P25RX vs. Airspy vs. RTL type SDR

[maus92]

I am still trying to understand the advantages of this device compared to other SDR + software solutions. I own several Nooelecs and two Airspys, and us several different software packages with generally excellent results. What does this device do that is superior to the other solutions I mentioned?

 

[btt]

Hi @maus92. The P25RX is a stand-alone device with hardware designed specifically for high-performance, narrow-band reception. The devices you mentioned require a PC or embedded PC and have wide-band inputs without narrow channel filters. The P25RX also has dual 17-bit A/D converters and superior symbol synchronization code that has been optimized for dealing with simulcast distortion. It is packaged in a small aluminum enclosure and supports Bluetooth audio. There is nothing wrong with the other solutions. This is another option.

 

[maus92]

@btt Thanks for responding so quickly. I like the fact that it is a standalone unit, but I am thinking it would require connection to a computer to exert complicated control over its functions via a software interface, and at the same time providing power and possible an audio interface. Any plans for control over BT or WiFi using an iOS device? I am also curious about its audio / decode quality, which I assume is roughly equivalent to OP25 - would this be a correct assumption?

 

[Mike_G_D]

@btt Thanks for responding so quickly. I like the fact that it is a standalone unit, but I am thinking it would require connection to a computer to exert complicated control over its functions via a software interface, and at the same time providing power and possible an audio interface. Any plans for control over BT or WiFi using an iOS device? I am also curious about its audio / decode quality, which I assume is roughly equivalent to OP25 - would this be a correct assumption?

Since Todd has likely knocked off for the night I'll take a stab at this...

I cannot speak toward the OP25 points as I have yet to try that - unfortunately for me I am Linux challenged though I have dived in numerous times.

As to the other aspects:

1) Extremely good audio! In my opinion, of course, BUT I have never been a big fan of P25 digital audio though I can tell the source vocoders keep getting better but still - not like, to my ear, "good ol analog FM". BUT this device comes soooooo close to the sound of full quieting narrowband FM. By that I mean the "old" +/- 5 kHz deviation narrowband FM and not the "new" +/- 2.5 kHz version. It is just amazing to me. Now, just for the record, I use the hardware line out port and NOT the Bluetooth audio, therefore I cannot comment on that feature.

2) It is powered from the USB port but, once initially programmed by a PC, it only needs DC power. I have powered it quite well with a simple external USB power source (USB battery).

3) To program it is a very simple process. I have used SDR's myself (have an AirSpy) and I have toyed with DSDPlus and SDRTrunk with the latter becoming my impending "favorite" UNTIL I stumbled on this device and took a chance with it. Once I did, I never looked back...The programming is simple and quick and pretty intuitive. Plus Todd (the developer of the hardware, firmware, and software) is VERY responsive which is a HUGE plus with me! He really listens to all input and you can tell he seriously cares! Yeah, I know, sounds corny but that is 100% my poor description and should not be used against him. I have no connection with Todd beyond being a fairly early user and receive no financial reward from my statements, positive or negative, whatsoever, just to dot that "i".

4) External control is currently limited to the USB port. It cannot be "controlled" by Bluetooth (or WiFi - as far as I know it has no WiFi capability at all) only stream out audio (and, I think, some system information) via Bluetooth. There are some who have been working on Android apps to interpret and display the trunk system information on an android device and RasPi devices and seem to have pretty good success doing so. Take a look at the other threads in this sub-forum concerning those. Plus, Todd has a display device available (when he can build them) which you can buy but you have to provide your own enclosure.

To the negatives:

1) Currently not really good at conventional non-trunked "scanning" - can monitor one frequency in P25 or analog FM alone but not much more. As I understand it, Todd is working on additional software to provide some traditional scanning capability but he is pretty swamped with all his other duties.

2) Does not go below 130 MHz - other radios can cover this and no US trunking currently below 150 MHz.

3) Does not fully cover the US T-Band UHF segment as it currently stops at 490 MHz rather than the full T-Band to 512 MHz. If your desired trunking system has frequencies between 490 MHz and 512 MHz this device won't work with it.

4) Though it is standalone there is no built in display nor a built-in audio power amplifier and speaker. It has line level and Bluetooth audio out only. An external display is available but without an enclosure. Other users with the knowledge needed have and are developing apps to display data and control the device. See the other threads in this sub-forum.

All-in-all in my opinion, this device is pretty amazing with fantastic audio and simulcast P25 P1 and P2 reception for well under the cost of either a Unication or Uniden alternative at the expense of conventional scanning capability and some portability aspects (display, keyboard, etc.).

The HUGE major plus to all of this is, simply put, Todd himself. He is pretty much a "one man show" (I am not privy to any details concerning any help he does have and would not expect to be) that does all hardware, firmware, and software development AND is the company "spokesperson" and representative.

Problem there is, of course, there can be delays at constructing new units and getting them sent to customers. But the patience involved is worth the wait.

-Mike

 

[WX4JCW]

Since Todd has likely knocked off for the night I'll take a stab at this...

I cannot speak toward the OP25 points as I have yet to try that - unfortunately for me I am Linux challenged though I have dived in numerous times.

As to the other aspects:

1) Extremely good audio! In my opinion, of course, BUT I have never been a big fan of P25 digital audio though I can tell the source vocoders keep getting better but still - not like, to my ear, "good ol analog FM". BUT this device comes soooooo close to the sound of full quieting narrowband FM. By that I mean the "old" +/- 5 kHz deviation narrowband FM and not the "new" +/- 2.5 kHz version. It is just amazing to me. Now, just for the record, I use the hardware line out port and NOT the Bluetooth audio, therefore I cannot comment on that feature.

2) It is powered from the USB port but, once initially programmed by a PC, it only needs DC power. I have powered it quite well with a simple external USB power source (USB battery).

3) To program it is a very simple process. I have used SDR's myself (have an AirSpy) and I have toyed with DSDPlus and SDRTrunk with the latter becoming my impending "favorite" UNTIL I stumbled on this device and took a chance with it. Once I did, I never looked back...The programming is simple and quick and pretty intuitive. Plus Todd (the developer of the hardware, firmware, and software) is VERY responsive which is a HUGE plus with me! He really listens to all input and you can tell he seriously cares! Yeah, I know, sounds corny but that is 100% my poor description and should not be used against him. I have no connection with Todd beyond being a fairly early user and receive no financial reward from my statements, positive or negative, whatsoever, just to dot that "i".

4) External control is currently limited to the USB port. It cannot be "controlled" by Bluetooth (or WiFi - as far as I know it has no WiFi capability at all) only stream out audio (and, I think, some system information) via Bluetooth. There are some who have been working on Android apps to interpret and display the trunk system information on an android device and RasPi devices and seem to have pretty good success doing so. Take a look at the other threads in this sub-forum concerning those. Plus, Todd has a display device available (when he can build them) which you can buy but you have to provide your own enclosure.

To the negatives:

1) Currently not really good at conventional non-trunked "scanning" - can monitor one frequency in P25 or analog FM alone but not much more. As I understand it, Todd is working on additional software to provide some traditional scanning capability but he is pretty swamped with all his other duties.

2) Does not go below 130 MHz - other radios can cover this and no US trunking currently below 150 MHz.

3) Does not fully cover the US T-Band UHF segment as it currently stops at 490 MHz rather than the full T-Band to 512 MHz. If your desired trunking system has frequencies between 490 MHz and 512 MHz this device won't work with it.

4) Though it is standalone there is no built in display nor a built-in audio power amplifier and speaker. It has line level and Bluetooth audio out only. An external display is available but without an enclosure. Other users with the knowledge needed have and are developing apps to display data and control the device. See the other threads in this sub-forum.

All-in-all in my opinion, this device is pretty amazing with fantastic audio and simulcast P25 P1 and P2 reception for well under the cost of either a Unication or Uniden alternative at the expense of conventional scanning capability and some portability aspects (display, keyboard, etc.).

The HUGE major plus to all of this is, simply put, Todd himself. He is pretty much a "one man show" (I am not privy to any details concerning any help he does have and would not expect to be) that does all hardware, firmware, and software development AND is the company "spokesperson" and representative.

Problem there is, of course, there can be delays at constructing new units and getting them sent to customers. But the patience involved is worth the wait.

-Mike

What he said

 

[btt]

Any plans for control over BT or WiFi using an iOS device?

Currently no plans for this. It would be possible in theory. The Bluetooth module can be programmed to have WiFi capability instead of the Bluetooth audio, but the current firmware only supports A2DP source (nearly all speaker devices work fine), and AVRC for lcd panel display (very few devices work with this so far. See the user manual for a list).

I am also curious about its audio / decode quality, which I assume is roughly equivalent to OP25 - would this be a correct assumption?

I'm not familiar with OP25 audio quality yet, but I would assume it is similar. One thing that may be different with the P25RX regarding audio quality compared to other solutions is that the 8 kHz audio samples are re-sampled to 48 kHz and low-pass filtered. The audio is also passed through an audio automatic-gain-control. The quality of the mics on the transmitters, the environment, and the speaker all can have a large impact on the final quality, but it can sound very good.

 

[goldmyne99]

I like the fact that it is a standalone unit, but I am thinking it would require connection to a computer to exert complicated control over its functions via a software interface, and at the same time providing power and possible an audio interface. Any plans for control over BT or WiFi using an iOS device?

Like many on this forum, I took a chance on the P25RX after using rtl-sdr software. My favorite is SDR Trunk. The P25RX gives the user mobile and handheld operation that sdr software may not.

I have not had my P25RX connected to a PC for over a month. That was to update firmware.

The P25RX offers a starting point for experimenting, if that is your thing. That is the main reason I bought the P25RX. I have had great success controling the P25RX via serial USB with both Android and Arduino devices.

As example, I built my Arduino/Teensy 4.0 mcu "handheld" complete stand alone unit for less than $80 in parts (mcu, touch screen, audio amp, speaker, battery, and case). I have very limited programming skills, so I would not say it is complicated to control the P25RX.

I have no connection to BTT. I am just a customer enjoying my P25RX.

 

[Cheeseburgers]

p25rx is the best for me, period. excellent audio, portable, and tbh i look forward to Todd's messages regarding firmware / feature updates. Really an incredible value.

 

[maus92]

Are there any band width limitations with this receiver? For example, there are several systems that I monitor that have system frequencies that range from 851.xxx to 860.xxx, and another that uses both 700 and 800 channels. In these cases, I must use at least two physical SDRs to cover the system: one locked on the cch, and the other free to tune any system channel.

 

[goldmyne99]

The P25RX user manual has very detailed specs and can be downloaded from the P25RX web page.

Frequency Coverage Summary
130 to 245 continous coverage P25 VHF
256 to 327 continous coverage P25 VHF/UHF
380 to 490 continous coverage P25 UHF
763 to 824 continous coverage P25 UHF
849 to 869 continous coverage P25 UHF
894 to 960 continous coverage P25 UHF

 

[maus92]

Info from the P25RX web page:

Frequency Coverage Summary
130 to 245 continous coverage P25 VHF
256 to 327 continous coverage P25 VHF/UHF
380 to 490 continous coverage P25 UHF
763 to 824 continous coverage P25 UHF
849 to 869 continous coverage P25 UHF
894 to 960 continous coverage P25 UHF

Unfortunately, this presentation of data doesn't answer my question specifically. Can the receiver decode a control channel and a voice channel simultaneous when the system frequencies are widely separated? Does the receiver leave the cch momentarily to tune a voice channel (and its subchannel data stream) as does OP25; are there actually two receivers: one dedicated to the cch and one to the traffic channel; or is the receiver design wideband enough for VFOs to tune frequencies seperated by 8-10 MHz or more in the case of 700/800 systems? "Continuous coverage" means something else in the context of "Frequency Coverage Summary" spec mentioned in the P25RX webpage.

 

[goldmyne99]

I'm sorry. I now understand your question. Todd will need to address how the firmware functions.

 

[btt]

Unfortunately, this presentation of data doesn't answer my question specifically. Can the receiver decode a control channel and a voice channel simultaneous when the system frequencies are widely separated? Does the receiver leave the cch momentarily to tune a voice channel (and its subchannel data stream) as does OP25; are there actually two receivers: one dedicated to the cch and one to the traffic channel; or is the receiver design wideband enough for VFOs to tune frequencies seperated by 8-10 MHz or more in the case of 700/800 systems? "Continuous coverage" means something else in the context of "Frequency Coverage Summary" spec mentioned in the P25RX webpage.

As mentioned earlier in the thread, the P25RX is a narrowband design. It receives a single filtered channel at a time. There really is no need to receive the control channel and voice channels simultaneously on a trunked system. The voice channels contain information about adjacent active channels. Think of it like an embedded control channel within the voice channel. This is how the "priority interrupt" feature on the P25RX works. In the case where you might want to receive audio from multiple traffic channels simultaneously, you would need two receivers. Currently, the P25RX does support monitoring of multiple trunked systems in different bands via the roaming feature.

 

[maus92]

As mentioned earlier in the thread, the P25RX is a narrowband design. It receives a single filtered channel at a time. There really is no need to receive the control channel and voice channels simultaneously on a trunked system. The voice channels contain information about adjacent active channels. Think of it like an embedded control channel within the voice channel. This is how the "priority interrupt" feature on the P25RX works. In the case where you might want to receive audio from multiple traffic channels simultaneously, you would need two receivers (with the exception of TDMA). Currently, the P25RX does support monitoring of multiple trunked systems in different bands via the roaming feature.

OK, so the answer is P25RX uses one radio / VFO, and uses the subchannel data stream on an active traffic channel to maintain connectivity with the system. This is what OP25 does, hence the reason why it only uses / needs one SDR. There is some argument that this approach is inferior to always reading cch data, but for "tracking" a conversation, this is adequate because it works. If one were interested in accurately logging control channel data as well as decoding voice, then this approach would likely not be adequate.

So when will more radio hardware be available?