Twisted pairs of wires

[rocketcharlie]

I know that it is good practice to twist pairs of wires to mitigate electromagnetic interference. In an AV bay which wires do you do this with? Battery cable, switch wires, wires leading to pyro charges?

Thanks,
Charlie

 

[FredA]

Everywhere you can.
Especially on long pyro runs or near transmitters.
There is no downside.

 

[mooffle]

You could always use some cat6. Pre twisted, 4 pairs, and shielded both internally and externally

 

[cerving]

You could always use some cat6. Pre twisted, 4 pairs, and shielded both internally and externally

I like using Cat-5/Cat-6 for deployment wiring, it's cheap and it's color coded. The twisting is a bonus.

 

[UhClem]

Twisting a wire pair together provides some protection from magnetic fields. But not all wire pairs are susceptible. Only those that form low impedance loops can pick up significant current.

Connections to e-matches don't really qualify. Unless someone has started selling an altimeter that actively shorts its inactive outputs.

But I tend to use STP because I have a spool of it under the workbench.

 

[JohnCoker]

When I first started in the hobby, there were still people using flashbulb filaments as primary initiators for ejection charges. These gave ejection charges a reputation for being susceptible to static electricity, but e-matches have a defined no-fire current which is way above what one would experience in normal circumstances (for that very reason).

I'm not sure how much current could be induced in a wire from the RF units we fly, bit it's hard to imagine it would be significant, and even more so to fire an e-match. At least this is something we could calculate: how much current could a 1W signal induce in a wire 1cm away?

FWIW, DaveyFire N28B e-matches have a no-fire current of 200mA.
https://royalarms.com/wp-content/uploads/PDfs/MSDS/squibb spec.pdf

 

[rocket_troy]

I once conducted a test with a 4W UHF transceiver and a grain of wheat bulb. The wires needed to be the right length (obviously) and oriented in a particular way for there to be a substantial illumination. If the wires were next to each other, there would be no illumination of the bulb.

www,propulsionlabs.com.au/Misc_Video_And_Images/RF_Test.MOV

Mind you, transmitting on 1W+ can have a have a considerable detrimental effect to your electronics. I found that out the hard way when I used to communicate via audio DTMF tones through a standard hand held transceiver. Threw a lot of time and energy at that problem before giving up on DTMF some years ago - Faraday cages, wire shielding, bypass caps, etc etc…

My current electronics transmits on 2W (that’s Chinese watts, not necessarily real watts) and utilises UART serial comms throughout which at least made the RF issues quite manageable with bypass caps. However, all my recovery is 100% non-pyro and one problem I never finished up finding a complete solution for was that whenever I transmitted, the miniature geared motor in my main chute latch device would rotate a bit. After (say) 5-10 transmissions, it (via a 60ish:1 gear ratio) would fully rotate the 90 degrees needed to open the latch. Fortunately it wasn’t an issue that occurred on my gas device for deploying my drogue, but still, it was a problem I only ever finished up finding a band-aid solution for (so far).

I’m certainly no RF expert, but FWIW, I’ve always used 1W+ to transmit and I generally agree with John. It would take particularly clumsy or bad luck wiring to initiate an Ematch from >1W transmission.

As for flash bulbs, I’ve never gone near them since one of our club members had one go off in his hands – no wires, no electronics – just the flash bulb.

TP

 

[rocket_troy]

FWIW, DaveyFire N28B e-matches have a no-fire current of 200mA.
https://royalarms.com/wp-content/uploads/PDfs/MSDS/squibb spec.pdf

200mA (to me FWIW) would render them quite safe unless, of course, you were transmitting on Tim Taylor power levels.

TP

 

[FredA]

Twisting is free

 

[John Kemker]

I once conducted a test with a 4W UHF transceiver and a grain of wheat bulb. The wires needed to be the right length (obviously) and oriented in a particular way for there to be a substantial illumination. If the wires were next to each other, there would be no illumination of the bulb.

www,propulsionlabs.com.au/Misc_Video_And_Images/RF_Test.MOV

Mind you, transmitting on 1W+ can have a have a considerable detrimental effect to your electronics. I found that out the hard way when I used to communicate via audio DTMF tones through a standard hand held transceiver. Threw a lot of time and energy at that problem before giving up on DTMF some years ago - Faraday cages, wire shielding, bypass caps, etc etc…

My current electronics transmits on 2W (that’s Chinese watts, not necessarily real watts) and utilises UART serial comms throughout which at least made the RF issues quite manageable with bypass caps. However, all my recovery is 100% non-pyro and one problem I never finished up finding a complete solution for was that whenever I transmitted, the miniature geared motor in my main chute latch device would rotate a bit. After (say) 5-10 transmissions, it (via a 60ish:1 gear ratio) would fully rotate the 90 degrees needed to open the latch. Fortunately it wasn’t an issue that occurred on my gas device for deploying my drogue, but still, it was a problem I only ever finished up finding a band-aid solution for (so far).

I’m certainly no RF expert, but FWIW, I’ve always used 1W+ to transmit and I generally agree with John. It would take particularly clumsy or bad luck wiring to initiate an Ematch from >1W transmission.

As for flash bulbs, I’ve never gone near them since one of our club members had one go off in his hands – no wires, no electronics – just the flash bulb.

TP

I'd like to second this. From learning to mitigate EFI/RFI in amateur radio, one of the things they teach us is that two equal length conductors running parallel to each other is a transmission line. If one of them is longer than the other, the excess length becomes an antenna.

 

[rocketcharlie]

Well thank you. I get that it may not be particularly important. On the other hand as Fred pointed out "its free" and I have to say it looks a lot nicer than a "rat's nest" of wires.

OP Charlie

 

[jimzcatz]

never heard of this,never done it.