293.600 Mhz In mercer county area?

[station32]

I was listining to my scanner and i had the mill air bank open and it kept stopping on 293.600 MHZ in am mode. so i stoped it from scanning and put it in FM mode and i heard people talking. Then i searched for a pl and came back with 103.5. It sounded like police or someone. Not really sure there was a dispatcher calling a car and something else. Anybody have any idea. I searchen the Fcc database and came up with nothing thanks.
Joe

 

[Tech792]

most likely an image from a nearby transmitter or tower since that freq is military and not in the land mobile band.

 

[station32]

I dont think it was from a tower nearby i know all the transmit towers in my area and the only thing that was close was mercer county central. and it didnt sound like anything from them. It was pretty clear to. Any possibility it could be something else.

 

[W2SJW]

It's got to be an image of something close to you then. Look at the PL you recovered - it's used quite a bit in your county...

 

[station32]

how close would the tower have to be for this to happen. The only thing is the transmition didnt sound like anything i heard before there was a beep before and after each transmition.

 

[robbinsj2]

Not especially close, it isn't like bleed-over. On an old double-conversion scanner I often got images of airborne aircraft some ways off on 155.205. What scanner are you hearing this on? Does it seem like a repeater channel, or base/mobile, or mobiles only? Are you able to receive it on any other scanners?

 

[station32]

I heard it on a Pro-164. It sounded like it was a mix between a reapeter and so mobile to dispatcher. because some of the comms were very clear and some sounded a little scratchy but the dispatcher was pretty clear. I went home and also heard it on my IC-T90a

 

[N2DLX]

A quick formula for finding the image source:

F1 + 2(If) = F2 [Up]
-or-
F1 - 2(If) = F2 [Down]

F1 = Image Frequency
F2 = Originating (Actual) Frequency
If = Receiver's First-Order Intermediate Frequency (ie. 10.7 MHz, 46.35 MHz, etc)

Example:

You hear something on 155.745 and your receiver IF is 10.7 MHz:

155.745 + 2(10.7) = 177.145 MHz
-or-
155.745 - 2(10.7) = 134.345 MHz

You can also change the 2(If) part to calculate third, fourth, etc products if necessary.

 

[fineshot1]

Sounds like he is getting a mix from two local stations from his description.

Rich - you peaked my curiosity

His IC-T90A is a double conversion receiver.

293.6 - (69.45 x 2)138.9 = 154.7 Mhz

Not sure how this would work for his Pro-164 which is a triple conversion receiver, any ideas?
I guess the math can be manipulated for the first IF.

First IF = 380.8
Second IF = 21.4
Third IF = 455Khz

 

[N2DLX]

Sounds like he is getting a mix from two local stations from his description.

Rich - you peaked my curiosity

His IC-T90A is a double conversion receiver.

293.6 - (69.45 x 2)138.9 = 154.7 Mhz

Not sure how this would work for his Pro-164 which is a triple conversion receiver, any ideas?
I guess the math can be manipulated for the first IF.

First IF = 380.8
Second IF = 21.4
Third IF = 455Khz

I believe the formula is only effective on the First IF. However, you can try different multiples of the IF to see if you're hearing say, 21.4 MHz up/down or 42.8 MHz up/down, etc etc. Of course the further away you get, the weaker the signal. So if the shifted frequency still doesn't match up to a likely band, try multiplying by 3, 4, and so on.

I'm no expert, so take this info with a grain of salt. I just pick up formulas here and there and apply them where necessary.

 

[fineshot1]

Rich - my point was only that since the IF freq of the Pro164 is much larger than the image freq the calculation using the formula above would yield a negative number. I don't think there is a Negahertz portion of the spectrum so I think the formula above can be manipulated to do the proper calculation but since math was never my strong point I do not know how to juggle the numbers to come up with a positive number result in the calculation. Hopefully some mathmatics major will look at this thread and help us out.

 

[N2DLX]

Ah, I see what you're saying. I was thinking the Icom T90, which has 69.45 MHz First IF.

In the case of the scanner, I'd try using the 2nd IF of 21.4 (twice 10.7). That still puts you in the middle of nowhere band-wise, so it's got to be a multiple of one of the IFs or he's getting bleedover from something right next to him.

I'm not a math person either, generally speaking. Simple stuff sure, but forget the "theoretical math" as I like to call it.