LA MTA Red Line Underground vs Surface

[transitman]

During a recent visit to the Los Angeles area, I found a unique frequency arrangement which left several questions in my mind and I'd like to hear the opinion of others who read this posting.

The LA MTA Red Line operates underground throughout its trip (except for the storage yard). While underground, trains transmit on 160.755 (PL 136.5) and receive on 160.695 (PL 136.5). A duplex system is used so both parts of the conversation were heard on the receive frequency. What I found unusual was the receive frequency for the Red Line (160.695) is also used as the transmit frequency for the Gold Line (PL 103.5).

On the surface, no Red Line transmissions were heard on the frequencies used underground. Instead simulcast Red Line duplex transmissions were heard on 160.935 and 161.505 (both frequencies used PL 123.0) in the downtown area. Beyond the downtown area, the transmissions were heard on either frequency depending on location.

So the questions are:

1. Can the same frequency (with different PL tones) be used for both transmit and receive purposes?
2. Why would the LA MTA use different frequencies (underground vs surface) for the Red Line.

I hope my description is not confusing, if further information is needed, please post and I'll respond.

 

[Mick]

Good monitoring!

I've not ride ridden on these trains. Here's what I've logged from above ground:

160.935R/160.755 123.0 L.A. Co. MTA Red Line Road
161.5050 123.0 “Red Line”; simulcast of 160.935 123.0

161.265R/160.695 103.5 L.A. Co. MTA Gold Line Road

 

[transitman]

Mick:

FYI, other MTA Rail frequencies I found during my trip:

153.815 Red Line Yard, PL 146.2
155.805 Gold Line Yard, PL 136.5
161.145R/160.725 Green Line Road Operations
155.85 Green Line Yard, PL 146.2
161.565R/160.47 Blue Line Road Operations, PL 103.5
160.785 Blue Line Yard, PL 146.2
160.425R/160.635 Rail Facilities Maintenance, PL 136.5

 

[Mick]

I have 153.815 146.2 for Long Beach local government in my logs. I've seen 97.4 reported for L.A. Co. MTA but have not heard them on 153.815 with that.

Terrific catch on the rest of the frqs!

Mick:

FYI, other MTA Rail frequencies I found during my trip:

153.815 Red Line Yard, PL 146.2
155.805 Gold Line Yard, PL 136.5
161.145R/160.725 Green Line Road Operations
155.85 Green Line Yard, PL 146.2
161.565R/160.47 Blue Line Road Operations, PL 103.5
160.785 Blue Line Yard, PL 146.2
160.425R/160.635 Rail Facilities Maintenance, PL 136.5

 

[karldotcom]

I will start off by saying I have heard the LA Red Line on 160.935 one hot day in Arizona while driving on I-10.

I seem to recall that the Gold Line frequency was changed a short time after it opened. I would venture to guess that there may have been interference from other licensed users in San Diego...but am not sure. Perhaps they switched pairs with the Red Line then.

Looking at 160.695 it appears the next closest licensed user is Fresno. Due to the passenger use, it is probably safer to have different transmit and receive frequencies underground. You want to have your dispatcher hear an emergency call if they happen to be talking at the time. (Whereas on a freight railroad, they would be stepping on each others calls)