SR 99 tunnel observations

[valvashon]

I have driven the 99 tunnel for a few days now and have noticed a few things about radio reception-

1- I usually listen to KSER Everett 90.7 on the way into work. I used to get a listenable signal on the viaduct but it disappears completely in the tunnel.

2- KEXP 90.3 and KUOW 94.9 have a great signal in the tunnel. Other full power Seattle stations come in too although I haven't listened to them extensively. Hitting scan on the radio won't have the radio stop on many of them, but if you tune in directly or have them on a preset they come in good.

3- Seattle AM stations come in well, also.

4- Flea powered 96.9 KODX from the U-district (essentially a Pacifica affiliate) used to come in good at my South Lake Union location, and I could follow them through the Battery Street tunnel but once on the viaduct the country station from down south (KYYO) would overwhelm them. I discovered that now, KODX comes in great the full length of the tunnel, getting an unexpected boost in coverage. In the early morning, when KODX isn't on, KYYO disappears once I enter the tunnel at the south end.

5- My mobile phone is on Verizon; in the middle of the tunnel the signal went to 1 bar and then to no signal.

Obviously there is an antenna and broadband amplifier inside of the tunnel for both AM and FM stations. I do find it interesting what stations it amplifies and what stations it doesn't.

Val

 

[The New Chico]

I have driven the 99 tunnel for a few days now and have noticed a few things about radio reception-

1- I usually listen to KSER Everett 90.7 on the way into work. I used to get a listenable signal on the viaduct but it disappears completely in the tunnel.

2- KEXP 90.3 and KUOW 94.9 have a great signal in the tunnel. Other full power Seattle stations come in too although I haven't listened to them extensively. Hitting scan on the radio won't have the radio stop on many of them, but if you tune in directly or have them on a preset they come in good.

3- Seattle AM stations come in well, also.

4- Flea powered 96.9 KODX from the U-district (essentially a Pacifica affiliate) used to come in good at my South Lake Union location, and I could follow them through the Battery Street tunnel but once on the viaduct the country station from down south (KYYO) would overwhelm them. I discovered that now, KODX comes in great the full length of the tunnel, getting an unexpected boost in coverage. In the early morning, when KODX isn't on, KYYO disappears once I enter the tunnel at the south end.

5- My mobile phone is on Verizon; in the middle of the tunnel the signal went to 1 bar and then to no signal.

Obviously there is an antenna and broadband amplifier inside of the tunnel for both AM and FM stations. I do find it interesting what stations it amplifies and what stations it doesn't.

Val

Sounds like the pickup antenna (headend, I guess) is somewhere up towards the north end of the tunnel. They put it where it would fit and not get in the way of anything else...if it moved 3 feet, you might lose KODX and gain KSER.

Wouldn't be surprised if eventually all the cell services came in there as well. If they can get coverage into the bus tunnel, they can get it there.

 

[crainbebo]

I've always worried about the 'Big One' when it comes to that tunnel. We won't know when the Cascadia fault wakes up until it's too late. Boom - 9.0 earthquake. Would people be trapped to death in that tunnel with the destruction? Always thought that tunnel was a horrible idea and a waste of money. The Viaduct was a piece of Seattle history, OTOH...
And with bad cell coverage in there, that doesn't help in a disaster. At least you can get 1000 KOMO in there...

 

[WDAE-FM101]

Its interesting that the viaduct was considered an eyesore, but we are building miles and miles of elevated railways! Just think if the Burke Gilman trail still had rails, a natural corridor for commuting!

 

[Kelly A]

Earthquake? Just wait till the first fiery crash half way through that stupid tunnel. That tunnel will always be part of Mayor McQuimby's legacy. Right up there with his other great ideas:

* Selling most of the City-owned snow plows to other cities, then outfitting what was left with rubber plow blades that left nice layers of ice.
* Working behind the public scenes with Howard Shultz and an Oklahoma City ownership group to move the Seattle Supersonics. to Oklahoma City. Oh, then lying about his role in the process.
* Building an underground tunnel right next to a 100 year old wooden seawall that holds back Elliot Bay from flooding the Seattle Waterfront.

Radio Radio.

 

[boombox4]

I've always worried about the 'Big One' when it comes to that tunnel. We won't know when the Cascadia fault wakes up until it's too late. Boom - 9.0 earthquake. Would people be trapped to death in that tunnel with the destruction? Always thought that tunnel was a horrible idea and a waste of money. The Viaduct was a piece of Seattle history, OTOH...
And with bad cell coverage in there, that doesn't help in a disaster. At least you can get 1000 KOMO in there...

Not only will the 9.0 shake long and hard enough that you won't be able to stand up for six to eight minutes, the Seattle fault runs across the tunnel also. I hope they ultra-reinforced the walls of that thing. Like, with solid rebar.

To bring it back to the point of the post, I haven't been inside the tunnel, so I have no idea of the radio reception. Thanks for the report.

I know in some countries where there are tunnels miles long they apparently have radio reception. How they manage to project the signals inside a several mile long tunnel I really don't know.

 

[LITTLEBOYBLUE]

For the engineering types … wondering how the tunnel rebroadcast works. Do they have to have a pickup/retransmit for individual frequencies … or can they essentially "amplify" an entire spectrum range and rebroadcast the amplified version as a repeater?

 

[Kelly A]

For the engineering types … wondering how the tunnel rebroadcast works. Do they have to have a pickup/retransmit for individual frequencies … or can they essentially "amplify" an entire spectrum range and rebroadcast the amplified version as a repeater?

It is probably something similar to what was installed in the I-90 tunnel: A broadband AM antenna outside the tunnel that feeds a broadband transmission system inside the tunnel. The ground above and concrete/steel of the tunnel isolates the transmit from interfering with the receive antenna. Something similar for FM: A broadband receiver that covers the FM band provides an equally broadband IF input to a transmission system in the tunnel. The antenna spanning the length of the tunnel is what's called a leaky cable antenna. The leaky cable is just that, a cable running through the tunnel with essentially holes that allow the transmit signal to leak out.

 

[Bongwater]

It is probably something similar to what was installed in the I-90 tunnel: A broadband AM antenna outside the tunnel that feeds a broadband transmission system inside the tunnel. The ground above and concrete/steel of the tunnel isolates the transmit from interfering with the receive antenna. Something similar for FM: A broadband receiver that covers the FM band provides an equally broadband IF input to a transmission system in the tunnel. The antenna spanning the length of the tunnel is what's called a leaky cable antenna. The leaky cable is just that, a cable running through the tunnel with essentially holes that allow the transmit signal to leak out.

It's also a technology with, shall we say, possibilities?

https://www.youtube.com/watch?v=dCD2YQmoq7Q

 

[AAllen]

AT&T wireless came in fine during the tunnel walk last week, though none of my photos were geotagged.