Re: [IRCA] [NRC-AM] Wobbler ...

["Robert Foxworth" <rfoxwor1@xxxxxxxxxxxxxxx>]

Earlier you wrote, to one list,

>And it's not likely radiated by the co-channel Cuban.
>
>I'm thinking some sort of artifact of a part of a downlink of a
>satellite signal. One in which a satellite receiver receives the beacon
>signal and heterodynes it down and
>generates an unwanted 910 or 930 kHz product in the frequency
conversion
>process. Even though the satellite beacon is stable at microwave
>frequencies, it still has minor phase/frequency instabilities that if
>measured directly look like fairly large excursions but which are still
>minor as a PERCENTAGE of the beacon frequency but large as a percentage
>of the artifact product. Instabilities of the satellite axis factored
>into doppler shift. The satellite wobbles to some extent. Or the
>radiating antenna shakes. Or something.
>
>Charlie


The variability of modulation quality on different signals on the same
red
or cadena (example the crispness of Reloj-950 and the muddiness of
Reloj-570) has always led me to believe that these stations are
connected
with nothing better than phone lines. It is not clear to me that Cuban
radio
has any need for a sat distribution system, and that they could afford
one,
if they did.

Using several receivers it should not be hard to measure propagation
delay between multiple stations by listening to them at the same time.
If one was getting a sat feed it should lag the other by approx 280 ms
and in my limited experience I have never heard this.

My earlier theory was that there is an artifact being created due to
instability in the carrier mux'ing for multiple voice channels on
inter-city
terrestrial telco links between cities and this wobbly oscillator
noise is somehow becoming modulated onto the transmitter input.
I soon abandoned this theory (I believe Curt will recall all this, it
was
on the NRC list so some of you never saw it) but now it seems the
thinking is starting to come back to some kind of idea like this.

If the T1 carrier pilot is off then the artifact is brought way up by
the AGC,
and becomes audible, otherwise the pilot is on and then programming
becomes normal. This could explain the apparent randomness
and variation in the presence of these signals, along with occasional
transmitter freq changes/reassignments..

And the signal delay between different sites would only be a few ms
and you would need a dual-trace oscilloscope to try and figure this
out. However forensically this would be a valid technique to try and
map out the layout of their networks if you had enough sample
points e.g. signals to compare.  Maybe during the next Castro speech,
when every station has the same audio, you use the Havana stations
as the reference point e.g. t=0 and measure the delay in audio for
every other signal/city behind that. Compare the Pv for the intercity
wired links to the Pv for air transmissions from each city to your rx
site (obviously you want to be in groundwave range and do this
during the day). I think it's complicated but doable with enough
resources..  If on the other hand Castro speaks from Santiago, then
just correct for that. If he is in Matanzas, then this won't work so
well,
or for multiple sites on the same frequency..

- Bob


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