Which Radio to Monitor HOT / EOT / DPU at Same Time?

[PoorInRichfield]

The following setup is something I'm testing based on the feedback from someone in the SoftEOT app group. Using AirSpy's SDR# application and the AirSpy R2 SDR

Requirements

• Software
  • AirSpy SDR #
    • Frequency Manager + Scanning extension
  • SoftEOT / SoftDPU
  • Virtual Audio Cable (VAC) or VB-Audio Virtual Cable (Free for 1 cable)
• Hardware
  • AirSpy R2 SDR
    • Any SDR with more than 5 Mhz of useable bandwidth should work. The R2 has 10 Mhz where as the less expensive SDRs, like the RTL-SDR V4 have less than 3 Mhz of bandwidth which won't work.
  • Windows 11 laptop with considerable processing power
    • Note that AirSpy SDR# is also available in a Linux flavor for possible Raspberry Pi installation. I have not tried this.
  • Antenna tuned for 455 Mhz range

Setup
This setup takes advantage of the "Frequency Manager + Scanning" extension to SDR# which allows for defining a group of frequencies and then scanning (or "frequency hopping") between each frequency until something is detected. This is a feature common to normal hardware scanners but isn't so common in SDR applications.

Since SDR # will stop on a single frequency and send it through the virtual audio cable, one only needs the single virtual audio cable since this setup isn't trying to stuff data from 6 frequencies through the pipe like my previous setup does.

I'm currently experimenting with this setup and so far I've successfully captured some HOT and EOT signals from a northbound Canadian National train. That's a promising sign as those two frequencies are 5 Mhz apart (thus the need for the higher-end AirSpy R2 SDR).



This same setup is apparently possible with the SDRPlay RSP1B SDR and SDRuno software. However, the SDRuno software only enables the scanning feature for SDRPlay SDRs, so I have not tried this setup to confirm that it works.

 

[oaktree_b]

That's quite the setup, sure is the next level after using the old Uniden Bearcat and guessing what the beeps mean. Nice job.

 

[PoorInRichfield]

A third potential solution to listening to the HOT / EOT / DPU frequencies with a single dongle. A member of the SoftEOT Group.io group is using this setup with good success:

Requirements

• Software
  • SDRuno
  • SoftEOT / SoftDPU
  • Virtual Audio Cable (VAC) or VB-Audio Virtual Cable (Free for 1 cable)
• Hardware
  • SDRplay RSPduo
    • This SDR is unique in that it has two outputs for a single antenna input. It's essential the same as buying two SDRs and a splitter (powered?) all in one package.
  • Windows 11 laptop with considerable processing power
  • Antenna tuned for 455 Mhz range

Setup
This setup takes advantage of the SDRplay's RSPduo dongle that has one antenna input and two outputs. With this SDR, one output is focused on scanning between the HOT and EOT frequencies using it's own instance of SRDuno (an SDR app that only works with SDRplay hardware) feeding to SoftEOT. The second output is focused on the 4 DPU frequencies and it's own instance of SDRuno feeding to SoftDPU.

This is the most expensive setup so far due to the cost of the SDRplay RSPduo dongle, but the software setup is almost as simple as the AirSpy R2 setup previously posted. The advantage of this setup is that one will likely miss few HOT or EOT signals if the train happens to have one or more chatty DPUs (of which I have observed that some DPUs emit frequent telemetry signals).

 

[va2dg]

Yeah, these channels certainly don't help detect train direction or that the train is even moving, but once ATCS goes dark, "something is better than nothing".

Yes it does tell you if the train is moving or not with the SoftEOT software running on my PC and i feed it with a Baofeng UV5X3 hooked up on a dual band antenna at 50' with only EOT and HOT frequency in scanmode.
I live 3km for the CN track and when the train passing by or siting in the siding waiting i see the EOT tell me the train is moving or not, and i see also Brake air pressure either in the 80 psi or 0 when parcked.
If you just listen to the audio you just know it is nearby but with the Software you see all the data. Data received on SoftEOT is matching when i hear the Local Hotbox talking.
Daniel, VA2DG
Montreal

 

[PoorInRichfield]

Yes it does tell you if the train is moving or not with the SoftEOT software running on my PC and i feed it with a Baofeng UV5X3 hooked up on a dual band antenna at 50' with only EOT and HOT frequency in scanmode.
I live 3km for the CN track and when the train passing by or siting in the siding waiting i see the EOT tell me the train is moving or not, and i see also Brake air pressure either in the 80 psi or 0 when parcked.
If you just listen to the audio you just know it is nearby but with the Software you see all the data. Data received on SoftEOT is matching when i hear the Local Hotbox talking.
Daniel, VA2DG
Montreal

Yes, correct. Apparently the "MOT" flag indications 1 if moving, 0 if not. For some odd reason I find that this flag often doesn't decode on the CN near me.

 

[PoorInRichfield]

Due to an SDR# configuration error on my part, I discovered one doesn't actually need a more expensive SDR like the AirSpy R2 in order to use the scanning feature of the SDR# "Frequency Manager + Scanning" plugin. Hence, the diagram below is by far the most cost-effective way to scan all 6 train telemetry frequencies and catch most of them. (With scanning, if more than one signal happens at the same time, one or all of them could be missed.)

Requirements

• Software
  • AirSpy SDR #
    • Frequency Manager + Scanning extension
  • SoftEOT / SoftDPU
  • Virtual Audio Cable (VAC) or VB-Audio Virtual Cable (Free for 1 cable)
• Hardware
  • RTL-SDR Blog V4 SDR
    • Any low-priced SDR with ~3 Mhz bandwidth will likely work. There are multiple other brands on Amazon such as those by Nooelec that should also work.
  • Windows 11 laptop with considerable processing power
    • Note that AirSpy SDR# is also available in a Linux flavor for possible Raspberry Pi installation. I have not tried this.
  • Antenna tuned for 455 Mhz range

Setup
This setup takes advantage of the "Frequency Manager + Scanning" extension to SDR# which allows for defining a group of frequencies and then scanning (or "frequency hopping") between each frequency until something is detected. This is a feature common to normal hardware scanners but isn't so common in SDR applications.

Important: Set the "Minimum Signal Strength" setting in the "Frequency Manager + Scanning" plugin to a value that prevents the noise floor static from stopping the scanner. If this value is set to low, the scanner won't scan... it'll just stay on one frequency because it's "hearing something".

Since SDR # will stop on a single frequency when it detects a signal and send it through the virtual audio cable, thus one only needs the single virtual audio cable.