Why are loco radios so bad?

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Why are loco radios so bad?

Postby CPSK » Thu May 31, 2018 11:04 am

Hi;
I have been listening to railroad radio on a variety of scanners and amateur equipment for a long time, and one thing still stands out: Reception of transmissions from the locomotives is not very reliable. Even when the signal is strong, I often have trouble understanding what was being said due to low or distorted audio. There is one CSX loco that has such a bad radio that even the dispatchers can't read it much of the time; yet no repairs/replacement was made for months, and I think I still hear that bad radio once in a while.

The situation is worse on some of my radios than on others. For example, after modding my Yaesu VX-150 2m HT, I get much stronger and clearer audio. The mod involved replacing a couple resistors and capacitors in the audio circuit.

On my (unmodified) Yaesu FT-60R, the audio isn't as clear. IMO, the audio response rolls off at too low a frequency, producing a muddy audio. It's fine for signals with strong audio, such as Amateur stations and repeaters, but on the RR band I find it a bit difficult to understand some transmissions; especially when the signal itself is weak.
The dispatchers even complain about not being able to hear some of the locomotives, but I think their problem is mostly weak signal reception. I believe they are all wearing headphones, which I have also found is a dramatic improvement. But I don't always want to listen using headphones.

I suppose that some scanners and amateur equipment are better than others for RR scanning. I would like to mod my FT-60 the same way I did the VX-150, but so far I haven't found a good enough schematic that will allow me to perform that mod. Besides that, I nearly ruined the VX-150 doing the mod, as I didn't really have the right soldering equipment. If I were going to mod the FT-60, I would purchase the correct soldering/desoldering equipment first.

Am I the only one with this problem, or are there others?

CP
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Re: Why are loco radios so bad?

Postby NorthWest » Thu May 31, 2018 10:00 pm

The radio stations that locomotive radios are designed to communicate with are pretty large, and the radios can be pretty low powered as a result. There are occasional troubles communicating, but if they were a big deal the railroads would install higher powered antennas.
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Re: Why are loco radios so bad?

Postby atsf sp » Thu May 31, 2018 10:11 pm

Railroad radios are quite tempermental. Many times a set of trees will even disrupt a transmission in certain known spots. Railroads will even install repeaters at certain locations.

Then again sometimes it is the radio itself. I have had one that you couldn't communicate past the long porch on a SD50 just out of rebuild. We sent it right back to the shops. Another time I had a SD40 that everytime you pressed to talk on the radio it shut down the engine. That was an interesting one.
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Re: Why are loco radios so bad?

Postby Gadfly » Sat Jun 02, 2018 6:27 pm

atsf sp wrote:Railroad radios are quite tempermental. Many times a set of trees will even disrupt a transmission in certain known spots. Railroads will even install repeaters at certain locations.

Then again sometimes it is the radio itself. I have had one that you couldn't communicate past the long porch on a SD50 just out of rebuild. We sent it right back to the shops. Another time I had a SD40 that everytime you pressed to talk on the radio it shut down the engine. That was an interesting one.


Usually caused by a "ground loop"- a condition where inadequate grounding allows "RF" energy to get onto cables, chassis, and into engine computer controls.
The RF finds a "resonant" ground that is close to the frequency that it "likes" and travels on that wire, etc and goes into places its not wanted. Symptoms include "hot" mikes and components, mikes that "shock" the lip (OUCH!), wierd noises coming from the radio as it transmits--even shutting off engines (cars, trucks, etc) at inopportune times. Solution? Adding short[ grounds that "interrupt" the RF travels and "shunts" it to true ground. You can also add chokes (capacitors, toroids) and wind "chokes" by coiling suspected cables around themselves. And, yes, locomotives could be shut off this way! :-D :wink:
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Re: Why are loco radios so bad?

Postby Ken W2KB » Sat Jun 02, 2018 8:29 pm

CPSK wrote:Hi;
I have been listening to railroad radio on a variety of scanners and amateur equipment for a long time, and one thing still stands out: Reception of transmissions from the locomotives is not very reliable. Even when the signal is strong, I often have trouble understanding what was being said due to low or distorted audio. CP


One issue, particularly for low audio, is that railroads are I believe all (or mostly) now on 6.5kHz narrowband while amateur radios use 15kHz bandwidth. That results in much lower audio from the ham receiver - the audio level depends on the deviation so the much lower deviation on 6.5 kHz channels is to be expected when not using a receiver designed to receive the narrow bandwidth transmissions.
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Re: Why are loco radios so bad?

Postby Gadfly » Sun Jun 03, 2018 8:34 am

Ken W2KB wrote:
CPSK wrote:Hi;
I have been listening to railroad radio on a variety of scanners and amateur equipment for a long time, and one thing still stands out: Reception of transmissions from the locomotives is not very reliable. Even when the signal is strong, I often have trouble understanding what was being said due to low or distorted audio. CP


One issue, particularly for low audio, is that railroads are I believe all (or mostly) now on 6.5kHz narrowband while amateur radios use 15kHz bandwidth. That results in much lower audio from the ham receiver - the audio level depends on the deviation so the much lower deviation on 6.5 kHz channels is to be expected when not using a receiver designed to receive the narrow bandwidth transmissions.


My scanners and amateur tranceivers (Kenwood, Icom, et al) receive RR just fine. Doesn't seem to be much loss in the receiver, if any.

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Re: Why are loco radios so bad?

Postby kc3br » Tue Jul 10, 2018 7:35 am

Most of the time it isn't the radio but rather the radio operator!

With the "clean cab" radios, they use a front panel area microphone and if the operator isn't looking at the face of the radio (looking out the window) the transmit audio will suffer greatly.
The audio compressor opens up to try and catch audio and ends up transmitting most of the cab noise.

With the move to narrow band (12.5khz), the people in scanner-land are going to hear a reduction of audio on older scanners...the very narrow band (6.5khz) hasn't been implemented as of yet, but it will come someday...

I believe the ham stuff is still defaulted to wide band on receive, unless you tell it in the channel programming to run on narrow.

There are a few "bad radios" out there...but that would decrease if the people reporting radio problems would actually report the true problem (ie: poor tx, poor rx, low audio, poor range) instead of just scribbling "JUNK" or "NO GOOD" on the defect tag - and it wouldn't hurt to put the date and loco number on the tag too!
Thirty seconds of you writing a problem description on the tag saves me an hour of chasing a non-existant problem on the service bench!
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Re: Why are loco radios so bad?

Postby krispy » Mon Jul 16, 2018 3:10 pm

Another thing to consider is that locos can't have a great antenna due to clearance issues. Especially in areas where you have catenary wire, etc. Most VHF antennas on rr equipment look like inverted ice skate blades in order to provide close clearance. Most are usually variations of the Sinclair Excalibur antenna, and are a compromise between making do with the space available and efficiency. While they try to be omnidirectional, they do have lobes so it you're having trouble catching it, try relocating or get out of your car and position the radio a certain distance from the body to the radio in the direction of the train, using the body as a impromptu reflector. If they antenna is bumped it can knock it out of tune, etc.
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