UP detector suddenly much harder to receive.

[JoshuaHufford]

Probably about 6 months or so ago, the detector at milepost 139.1 on the UP Sedalia Sub, located in central Missouri, has become very difficult to receive. I used to easily pick this one up from my house and my remote receive site where my audio stream equipment is located, but now I can't pick it up from either location even though I still pick up other detectors, some father out with no problems.

I thought at first maybe this detector was changed to talk on defect only with no entrance message, but I parked right next to it about a month ago when I knew a train was coming, and sure enough it still gave it's standard entrance message when the train went though. However, I've been within 1 mile of the detector, at a location I know I've previously had no problems whatsoever receiving it, and I no longer receive it now at 1 mile distant with a 5/8 wave antenna tuned to the railband properly mounted on the roof of my van.

Just wondering if anyone else has experienced this with other detectors? Maybe UP turned down the transmit power for some reason? With the length of trains UP has been running lately, some 15-16k feet long, I'm wondering if the crew would even hear a defect transmission if their happened to be one. Although I think the dispatchers are also sent an alert if a defect is found with the train. Maybe there is something wrong with the radio/antenna/coax at the detector and nobody has noticed yet?

 

[626hawkeye]

I've also noticed the detector by Sedalia station is harder to heard I'm 1/4 of a mile east of the station and the detector is about the same give or take west of the station. I've also noticed dispatch is hard to hear unless a train is in the block.

 

[JoshuaHufford]

Maybe they are turning down the power on some of these to help with radio traffic, seems they wen't a bit overboard though.

 

[wwhitby]

Here in CSX land, I've noticed that the local DD is much harder to receive, even with a Kenwood commercial mobile radio and a 3 dbi gain antenna. I've long suspected they turned down the power. After all, they only need a couple of miles range at most.

 

[jbhunt04]

The way I understand the mainline communications work, is there are base stations w/ a tower and satellite every so many miles. When a train needs to talk to the dispatcher, they dial(DTMF tone) the dispatcher and it opens open the base station they are nearest. If the dispatcher sounds weak, it is likely a base transmission from farther away. Train radios put out less watts than the base does, so you can usually only hear the dispatcher conversation unless you are within range of the train crew.

 

[Giddyuptd]

I've noticed union Pacific in el paso area was doing work on their detector stations while back.

I was thinking the range was lowered or narrow banded if they weren't?

 

[Giddyuptd]

The way I understand the mainline communications work, is there are base stations w/ a tower and satellite every so many miles. When a train needs to talk to the dispatcher, they dial(DTMF tone) the dispatcher and it opens open the base station they are nearest. If the dispatcher sounds weak, it is likely a base transmission from farther away. Train radios put out less watts than the base does, so you can usually only hear the dispatcher conversation unless you are within range of the train crew.

Or live on a Mesa and the railway is line of sight clearly down in the basin

 

[jbhunt04]

Or live on a Mesa and the railway is line of sight clearly down in the basin

Depending on the atmospheric conditions I can usually receive signals from 7 to maybe 15 miles. I monitor The CSX Henderson Sub in Western KY.

 

[icom1020]

If you’ve checked everything on your end and parked next to it, and still have a weak signal, it’s possible the detector is on it’s last legs but not reported as bad order yet , as it’s still doing an “ok” job for the passing trains. Signal maintainer will probably do a routine check at some point.

 

[Floridarailfanning]

Not sure about UP but I know CSX has been replacing omnidirectional antennas with dipoles at most of the DD's. Could possibly cause the issues you described.

 

[JoshuaHufford]

If you’ve checked everything on your end and parked next to it, and still have a weak signal, it’s possible the detector is on it’s last legs but not reported as bad order yet , as it’s still doing an “ok” job for the passing trains. Signal maintainer will probably do a routine check at some point.

I hope so because I do miss hearing it. It has probably been 6 months at least now since it changed, I would think a maintainer would have caught it by now. I just don't see how a crew running some of the 12k foot or longer trains would hear the transmission if there was a defect. Perhaps it transmits at lower power for the entrance message then if there is a defect transmits at high power? I haven't noticed any other changes with the 4 other detectors I can normally receive however.

Also I have not seen anything but Omni antennas on UP detectors around here.

 

[empireco]

When Norfolk Southern switched their major frequencies in Ky I can no longer pick up ANY detector from my Home QTH.
I believe they most certainly turned the power down. You can still hear them mobile if you get close to them.

Switching from 160.950 to 160.515 would not be enough of a mismatch on the tx antenna to make this much difference.
Perhaps they didn't just change the frequencies perhaps they completely changed out the detector transmitter to a different model with much lower output power.

 

[JoshuaHufford]

Sad to hear, they can be such a useful tool.

 

[wa8pyr]

When Norfolk Southern switched their major frequencies in Ky I can no longer pick up ANY detector from my Home QTH.
I believe they most certainly turned the power down. You can still hear them mobile if you get close to them.

Switching from 160.950 to 160.515 would not be enough of a mismatch on the tx antenna to make this much difference.
Perhaps they didn't just change the frequencies perhaps they completely changed out the detector transmitter to a different model with much lower output power.

Part of what NS has been trying to accomplish with moving dispatcher and road channels to new frequencies is interference reduction, so setting the transmitter to lower output power is very likely what's happened. As long as the trains can still hear it within 3-5 miles in either direction they should be good.

The FCC has been paying closer attention to transmit power violations so I suspect that might have something to do with it as well.

 

[wwhitby]

Not sure about UP but I know CSX has been replacing omnidirectional antennas with dipoles at most of the DD's. Could possibly cause the issues you described.

If you want to see what one of the folded dipoles looks like installed at a DD, Danny Harmon has one in his railfan video here.

 

[JoshuaHufford]

If you want to see what one of the folded dipoles looks like installed at a DD, Danny Harmon has one in his railfan video here.

Yeah I saw that, sad to see. It keeps getting harder and harder to be a railfan.

 

[wa8pyr]

If you want to see what one of the folded dipoles looks like installed at a DD, Danny Harmon has one in his railfan video here.

Actually, the way that antenna is configured it’s still going to be pretty omnidirectional except on the bungalow side. The mast and bungalow will serve as a reflector, so if you’re on the backside of the bungalow reception range will be reduced. To make it mostly directional along the tracks there would have to be two elements, on either side of the mast facing up and down the line and one about two feet above the other.

Great antennas, I’ve used them on repeaters. The spec sheet is here:
http://www.repeater-builder.com/antenna/db/pdfs/db-224-data-sheet-(andrew).pdf

Danny‘s videos are great. I’ve binged on them several times.

 

[cbehr91]

In my listening experience anyway, with CSX putting those Sinclair folded dipoles on the detectors it's actually boosted their range. Many of the ex-Conrail detector boxes simply had a 1/4 wave whip on an NMO mount in an awkward spot for it to work well. Not many of the CSX detectors in Ohio seemed to use the fiberglass 5/8 wave shown in the video, but many in the south did.

Side note: Does anyone know what make-model those 5/8 fiberglass antennas were? I think Laird?

 

[N4DJC]

I’m not hearing much on NS dispatch frequencies. I was hearing clear signals on my Kenwood a few weeks ago, broken squelch is about all I’m getting now.

 

[cbehr91]

When Norfolk Southern switched their major frequencies in Ky I can no longer pick up ANY detector from my Home QTH.
I believe they most certainly turned the power down. You can still hear them mobile if you get close to them.

Switching from 160.950 to 160.515 would not be enough of a mismatch on the tx antenna to make this much difference.
Perhaps they didn't just change the frequencies perhaps they completely changed out the detector transmitter to a different model with much lower output power.

The road channel from Blanchet to Tateville, KY is 160.575, not 160.515.