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Yes, I know wirelessly != cable.

What I have: A cheap first person view (FPV) car. The FPV part of it is standalone - essentially a camera connected to a battery-powered WiFi module. The remote control is a 2.4GHz model. You can stream the video over the WiFi to your smartphone screen while using the remote to control the car.

What I would like: A simple way to 'guide' the signal while the car is in a long tube. I want to drive the FPV car into a 10cm diameter cast-iron tube, around some bends, and then still be able to stream video and control the car. Currently, video drops out before the control does, after the first bend and ~5m, with the smartphone and remote both huddled at the entry-point of the tube.

Is there a way to do this? I do not want to open the car and start soldering. I'd like to know if it was possible to somehow attach a wire to the antenna so the signal is guided through the cable, and position the other end of the cable near the smartphone. On the side of the car, the options are very limited, as that needs to stay small, but on the smartphone-side of the cable I could attach some electronics, if needed. Do not worry about the stiffness of the cable (if, say, coax would be needed,) I can push it along with the car, the car does not have to drag it.

Ideally, the pick-up at the car would not be rigidly attached to the antenna, but allow for some rotatory movement.

can i connect two similar antennas to two ends of a cable to to re-transmit the signal received from one end? this Q&A seems to indicate that the idea is doable in general, but I'd need some details on the best passive-antenna shape for this application.

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    \$\begingroup\$ a cast iron tube honestly sounds pretty good – while certainly lossy, most of the signals energy should be guided along the tube anyway. Have you verified this doesn't simply work? \$\endgroup\$ Nov 20, 2021 at 13:11
  • \$\begingroup\$ Yes, i tried it, video signal is lost after the first bend, and i did not care to try how far the control works :) \$\endgroup\$
    – loonquawl
    Nov 20, 2021 at 14:46

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What you are asking is possible in theory but you may find it difficult to achieve in practice with what you are working with.

Yes, you can transmit 2.4GHz signals over a coax cable of the proper type but you can't just hook a wire to the antenna and expect it to work. There are impedances to match so that your 2.4GHz signal does couple into the coax and travels to your receiver.

Another issue is that 2.4GHz signals don't travel on coax well because at the frequency the attenuation is significant. That's why you see antennas for devices in this this frequency range very near the radio portion of the device. It can be done but it takes careful design.

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  • \$\begingroup\$ how would that impendance matching work? the free ends of the cable would need to be attached to antenna-shapes, i gather. is there an online resource that sows the bends and lengths neccessary? \$\endgroup\$
    – loonquawl
    Nov 20, 2021 at 11:51
  • \$\begingroup\$ Do you have the specs for the transmitter output? If not, then you don't know its output impedance, you also don't know the existing antenna's impedance so you don't know how to match it to a length of coax. There are numerous variables but I suppose you could just try it and see what happens. It might work. \$\endgroup\$
    – jwh20
    Nov 20, 2021 at 12:04
  • \$\begingroup\$ So would this (oscarliang.com/repair-2-4ghz-antenna-rx) or this (emworks.com/application/…) be the better starting point, or is there another antenna design that would come to mind as easily tunable? I mean the 'strip some coax'-approach seems trivial enough, but if it is 31.23mm then that seems a bit excessively exact... \$\endgroup\$
    – loonquawl
    Nov 20, 2021 at 12:35
  • \$\begingroup\$ In OP's application, I doubt that loss (or attenuation) in the coax would be much of a problem. A lot depends on the exact type of coax being used, but at 2.4 GHz a typical coax has a loss of maybe 0.08 dB/foot. So even 10 feet of cable would only mean a loss of less than a dB. \$\endgroup\$
    – SteveSh
    Nov 20, 2021 at 13:23
  • \$\begingroup\$ "don't travel on coax well" as long as the impedances are right, the insertion loss for 2.4G over a decent SMA cable isn't bad. \$\endgroup\$
    – nanofarad
    Nov 20, 2021 at 15:08

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