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Exalted carrier reception in pt 15 fringe zone?

T

Tom Wells

As I often drive to see what my coverage is, and if I am zero on frequency, I notice that at the edge of
my coverage, I can hear 1620 Omaha, while another 1/4 mile or 1/2 mile out from my house, I cannot hear 1620 Omaha.
Is this not exactly the same a zero-beat bfo "exalted AM" detection, simply occuring outside a radio?
Were I off freq, I'd still be there as a beat frequency, but as a zero-beat my pt 15 signal seems to equal a ring of reception
where AM 1620 Omaha, otherwise unreceivable here in Chicago, is listenable.

Has anyone else noticed such an effect or is everyone else blessed with a nice clear frequency?
 
It must be that your carrier is filling in the missing/weak carrier for the other station, and there are enough of their sidebands present to make them detectable. Just a guess..

df
 
Well, yeah. That's exactly how it seems, from watching this over a long time.
I just was never was able to get such a sensitive detection from any radio using zero-beat detection, even if I had full control of mixer %.

In a similar vein, I checked AM 920 this AM on the way to work to see if they were there. But no,
I hear a strong image of WGN AM 720, as the 100kc imtermod image of W? 820 , on 920....freaky.. and repeatable.
I've heard this many times before.
It's not the radio, it has a tuned RF input stage of real physical parts.
Then as I go toward both xmit sites, the effect quits.

I was enjoying the image this morning quite a bit, as it did not seem to have the iBOC hiss!
This led me to wondering what a superhet would do if tuned to the "wrong" IF image, and gosh darnitall,
I am thinking about tracking problems, but there could be something to the idea of remashing to the wrong IF image as a
way to escape iBOC hash...just thinking out loud. Hmmmmm.
 
Is this possible with FM? I've noticed that, around the coverage fringes of my "LPFM" (heh, heh), there's a "ring" of another signal, a Class A from 110 miles away, with a theoretical 25 dBu or so at the location. 25 dBu is not usually enough to receive in my car... but this signal sometimes shows up around the fringes of my signal, then -- as I drive out of my coverage and toward this other signal -- completely disappears until I hit the place where it "normally" starts coming in (32-33 dBu theoretical, or so).

My (limited) engineering knowledge makes me skeptical, since the frequency of a frequency-modulated carrier changes instantaneously -- hence, it doesn't seem very likely that two signals would really "line up" for any period of time without cancelling one another. I suppose it's possible, given 100 million vibrations per second, that what sounds like a semi-steady signal is actually cancelling itself a few million times along the way... anyone care to opine?
 
Grrrradio said:
I've noticed that, around the coverage fringes of my "LPFM" (heh, heh), there's a "ring" of another signal, a Class A from 110 miles away, with a theoretical 25 dBu or so at the location.
Click to expand...

If this is any help to you, the FCC F(50/50) curves for a Class A FM (6 kW ERP from 100 m HAAT) show its 25 dBµV/m (20 µV/m) contour at about 67 miles from the transmit antenna.
//
 
I can't explain the FM situation. Normally you would have the "capture effect" on an FM signal, and whichever signal is more prevalent will be heard. I think the magic number is 6db difference, and your receiver will capture the stronger of the two, although you may hear some squiggles in the background from the weaker signal..

df



Grrrradio said:
Is this possible with FM? I've noticed that, around the coverage fringes of my "LPFM" (heh, heh), there's a "ring" of another signal, a Class A from 110 miles away, with a theoretical 25 dBu or so at the location. 25 dBu is not usually enough to receive in my car... but this signal sometimes shows up around the fringes of my signal, then -- as I drive out of my coverage and toward this other signal -- completely disappears until I hit the place where it "normally" starts coming in (32-33 dBu theoretical, or so).

My (limited) engineering knowledge makes me skeptical, since the frequency of a frequency-modulated carrier changes instantaneously -- hence, it doesn't seem very likely that two signals would really "line up" for any period of time without cancelling one another. I suppose it's possible, given 100 million vibrations per second, that what sounds like a semi-steady signal is actually cancelling itself a few million times along the way... anyone care to opine?
Click to expand...
 
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