121.5 mhz

[toydriver_det]

Actually one thing I have found in some research which might be of interest to anyone reading who doesn't already know....

The AFRCC is phasing out 121.5/243.0 ELT satellite monitoring in 2008. It seems the frequncy used for EPIRBs 406.0250 will now become the ELT frequency.

So those who often monitored 121.5 might want to program in 406.0250 as well. And here is a link on this.

http://www2.acc.af.mil/afrcc/406 brochure.doc

very interesting stuff, for sure. The one thing I could not find was the mode. AM or FM? I did see where it is a digital signal so it may be FM. Has anyone ever heard the 406.025 signal? I am guessing it may be just a digital buzzing sound.
Toydriver

 

[INDY72]

Umm its FM .. but also realize that new narrowband AM Aviation freqs, and digital for aviation is eventually occuring also.

 

[JoeyC]

and digital for aviation is eventually occuring also.

I thought there was some kind of "issue" with digital and mobiles travelling at high speeds. I'm certainly no techy-type but I didn't think that could be done.

 

[ECPD279]

You will hear " ON GUARD" callouts on 121.5 Essentially all aircraft have at least 2 VHF radios and all are supposed to monitor 121.5 at all times for the purpose of being able to receive an ON GUARD alert at any time. This pertains to Visual Flight Rules and other urgent purposes. When you have 2 craft coming into close proximity of each other, invariably 1 of the craft notices the situation first. They all have to have the capability of craft #1 calling out to craft #2 to say: "hey you white beechcraft, I'm here and we're getting close to each other, I'm right behind you ect...." Such a radio call is made on 121.5 This is a nationwide frequency....perhaps worldwide.

You make it sound as if you think that all aircraft are required to monitor 121.5 all the time. I can tell you that this is not the case. It is ADVISABLE to do so if you have the capability, but not all aircraft have multiple radios. In some classes of airspace, aircraft are not even required to HAVE a radio! There is no requirement to tell another aircraft that you are coming up behind them, or that you are getting close. It is the responsibility of EACH PILOT to watch for traffic and make proper course corrections.

 

[INDY72]

Umm if there was an issue with digital and high speeds, there would not be digital radios in Public Safety Aircraft.

The issue with using digital for civilian aviation is not one of high speeds yadda yadda,.. its of logistics. Replacing every avaition system worldwide is NOT gonna be easy or cheap. Just like replacing every railroad system nationwide in the USA is not cheap, or simply done.. but thats happening too. Already happened on at least 4 systems nationwide that we are aware of. Digital is also planned for VHF/UHF maritime usage very soon. Now back to digital AM on aviation....

Itll start in the US, and then most likely the UK... then other EU nations will transition over time.... It will be probably close to 10 or more years before it even begins implementation in the experimental phases... and probably closer to 20 years for true implementation on a multinational basis.

 

[N_Jay]

Umm if there was an issue with digital and high speeds, there would not be digital radios in Public Safety Aircraft.

The issue with using digital for civilian aviation is not one of high speeds yadda yadda,.. its of logistics. Replacing every avaition system worldwide is NOT gonna be easy or cheap. Just like replacing every railroad system nationwide in the USA is not cheap, or simply done.. but thats happening too. Already happened on at least 4 systems nationwide that we are aware of. Digital is also planned for VHF/UHF maritime usage very soon. Now back to digital AM on aviation....

Itll start in the US, and then most likely the UK... then other EU nations will transition over time.... It will be probably close to 10 or more years before it even begins implementation in the experimental phases... and probably closer to 20 years for true implementation on a multinational basis.

I think the NEXCOM program is comming a bit faster than that.

As for the AM vs FM, thing, most digital modulation, while related to AM or FM is its own unique form.
AM and FM are analog modulation methods.

As to the speed issue, it is all a matter of design.
You have to design the modulation system to tolerate the dopler shifts expected. But it is not a significant problem.

 

[nexus]

ELTs and EPIRBS aren't digital though...

on 121.500/243.000 the transmission on elt's and epirbs is AM.

on 406.0250 I keep hearing that it's FM, which I don't doubt since that portion of the government spectrum is primarily FM.

ELT's send out an audible tone over amplitude modulation.

Newer fancier EPIRBS will send out an additional digital transmission which happens to sound like a burst of packet radio providing fcc license data.

 

[INDY72]

And then the Master of the knowledge has a chink in his armor LOL---

Umm digital modulation in P-25 requires iether CQPSK.. or can we all say it... C4FM.... hmmm FM in that thar animal..... Digital applied to the AM format thus creating DAM, or AMD if you will, is another beast altogether from digital on NFM/SNFM. No its not that much of a problem,.. but yes its gonna be a hassle for worldwide implementation. You can expect at least for ten years its usage as an experimental phase.... and expect worldwide for at least 20 years dual moded aviation radios. I can promise you that itll take that long to change EVERY SINGLE airport worldwide to the proper formatted radios.. even using SDR.... Heck there is a town in Louisianna that just got for the first time ever-landline telephone services- If it takes till 2005 for that to happen to a lil podunk LA village.... you really think that worldwide transition on the aviation band will happen fast and easy?

 

[N_Jay]

And then the Master of the knowledge has a chink in his armor LOL---

Umm digital modulation in P-25 requires iether CQPSK.. or can we all say it... C4FM.... hmmm FM in that thar animal..... Digital applied to the AM format thus creating DAM, or AMD if you will, is another beast altogether from digital on NFM/SNFM. No its not that much of a problem,.. but yes its gonna be a hassle for worldwide implementation. You can expect at least for ten years its usage as an experimental phase.... and expect worldwide for at least 20 years dual moded aviation radios. I can promise you that itll take that long to change EVERY SINGLE airport worldwide to the proper formatted radios.. even using SDR.... Heck there is a town in Louisianna that just got for the first time ever-landline telephone services- If it takes till 2005 for that to happen to a lil podunk LA village.... you really think that worldwide transition on the aviation band will happen fast and easy?

NEXTCOM is not "Experimental", but I will agree with you that teh full transition will be relitivly lengthy. 20 years is not unreasonable.

Yes, digital modulation does sometime fit into one of the fundemental families, AM, FM, PM, Pulse, SS, etc, but most advenmced forms actulally create a waveform on teh aire which does not fit neatly into any single catagory. i.e. C4FM/CQPSK. Hmm, is it FM or is is it PM??? I'm betting with a little bit of math you could create a compatable AM version also.

(just to be clear, the modulation part of the post was an answer to ToyDriver's post not yours, MILF.)

 

[LiberaFan08]

General Questions

What do Multicom and Unicom mean? I have recently named the frequency of 123.050- Helicopter/ Air to Air. I'm not sure I have correctly named it, can someone help?

 

[RiceCake]

121.5 and 243.0 beacons are low-power and simply emit a siren tone using AM modulation. They are, well, terrible. Something like ninety percent of them are false positives. They also have issues for detection so its advised to listen to the frequencies if possible to assist anyone.

The new beacons use a simple code burst that's emitted at higher power. It can contain serial numbers, GPS location, names, phone numbers, etc. If registered, when detected, people can be contacted for you and such using a database on the beacon. LEOSTAR/GEOSTAR satellites can more readily detect this signal and in some places SAR operations can be notified within minutes, rather than hours.

If you scan this you'll hear a code burst every ~50 seconds, assuming a beacon is tripped nearby.

As for analog voice;
http://en.wikipedia.org/wiki/Aircraft_emergency_frequency

This channel is quickly becoming the "aircraft distress" channel.

 

[nd5y]

What do Multicom and Unicom mean?

http://frwebgate1.access.gpo.gov/cg...SdocID=777109303241+2+0+0&WAISaction=retrieve

http://frwebgate5.access.gpo.gov/cg...SdocID=777271151777+1+0+0&WAISaction=retrieve

http://www.faa.gov/airports_airtraffic/air_traffic/publications/ATpubs/AIM/chap4toc.htm

 

[n8emr]

I hear lots of traffic on 121.5, lots of casual chit chat. Sounds like commercial pilots chatting with other commercial pilots.

 

[RiceCake]

Apparently that happens alot, probably because pilots are looking for 123.45 and don't notice the radio is on the wrong frequency. If 1 pilot grabs 121.5 and starts talking, the next pilot with his radio turned on monitoring the frequency for emergencies might not notice (or care) and simply start chitting back on it, blissfully unaware.