Railfan Technology > Railroad UHF Signal Range, Observations and Questions

For the past 5+ years I've relegated my 20 year old Yeasu VX-170 to the car, as the NiMH batteries no longer hold a charge. This radio, plugged into a 12V accessory port, works just fine for monitoring the AAR VHF road channels using a roof mounted 1/2 wave antenna on top of my car.

Wanting to have something small and portable to clip to my camera backpack while away from the car, last year I picked up a Yeasu FT-4XR radio which was on sale. I replaced the stock antenna with a light, flexible, Comet SMA-24J Dual-Band HT antenna. I also bought an extra battery, and I'm hopeful the Li-ion batteries for this unit will last me for years to come and perform better over time than the NiMH batteries for the VX-170.

I recently tapped into an added bonus that the FT-4XR provides compared to the VX-170. The new radio is capable of dual band VHF/UHF monitoring capabilities. This allows for monitoring of HOTD, EOTD, and DPU frequencies in the 452-457 MHz range. I'm lamenting not tapping into this capability sooner, as it's so straightforward to program this little radio's memory channels for dual band scanning of both AAR road frequencies and train telemetry frequencies.

I'm almost exclusively using this radio on Donner Pass, predominantly around Donner Summit. Based on what I've been able to uncover regarding monitoring of UHF train telemetry signals on this site and others, the typical range is 2-6 miles. I understand that this is fairly terrain dependent due to attenuation of these signals. I have been surprised at the distance I've been picking up these signals, however, especially when considering the fact that there are often mountains, trees, glacial moraine, etc., obstructing my line-of-site between the trains and radio. As I've been playing around with this over the past week and a half, I've picked up trains on the east slope of Donner Pass coming up from Truckee while at my cabin on the west side of the Summit. It is ~5 miles straight line from my cabin to the east portal of Tunnel 41, with Mt Judah between the locations, and I'm sure the trains I've started picking up are closer to Truckee and further away than 5 miles. I'm getting similar results with eastbound trains, picking up signals long before they hit the defect detector at Troy 3.6 miles away. I was really impressed yesterday morning when I was receiving pings from an eastbound train approaching Emigrant Gap while I was at Cisco, approximately 7.5 miles straight-line distant. I am, in many of these situations at elevations above or below the train which is potentially beneficial to improving my chances of reception.

So, I'm curious if others have seen results like this in mountainous terrain. If so, how far have you been able to get a signal, and what type of equipment/setup have you used? Also, do railroads increase the broadcast power or use repeaters for train telemetry equipment in mountainous terrain like Donner Pass due to restrictions of tunnels, trees, terrain, etc.? I have noticed an array of different antennas around tunnel portals on Donner which appear to be folded dipole designs. Is it possible that these antennas are boosting the train signals and are therefore responsible for why I'm able to pick up trains from such relatively long distances? Is it unusual that I could have a better chance of picking up UHF train telemetry signals versus the VHF signals from a defect detector that is closer by? Any insights into this would be welcomed and appreciated, as I'm relatively new to and ignorant about this technology.

Thanks,
Sean

in brief, yes. ground based repeaters and other locations for the EOT frequencies but also in the DPU equipment.

not real sure the dpu frequency goes thru the repeaters at every location but it would make sense and has been in the past. theres also in house data that would archived or networked.

check whether you are receiving the eot or the dpu. nearby frequecies but they can be handled seperatly.

theres comments in the archives about chasing with dpu and eot channels. its pretty useless in dense areas but works great in the right conditions.

i've been using an ft-60. note that the battery packs can found on amazon.

hope that helps.



Edited 1 time(s). Last edit at 06/20/25 18:07 by TCnR.

Thank you for the reply.

I programmed the scanner memory channels with names for HOTD, EOTD, and DPU1 through DPU4 for their respective frequencies. I'm therefore able to discern that I am receiving signals for all of these configurations when scanning the memory banks when I get hits. (I've similarly programmed the AAR voice/road channels with the memory number corresponding to the AAR channel number and then name them accordingly.) It's actually kind of cool when there have been multiple trains in the area, as I've had hits for different DPU channels nearly simultaneously, confirming the presence of multiple trains.

broken_link Wrote:
-------------------------------------------------------
> For the past 5+ years I've relegated my 20 year
> old Yeasu VX-170 to the car, as the NiMH batteries
> no longer hold a charge. This radio, plugged into
> a 12V accessory port, works just fine for
> monitoring the AAR VHF road channels using a roof
> mounted 1/2 wave antenna on top of my car.
>
> Wanting to have something small and portable to
> clip to my camera backpack while away from the
> car, last year I picked up a Yeasu FT-4XR radio
> which was on sale. I replaced the stock antenna
> with a light, flexible, Comet SMA-24J Dual-Band HT
> antenna. I also bought an extra battery, and I'm
> hopeful the Li-ion batteries for this unit will
> last me for years to come and perform better over
> time than the NiMH batteries for the VX-170.
>
> I recently tapped into an added bonus that the
> FT-4XR provides compared to the VX-170. The new
> radio is capable of dual band VHF/UHF monitoring
> capabilities. This allows for monitoring of HOTD,
> EOTD, and DPU frequencies in the 452-457 MHz
> range. I'm lamenting not tapping into this
> capability sooner, as it's so straightforward to
> program this little radio's memory channels for
> dual band scanning of both AAR road frequencies
> and train telemetry frequencies.
>
> I'm almost exclusively using this radio on Donner
> Pass, predominantly around Donner Summit. Based on
> what I've been able to uncover regarding
> monitoring of UHF train telemetry signals on this
> site and others, the typical range is 2-6 miles. I
> understand that this is fairly terrain dependent
> due to attenuation of these signals. I have been
> surprised at the distance I've been picking up
> these signals, however, especially when
> considering the fact that there are often
> mountains, trees, glacial moraine, etc.,
> obstructing my line-of-site between the trains and
> radio. As I've been playing around with this over
> the past week and a half, I've picked up trains on
> the east slope of Donner Pass coming up from
> Truckee while at my cabin on the west side of the
> Summit. It is ~5 miles straight line from my cabin
> to the east portal of Tunnel 41, with Mt Judah
> between the locations, and I'm sure the trains
> I've started picking up are closer to Truckee and
> further away than 5 miles. I'm getting similar
> results with eastbound trains, picking up signals
> long before they hit the defect detector at Troy
> 3.6 miles away. I was really impressed yesterday
> morning when I was receiving pings from an
> eastbound train approaching Emigrant Gap while I
> was at Cisco, approximately 7.5 miles
> straight-line distant. I am, in many of these
> situations at elevations above or below the train
> which is potentially beneficial to improving my
> chances of reception.
>
> So, I'm curious if others have seen results like
> this in mountainous terrain. If so, how far have
> you been able to get a signal, and what type of
> equipment/setup have you used? Also, do railroads
> increase the broadcast power or use repeaters for
> train telemetry equipment in mountainous terrain
> like Donner Pass due to restrictions of tunnels,
> trees, terrain, etc.? I have noticed an array of
> different antennas around tunnel portals on Donner
> which appear to be folded dipole designs. Is it
> possible that these antennas are boosting the
> train signals and are therefore responsible for
> why I'm able to pick up trains from such
> relatively long distances? Is it unusual that I
> could have a better chance of picking up UHF train
> telemetry signals versus the VHF signals from a
> defect detector that is closer by? Any insights
> into this would be welcomed and appreciated, as
> I'm relatively new to and ignorant about this
> technology.
>
> Thanks,
> Sean

First, to my knowledge, the UHF train telemetry signals are not generally  "repeated", with just one significant exception that I will get to in a minute.  UHF train telemetry is not used for any other purpose than to allow the controlling locomotive to communicate with the DPUs  and the EOT device on its own train.  So, a range of  about 2-4 miles, give or take, will allow that communication, even with today's 2 mile-plus-long monster trains.  That sole exception is tunnels--in those what is commonly referred to as  "leaky antennas" are used, basically  wires running the length of the tunnel to receive and re-transmit (via a small repeater) radio signals within the tunnel.  UHF, even more than VHF, is a line-of-sight signal that does not "bend" well.  Because its signal width is smaller, a UHF signal  can travel through smaller openings (that is why police and fire departments often use UHF in urban areas because the signal will pass through smaller diameter doors and windows, etc.), but it won't bend around physical obstructions very well.   By the way, cellular telephone signals (and most P25 digital radio channels) are even higher up in the UHF frequency range and will go through very small openings, but are also very linear and don't have long range.  Leaky antennas were used (and still are used) to repeat VHF and UHF radio signals in long tunnels.

Now, as to the UHF train telemetry signals.  There are 6 channels (frequencies) used.  One for the head-end (HOTD), one for the end-of-train-device (EOTD), and 4 Distributed Power Unit--DPUs--DPU01, DPU02, DPU03, DPU04.  Each set of DPUs in a train must have its own DPU channel, so--for example--a long train with two DPU sets and a FRED, would have the HOTD channel, EOTD channel, and 2 DPU channels.  When the train is set up, there is a digital "handshake" selected so that the lead locomotive can only control the EOTD and DPUs in its own train.  By design the UHF transmitters on all of the train telemetry channels are purposely set up with limited range only somewhat longer than the longest train length that they might encounter, such that the radio signal itself  won't interfere with other train's radio telemetry some distance away.  The actual UHF radio receivers for the train telemetry are also degraded a bit so that they won't pick up distant signals.  

In my area (out on the plains) my portable radios--very sensitive radios--will generally not pick up train telemetry more than about 4-6 miles away, sometimes even less.  My mobile UHF radio (also very sensitive) will do at bit better maybe up to 8-10 miles maximum.  That range might be slightly longer in, say, mountainous terrain, where the listener has better line-of-sight to the train.  Now, in areas with a lot of rail operations within a small area (say a big metro area), the train telemetry channels become pretty useless because your radio may pick up lots of transmissions and you will likely not be able to discern what trains are making them.  Also, to be clear, all one will hear on an analog radio monitoring those UHF telemetry channels are "blurrrrps" when a transmission is made.  Finally, what initiated the signals is the engineer's manipulations of the locomotive's controls--throttle, brake, etc.  If a train is running on level ground with no throttle or brake changes, there may be nothing to hear.

Finally, none of the UHF train telemetry channels should be confused with the PTC system.  That uses an entirely different protocol and uses channels in the 220 mHz band.  The PTC system sends and receives a ton of digital data to and from the train almost continually.



Edited 1 time(s). Last edit at 06/21/25 10:08 by WW.

theres a dpu features post by a locomotivr engineer in the archives. i'll try to find it later.

agree a tunnel repater would use leaky cable, external antennas would be part of a complete design.

some of the observed equipment could be PTS.

there are also data links for extensive telemetry from locomotives. thats another world alluded to by the antennas on the cab roof. there is basic live data between the dpu consoles. the help desk discussions are an interesting source of info.

This guy has some info, response from MP683 about half way down:

https://www.trainorders.com/discussion/read.php?1,5109980,5110199#msg-5110199

It's not the description I had in mind but it describes being able to seperate multiple  EOT's by their address and then repeat the desired EOT. I need to go through more posts to satisfy my questions. Other posts show a really good understanding of the DPU Comms. Some of the info is dated since the available technology has moved so fast, at this industrial level anyways.

The post I'm looking for talks about shutting off seperate EOT and DPU radio repeater switches when seperating the locomotives and / or when tied down.