Horizontal Yagi on a GP-30

[N9JIG]

On the long hood of this TC&GB GP-30 there is a horizontally polarized yagi antenna. I assume it was to allow communications from the Ajo mine to trains going up the Gila Bend. The question is why was it not vertical? (Ajo AZ, 7-13-2017)

(It is much more clear on a full size image, available by email upon request...

 

[AK9R]

Interesting photo, Rich. As for horizontal vs. vertical, the radio waves don't care as long as both antennas are oriented the same. Maybe they found that they had fewer multipath problems in the mountains with horizontal antennas. Or, maybe they went horizontal with these link antennas to give them more isolation from the voice comms using vertical antennas.

 

[exkalibur]

Or, maybe they went horizontal with these link antennas to give them more isolation from the voice comms using vertical antennas.

That'd be my guess. Years back there was a linked VHF ham repeater near me that used UHF to link a remote receiver. The site also had a UHF repeater. The link antennas were made to be horizontal for exactly that reason.

Also I have heard (though I'm not sure if it's true) that horizontally polarized signals actually propagate further, hence why TV uses them.

 

[DaveNF2G]

Maybe they need to get under bridges.

 

[radioman2001]

Not sure the FCC would allow horizontal polarity. I accidently put H for antenna polarity on a license application and it was vary quickly rejected. Sounds more like the radio shop did it that way for clearance. You only get about 10db isolation verticle vs horizontal, so your guess is as good as mine?

 

[KK6ZTE]

Is that a UHF antenna? How long are the trains? If UHF, perhaps they're using it to receive EOT device signals?

I've heard 20dB as the rule of thumb for x-polarization loss

 

[N9JIG]

It is hard to tell even on the hi-res image as to the band, but I am leaning toward VHF. They ran with cabooses then (even sold passenger tickets for it!) so I don't think they ever had EOT's.

I would think they probably had a single base station radio at the office in Ajo, the line went north to Gila Bend, about 45 miles cross flat desert land. That might be pushing it for a locomotive radio...

 

[wa8pyr]

On the long hood of this TC&GB GP-30 there is a horizontally polarized yagi antenna. I assume it was to allow communications from the Ajo mine to trains going up the Gila Bend. The question is why was it not vertical? (Ajo AZ, 7-13-2017)

(It is much more clear on a full size image, available by email upon request...

Must be a newfangled Trainphone antenna. Shades of the PRR. . . .

My guess would be that vertical polarization would make it too tall and run too much risk of damage to the antenna elements.

 

[N9JIG]

I have come to find out that the GP-30's were used in the mines and yard and is why they were lettered "New Corneila Branch" (Ajo was the New Cornelia Mine). The switchers were actually used on the road trains up to Gila Bend. I think they were actually separate entities, the TC&GB was a common carrier that also carried passengers in the caboose while the mine operations were a private (as in not a common carrier) operation by the mining company.

Sometimes around the 1950's the mine tracks were electrified. While I was at the mine office* they had pictures on the walls of the mine over the decades. The 50's picture showed the overhead wire and a couple center cab locomotives in the pit. I suspect that the GP-30's were bought to replace these and there may well have been wire present that limited clearances.

The picture from the 60's showed the electrification gone in the pit and yard. The mainline to Gila Bend was never electrified.

* I had requested that I be allowed to recover a couple TC&GB switch stands I found from the track outside the gates at Ajo . They allowed me to take them and (after the wife wouldn't allow me to put them in our backyard) I donated them to the Arizona Railroad Museum.