[MRCA] URC-4

[D. Platt]

Peter's comments provide a very good description of the current and past 
setup for the Guard channels. I'll add that 243.0 (2 x 121.5 mHz) is the 
standard UHF guard channel along with a couple of others.  The 402Mhz 
EPIRB or ELT use burst technology and /can/ include identification and 
location information.  NOAA maintains the US registry of registered 
units.  One point of curiosity is that, way back, the military wanted to 
ensure that their distressed aircraft and aircrew were distinguishable 
from civil assets.  Thus, the tone sweep of civil beacons is a 
downward.  The military used an upwards tone sweep.  The normal test 
period for non-405 ELTs and EPIRBS is, if I recall correctly, 5 minutes 
past the hour for no more than 5 sweeps.  I will tell you, though, that 
the monitoring of 121.5 has deteriorated a lot.  Except maybe for the 
Baltimore/Washington/Dulles/Andrews area and other "hot" airspace around 
the country, many tower and RAG facilities just don't test and maintain 
Guard receivers and alarms properly.  CAP can still track older VHF/UHF 
beacons, once their detected, but no more midnight alert phone calls for 
them from the AFRRC, anymore. SARSAT and COPAS, etc. satellites do a 
very good job with the new beacons.....

Now, that said.. and if you live in/around the DC area, monitoring 121.5 
Mhz can provide some interesting conversations with errant aircraft in 
the local SFRA (Special Flight Restriction Area), and never mind those 
unfortunates who violate the Camp David P-40 and R-4009, especially when 
they're hot.  The JADOC has remote outlets all around the periphery of 
the DC airspace to ensure reliable comms on Guard channels.

Jeep - K3HVG
(Based at KFDK and KDAA)

On 8/19/2014 5:40 PM, Peter Gottlieb wrote:
> Originally the Emergency Locator Transmitters for aircraft and boats 
> (they called them EPIRBs) were on 121.5 along with voice emergency 
> comms.  LEO satellites monitored 121.5 and could get a rough position 
> fix by the use of doppler techniques.  Some years ago the locator 
> beacons were relocated to the 406 MHz area and the satellite 
> monitoring discontinued, although there are still a lot of 121.5 ELTs 
> out there.  Most all aviation control towers still monitor ("guard") 
> 121.5 but mostly for voice use, and many airlines also guard that 
> channel as well.  If you are an aircraft in distress you can use that 
> frequency but many times the controllers will just have you stay on 
> their frequency if it isn't busy.  I've had a few times where I was 
> flying in the middle of nowhere and been asked to go to 121.5 to test 
> comms with the ground station.
>
> After 9-11 when they created all these restricted flight areas, if you 
> wander into one the fighters (if capable of VHF) or ground stations 
> will try and reach you on that frequency.  I've heard that many times 
> in the northeast as I always make a habit of guarding it while flying.
>
> Civil Air Patrol generally does DFing for the beacons and it can take 
> hours.  If you're going to test, it won't raise alarms but PLEASE keep 
> it VERY short (as in a second or two) and preferrably use a dummy 
> load.  If there is an aircraft in distress (which you might not even 
> be able to hear) you might very well be interfering with the comms.
>
> Peter
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/mrca/attachments/20140820/e482aaeb/attachment-0001.html>