Passenger Radios On Board Burlington's 1937 Denver Zephyrs

[ButchKnouse]

What would be ON frequencies like 720.2 AM?

[rjemery]

... In the 1930's electric razors ... etc didn't exist.

Guess again!  From a 1937 Denver Zypher brochure:

 

 

 

 

[Poppa_Zit]

I seem to  recall self-service tube testers (with inventory below?) in hardware or variety stores back in the 50's. Anyone else?

 As a kid in Reading PA, I was properly steeped in the lore and legends of my Dad's (he grew up in Highland Park) Detroit Tigers. Summer was our busy season and we'd often work into the night listening to the games worked by Ernie Harwell on WJR. We'd do the same in the Safari coming back from delivery/sales trips. Ernie seemed like an uncle to me. Great WJR signal then.

If WOR's ("I am not reminiscing!!!) Jean Sheperd was on a roll, we'd bounce between Jean and Ernie.

Doubt there was music on Western Star when I rode it coming back from Vietnam ca. 1969. People's tastes had become too diverse.

R. Flix 

I have one of those tube testers w/inventory below in storage, bought when a local hardware store went out of business years ago. Use the tubes to repair old non-transistor radios I have restored.

And -- oh yes! -- the days of old before global cable TV, where as a youth I used to scan the AM dial from one end to the other, listening to the wonderous, crackling sound of major league baseball games being broadcast from cities faraway at night... radio, it was like a miracle that transported us kids elsewhere as we lay in our beds learning to develop and use an imagination to "see" the games in our minds.

I still have in working order the first art deco Zenith cabinet radio with push buttons and green "Magic Tuning Eye" from my folk's house.

From Chicago we could on most nights hear games from romantic-sounding places like Crosley Field in Cincy on WLW... Forbes Field in Pittsburgh on KDKA... Busch Stadium in St. Louis on KMOX... Tiger Stadium in Detroit on WJR... In today's world, listening to baseball on the radio demands no special mental skills, no imagination, because thanks to TV we know what the ballparks and the players look like... which may be why today's generations aren't as smart as we are.

 

[Poppa_Zit]

What would be ON frequencies like 720.2 AM?

Nothing. Just more precise tuning. Sometimes because of atmospherics, terrain, nearby buildings or weather you can improve a signal by moving slightly off-frequency. You could do that with an analog tuner, but not with a regular digital. Commercial AM signals -- compared to commercial FM -- are much "wider".

[erikem]

Also keep in mind most AM transmitters also send their signal through the earth via a ground plane antenna, which is in-ground and radiates outwards from the antenna mast. Remote areas that have a high iron content in the bedrock typically do not offer good AM reception. FM, other other hand, does not require a ground plane -- just an antenna on top of a tall mast or building.

To be more correct, the AM transmitters are designed to send out a surface wave which more or less follows the contors of the earth. The surface wave propagates best when going over high conductivity soils (e.g. well fertilized farmland) and even better over sea water. For the most part the surface wave peters out after about 70 to 100 miles or so, depending on frequency and ground conditions.

During the daytime hours, the D layer of the ionosphere presents too much loss to allow the sky wave to propagate by reflection (actually refraction) off the higher levels of the ionosphere (E or F layers). At night, the D layer goes away and allows for propagation up to halfway around the world.

erikem, however you care to slice it, what I was talking about was not how it sends out a signal -- but the physical apparatus itself. Here's what I wrote, the key word being "also":

'keep in mind most AM transmitters also send their signal through the earth via a ground plane antenna"

Part of the FCC required transmitting apparatus at a commercial AM transmitter site is the ground plane, buried cable radials -- usually 20 each, 100-foot long ground radials of 8 AWG bare tinned copper wire. The ground plane is arranged in a circular pattern out from the antenna mast -- buried at an approximate depth of 18 inches below existing surface. At the center, the 20 radials are joined together. The end of each ground plane radial is equipped with a 4 foot ground rod mechanically and electrically attached to the wire. The ground rods are driven into the soil to ensure a maximum grounding of the system.

This is why most commercial AM transmitters are built on sites with some open land around the antenna(e) -- as I said, not needed in FM setups, which can be mounted on masts or tall buildings, like the Sears Tower in Chicago.  

Point taken, though my understanding is that the ground system is more like 120 wires each one-half wave long (~500' for 1,000 kHz). One purpose of the radial ground system is to provide a stable feedpoint impedance to the antenna, which is particularly important for a directional array (FCC regs typically call for a 30 to 40 dB null) - this from a Tab book on setting up directional broadcast arrays (my copy is at work).

AM station transmit with vertically polarized signals in order to excite the surface wave mentioned in my previous post. FM (and TV) stations transmit horizontally polarized waves which do not require a ground plane. 

[Poppa_Zit]

AM station transmit with vertically polarized signals in order to excite the surface wave mentioned in my previous post. FM (and TV) stations transmit horizontally polarized waves which do not require a ground plane. 

Not for you erikem, but anyone who is interested, for an illustrative purpose of the discussion as to why AM radio waves travel farther than FM (and TV, which are similar), the shape of the wave makes all the difference. I'll try to keep it fairly simple.

AM radio waves look like the top graphic, and because of the low frequency (of the peaks) are more "bendable" and can follow the curvature of the earth and therefore travel greater distances. And can bounce off the Ionosphere (which "rises" after sunsets and allows for "skip" (bounce back to earth) which helps bring in distant stations at night. But also bounce off the sides of buildings and other obstructions -- like in Downtown Chicago.

FM (and TV signals) are of a higher (number of peaks in the bottom graphic) frequency and do not bend -- so the receiver has to be within "line of sight" to the transmitting antenna -- which is most cases depending on height rolls off the curvature of the earth at about 30-40 miles. They do, as we know, penetrate walls of buildings, etc.

Hypothetically, if no other FM station was transmitting (and interfering -- aka Multipath Distortion) on the same frequency as a station say, broadcasting from Chicago, if you lived in St. Louis and had a receiving antenna maybe two miles high, you could listen to that station because that signal is up there at some altitude. That's why in some towns far from a major city people receiving non-cable TV signals have their antennas mounted on a high mast. 

Radio signals go off into space indefinitely, though. What was the movie/TV show where the crew of a spaceship many light years distance from Earth was in position in the "stream" to listen to the National League baseball playoff game from 1951 at the exact time when Bobby Thomson hit the home run that won the pennant for the NY Giants?    

[rjemery]

For those interested, there are articles and discussions of AM and FM wave propagation and antennas available at http://en.wikipedia.org.

These latest responses to my original query have gone far afield, but I still consider these sidebar explorations to be relevant, if not very interesting.  Keep them coming.

 

[larsend]

Inasmuch as this is a Trains Forum, I have hesitated to prolong the discussion of the technical aspects of radio.

 

My first job as a Broadcast Engineer was helping and learning about AM directional antennas from a Consultant.  My last job, before retiring, was for a client, designing, constructing, and adjusting an AM directional antenna.  In the intervening 50 years, I was involved, not only with many AM stations, but FM and TV stations in an engineering capacity.

 

Much of what has been discussed here is correct, but a lot of it was not.

 

Getting back to the original topic, railroads promoted the installation of radios as a statement that the railroad was up to date with their use of technology for the pleasure of their customers.  Today, those offering transportation of passengers are still promoting the fact that they offer the latest in technology for the pleasure of their passengers, only now they are promoting cell phone service and WiFi, the present "State of the Art"

 

The installations of radios on trains in the 1930s, as well as the availability of WiFi today, are due to the very smart moves of the railroad, marketing departments.  The airlines are now beginning to follow the long time smart actions of the railroads.

 

If anybody wants to discuss any aspects of AM, FM or Television signal coverage and reception please E-Mail or PM me.  I would love to talk about it, but I think we should let Kalmbach use their Forum for Railroading.

[rjemery]

Much of what has been discussed here is correct, but a lot of it was not.

Please feel free to correct the record. 

If anybody wants to discuss any aspects of AM, FM or Television signal coverage and reception please E-Mail or PM me.  I would love to talk about it, but I think we should let Kalmbach use their Forum for Railroading.

If there were a Water Cooler or Off Topic section, I would sugest posting there.  However, there is not.  Since the original question has now been answered, I would encourage you and everyone else who wishes to pursue the technicalities of radio transmission to continue posting right here.  In its own way, it all relates to radio reception aboard late 1930's or newer long distance trains.