How many Nooelec v5's do I need for this P25 Phase 1 system

[KN4ERY]

Hello all, I am looking to use an old laptop and sdr dongles to monitor my university's PD and public safety frequencies, which are part of a larger county-wide single site simulcast P25 Phase I system, on the cheap since I am on staff at the student newspaper there. I was wondering, if my SDR of choice is the nooelec v5, how many I would need to adequately monitor the feed? Also, if anyone has any good 850mhz SMA antenna recommendations I'd welcome those. Thanks!

RR link, interested in the Emory University group of channels: DeKalb County Public Safety P25 Trunking System, DeKalb County, Georgia

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[KevinC]

Hello all, I am looking to use an old laptop and sdr dongles to monitor my university's PD and public safety frequencies, which are part of a larger county-wide single site simulcast P25 Phase I system, on the cheap since I am on staff at the student newspaper there. I was wondering, if my SDR of choice is the nooelec v5, how many I would need to adequately monitor the feed? Also, if anyone has any good 850mhz SMA antenna recommendations I'd welcome those. Thanks!

RR link, interested in the Emory University group of channels: DeKalb County Public Safety P25 Trunking System, DeKalb County, Georgia

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If they truly do 3.2 MHz then you'd need 2.

Take the difference between the highest and lowest system frequencies and divide that by the bandwidth of the SDR.

 

[KN4ERY]

If they truly do 3.2 MHz then you'd need 2.

Take the difference between the highest and lowest system frequencies and divide that by the bandwidth of the SDR.

Ah thank you! I'll try those two. For a single site system like this, is there only one active control frequency at a time or are all three frequencies marked as "control channel capable" active at once? If the latter is true, would I need three SDRs if I'm using SDRtrunk?

 

[KevinC]

Ah thank you! I'll try those two. For a single site system like this, is there only one active control frequency at a time or are all three frequencies marked as "control channel capable" active at once? If the latter is true, would I need three SDRs if I'm using SDRtrunk?

Only one active CC per site.

 

[AB5ID]

Hello all, I am looking to use an old laptop and sdr dongles to monitor my university's PD and public safety frequencies, which are part of a larger county-wide single site simulcast P25 Phase I system, on the cheap since I am on staff at the student newspaper there. I was wondering, if my SDR of choice is the nooelec v5, how many I would need to adequately monitor the feed? Also, if anyone has any good 850mhz SMA antenna recommendations I'd welcome those. Thanks!

RR link, interested in the Emory University group of channels: DeKalb County Public Safety P25 Trunking System, DeKalb County, Georgia

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You could use just one dongle with op25 and Linux.

 

[KN4ERY]

You could use just one dongle with op25 and Linux.

Thanks! If you don’t mind me asking, how does op25 purport to cover the whole bandwidth of the system if one dongle is limited to 3.2 MHz? Would it be able to monitor two channels at once?

 

[boatbod]

Thanks! If you don’t mind me asking, how does op25 purport to cover the whole bandwidth of the system if one dongle is limited to 3.2 MHz? Would it be able to monitor two channels at once?

OP25 doesn't purport anything; it absolutely is capable of producing a single voice stream from an arbitrary P25 system using a single dongle irrespective of the system or dongle bandwidth.

The "how" is simple; P25 systems transmit group voice grant and group voice update messages alongside the voice frames, so regardless of whether the op25 app is monitoring a control channel or voice channel, it always knows exactly what is going on across the entire system. Decisions can then be made real-time whether to continue monitoring the existing voice stream, or switch to a higher priority tgid etc.

If there is a need to monitor multiple simultaneous voice streams, you just add another dongle (or as many as you want simultaneous streams) and it all integrates together using the shared view of system activity. There is total flexibility to use a mix of narrow-band sdr (RTL) and wide-band SDR (e.g. Airspy/RSP/...) for reduced dongle count if you'd like to monitor multiple overlapping P25 systems or other complex scenarios.

 

[jasonk]

Hello all, I am looking to use an old laptop and sdr dongles to monitor my university's PD and public safety frequencies, which are part of a larger county-wide single site simulcast P25 Phase I system, on the cheap since I am on staff at the student newspaper there. I was wondering, if my SDR of choice is the nooelec v5, how many I would need to adequately monitor the feed? Also, if anyone has any good 850mhz SMA antenna recommendations I'd welcome those. Thanks!

RR link, interested in the Emory University group of channels: DeKalb County Public Safety P25 Trunking System, DeKalb County, Georgia

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Heres a tool we have developed - just paste all of the frequencies and it will determine the number needed and the proper spacing - avoiding any of the Control Channels. https://alertapi.alertpage.net/sdr/