Topband: 1.810 BCB interference

[ws6x at comcast.net]

At 04:19 AM 2007-01-03, Steve Flood wrote:
>Throughout the winter so far, I've detected a carrier on 1.810 in the 
>mornings before sunrise.  The past two mornings, I could hear some 
>modulation - some sports talk - but could not pick up the station i.d. 
>other than I think it begins with 15 or 16 - so say
>somewhere between 1500 and 1690.     At first, I thought it might be 
>our local strong 1290 station beating with the strong 520 MSO airport 
>beacon (INE), but I could definitely hear sports talk instead of 1290's 
>Coast-to-Coast programming.
>
>Any other observations in the northwest?
>Steve, KK7UV

The carrier is just audible here at 8:50 am local time near San Diego, just above my abysmally high S7 noise floor (in the 250 Hz filter).  It was much stronger on Saturday night during the Stew, making copy of stations very near 1810 difficult.  However, even then I couldn't detect any modulation on it.

73, Terry N6RY 

=====
Our local experience here with BCI on that exact frequency might provide some insight. We have an enormous BC spur which obliterates 1810 +/- 5 kHz. The audio on the signal sounds like several stations mixed together, but
the audio from one -- ironically, a sports talk radio station --  is predominant.

One of our local hams, and former BC engineer, Vic - K2VCO, spent a long time trying to track down the offender. When he discovered a strong BC second harmonic at 3360 kHz. he was able to solve the puzzle. It turns out to be a mixing by-product from two AM stations sharing a TX site, as follows:  

XMTR A  broadcasts on 1680 kHz; XMTR B on 1550. Doing the math: 1680 x 2 = 3360; 3360 - 1550 = 1810. The 1680 second harmonic (3360) is copyable for about a 5 mile radius from the TX site.  I am located approx 20 miles from the TX site and copy the spur at 20 over during prime evening hours. It is weak, but copyable about 100 miles SE from the site.

Unfortunately, even after numerous communications with the engineers in charge, there has been no resolution of the problem. So we Fresno area topband masochists seriously dislike it when a much-needed entity decides to park on 1808 - 1812.  :(  

Good luck with your sleuthing process.

Jim - WS6X