Radio interference in a crowded layout room?

[joelm]

Hi all: Using Digitrax radio using both the UR91 and UR 92 in a 20 x 20 finished garage. Throttles work fine via radio normally. A couple of weeks ago I held an open house, and rather than the 8 people in the garage for a typical ops session, there were 15 to 20.

During the open house, I noticed that some of the radio throttles (UT 4) were not communicating with the locomotives, they responded when plugged in. Fresh batteries were applied, same issue, but only in some locations on the layout (one location is beyond an 18" high backdrop (1/4 inch fiberboard). The URs are located next to each other, on the ceiling, at one end of the room.

So, two questions:
1: Would a lot of bodies affect the radio (I think I read this someplace many moons ago, but I'm not sure)
2: Would adding another UR on the opposite end of the room likely resolve the issue?

Thanks. Joel

[jdcolombo]

I have had the exact same problem with the Digitrax radio system, whether simplex or duplex.
Everything worked fine when it was just me in my 15x30' layout room.  But the moment I had 8 operators down there, the radio system went haywire, with engines not responding to throttles.  At first, I thought this might be the result of cell phone interference, but it persisted even after I asked my operators to turn their phones completely off.  I tried a bunch of other things, including adding another UR92; changing the position of the UR92's; etc.  All to no avail - there were always problems once I got 8 bodies in the room.

So . . . I ditched all my Digitrax radio throttles and replaced them all with TCS wi-fi throttles connected to my layout via an old router I'm using as a wi-fi access point and JMRI on my laptop (note: the router is NOT connected to my home wifi or internet; it is simply acting as a wifi access point for JMRI to communicate with the throttles).  This system has been bullet proof; I use six of the UWT-100's, which most of my operators prefer, and two of the UWT-50's because a couple of the guys REALLY like knobs.  No problems whatsoever.

My resulting advice: ditch the Digitrax radio system and move to WiFi.  Yes, it will cost you money and some complexity in setup.  But then problem solved.  Note that I have not tried Digitrax's own WiFi throttle interface, the LNWI, because it is limited to 4 throttles.  However, I think you can use more than one of these to expand throttle capacity.  Maybe others who do use the LNWI can chime in on this.  It would be easier to use than setting up JMRI connected to a DCS command station (I have a DCS 200) and an external wifi access point.

John C.

[Rasputen]

Joel, are you using simplex or duplex radio throttles?
We had some difficulty trying to mix UR91s and UR92s at my friend's house.  After installing all UR92s, we've had at least 12 operators with no trouble.

[John]

At some point, you tend to get interference when there are too many transmitters on a frequency band ..

dccwiki has this under the UR93 entry

The UR93 transceiver supports up to twenty Digitrax Duplex throttles simultaneously. Adding a UR93 to an existing UR 92 duplex radio equipped layout will offer improvements, such as a 15dB increase in signal strength. All duplex throttles will attempt to connect to the UR93's stronger signal for better operation. As the UR93 is not limited by the number of connections it can handle much more traffic than a wireless router or other device.

That implies to me that the UR92 will handle less than 20.   It might be that you need to upgrade to a UR93 ..

There is a UR92 Firmware update that might fix some issues

Dec. 10, 2015 (version R8) - This rev 8 fixes UR92 link issues with multiple UR devices on the LocoNet and improves Duplex reliability. We want to thank Frank Fezzie Jr. and others that have supported him in helping isolated this intermittent problem.

There is also a UR93 firmware upgrade Aug 2021

UR93 Setup and Operation: 31Aug2021- IPL-version 1, Improved UR92 inter-operation timing margins and locking Channel and NetName.

    Like all Duplex units, the UR93 is configured with a unique 8 character Digitrax Duplex NetName and a RF Channel number from 11 to 25. Any Duplex throttle unit trying to access LocoNet with a particular UR93 must have exactly matching NetName and Channel number as the UR93 it is trying to use for Duplex connectivity. Any differences will break a duplex link.

    UR93 and UR92 units will automatically invoke a NetName and Channel resolution protocol when a LocoNet Power On <83><7C> message is seen or it is powered up. On some layouts, usages, configurations and combinations of UR93's and UR92's, if this resolution is unsuccessful the UR93 or UR92 may suddenly seem to freeze or stop working on an untethered; UT4D, UT6D, DT402D, DT500D or DT602D.

    To avoid connection problems, after you setup required UR93's Duplex settings to run the layout, best practice is to set OPSW11 =C to turn OFF Channel Changes and OPSW12= C to turn OFF NetName Changes. This will ensure the Duplex settings cannot be modified in operations, and the UR93 will then not be involved in NetName and Channel resolution.

    To subsequently edit system Channel/NetName you will need to temporarily set OPSW11/12 back to T to allow changes.

    A UT6D or DT602D plugged into LocoNet with UR93 and UR92 units can conveniently edit NetName, Channel and also Key settings of any units that allow changes of these settings. Press menu>3>6 and follow the prompts. You may also use the free Digitrax Duplex Setup PC application to do the same thing.

    Any Duplex enabled throttle plugging into LocoNet will use the first Duplex Channel and NetName received. If there are differing sequential values of these seen, it may lead to some confusion.

    For remote joining, or diagnostic purposes, with untethered UT6D or DT602D units you may invoke the Duplex RF Scan capability with menu>3>5, and then the soft key "Scan All". After the scan time, you will see a list of Digitrax Duplex beacons visible from UR93 and UR92 units, so you can be sure what is currently available, look for any unexpected setting changes, and also can then use a soft key to join a visible network.

    In a system with mixed UR92 and UR93 units, the UR93 have about 33x more transmit power and also about 33x higher receiver sensitivity and so longer beacon range. Duplex throttles track and change to beacons of the same Channels and NetName with the strongest RF signal, so most throttles will usually track the beacons of UR93 units. Duplex links are "connectionless", so a single UR93 can handle an "unlimited" number of duplex throttles' RF traffic sequentially.

    It is recommended that all UR93's be updated with the latest IPL on the Digitrax web site. The latest UR93 IPL version has improved legacy UR92/Duplex timing tolerances and also implements a new IPL-version number that will uniquely identify the IPL version related to the IPL date code, when using the DigiIPL II v2.9.1 downloading utility program. An IPL_ver number of 0 means the current UR93 installed firmware does NOT support IPL-version capability. Downloading the latest UR93 firmware will enable IPL-version display

Hope some of this helps

[jagged ben]

...
So, two questions:
1: Would a lot of bodies affect the radio (I think I read this someplace many moons ago, but I'm not sure)

Possibly. 

Also perhaps it was all their phones.  Next time (if you dare) ask them all to put their phones in airplane mode and see if that makes any difference.

2: Would adding another UR on the opposite end of the room likely resolve the issue?

Possibly.  You really never know what's going on with radio waves until you try something.

[John]

Possibly. 

Also perhaps it was all their phones.  Next time (if you dare) ask them all to put their phones in airplane mode and see if that makes any difference.

Possibly.  You really never know what's going on with radio waves until you try something.

Thats a possibility .. wifi is in the 2.4ghz range .. so are the earlier models of Digitrax radio ..

[CRR Chase]

We ran into this issue, disconnecting the UR91, helped, however, the solution is in the post above about upgrading to the 93.

[peteski]

I'm not into Digitrax, but my NTRAK club uses that system for running the layout we set up during train shows.  We always have issues with the radio throttle response.   I don't recall which throttle model we have, but they are the duplex older units.  I was told to watch the white LEDs on the end of the throttle.  If they are flashing when I turn the speed knob (throttle sending commands to the command station) that means the commands are not being received/acknowledged by the command station (problem with radio connection).  So that is a good clue indicating that there is a radio-related issue.  Seems like a good troubleshooting aid.

In my example, there are bunch of spectators at the show (walking around with smart phones, and with uman bodies also blocking.deflecting radio frequency signals), and also several other clubs also using radio throttles (multiple brands of radio-based DCC systems).

Our Digitrax setup also includes their WiFi interface module, and the last few shows I have been using the Engine Driver WiFi throttle app.  That works reliably for me.

[C855B]

[…sigh…]

I have training in this area and used to be an antenna designer, and have been pondering this scenario since it was asked last night. The question as posed needs a lot of clarification.

For one, Joel asked whether the number of bodies was the issue, with no mention of those extra bodies having throttles beyond what there would be in a normal multi-operator scenario. It was an open house, so probably not, just visitors. He also said “UT4” throttles, not noting whether they were UT4D or UT4R, or a mix, and, more importantly, how many were in use.

The UR91 and 92 up on the ceiling - good, though it would be marginally better if they were in the center rather than one end of the room. Joel didn’t say where the problem area was relative to the transceivers (URs).

The earlier Digitrax radio system (UR91) is in the 900 MHz low-power utility band (902 to 928 MHz), specifically 916.5 MHz. This band was shared with things like garage door openers, baby monitors and plug-in phones with wireless handsets. The “duplex” system operates in both the original 900 band and the 2.4 GHz low-power utility band, shared with… f’in’ everything: Wi-Fi, microwave ovens, point-to-point links, baby monitors, wireless corded home phones, for starters. Anything wireless, ‘cept garage door openers, which are mostly around 430 MHz now.

The special quality of the 2.4 GHz band is why it is so popular - 2.4 GHz is the lowest resonant frequency of water, which is how microwave ovens work. The electromagnetic waves vibrate the water molecules. IOW, the water absorbs the radio signal. That makes the frequency self-attenuating - it has very limited range as even the humidity in the air absorbs it.

Now the Digitrax wireless protocols are very crude. There is no collision protection in their 900 MHz single-frequency scheme. The throttle just burps-out a command when you twist the dial, to heck with anybody else. The result there is obvious - the more operators, the greater chance of collision, the greater chance of nobody’s command being understood by the UR91.

I can’t speak with any authority to the ‘D’ duplex system. I don’t know which frequency is up or down, or if there is collision detection, where the UR92 tells everybody to shut up, via the downlink, while it’s listening to commands on the uplink. There is likely no detection of non-Digitrax signals which might interfere*. What I do know is that people are big bags of water (98% of us is water!), so it is plausible that Joel’s problem was indeed absorption of one of the ‘D’-system frequencies, which hints at 2.4 GHz being the throttle-to-UR uplink.

* - Our N-trak club had our usual UR91/UR92 system at a big train show. Next to us was an HO group with an NCE system, with gain-type add-on antennas at both ends (a very big FCC no-no). Our ‘D’-system throttles simply did not work, and Digitrax reps were at the show and unable to help. I didn’t know the NCE wireless protocol, had no reason to, but I learned in about an hour or so that NCE puts the entirety of their wired network traffic out on the air, on the same frequencies as Digitrax. Our receivers were rendered deaf by the NCE activity.

As to smartphones possibly being an issue in Joel’s situation, maybe yes, maybe no. Cell frequencies are well outside of the 2.4 GHz area. If everybody had the Wi-Fi enabled on their phones, maybe the frequent searching for a Wi-Fi router to connect to might have created enough of a fog on the channel to interfere in some circumstances.

Bottom line: lacking other information I’m leaning toward the “big bags of water” absorbing 2.4 GHz uplinks from UT4D throttles.

I’ll take off my Bob Gibson hat now and let the rest of you enjoy your day. 

[C855B]

OK, somebody raised their hand, “What do you do on your layout, Mike? You've mentioned you use a Digitrax control station.”

Wi-Fi only via JMRI and a professional Wi-Fi access point. No UR-anything. I put up with WiThrottle on decommissioned iPhones when I got the layout running, but immediately acquired a TCS UWT-100 when they came out (Ser. #6!), and added a UWT-50 since.

Motivation was learning the hard way about operators reprogramming entire layouts' worth of locomotives by programming in ops mode on DT402Ds. That was not going to happen on my pike!

Great decision - the Wi-Fi has been fabulous.

[joelm]

Thanks for your responses. A little more information and some follow up questions regarding suggested solutions.

My strong preference is to stick with the Digitrax system as I do not have the knowledge nor desire to acquire the electronic skills needed to delve into other than simple off the shelf solutions.   Nor looking to drop the system entirely due to cost. BTW: I dislike using a cell phone as a throttle.

I have an additional UR 91, which is why mounting it across the room was my initial simple approach, but the there is substantial work needed to do that, which is why I asked my question before embarking down that path. If it's unlikely to help, I'm reluctant to expend the effort.

Acquiring and adding a UR 92 in a different part of the room,  removing the UR 91, or adding/replacing both with a UR 93 are all possibilities.  My main concern with the UR 93, is whether the UR 93 is compatible with the UT4 R throttles.

1) There were 3 UT4R and 2 UT4D, plus one DT 402 in operation.
2) The distance between the UR91/92 and the operator where the phenomenon was detected was about 12 feet, possibly not with direct line of site (there's an 18" backdrop between the transmitters and the throttle).
3) I have heard before that using the UR 91 and 92 in the same room could be a problem, but have had numerous sessions with 8 guys in the room without a problem.

My follow up questions:
1) Will the UR 93 operate with both the UT4 R and UT4 D throttles?
2) Do I need to replace the UR91 and UR 92 or can I add the UR 93?
3) Please direct me to instructions for the identified UR92 firmware update.
4) Any further suggestions now that you have additional information?

Thanks.

[GaryHinshaw]

I can address some of these questions:

1) Will the UR 93 operate with both the UT4 R and UT4 D throttles?

It will definitely work with the UT4D, but apparently not with the UT4R:

https://www.digitrax.com/tsd/KB16/which-throttle-works-with-which-universal-panel-ur/

2) Do I need to replace the UR91 and UR 92 or can I add the UR 93?

You can add it.  I have a UR93 and a UR92 working together with no issues (but all duplex throttles).

3) Please direct me to instructions for the identified UR92 firmware update.

https://www.digitrax.com/downloads/ur92-firmware/

If you're going to add a UR93, then don't mess with this upgrade unless you still have problems.

4) Any further suggestions now that you have additional information?

I will add the following: bodies definitely absorb 2.4 GHz; the backdrop should pose no issue (unless it is made of metal or water); placing two UR devices next to each other is not doing anything useful for you.  You might actually try disabling one of them.

[joelm]

Thanks, Gents. All this is very useful. I will likely add a UR 93 and mount it on the other side of the room. And disconnect the UR 91, since the UT-R and UT-D are covered by the 92 and 93. Unfortunately, I won't know if this fixes anything until I have a room full of people again. Probably during the 2024 SurfLiner National Convention layout tour.   Joel

[Rasputen]

I think you will want to keep the UR91s in order to use UT4Rs.

[joelm]

Rasputin - Yes, realized that this morning when I looked again at  the table. Thanks, all. Joel