Can SAR Heli use 121.5 as a VOR?
Thread Starter
Can SAR Heli use 121.5 as a VOR?
We are just talking in our aircraft owners group about the ELT / PLB options. I wondered, once your aircraft had sunk beneath the waves, if a hand-held radio on 121.5 could be used as a VOR beacon by the SAR bods, whilst you bob up and down in the life-raft?
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@T/S: "to use as a VOR" they cannot, because it doesn't behave like a VOR, it behaves rather like an NDB. Shouting "I am here! I am here!" but without adding any directional information, which is the essential advantage of a VOR over an NDB. And by the way your PLB and ELT will be doing the exact same thing if/when activated (plus they may be adding useful information such as GPS-derived coordinates).
But it has rightly been stated that, among an impressive load of equipment, the rescue crew are bound to have some kind of direction finder which they can apply to anything you are transmitting with. With particular attention for the civilian distress frequencies of 121,5 and 406 MHz. They may even well be able to home in into your mobile phone.
But it has rightly been stated that, among an impressive load of equipment, the rescue crew are bound to have some kind of direction finder which they can apply to anything you are transmitting with. With particular attention for the civilian distress frequencies of 121,5 and 406 MHz. They may even well be able to home in into your mobile phone.
Originally Posted by Jan Olieslagers
They may even well be able to home in into your mobile phone.
406MHz PLBs also transmit on 121.5 for just this reason - so that SAR can home in on you at relatively short ranges.
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Ok, thanks, but an ELT does not transmit DF specifically, or does it?
For as little as I know about HF-electronics (I always considered it a kind of black art ... ) DF is done on the receiving side, not at the transmitter?
And if "transmitting DF" confuses me, I'm afraid I am utterly flabbergasted with "transmitting DF to the signal" - perhaps I am too much trying to understand? What is being meant?
For as little as I know about HF-electronics (I always considered it a kind of black art ... ) DF is done on the receiving side, not at the transmitter?
And if "transmitting DF" confuses me, I'm afraid I am utterly flabbergasted with "transmitting DF to the signal" - perhaps I am too much trying to understand? What is being meant?
Originally Posted by hoodie
I am pretty sure they can't do this.
They could DF on a transmission from 121.5 and 243 or if your ELT is transmitting, (they could) DF to the signal.
To direction find a radio signal you need a carrier wave, so any transmitter that produces a carrier, typically an AM airband transmitter, then it can be located. Phone signals tend to be transmitted in bursts or packets, so do not lend themselves to conventional DF. Phone locations are determined by ranging from the different cells that they communicate with, not much use off the coast in a dinghy!
Ok, thanks, but an ELT does not transmit DF specifically, or does it?
For as little as I know about HF-electronics (I always considered it a kind of black art ... ) DF is done on the receiving side, not at the transmitter?
And if "transmitting DF" confuses me, I'm afraid I am utterly flabbergasted with "transmitting DF to the signal" - perhaps I am too much trying to understand? What is being meant?
For as little as I know about HF-electronics (I always considered it a kind of black art ... ) DF is done on the receiving side, not at the transmitter?
And if "transmitting DF" confuses me, I'm afraid I am utterly flabbergasted with "transmitting DF to the signal" - perhaps I am too much trying to understand? What is being meant?
ELTs do not work on HF.
121.5 is VHF and the civilian normal frequency band, 243.0 is UHF and used by the military. An ELT is a transmitting 'beacon' on which a suitably equipped aircraft can home using what is essentially a variant of an ADF, able to receive the VHF and/or UHF bands.
DF (Direction Finding) is what an ADF does using signals from an NDB; we also used to tune in to commercial radio stations on a boring leg, or even use the transmission from the station to track for the transmitting antennae co-located with a small township where no enroute beacons existed in the GAFA.
So for the OP: yes, that's always been what an ELT/PLB/SARBE is designed for. To provide a homing signal on which another aircraft can find you
Modern ELTs are required to use 406mHz and be located by satellite. The location is then transmitted to the National SAR Centre for the area in which the distress call is received. The more expensive/better equipped 406 units will have inbuilt GPS which will significantly refine the location for searching.
The old S61N helicopters certainly could home to a 121.5 AM signal or, for that matter, any AM signal radiating in the aeronautical VHF spectrum. One of the two VHF transceivers was connected to a homing device, which drove a needle display. Now I must correct what I wrote earlier, but time has eroded the memory somewhat. It was a crude and basic display of signal strength and I think the procedure was to fly on any constant heading until the needle showed maximum gain and continue flying the same heading until the signal started to weaken.
Then turn 180 degrees and fly back to the point of maximum gain. At this point there was the choice of whether to turn left or right. If the aircraft was turned 90 degrees and the signal started to weaken, then simply turn back to the reciprocal and hopefully the aircraft would be going in the general direction of the beacon transmission. Those were the days! Oooaarrrh, Tom me lad. Shiver me timbers! Lash me to the wheel and hand me my trusty GPS. Don't even get me going on the joys of Decca Mk 19 hyperbolic navigation with moving "toilet roll" maps.
I'm fairly certain that some of the AS332L Super Pumas had something similar and I would think it unlikely in the extreme that the modern S92 SAR aircraft aren't fitted with an even better version of these homers. After all, it's their "bread and butter", their whole raison d'etre!
Then turn 180 degrees and fly back to the point of maximum gain. At this point there was the choice of whether to turn left or right. If the aircraft was turned 90 degrees and the signal started to weaken, then simply turn back to the reciprocal and hopefully the aircraft would be going in the general direction of the beacon transmission. Those were the days! Oooaarrrh, Tom me lad. Shiver me timbers! Lash me to the wheel and hand me my trusty GPS. Don't even get me going on the joys of Decca Mk 19 hyperbolic navigation with moving "toilet roll" maps.
I'm fairly certain that some of the AS332L Super Pumas had something similar and I would think it unlikely in the extreme that the modern S92 SAR aircraft aren't fitted with an even better version of these homers. After all, it's their "bread and butter", their whole raison d'etre!
Last edited by Colibri49; 3rd Oct 2016 at 00:07.
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Certain modern military aircraft have DF receivers which cover the VHF navigation frequencies, VHF civil and military bands, Marine band, military UHF and 406 MHz PLB frequencies.
So if you're bobbing about in the briny with a decent 406 MHz PLB, it won't be long before you're located!
So if you're bobbing about in the briny with a decent 406 MHz PLB, it won't be long before you're located!
Following the RN Sea Kings in 1970, and the Wessex in the 1960's and the Whirlwind: Violet Picture was the DF display
As already stated, yes the CivSAR are all able to find you with your ELT
Thanks John, no idea it went back that far.....just wanted to make the point DFing sn't a new fangled gizmo thingy....worked really well one dark and stormy night when I needed it...
Last edited by wiggy; 3rd Oct 2016 at 08:26.
My point was that certain modern military aircraft have DF receivers which cover a vastly greater range of frequencies and modes than did old helicopters' systems.
DF'ing a 156.8 MHz FM signal from a mariner in trouble is a handy function - particularly as the aircraft can also communicate on the same frequency and mode.
DF'ing a 156.8 MHz FM signal from a mariner in trouble is a handy function - particularly as the aircraft can also communicate on the same frequency and mode.
Certainly modern aircraft have far more sophisticated receivers; it's to be expected. But Violet Picture goes back to the 1960s and was used on far more than just SAR aircraft and had more uses than finding SARBE transmissions.
We had them in bog standard squadron aircraft and were routinely trained in their use for locating a beacon, but the stiff-wing also had them for such odd routines as finding the tanker, as BEagle will no doubt tell.
So the ability to find an ELT has been around in most military rotary squadrons for well over half a century, and has only got better as technology improves. Us old f@rts are harking back to that strange era, pre-mobile phones, pre-internet, pre-digital computers and pre-PC!
We had them in bog standard squadron aircraft and were routinely trained in their use for locating a beacon, but the stiff-wing also had them for such odd routines as finding the tanker, as BEagle will no doubt tell.
So the ability to find an ELT has been around in most military rotary squadrons for well over half a century, and has only got better as technology improves. Us old f@rts are harking back to that strange era, pre-mobile phones, pre-internet, pre-digital computers and pre-PC!
