> Evidentially Broadcast Works has the unfortunate task of
> trying to clean up both 700 and 990. According to my
> conversation with one of their engineers:
>
> "I reported them interfering with the 1.5 degree radial on
> 700. He [another engineer] found them all over the band. I
> think he said they were centered around 800."
>
> Me: They've been having interference problems with 820 and
> 1190 also
>
> Him: Yeah, I heard them on my FIM around 1120 and 700 +/-.
>
They, 990/KFCD has a very strong component (read that as 'spurious
signal') present during lulls in program audio at 836 KHz, as
shown below:
(Note the square spectrum blip dead center in the screen; this square
'noise' area appears when no prgram audio is present on 990/KFCD. The
taller blip on the left is WBAP 820 and the one on the right is 850
Super Tejano.)
<hr noshade>
I'm not familiar with the specs on a FIM, but if you choose
a sufficiently narrow enough IF bandwidth (like 3 KHz) and
tune in 836 to 837 KHz with the product detector active (SSB
receive mode) one can 'hear' this spurious signal during quiet
audio passages (sounds like white noise - tastes like chicken)
that seems to 'FM' up and down the band during modulation
(program audio appearing) 990/KFCD's carrier.
I think its a switching component of a PWM transmitter.
With a standard AM radio one can also hear a lot of 'shotgun
splatter' around 1140 KHz, in among the IBOC sidebands from
1160.
Hint: use two AM receivers, one tuned to 990 and the other to
'prowl around' with and note the appearance and coincidence
with or abscence of program material on 990/KFCD.
G. Gordon Liddy and his program audio was really producing
some easy to spot artifacts a couple of weeks ago.
Below is what the spectrum above looks like when 990/KFCD has
program audio present - the blip goes away, and seems to
spread (can be heard) on WBAP as 'scratch' (as opposed to
"shotgun noise splatter"):
