Cypres firing at Otay

[billvon 2,426]

We had a cypres firing at Otay last weekend. A JM wearing a student rig had just landed; he was talking to a student with a radio transmitter. The Expert Cypres fired and the reserve PC popped out. It had been back for service since the EMI issue was identified, and still had its "EMI shield" on the control unit. It is being sent back to SSK for evaluation.

JM's out there may want to consider if they want to talk to students before they land; a misfire in the air is a lot bigger problem than a misfire on the ground.

[quade 3]

Along with the Cypres unit itself, did you also send the walkie-talkie that triggered it?

You wouldn't happen to know the power output of that particular walkie-talkie would you?

Side topic. Do you think it would be ok to use a cell phone near a Cypres?

quade -
The World's Most Boring Skydiver

[billvon 2,426]

>Along with the Cypres unit itself, did you also send the walkie-talkie
> that triggered it?

Nope, although we will if Cliff wants it. It's unlikely they will do the testing there; he will have to decide if he wants to send it to Germany.

>You wouldn't happen to know the power output of that particular
> walkie-talkie would you?

No. No one seems to know anything about them. I _think_ they are around 49mhz.

>Side topic. Do you think it would be ok to use a cell phone near a
> Cypres?

CDMA yes, TDMA maybe, analog no. The power output of CDMA phone is so low and broadband that rectification is _very_ unlikely. TDMA is higher power and single frequency, analog is very high power and constant.

[quade 3]

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No. No one seems to know anything about them. I _think_ they are around 49mhz.

I'm not too concerned about the frequency, but rather the power.

1 watt? 5 watts?

quade -
The World's Most Boring Skydiver

[MarkM 0]

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JM's out there may want to consider if they want to talk to students before they land; a misfire in the air is a lot bigger problem than a misfire on the ground.

Heh, just don't tell students why you wait to land before using the radio.

Student: "What do you mean you're worried about the radio firing off your Cypres? Don't I have a Cypres?"

[nigel99 144]

usually licence free walkie talkies (I assume that is what was used) are about 10dBm output power (10mW) this is a fraction of a phone normally. Frequencies - 49Mhz is ligitimate in Europe (I know nothing about USA 49Mhz) but pretty much outdated. Most cheap walkie talkies operate around 400Mhz - 450Mhz these days.

Experienced jumper - someone who has made mistakes more often than I have and lived.

[skybytch 259]

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Student: "What do you mean you're worried about the radio firing off your Cypres? Don't I have a Cypres?"

Shouldn't the student know that their Cypres can malfunction? Oh, wait, if they knew that they might think skydiving isn't a safe thing to do...

[diverdriver 5]

Bill, I've seen this with a cypres also....when the rig was opened up the Cypres unit had cracks in the casing from packers abuse in packing. They also carried the rig by its' yoke where the control unit cable ran creating cracks in the cable housing. There seemed to be many ways the shielding could be corrupted and allowing interference.

Chris

[quade 3]

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usually licence free walkie talkies (I assume that is what was used) are about 10dBm output power (10mW)

Here in the U.S. our power output for non-licensed radios can be quite a bit higher. For instance, Motorola makes some fairly inexpensive ($30) "Talkabout" Family Radio Service radios with 500mW output. Step up to a minimal lincense for business use and the power output can similar, but more expensive radios can be a 1 Watt. Need more power? 5 Watts is not out of line. Obviously more power means more money, but I think you get the idea.

Contrast this with the power outputs of my cell phone. 40mW to 490mW in analog mode and 0mW to 570mW in the digital mode.

So, if somebody keys a 5 Watt radio next to a Cypres and it fires, well, that might not be too unexpected even with shielding and what not, but a 500mW radio firing one would be rather unexpected (at least by me). So, I think knowing the exact model and power output of the radio is pretty much vital in this case.

quade -
The World's Most Boring Skydiver

[thrillseek 0]

Wait a minute...
The JM was the one talking the student down???
Am i the only one that thinks this is a terrible idea???? Maybe it's just the way we do things at my DZ, but there is someone else on the ground that talks to students, NOT the JM that was in the plane. If i mis-read this, forgive me

[justme 0]

>>JM's out there may want to consider if they want to talk to students before they land; a misfire in the air is >>a lot bigger problem than a misfire on the ground.
When you have the transmitter in close proximity with the cypres unit..ok..that can happen..although it should not have occured. On the other hand..the emi-shielding of the unit can't be and isn't 100% effective..is the transmitter is strong enough and close enough..this can happen I think.
But a misfire in the air because someone is talking on the ground...That's not going to happen. Don't worry about that. I presume there is only one-way communication here.. the student is not transmitting but only receiving.

[billvon 2,426]

>The JM was the one talking the student down???

In this case, yes. Often, if there's only one student, the same JM that jumps with them talks them down. When there's more they generally have someone on the ground and someone in the air with a radio. They need a radio on the aircraft to do a final gear check, so it has to be with a JM anyway.

[nigel99 144]

ok - I didn't realise that the US allowed so much higher licence free output powers. I also assummed that a DZ would not be using (commercial/business/licenced radios). If they are yes I think definate caution as it is the same in Europe 1 to 5W output powers.

It is a bit concerning that the Cypres guys have not mastered immunity to interference at pcb/design level - considering that this is a safety/life critical device (by life critical I mean that you cannot afford it to go off ad-hoc).

Along these lines - why do people not get mis-fires from the aircraft radio - the antenna is usually external so the body of the plane should shield - but what about an RW exit where people (float? - not sure on terminology)

Experienced jumper - someone who has made mistakes more often than I have and lived.

[thrillseek 0]

Hmm...guess my "small town roots" are showing.
We do gear checks in the plane as well, but the JM doesn't need a radio for that. The pilot signals that they are on jump run, or that they have jumpers away and then it is up to the personnel on the ground to control the air traffic of the student(s). We have never had any trouble with this, but then again, we are a smaller dz.

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