ADF can tell you where an ELT is coming from?

[nouseforaname]

Heard something on the radio today a Vatlantic pilot was able to tell London term ctrl that the ELT they could hear was coming from 200 deg. When the controller asked how he knew that, the pilot replied 'by tuning my adf into 500mhz'......finally a use for the ADF ?! (joke)
Did anyone else know you could do this?

[2 sheds]

kilohertz, perhaps?

2 s

[DX Wombat]

Why not? The ADF was tuned to the ELT's frequency just as it is usually tuned to the beacon's frequency when being used for navigation.

[Captain Smithy]

You can pick up AM radio on it too.

[Pilot DAR]

No, it's the other universe in which an ADF can be tuned to 121.5 mhz

[IO540]

That's right; no ADF can receive the 121.5MHz ELT emission, never mind the 243MHz or the 406MHz ones.

Especially as the 406MHz is active for only a few seconds each minute so you would need to be the resident CAA NDB hold examiner to get a bearing :)

[411A]

There were some older ELT's in the past that transmitted on 500 KHz, which was...one of the recognised international distress frequencies...don't know about today however.
All newer ELT's use 121.5 and 406 MHz, and none that I am aware of use 500KHz any longer.

[SNS3Guppy]

An AM radio, tuned until the ELT audo warble is heard, can be used to DF (directionally find) an ELT. I've done it many times. Likewise, the same can be done airborne with an ELT and an ADF, or simply the aircraft radio tuned to 121.5.

Many ELT's which are now produced in 243 will continue to broadcast on 121.5, as it's constantly monitored my much of the air traffic overhead.

If one knows where one's antenna is, one can fly a steep 360 to locate the "null," or area where the signal is weakest. If the antenna is on the bottom of the turn, a steep turn with the antenna away from the signal will produce the null; the signal is "above" the aircraft, or 90 degrees to the direction of flight in the topside direction.

The aircraft then flies to another location and does the same thing, finding the null line, and finally triangulates the signal. I've done it a number of times in the air and on the ground, accurately enough to finally fly right to the ELT. It's a simple exercise to do the same thing with a battery powered, handheld AM radio, when an ELT is going off on the ramp. One can locate it using null to some degree, and when one has an idea where it is, simply approach suspect aircraft and bring the AM radio near the ELT antenna. The offending aircraft will be painfully obvious.

One can tune the AM radio away from the loudest signal and use that as a sqelch. When nearly on the ELT, it will be squawking through the AM radio regardless, and the louder and more pronounced the warble, the closer one is to the ELT purely on the basis of signal strength.

A handheld transceiver works the same way; squelch it down (turn the gain down) until the signal is nearly non-existent, and it will still howl when close to the signal.

I've not seen an ADF used to point to the signal, but I suppose it would work. I don't know what frequency would produce a lobe or otherwise, cause the ADF to point, but you can certainly DF the ELT by hand using audio, alone.

[IO540]

The only way a standard long-wave ADF would pick up 121.50MHz is if it was totally broken. The frequencies are apart by nearly a thousand times.

[SNS3Guppy]

It doesn't matter. The ELT signal is strong enough it will bleed over. I've done it many times. It can be heard over the AM radio/ADF.

I used to train people in locating ELT's using various method, in the air and on the ground.

[nouseforaname]

oh right so the bearing that was given probably wasn't accurate. I just wondered because I didn't know you could possibly use the ADF for that. As for the signal coming through on my ADF because of a strong elt I don't think so because it was a really weak xmission from whatever elt was going off. Anyway. Obviously you can't use the ADF for that then. So another reason why it should be thrown out the window at 20,000 feet!

[IO540]

An ELT 121.5MHz emission is very weak. I don't recall the power but it is only milliwatts.

There was some quirk in the specs enabling an old 121.5+243 beacon to emit more power on 121.5 than a 121.5+406 beacon was allowed to emit on 121.5, but the difference was not great.

That's why one cannot pick it up from more than about 20nm away; the 121.5 emission from a normal modern ELT is good only for short range VDF, using equipment mounted on the search & rescue aircraft.

The idea is that the 406MHz emission (and previously the 243MHz emission, before they shut down the satellites) gets the agencies within not too many miles and then they use VDF to home in.

(If you have a 406+GPS beacon, the agency should get your lat/long from that, which is great, but AIUI the vast majority of S&R vehicles in Europe have no way to fly to a lat/long position. I find this a bit odd since they must all have a GPS. I think what they haven't got is the capability to receive the 406 emission directly and use the GPS data from it to home in).

If my KR87 ADF picks up a 121.5 emission, I will gladly eat my pilot's seat, including the metal frame (can't be that hard; it is made by Renault) and I will do it while dodging small arms fire :)

If you think about it, if an ADF picked up 121.5, which lies bang within the VHF AM comms band, the ADF receiver would be completely useless for receiving NDBs. It would be forever led astray by every damn VOR within god knows how many miles, and every VHF voice transmission.

No, sorry, I don't believe this one at all. Not even 1%.

[forget]

No, sorry, I don't believe this one at all. Not even 1%.

Agreed. Opening Post is technically impossible.

[FlyingStone]

I have heard and witnessed VHF interference when flying very (!!) near a FM station transmitter, the music started playing in the headset, since VHF COMM (118-137 MHz) and FM broadcasting (87.5 - 108 MHz) are very close, but to hear 121.5 MHz on ADF - c'mon guys, probability of that happening is probably infinity to one :=

[24Carrot]

Not really relevant to the OP, but if you are very close to a transmitter you may pick up stuff at lower intermediate frequencies which aren't mean to be transmitted, and are only transmitted at very low power.
In my student days I spent a year close to a police station, and on a bad day even my cassette player picked them up. I think somebody told me it was non-linear amplification behaving like a rectifier. Or something.
And Mr Plod was very boring indeed, totally spoiling my Bachman-Turner Overdrive...:bored:

[IFMU]

I thought one of my buddies formerly of the USCG told me they had equipment to DF in on an ELT. I'll ask him tomorrow.

-- IFMU

[SNS3Guppy]

I thought one of my buddies formerly of the USCG told me they had equipment to DF in on an ELT. I'll ask him tomorrow.

Commercial equipment is available for DF'ing an ELT, both in the air and on the ground. It receives on 121.5, 243, and 406.

The aircraft radio can be used for the same thing.

An AM radio or ADF (same thing; the ADF is an AM radio receiver) can only be used when a strong enough signal is available to pick up the ELT. This generally requires close proximity.

No, sorry, I don't believe this one at all. Not even 1%.

You don't have to believe it. I was involved in quite a number of aerial and ground searches for ELTs over an eleven year period (all successful, when we had a signal). I instructed aerial and ground search.

An ADF is not used for aerial search. An AM radio, however can be used on the ground, and works quite well. On a ramp where an ELT is going off, one can locate an ELT easily enough with simply an AM radio, if one wishes.

Your belief was never required to locate an ELT, for fortunately we did just fine without it.

[IO540]

I thought one of my buddies formerly of the USCG told me they had equipment to DF in on an ELT. I'll ask him tomorrow.

Yes, this is standard. That is how one homes in on an ELT: standard VDF equipment. One homes in on the 121.5 transmission, which is continuous.

AIUI, few S&R assets in Europe have any VDF capability on 406MHz.

All ELTs emit on 121.5, regardless of any other capability, and in the USA the equipment carriage regs are met with a 121.5-only unit.

[Captain Smithy]

I have heard and witnessed VHF interference when flying very (!!) near a FM station transmitter, the music started playing in the headset, since VHF COMM (118-137 MHz) and FM broadcasting (87.5 - 108 MHz) are very close, but to hear 121.5 MHz on ADF - c'mon guys, probability of that happening is probably infinity to one :=

That's very worrying. Wasn't the whole point of FM Immune all those years ago to stop that from happening? :uhoh:

[forget]

Your belief was never required to locate an ELT, for fortunately we did just fine without it.

Guppy, I think you've missed the point of IO540's post. The OP said that a commercial airliner's ADF had been able to get a bearing on a 121.5 transmission. Not possible.

No one's doubting that airborne VDF exists (Collins DF-301 etc) and that other home-made methods may work.

[Fuji Abound]

Likewise, the same can be done airborne with an ELT and an ADF, or simply the aircraft radio tuned to 121.5.

I think this was the statement of Mr Guppy's that everyone was reacting to.

[Aerials]

Several contributers have taken the view that it is impossible to receive Amplitude Modulation transmissions on 121.5 MHz on an ADF receiving on a few hundred Kilohertz and I have the same opinion. The frequencies are separated by a huge margin which is most definitely outside the frequency range of receivers designed for ADF.

That said, Amplitude Mod as a transmit-receive system is susceptible to being able to detect signals outside the normal operating range provided that they are in close physical proximity, such that the first stages of signal filtering in the receiver are “overpowered” as has been described by the reception of strong local signals from Police stations (and local taxis etc).

Another factor is how pure the transmitted signal is – a “dirty”, mal-adjusted one will radiate on several frequencies simultaneously. Indeed, it may be that historically, 243.0 MHz came into use to be able to capture the second harmonic of 121.5 MHz.

So, using a cheap transistor radio on the “AM” waveband in close range on the ramp would probably work and tuning across the range wouldn’t have much effect on how well the ELT is received. The VA offering to use ADF to locate the ELT is very commendable but completely misguided for not appreciating how frequency is measured, equipment capability and for my reasons above.

[forget]

Here's the only practical way of homing in on a VHF transmission (121.5 perhaps) with commercial aircraft equipment. Copybook effort. :ok:

http://www.pprune.org/5879539-post27.html

[IO540]

That said, Amplitude Mod as a transmit-receive system is susceptible to being able to detect signals outside the normal operating range provided that they are in close physical proximity,

I agree (as an electronics engineer who at the age of 13 used to build pirate radio transmitters comprising of a pair of 807s, followed by a less than exhaustive PI-tank :) ) but I think if this worked habitually, it would soon be realised that the NDB at any airport which also has a VOR there would be pretty useless.

Very interesting about 243 being 121.5. Never spotted that :) It must be that they simply generated a dirty 121.5 and then filtered everything above 243, to achieve a simple design. 406 is much more complicated in comparison.

[JW411]

Airborne DF has existed for over 50 years. We had the facility on the old HS Argosy to home in on a buddy using a UHF frequency. He transmitted (a sprung loaded 1000 kcs tone switch was also supplied for this purpose) and the homing aircraft followed an instrument just like a zero reader which gave a fly left/right and a fly up/down indication.

The equipment was known as "Violet Picture".

Needless to say, we could find an ELT (we called them SARBE) with great accuracy. I can remember doing an exercise at Thorney Island. The ELT was inside a hangar and we were even able to tell them which corner of the hangar it was in!