SDR# ATCS Monitor - Capturing MCP Data at Two Nearby Frequencies

[PoorInRichfield]

I'm using an RTL-SDR v4 dongle with SDR# too capture signals from two nearby MCPs for a mobile ATCS Monitor setup to know when trains are coming. Both MCPs are about 1 mile from my location and I am able to receive signals from both using the dipole antenna that came with the dongle. However, I can only get ATCS monitor to read from one MCP at a time unless I tweak the frequency in SDR#. I'm wondering if there's a setting I'm missing that will allow SDR# to pick-up both nearby frequencies w/o having to manually move between the two.

To clarify, these are the two MCP frequencies I'm listening to which are both on the same rail line and both about 1 mile from my house:

• South Rugby: 896.990 or 896.9875 w/ -3 ppm correction
• North Rugby: 896.895 or 896.9875 w/ -2 ppm correction

As you can see, both frequencies are pretty close to each other and I would've thought they'd be exactly the same because they are both for the same railroad on the same line and both should be 896.9875, but I digress. I can only pick-up one MCP or the other if I change the frequency slightly in SDR# or change the frequency correction (ppm) setting from -2 to -3 if I use the same frequency.

Is there a setting in SDR# that I can change so that both MCPs can be read w/o changing the frequency or the frequency correction settings?

 

[UPCoffeyvilleSubMain2]

My experience with the MCPs in my own local listening post is that they all talk on the same frequency, 932.36875 and they are polled one at a time, about a half second apart.

I don't have ton of experience with this but I've never had the need to monitor multiple mcp frequencies.

What is your bandwidth setting? I'm using 12500 hz and the mcp transmissions pretty much cover the whole 12500 with a little room to spare.

I would think that widening the bandwidth a little should help improve yourreception with a slight cost in additional noise due to it being FM.

I'm using the NooElec SMArt v5 and cubicSDR as the driver on the laptop with some serious yagi antennas pointing in the correct directions..

Two mcps on the same freq are no problem with this setup, they chime in a fraction of a second apart.

Let me know what you think.

 

[PoorInRichfield]

My experience with the MCPs in my own local listening post is that they all talk on the same frequency, 932.36875 and they are polled one at a time, about a half second apart...

Thank you for the reply. I had at least one other person on the ATCS Monitor forum confirm that not all MCPs communicate on the frequency that they should, with some MCPs having a slight offset like I experienced which makes things challenger for reading the signals. Using SDR#, I was told to use 12.5Khz for the bandwidth setting as well and tried bumping that up to a wider swath to try and capture both of the MCPs near me, but so for I've had no success with getting that to work. I even went trackside where I was almost within line-of-site of both MCPs and that didn't improve anything.

I'm guessing that with SDR#, I could purchase a second SDR to pick-up the other MCP frequency, but I'm trying to minimize costs on this "ATCS backup system" that I'm experimenting with, especially knowing that the railroads will likely switch to digital someday and render ATCS Monitor itself useless at some point.

 

[UPCoffeyvilleSubMain2]

Hi,

Lately I've noticed the MCP radio needs to have the gain set pretty low in order to capture the both MCPs that I do receive.

It appears that either the radio is clipping when the MCP with the stronger signal is received, resulting in loss of some packets due to distortion, or the weaker MCP signal is drowned out by the stronger signal that is received a fraction of a second before the stronger signal.

So I try to set the gain as low as possible and I have much better results with that.

With very low gain there are two visible bursts of similar but not identical shapes every poll cycle, which I do not see when gain is turned up

I do have AGC active but Digital AGC inactive.

CubicSDR 2.6 that I use has the capability of a high CPU usage setting whihc it says does more Digital Signal Processing than the normal setting, which also seems to help. It happens this laptop which only runs the radios and Protocol Monitor has plenty of available CPU.

Good luck.