a situation you might be familiar with. When traveling along I-75 about 4 miles from the 5000 Watt Uncle Henry Rd. WSGW 790 facility, numerous Broadcasting and Hobbyist radio people have noticed a weak modulated WSGW signal along there. One question is whether this is receiver induced or a radiated signal from WSGW. Check my Math here. Spurious radiations are supposed to be 80 dB down from the main carrier. The way I calculate, 5 watts would be 30 dB down, 500 mW would be 40 dB down, 5 mW would be 60 dB down, 500 uW would be 70 dB down and 50 microwatts would be 80 dB down. Assuming this were feeding a half wave monopole, this would be 50 X 10^(-6) watts or 50 X 10^(-9) nano kilowatts into a half wave antenna @ 1580 kHz. The inverse field would be 52.5 uV/m at 1 mile, so assuming M-3, the field strength would be about 13.1 uV/m at close to 4 miles along I-75, and still be 80 dB down. In your opinion, is it more likely to be a radiated harmonic or a receiver induced harmonic? I think it is stronger than 13.1 uV/m from my experience, probably the equivalent of 50-100 uV/m.

 

[rfry]

WSGW Daytime Fields at 4 mi, N254°E

Some "bullets" about this:

• A distance of 4 miles at an azimuth angle of N254°E from the WSGW array crosses I-75 just south of its junction with highway M-81, East of Saginaw
• WSGW radiates a daytime ERP of about 17,500 watts toward that location
• The WSGW field at that location is about 168 mV/m (see graphic below)
• The -80 dBc field of a 1580 kHz 2nd harmonic of WSGW for that location = 16.8 µV/m
• That 16.8 µV/m field at 1580 kHz assumes the same radiation pattern, and the same groundwave propagation loss at 1580 kHz as at 790 kHz (which are both unlikely)

Comments, given the assumptions above:

1. A 16.8 µV/m field is near/below the radio spectrum noise level on 1580 kHz, at most receive locations
2. If WSGW is heard on 1580 kHz at/near that 1-75 location, it is likely that the receiver itself is producing it, and/or that it is being radiated and received as a rectification product of poorly-bonded conductors near that receive location