Topband: 1940 kHz intermod from WRRU and WKDM

[James V Redding PE]

Broadcasters are permitted:

(b) Emissions 10.2 kHz to 20 kHz removed from the carrier must be
attenuated at least 25 dB below the unmodulated carrier level, emissions 20
kHz to 30 kHz removed from the carrier must be attenuated at least 35 dB
below the unmodulated carrier level, emissions 30 kHz to 60 kHz removed
from the carrier must be attenuated at least [5 + 1 dB/kHz] below the
unmodulated carrier level, and emissions between 60 kHz and 75 kHz of the
carrier frequency must be attenuated at least 65 dB below the unmodulated
carrier level. Emissions removed by more than 75 kHz must be attenuated at
least 43 + 10 Log (Power in Watts) or 80 dB below the unmodulated carrier
level, whichever is the lesser attenuation, except for transmitters having
power less than 158 Watts, where the attenuation must be at least 65 dB
below carrier level.

Here is what the NRSC RF Mask “looks like” in an amplitude versus frequency
graph:

[image: frequency from carrier 1]



The typical amateur receiver will hear "something" at -120 dbv.

The graph is in "WATTS"

I think the "curly fry" fluorescents and older plasma TV's caused worse
interference

JIm Redding

wa9vez (61 years)

On Sat, Jan 7, 2023 at 1:57 PM <donroden at hiwaay.net> wrote:

>
>
> > This is true ,    I contract for quiet a few AMs and FMs that can't
> > find anyone that want to be on 24/7 call.   There is this "thing"
> > called FCC Yearly NRSC Tests where an engineer with an analyzer checks
> > the spectrum and the station(s) must meet spectral purity ... ie: no
> > spurious emissions higher than XX db removed yy Kc from carrier.    It
> > sounds like one or both stations are producing an unwanted mixing
> > product.   "IF" they are co-located on or at the same site,  the
> > combiner "should" include traps that filter or reject each other's RF.
> > It's possible that lightning / age / rats / snakes / birds have changed
> > the inductance of one of the traps.
> > So, both of the stations may be unaware of the interference except on
> > the day of the NRSC test.
> >
> > Don W4DNR
> >
> > Jim VE&RF said :
> > Problem is most AM / FM stations these days all contract out the work
> > for regular maintenance.
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