ELT Antenna

[♠SARKID♠]

I know that if you transmit on a radio without an antenna connected, it can cause serious damage to the radio.  If an ELT's antenna is broken/snapped off on impact, would it cause damage to the beacon?  Would that damage completely destroy the beacon?

[SarDragon]

I know that if you transmit on a radio without an antenna connected, it can cause serious damage to the radio. [Q1] If an ELT's antenna is broken/snapped off on impact, would it cause damage to the beacon?  [Q2] Would that damage completely destroy the beacon?

A1. Possibly. Some ELTs have a second antenna mounted directly to the unit, to enable its use outside the plane. As long as the transmitter has the correct load on it, it will not be damaged.

A2. Probably not. See A1.

[lordmonar]

With the power levels that an ELT can put out.....probably not.

The ELT puts out 5-10 Watts or much less.  Today's electronics can usually withstand that sort of SWR (Standing Wave Radio) that you get from and "open" antenna.

[sardak]

121.5 MHz ELTs transmit at a nominal 1 watt.

The 1/2 second 406 MHz burst on "new" beacons is transmitted at a nominal 5 watts.  The 121.5 MHz homing signal is a nominal 25 mW.

The technical specs for 406 beacons require them to meet all transmitter requirements at a VSWR up to 3:1.  Beyond that, the transmitter "shall not be damaged by any load from open circuit to short circuit."

The radiation pattern without an antenna, or a damaged antenna, is going to be screwed up, though.  If the transmitter itself is damaged on impact, who knows.

Mike

[Al Sayre]

If you have a crash and the ELT antenna gets snapped off, your chance of getting a signal out drop to miniscule, that's why a lot of them use a rather flexible wire antenna.  On the other hand burning out the final amp on your ELT is probably not going to be your biggest worry...

[capchiro]

lordmonar probably meant standing wave ratio for SWR in the above post.

[Eclipse]

If you have a crash and the ELT antenna gets snapped off, your chance of getting a signal out drop to miniscule, that's why a lot of them use a rather flexible wire antenna.  On the other hand burning out the final amp on your ELT is probably not going to be your biggest worry...

Right - most ELT's I have seen do not have the rigid, telescoping antenna found on practice beacons.

With no antenna, your transmit range is in feet - that's why removing the antenna on L-Per or scanner is a close-quarters DF technique.

[BillB]

I disagree. I've been to a crash where the antenna cable was torn loose from the ELT and the search aircraft still was able to vector in on the crash site from the ELT signal.

[♠SARKID♠]

Okay, I didn't think the SWR would be that important.  I ask because I was thinking about a crash scenario

Situation - A pilot crashes in the wilderness, setting off his beacon.  He survives the crash, but the antenna on his ELT doesn't.  He then tries to reconnect or fix the antenna.  Here's where my question comes into context: would the ELT have already been damaged by transmitting with no antenna, to the point that it would become inoperable?  I see now that it is unlikely that it would be.

[desert rat]

Now if the antena splits won't it give out a distorted signal and leaving the search in wrong directions.

[SarDragon]

Probably not. The one I got when I went Dumpster diving had the flexible antenna wrapped around it. The signal was detectable about 3 miles away, with the unit inside a large Dumpster with a bunch of metal scrap.