[RFI] AM Radio Interference On 75 meters

[David Robbins]

It appears kfbk does switch patterns from day to night, see if you can correlate the start/end of the signal with their switching patterns... it should roughly follow sunrise/set time, but i'm not sure of the details, they may be able to use the same time for a month then change, or may have special exemptions to the times...  this gives the patterns, see if you are in one or the other of their patterns.  if it is correlated with their switch times maybe they have a problem in their phasing system that is mixing in some other station, see if they are co-located with or even very near other broadcast stations.
http://fccinfo.com/CMDProFacLookup.php?sCurrentService=AM&calls=kfbk&tabSearchType=Call+Sign+Search
 
general complaints to their engineer will likely get filed with the music out of the toaster complaints... do some homework and see if you can pin it down to coming from their equipment or not for sure.  


Sep 18, 2012 01:23:36 PM, wa6rkn at gmail.com wrote:

 
 
----- Original Message ----- 
From: "David Robbins" <k1ttt at verizon.net>
Subject: Re: [RFI] AM Radio Interference On 75 meters
> 
> 3960khz is not a harmonic of 1530khz so something else is also happening here.  listen carefully to the kfbk signal and see if there is some other signal mixing with it.  check for other harmonics and other signals that it might be mixing with to end up on 3960...
> 
> 1530 + 2430khz?
> 1530*2 + 900khz?
> 1530*3 - 630khz?
> 1530 + 2*1215khz? 
> 5490 - 1530khz?
> etc, etc.
> 
> Then it must be mixing somewhere.  add lots of attenuation, if the signal suddenly dissappears its mixing in your radio... if not then its likely outside, which you may have already confirmed by using other radios... Yup..not in the radio...other radios brought to the location, both mobile and fixed, exhibit the same RFI assuming they aren't overloaded the same way, you don't say how far away you are or how strong the kfbk signal is at your location by itself.  try driving around with a well attenuated mobile radio and see if the signal gets stronger or weaker, is it there a long distance from your home station?  Approximately 8 miles, give or take   if so it is probalby not being generated near your station.  does it switch pattern or power from day to night and does the signal appear/dissappear at the switch time?  As stated in the original post..starts early evening, and goes away a 6am   can other hams hear it inside the normal ground wave distance for 3960khz? Some yes, others no.  can anyone get a bearing on it with a loop or beverages or 4-square??  Will try that. can anyone hear it farther away at night? Dunno lots of questions... 
> 
> 
> Sep 18, 2012 12:09:53 PM, wa6rkn at gmail.com wrote:
> 
> Here is the scenario. In the evening, through 6 am, radio station KFBK Sacramento (1530 KHz) *blasts into 75 meters with a 25k wise signal at 3.960. The signal is so stron, SSB conversations on 3.959 are impossible.
> 
> Notch and DSP filters in the radio do not work (Icom 757Pro) and other radios set up at that location, either fixed or mobile, suffer the same issue.
> 
> Here is are 'RFI present', and 'RFI Absent' Videos to exhibit the problem. 
> 
> Interference Present: 
> http://s1255.photobucket.com/albums/hh635/WA6RKN/?action=view¤t=RFIPresent.mp4
> 
> Interference absent:
> http://s1255.photobucket.com/albums/hh635/WA6RKN/?action=view¤t=RFIAbsent.mp4
> 
> Any suggestions? Nothing has helped so far...line chokes, coils, Band pass filters, etc.
> 
> Definitely a 3rd order harmonic..Radio station is blowing off the complaint, so a formal complaint has been filed with the is so bad, we cannot communicate with the involFCC, but that will umpteen years to get acted upon. (: It is so bad, we cannot communicate with ham involved! 
> 
> Thanks in advance for any help and suggestions.
> 
> Joe Wolfe
> WA6RKN
> 
> 
> 
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