Topband: 1940 kHz intermod

[Eric Scace K3NA]

Hi Frank, everyone —

   One does not need another person to be harmed by the intermod on 1940 kHz

   AM broadcast regulations include a very strict bandwidth mask for any form of radiated spurious signal more than ±75 kHz from the carrier frequency. At these power levels, such spurs must be less than -80 dB below the carrier (measured at a point about 10 wavelengths from the center of a directional array, usually in the main beam).

   There are very specific measurement procedures to be followed for compliance. Every AM station is required to measure — and retain a report of compliance in their station transmitter logs — annually (no more than 14 months between measurements). The measurement procedures require some care, a very good spectrum analyzer, and a calibrated antenna.

   If the station is out of compliance, it has 10 days to return to compliance before notifying the FCC. If the problem cannot be repaired within 28 days, the station must obtain an STA to continue operations.

   ===

   Now, as to the identity of the stations. The FCC’s AM Query <https://www.fcc.gov/media/radio/am-query> webpage is invaluable for researching issues like this.

   Rick identified one audible program as from WWRU. WWRU operates 10 kW daytime with a 2-tower directional array at 40° 49' 13.36" N  74° 04' 02.51” W. The tower registration numbers are 1040103 and 1242403. At night it runs 10 kW into a 4-tower array 

   A search of AM stations within 3 km reveals, as reported by others, WKDM on 1380 kHz. [Note: Be careful using AM Query’s “radius around a lat-long” search tool, as the input must be in NAD-27, not NAD-83 coördinates.]

   WKDM uses a 3-tower directional array (daytime) at the same coördinates, and a 4-tower directional pattern at night. Tower #1040103 is shared by both stations. That means a diplexer is employed to combine the signals into this tower — and would be the first place to look for generation of a mixing product.

   ===

   What to do?

   Both stations run 10 kW or more. On that basis alone, the chief engineer of each station is required to be an employee of the station — not a contract engineer. (The same requirement applies to any AM station running a directional pattern.) That means the chief engineers will be easy to contact — just call the station’s main phone number. WKDM’s website is here <https://www.am1660.com/>, and info at am1680.com <mailto:info at am1680.com> is the general email address. +1-718-352-1660 is the phone number at their headquarters location.

   If this is unsuccessful, one can escalate to the points of contact registered with the station license. In this case, a search of the FCC LMS database reveals both stations are owned by the same company and have the same points of contact:
seank at mrbi.net <mailto:seank at mrbi.net> … and the legal representative is Mark Lipp at lipp at fhhlaw.com <mailto:lipp at fhhlaw.com>

   If no satisfaction has been obtained, anyone can file a complaint with the FCC Enforcement Bureau explaining that these two stations are operating out of apparent compliance, with the support data and information about how the station management has been unresponsive. The Enforcement staff maintain contact numbers for each station to use in cases of emergency, and will follow up (as I have personally witnessed).

   I hope this helps.

— Eric K3NA




> On Jan 6, 2023, at 18:03, Frank W3LPL <donovanf at starpower.net> wrote:
> 
> Hi Fred, 
> 
> We've figured out the mystery, now we need to determine if anyone is 
> being harmed by the weak, intermittent intermod on 1940 kHz 
> 
> 73 
> Frank 
> W3LPL