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Old Jul 21, 2015, 01:41 PM
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Transmitter antenna relocation

What do you guys think about this:
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I broke my antenna connection off twice and decided to try this as a way of relocating it to the center of the quad. It works but I wonder if I'm loosing quality and range by using plain ol wire instead of a shielded cable. I don't have much experience with fpv so I'm not sure if what I'm seeing is normal but I am getting some static. Here's an example of what I'm seeing with this setup. I probably never got more than 300ft away in this video.
MK I (3 min 53 sec)
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Old Jul 21, 2015, 09:29 PM
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If I understand RF theory correct, signal in a RF wire travels in between the middle rod and the shield (so if you look into either end of a coax cable and see a white foam-like separator between the main "wire" in the middle and the thin metal outer shield, then this foam is what I am referring to).

From your photos it looks like you are simply using a positive and negative wire to move the RF signal and thus I don't think there is much RF signal leaving the transmitter into the antenna. RF signal is not the same thing as electrical signal in a cable, hence different types of cables exist specifically for RF signals and the like.

Correct me if I'm wrong.
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Old Jul 22, 2015, 04:12 PM
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That's pretty bad. Use proper coax. Coax cable has an impedance of 50ohms, so that all the signal from the transmitter is transfered directly into the antenna.

The wiring you have has an impedance that will be very far from 50ohms. This means that most of the signal from the FPV transmitter will be reflected back into the transmitter itself. This causes (a) the FPV transmitter to get hot (b) very little signal to actually reach the antenna, reducing your range a lot.
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Old Jul 24, 2015, 11:37 AM
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That's what I was thinking. Do you think I could solder a coax cable directly to the tx board or does it need the connector? I'm trying to salvage the tx. After two breaks there's not much room to solder the connector back on.
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Old Jul 28, 2015, 04:56 PM
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Revised:
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Needless to say it works much, much better now. Went out to about 745 ft on a test flight and the video was crystal clear. I'm kinda smacking myself for ever thinking the first wiring was going to work. Not an electronics expert (obviously) but that should have been more obvious. Live n learn. I'm kind of amazed I didn't fry the vtx!
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Old Jul 28, 2015, 06:51 PM
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Cool, I'm glad it works. Sorry I didn't reply earlier, but yes, it should be fine to solder the coax directly to the PCB as you did.
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