What if a scanner ISN'T needed?

[tyketto]

I just thought about this. What if, and how would one go about setting up a feed that doesn't require a scanner?

As most of us know, At Las Vegas McCarran Int'l and at North Las Vegas airports, there is a settee/parking area where you can sit and planespot and listen to ATC without the need for a scanner. The Clark County Dept. of Aviation has set up a transmitter near the field that will broadcast Tower communications around the sitting area over FM radio (If you're ever at these areas, tune your radio to 88.5fm).

If one were there, or in a permanent place (such as an apartment or home) that can pick up this broadcast, what would be needed to plug to/from the radio to the soundcard for a feed? Mind you, these are broadcasting permanently; when VGT closes shop at 2100 local, the tower frequency is the CTAF; LAS never closes.

So, what would be needed to set up a feed going over FM radio?

BL.

[keith]

This doesn't change the picture much. The scanner is just a radio receiver. The output from the scanner is fed into the headphone or line-in input on your soundcard.

Encoding software takes that analogue signal, converts it to digital, performs various forms of compression, and then streams the data to the liveatc servers, where its archived and distributed to listeners.

The only part of the equation you're contemplating changing is swapping out a 'scanner' for a more traditional radio receiver.  'Rest of route unchanged'

[tyketto]

So if I just plugged the headphone jack of a stereo into the mic jack of the soundcard, it should be good to go?

BL.

[Jason]

So if I just plugged the headphone jack of a stereo into the mic jack of the soundcard, it should be good to go?

BL.

Substiute "stereo" with "scanner" add the same software, and it's the exact same thing.  The only difference would be with the radio: more interference (FM bleed-over, etc) signal strength problems, etc, etc.  The only thing that would be easier feeding through a regular FM radio receiver would be cost....but not many places broadcast airport transmissions on an FM frequency.

Hard to come by...

Jason

[PHL Approach]

more interference (FM bleed-over, etc) signal strength problems, etc, etc.

I disagree. You would have the same if not more interference with a scanner. Now if they were doing that on AM, yea on some stations you could pick up bleed over, electrical interference. But since it's FM, I imagine it 1. has to be clear and 2. will not have other stations bleeding over since it is dedicated. In actuality it should sound the same as any of the other feeds.

[Jason]

2. will not have other stations bleeding over since it is dedicated.

It all depends on how dedicated it really is....dependant on who runs the FM feed, and what frequency they transmit on.

Jason

P.S. Interesting to compare the two, I just don't see a major difference besides lower cost on the receiving side.  This all includes added cost at the point of the FM re-broadcast.

[sean]

What everyone is really concerned with, though, is quality.  Re-sampling is bad, no matter how you look at it.  So to take this down a notch to a slightly more technical level, consider the signal path:

Aviation Band -> receiver -> audio -> 88-108 MHz transmitter -> receiver -> audio -> soundcard ..  and so on..

Ideally it would be:  

Aviation Band -> receiver -> audio -> soundcard

Most of the steps in there are going to have filters of different kinds, different properties of the audio, etc.  

In general I would agree that you're more likely to suffer harmful interference (yes, there is such thing as beneficial interference) in the 88-108 MHz band - in this circumstance.  That is, this re-broadcast setup surely uses a very low power unlicensed transmitter, and thus is going to produce a very weak signal at your receiver.  That's fine if you're close to it, but once you get outside of the "capture" area you're going to suffer from co-channel and adjacent channel interference from the booming stations that are nearby.  Down in the aviation band that isn't likely to be an issue -  the FCC rarely licenses another Class B tower on the same frequency in the next town over.  

So you want ideal?  Run the stream from the conditioned audio coming out of the FAA's transceiver.  If you can get us in the shacks (legally) I'll supply the PCs.

And while we're having a technical discussion  - for the purists - keep in mind that AM and FM are the modulation techniques, an in a purely technical environment shouldn't be used to describe frequency ranges.  Think of it like telling someone you drive a "car with 4 wheels."   Well, that tells me something about how it gets around, but doesn't do much to pin down a make, model, year, etc.  Every airplane has an "AM radio"...  both in the sense of the 720 channel aviation radios, and in some cases ADFs, which we all know can be used for "AM Radio" listening, and lightning detection - but that's a thread for another time!

Sean

[tyketto]

For this one, it's the actual county that runs the FM feed.

Pre-2001, both feeds used to be on the AM band; 1610, to be exact. They took it off altogether after 9/11, and reallocated 1610 for use for road construction alerts around the Las Vegas area. It was at that time they put it back up on FM radio. I've listened to it on a car stereo, and it came through clear without any bleeding whatsoever, and very clear, especially if you have a digital tuner. I would back into the parking area, open up the back of my car, and sit on the tailgate of my car, and listen to it from there, while tuning my scanner to the final approach frequency, so I could hear things from approach all the way down. They even encourage it:

http://www.f-16.net/modules/PNphpBB2/files/imag0009__small_.jpg

This is what got me thinking about it.

BL.

[KSYR-pjr]

For this one, it's the actual county that runs the FM feed.

Not meaning to rain on this parade, but my first thought is that just when you get all the pieces in place to start feeding this transmission to LiveATC, the county will pull the plug on this free transmission for some silly reason (not related to the fact that you are transmitting it, but rather some other reason - funding, security, or whatever).

If it were me and I lived in the Las Vegas area, I would spend the money for an inexpensive scanner and be completely self-reliant.     Additionally, you can also provide approach/departure control, in addition to the tower.

[sean]

Truth be told, when it comes to new sites in GOOD QUALITY locations, its less about equipment than it is finding a GOOD HOME.  If we could find a decent location near every Class B and major Center outlets, the equipment wouldn't be a problem, in my opinion.

Trying to find a site that has a reliable connection, external antenna (or capability for one), and a responsible "lighthouse keeper" is not easy.  Finding scanners, PCs, and configuring software is something that can be done in the sleep!  The former is the impossible task!

[tyketto]

For this one, it's the actual county that runs the FM feed.

Not meaning to rain on this parade, but my first thought is that just when you get all the pieces in place to start feeding this transmission to LiveATC, the county will pull the plug on this free transmission for some silly reason (not related to the fact that you are transmitting it, but rather some other reason - funding, security, or whatever).

If it were me and I lived in the Las Vegas area, I would spend the money for an inexpensive scanner and be completely self-reliant.     Additionally, you can also provide approach/departure control, in addition to the tower.

In this case, the county couldn't do something that they're already guilty of to begin with. They would be the ones providing the very reasons they'd use to pull the plug (security, funding, etc), by broadcasting it themselves!

Anywho, the reason I'm asking this, is because a friend of mine just moved, and is now at the apartment across the street from the 25s, and can pick up the radio transmission clearly. I thought I'd save him the money in buying a scanner and get him to feed the FM radio broadcast through to LiveATC. The feed has been there for at least 8 years (since I moved there), and don't believe it is going anywhere anytime soon.

BL.

[Tomato]

Hm, I can't say I'm continuing the thought here, but I think it's really cool that the county is running the FM station that re-broadcasts the ATC voice!  How does it work though - which frequencies are transmitted?  For example, ATIS wouldn't be as it would collide with other control...?  

[tyketto]

Hm, I can't say I'm continuing the thought here, but I think it's really cool that the county is running the FM station that re-broadcasts the ATC voice!  How does it work though - which frequencies are transmitted?  For example, ATIS wouldn't be as it would collide with other control...?  

In KLAS and KVGT's case, they limit the range of the broadcast, as they both use the same FM frequency. It's limited to a few hundred feet. Also, in their cases, it is only the Tower frequency that is transmitted. KVGT only has 1 tower frequency, so it covers the entire field as far as tower is concerned. the settee area for that is at the intersection of the approach end of runways 12L/R and runway 7 (corner of Rancho and Cheyenne).

At KLAS, the settee area is parallel to runways 25L/R. As there are two frequencies at KLAS, they only broadcast for the 25s, on 119.9 (this will also be hte combined frequency when the other tower closes). Only setback with this is that if the winds favour arriving on runways 1L/R, only the other tower frequency will be used, as the majority of the traffic will be headed there. Those arrivals aren't able to be seen at the settee area, so winds play a big part on if you're going to planespot there or not.

BL.