Author Topic: Simulcasting on Center Freqs  (Read 7504 times)

Offline BMT

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Simulcasting on Center Freqs
« on: January 24, 2007, 01:46:38 PM »
Anyone know why the FAA got away from simulcasting on Center freqs??
I'm lucky to hear either KZJX and KZMA simulcast on any freq. I know most military A/C are equipped with both VHF and UHF radios.

BMT



Offline PHL Approach

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Re: Simulcasting on Center Freqs
« Reply #1 on: January 24, 2007, 01:59:06 PM »
Never heard of the term Simulcasting used in monitoring... You mean combined?

Offline BMT

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Re: Simulcasting on Center Freqs
« Reply #2 on: January 24, 2007, 03:44:39 PM »
That will also work. ;-)0

BMT

Offline dave

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Re: Simulcasting on Center Freqs
« Reply #3 on: January 27, 2007, 03:09:48 PM »
I think simulcasting means broadcasting on the same frequency from two different physical sites. 

That is different than combining.  Combining is a single controller broadcasting on more than one frequency (and possibly different physical sites on the "other" frequency).

For the CON 37 sector Boston Center seems to broadcast simultaneously on 134.7 from both Gardner, MA and Lebanon, NH.  Not sure if they still do it...I know they do switch between the transmitters a lot, but there are times when you can hear them simulcasting.

The theory with simulcasting is that a given airplane will only hear one of the transmitters at a time.  If they hear both, it can sound distorted due to the physical paths being different - the signals arrive at the plane's receiver with different signal strengths and phase.

-dave

Offline BMT

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Re: Simulcasting on Center Freqs
« Reply #4 on: January 27, 2007, 06:42:53 PM »
Maybe I need to reword my question. ;-))

When a ARTCC RCAG vhf and uhf freq are paired, why doesn't Center key up both freqs when transmitting?

Jacksonville and Miami Center only key up both freqs mostly early on Saturday or Sunday mornings.

BMT

Offline dave

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Re: Simulcasting on Center Freqs
« Reply #5 on: January 27, 2007, 10:22:59 PM »
Maybe I need to reword my question. ;-))

When a ARTCC RCAG vhf and uhf freq are paired, why doesn't Center key up both freqs when transmitting?

Jacksonville and Miami Center only key up both freqs mostly early on Saturday or Sunday mornings.

BMT


It depends somewhat on the level of military aircraft in the area at any given time.  Some facilities (Tower, Approach, Center) key both all the time and some key both intermittently.

Each facility has a reason - and for some it's probably in their SOPs.

-dave

Offline davolijj

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Re: Simulcasting on Center Freqs
« Reply #6 on: January 27, 2007, 10:58:15 PM »
I can't speak for ZJX or ZMA but where I work every sector transmits on both VHF and UHF continuously and simultaneously.  Regarding Dave's post, we have some low sectors with multiple transmitter sites so as to insure continuity of frequency range for low-level aircraft.  In those cases we receive from both tranceiver sites but only transmit on one at a time (depending on where the traffic is reference the transmitter site).  That way aircraft within reception range of both sites don't receive a signal interferance from both transmitters.  I'd imagine aircraft hear transmissions of differing quality as the sites are changed.

We receive aircraft transmissions from both sites and use a tool called diversity algorythm to filter the signals into the best usable reception.

Offline JetScan1

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Re: Simulcasting on Center Freqs
« Reply #7 on: January 27, 2007, 11:20:51 PM »
Anyone know if there is there any talk in the US of installing a link system like they have in Canada and Europe were if one controller is working multiple frequencies they can link the frequencies together so that aircraft monitoring one frequency can hear aircraft on the other frequencies ? This is really nice in some cases for situational awareness, it's also really annoying sometimes in the US when you are transmitting on one frequency and you keep blocking someone else out because you can't hear them on the other frequencies. Anyone know the technical name of this linking system used in Canada and Europe ? DJ

Offline Pygmie

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Re: Simulcasting on Center Freqs
« Reply #8 on: January 28, 2007, 02:20:23 PM »
JetScan1:  It's called frequency coupling.  And yes, it's a very nice system to have in place, for both sides of the mic.