I'm not really sure where I'm going with this, as I think there may be many possibilities going on here (imaging, bleed over, un-selectivity?). I'm not new to scanning but I am certainly not a veteran either, as you will probably realize by my post.
A little background information, I am an undergrad student located in Newark NJ and I am using a Radioshack Pro-97 and Uniden BC796D.
I was listening to the FRS/GMRS/MURS frequencies with my Pro-97 today when I overheard, quasi-clearly, what sounded like a police dispatcher talking on 462.5875 MHz (FRS Channel 02). I soon recognized the dispatcher's voice because I had been recently listening to the Newark North Precinct (KRI750 460.1250 MHz PL 123.0) The signal was weak, but I could clearly distinguish the transmission. I think I am located close to the KRI750 repeater (within a half-mile). I flipped on my BC796D and set it to the North Precinct. Sure enough the transmissions were in sync, but the one coming in on the FRS channel was certainly less powerful. The Pro-97 has no S-Meter but the Uniden does have a digital 6-bar S-Meter, and police frequency always comes in 100% so I must be very close to the repeater.
I fiddled around with the search range on my Pro-97 and found I can pick up the transmission on:
460.12500 MHz (the center frequency)
+/- 2.38750 MHz @ 462.51250 & 457.73750
+/- 2.45625 MHz @ 462.58125 & 457.66875
+/- 2.46250 MHz @ 462.58750 & 457.66250
Possibly others but I gave up at this point and decided it was time to ask the kind people on RR.com!
When I try 462.5875 MHz on my Uniden, I cannot hear them even with the squelch open...
I am really interested to figure out what is going on here because I have had some doubts about my Pro-97 in the past. I don't have enough experience with receivers to know if this is totally normal or possibly a defect with the Pro-97.
The FCC Database says the power output for the KRI750 repeater is 110.0 (Watts?) and maximum ERP is 220.0 (units?)
Here is some additional information I found in my Pro-97 manual that might assist anybody interested in explaining this to me! =D
Radioshack Pro-97
Sensitivity (20 dB S/N):
FM:
406–512 MHz ....................... 0.5 µV
Selectivity:
All frequencies at AM and FM mode except 25 – 27.995 MHz at AM
–6 dB ............................. ±10 kHz
–50 dB ............................ ±18 kHz
Intermediate Frequencies (IF):
1st ............................... 380.8 MHz
2nd ............................... 21.4 MHz
3rd ............................... 455 kHz
IF Rejection:
380.8 MHz at 154.1 MHz ............ 60 dB
21.4 MHz at 154.1 MHz ............. 100 dB
The Uniden BC796D does not give any of this information in the specifications, nor could I find any information on the web.
Antennas
BC796D - Stock collapsible whip antenna fully extended.
Radioshack Pro-97 - Radioshack Center Loaded Collapsible whip antenna tuned to about 1/4 wave of 450Mhz as recommended in the instructions.
On a side note, I've also had interference between public safety frequencies. For example, the police in Newark are separated on channels such as 460.1250 MHz, 460.1500 MHz and 460.1750 MHz (25kHz between channels). If I tune to ANY of the three, I can hear both the other two (at about half power according to the S-Meter and my ear) on both my Pro-97 and my Uniden BC796D. I can't believe that BOTH could be defective. Thank god for CTCSS tones!
According the my Pro-97 specifications, the receiver attenuates the nearby frequencies by -50dB @ +/- 18kHz. These frequencies are 25kHz and 50kHz away from the one I am tuned to, so why am I still hearing them? Do these police channels really use than much bandwidth?
Ok so I know all of that is a lot of information, and I probably should break it up into more than one post, but my main question here is:
Why can I hear Newark PD on FRS channel 02? And why only with the Pro-97, but not with the Uniden?
A little background information, I am an undergrad student located in Newark NJ and I am using a Radioshack Pro-97 and Uniden BC796D.
I was listening to the FRS/GMRS/MURS frequencies with my Pro-97 today when I overheard, quasi-clearly, what sounded like a police dispatcher talking on 462.5875 MHz (FRS Channel 02). I soon recognized the dispatcher's voice because I had been recently listening to the Newark North Precinct (KRI750 460.1250 MHz PL 123.0) The signal was weak, but I could clearly distinguish the transmission. I think I am located close to the KRI750 repeater (within a half-mile). I flipped on my BC796D and set it to the North Precinct. Sure enough the transmissions were in sync, but the one coming in on the FRS channel was certainly less powerful. The Pro-97 has no S-Meter but the Uniden does have a digital 6-bar S-Meter, and police frequency always comes in 100% so I must be very close to the repeater.
I fiddled around with the search range on my Pro-97 and found I can pick up the transmission on:
460.12500 MHz (the center frequency)
+/- 2.38750 MHz @ 462.51250 & 457.73750
+/- 2.45625 MHz @ 462.58125 & 457.66875
+/- 2.46250 MHz @ 462.58750 & 457.66250
Possibly others but I gave up at this point and decided it was time to ask the kind people on RR.com!
When I try 462.5875 MHz on my Uniden, I cannot hear them even with the squelch open...
I am really interested to figure out what is going on here because I have had some doubts about my Pro-97 in the past. I don't have enough experience with receivers to know if this is totally normal or possibly a defect with the Pro-97.
The FCC Database says the power output for the KRI750 repeater is 110.0 (Watts?) and maximum ERP is 220.0 (units?)
Here is some additional information I found in my Pro-97 manual that might assist anybody interested in explaining this to me! =D
Radioshack Pro-97
Sensitivity (20 dB S/N):
FM:
406–512 MHz ....................... 0.5 µV
Selectivity:
All frequencies at AM and FM mode except 25 – 27.995 MHz at AM
–6 dB ............................. ±10 kHz
–50 dB ............................ ±18 kHz
Intermediate Frequencies (IF):
1st ............................... 380.8 MHz
2nd ............................... 21.4 MHz
3rd ............................... 455 kHz
IF Rejection:
380.8 MHz at 154.1 MHz ............ 60 dB
21.4 MHz at 154.1 MHz ............. 100 dB
The Uniden BC796D does not give any of this information in the specifications, nor could I find any information on the web.
Antennas
BC796D - Stock collapsible whip antenna fully extended.
Radioshack Pro-97 - Radioshack Center Loaded Collapsible whip antenna tuned to about 1/4 wave of 450Mhz as recommended in the instructions.
On a side note, I've also had interference between public safety frequencies. For example, the police in Newark are separated on channels such as 460.1250 MHz, 460.1500 MHz and 460.1750 MHz (25kHz between channels). If I tune to ANY of the three, I can hear both the other two (at about half power according to the S-Meter and my ear) on both my Pro-97 and my Uniden BC796D. I can't believe that BOTH could be defective. Thank god for CTCSS tones!
According the my Pro-97 specifications, the receiver attenuates the nearby frequencies by -50dB @ +/- 18kHz. These frequencies are 25kHz and 50kHz away from the one I am tuned to, so why am I still hearing them? Do these police channels really use than much bandwidth?
Ok so I know all of that is a lot of information, and I probably should break it up into more than one post, but my main question here is:
Why can I hear Newark PD on FRS channel 02? And why only with the Pro-97, but not with the Uniden?