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Author Topic: Posible to do an low frequences radio?  (Read 6986 times)
Shironia
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« on: August 22, 2008, 05:30:21 PM »
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Micro
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« Reply #1 on: October 15, 2008, 08:50:06 AM »
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Around here the police have frecuencies ower the FM band (88-108Mhz) on ~120mhz.
The police in the us also use some phones on the 450mhz band.
But my knowledge on us police bands is limitted. Now days scanners are nearly useless here as the pigs are using a encrypted digital network, like the gsm cellular one.

But in the us a scanner radio would be a good investment.
Also, don't forgret http://www.scanamerica.us/index.php
They stream trafic from police scanners to the net! "ScanAmerica: Live Police, Fire, and EMS Scanners"
 
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hydraliskdragon
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« Reply #2 on: March 03, 2009, 02:16:42 AM »
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There would be no cheap way to build a radio that has the capability to go into frequencies lower then A.M. Even if it was achieved, the main problem would be the limited encoding space that a signal has.

And example of this can be explained on a simple FM radio and AM radio. When we usually listen to the AM radio and then listen to a FM station, we can clearly see that FM has a much higher audio quality. The reason to this all lies in the distance of each wave length, and the amount of information that can be stored in a set frequency. The lower the frequency, the less information that is transmitted.

Now if we go into very low frequencies, it will become harder and harder to try to encode a certain message in that low frequency. Either you need to find a better way to encode this data (which requires more electronically components.) or have your radio quality so low that you won't be able to understand a thing that the opposite user is saying.
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« Reply #2 on: March 03, 2009, 02:16:42 AM »




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Micro
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« Reply #3 on: February 28, 2010, 01:55:02 PM »
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I dont get this talk about encoding, most of the older police radios are FM or AM (that's Frequency Modulation and Amplitude Modulation) ones to be used for voice transmission. And you can sen reasonable sounding voice as low as 300Khz.
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Probie715
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« Reply #4 on: June 20, 2013, 12:05:33 PM »
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The radio technology is rapidly developing, at least in the US. What you could us a scanner for 5 years ago is almost worthless now, unless you want to spend $500+ for a digital capable one. With the implementation of the P25 standard, some Phase 1 P25 systems can not be monitored, let alone transmitted on with conventional equipment.

Example is the county where I live, we currently operate on a VHF lowband system (33MHz), but are well on the way to switching to a T-Band trunked system (470MHz). This system is not able to be monitored with any scanner on the market today. The only way you can get a radio on the system to transmit is with a NAC (Network Access Code). Encryption is another layer of protection on top of the Trunked digital signal. The cost of a DES module is more than what the home technology brewer is willing to put into a DIY project.
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