Question About Radio In Locomotive

I once heard a crew tell me that they could pick up radio communcations with ease from over 100 miles away while in a newer GE locomotive? Is this a real possibility?

Locomotive has nothing to do with it - the radio and, more importantly, the antenna, these do.

"Skip" patterns play into it a lot, also. There are days when we can receive detector transmissions nearly 100 miles away. There are days when we can barely hear them, five miles away.

It's not a benefit...if you're picking up chatter fifty miles away, it's distracting.

Repeaters also play a large role in the radio reception.

Correct, the engine's radio has limited range, the repeater doesn't. All the engine's radio has to do is find a suitable repeater, and that signal can be accessed in Europe. Right the repeaters can access a satellite and you are gone. Something like five watts of power controlling ten to one hundred times that power and beaming it up to a satellite.

All radio is 'line of sight', so not only the power of the radio in the cab, but the terrain, and even whether or not there are trees with leaves on them will affect the distance you can hear or talk. Portable VHF radios are usually 5W power, cab radios 25-45 W and repeaters 40-100W ...or more. So on any given day, in any different territory, things will vary. Uplink to satellites certainly can help, if the infrastructure exists to do so.

Well, locomotives are in a better situation than most of us railfans - they have high quality radios specifically DESIGNED for the rail band for maximum reception. Their antennas may not be as high of gain as the Railcom's many railfans use, but they're higher up and have a massive ground plane to work with, so they'll ultimately pull in a lot more (height makes a big difference!). If they're on the rails and up high, they have a lot less stuff in their way to block transmissions. And, as was said earlier, it all depends on the day. During a day where the VHF propagation is extremely good (check this site out for a live map: http://www.mountainlake.k12.mn.us/ham/a ... cgi?map=na), they probably will hear stuff 100 miles away...during days where it's really bad, you might have trouble getting that detector just a few miles away...there's a lot of factors in it. On a great day, a scanner with an untuned antenna may be picking things up 30+ miles away...and on a crappy day, a several hundred dollar Motorola radio with a tuned antenna might not even get a detector a few miles away.

A lot depends on the condition of the radio and antennae, and whether they're connected properly. Railroad radios get banged up a lot - Conrail was always short of them, and SOP was to take the radio OUT and carry it into the engine-house office when turning in power. When getting power off the pit, a radio may or may not have been installed beforehand...if not, the crew had the choice of waiting for a maintainer to come do his job, or speed things up by putting it in themselves.

CSX is better at this...back in 1999, they made a big deal of buying radios, putting them in locked "permanent installations" and leaving them in. That has changed; we're again a little short of radios. So they're getting moved about and banged about.

A lot of times, a not-so-qualified maintainer will confuse the antenna connections for the radio and the EOT...they have the same plugs, but very different electrical values. This limits effectiveness of both, and can damage the radio when transmitting.

So yes, a new locomotive with an optimized antenna and a new radio will receive and transmit better than old battered junk.

Not that receiving signal-calls from crews 100 miles away is any help...as noted, it's a real distraction.

Conrail4evr wrote:. During a day where the VHF propagation is extremely good (check this site out for a live map: http://www.mountainlake.k12.mn.us/ham/a ... cgi?map=na), they probably will hear stuff 100 miles away.

Thanks for the propagation map reference, first I've heard of it. My APRS station is there somewhere.

See: http://map.findu.com/w2kb*

To add to the topic...locomotive antennas are actually unity gain (or 0 dB of gain), the same as a 1/4 wave antenna. Many railfans have the Railcom antenna, a tuned 5/8 wave antenna boasting 3 dB of gain. Where locomotives succeed, once again, is that they're really high up and have a truly massive ground plane to work with.

As for the radios themselves, they're actually rather deaf...meaning they don't pick up nearly as much as they could. Granted, this has its benefits...first off, they really don't need to, as they're still getting some transmissions from a good distance away as it stands, and generally don't have issues hearing dispatchers and other trains and such. The other thing is, by cranking the squelch up (in effect making them "deaf"), you won't hear any static-filled "What the heck did he say??" transmissions - only crystal clear ones.

I do know for a fact that these radios can be modified to have far better reception, and if you were to hook it up to a 3 dB antenna on a locomotive, I wouldn't be surprised if you could hear 150+ miles on a good day...but ultimately, the railroad has no use for such a thing, even if we railfans drool at the very prospect of seemingly infinite reception.

The RR Spectra has a very high gain front end and the bench sensitivity is outstanding but it overloads and desenses to the point of uselessness if it is used with a gain antenna in a high RF area.

I guess it was designed to work with the low profile locomotive antennas that are low gain and somewhat sharply tuned.

If I connect a Spectra to my base antenna, the desense is so bad even the dispatcher base a few miles away gets cut out or noisy at times. It works fine if I put a helical resonator filter ahead of it.

I tried a Spectra in my truck on a gain antenna once. I compared it to my regular Kenwood TK760G mobile. The Spectra was terrible until I got out into rural areas about 20 miles away from high power RF sources before it was equal to the Kenwood.

I have confirmed this with other radio maintainers. A maintainer from the Chicago area told me they use the front end filters out of old Harmon radios when they use a Spectra in a base application.

It is normal practice to set a locomotive radio squelch somewhat tight as you described to minimize annoyance from weak transmissions.

BN uses the same freqs. every so many subdivisions. There was on time that there was good "ducting" in the atmosphere. I was in Wisconsin, and was hearing the dispatcher talking to a train about 3 states away.

[quote="clearblock"]The RR Spectra has a very high gain front end and the bench sensitivity is outstanding but it overloads and desenses to the point of uselessness if it is used with a gain antenna in a high RF area.
[/quote]

This is true on SOME Spectras. They usally have the 'pre' RF frontends in them. The 'pre' frontends can overload in a high RF enviroment. But they can hear a broken HT way down the right of way...
Most applications, like Loco's do not need the 'pre' frontend option, so I change them depending on the application.

My VHF amature/train radio has the standard frontend and I have no problems, even in one of the worst RF sinkholes.

But then, I rebuild and repair Spectras.

I suspect the high gain front end was common on the locomotive Spectras to compensate for the realtively low gain low profile antennas.
When the Spectra is on a Locomotive with a low profile antenna the desense problem is not apparent.

The problems I have observed seem to be the preamp being overloaded by strong TV and FM broadcast signals. I have never observed any intermod, just extreme desense, usually with some indication of video noise. In my area, TV Ch8 seems to be a major contributor to the problem. A notch filter for the Ch8 video carrier is a big help but a helical resonator filter with a 160-162 MHz bandpass is needed to get the full benefit of the Spectras extreme sensitivity.

I have not encountered a Locomotive Spectra without the preamp option. I think you are correct about the source of the problem since the regular VHF Spectra mobiles do not seem to have this issue.

I still tend to recommend Aerotron Alpha 1700s for the railfan that wants a locomotive radio since it has good sensitivity, does not have the leaky capacitor issues and usually is a lot cheaper than a working RR Spectra on eBay.

The Spectra leaky capacitor issues are no problem as I repair them. It is good to get them before the 'stuff' leaks out on the circuit board and distroys the traces. I use Mil spec. capacitors for replacements. There are some minor changes I also include in my repairs.

I have been thinking on the desense and the need for the fliter on the Spectra. I think I can retune the frontend for better performance in the RR band.

If you have the 'PRE' frontend, it can be changed to the standard very easyaly. Biggest problem is surface mount soldering on the brillia substrate.

railroads don't use repeaters for the most part, there are very few non-simplex operations on todays railroad