Second question. The VTX works fine as I put on a spare UFL/IPEX 2.4 Ghz aereal at home (a ERLS module one I had spare), probably not the best idea, hense asking above for what to replace with. The Betaflight overlay is appearing, but there is no camera image. This is weird as when were flying all was fine (although when the antenna fell off, anyones guess!) So my question is about diagnosing the camera. I can check it’s getting 5v. Can check the continuity of the cables, no problems. If I was to check for signal from the camera would I link up the 5v and gnd to a supply, and then make an RCA plug with the “yellow” video signal cable to the centre pin, and ground the outer circle bit of the RCA plug? I hope that makese sense. Can then check if it’s the cam or the VTX? Any other suggestions of why a cam might not be working be great.
Easiest way would be to swap the camera from one of your other quads. I dont know if a 2.4GHz antenna will work at all on a 5.8GHz vtx? It may work enough for short range testing possibly but certainly wont be effective. Im sure one of the smart guys will be along shortly to confirm
The VTx expects to see a load close to 50 Ohm, which a resonant 1/4 wave length provides. Anything else will have a different impedance and subsequently require some form of matching. You can get away with a halfwave dipole (2x1/4wave back to back) as that has an impedance of around 75 Ohms. Anything else will be extremely lossy and may damage your VTx.
I’ve always considered antennas to be the physical manifestations of complex mathematical calculations.
In simple terms they can be considered as three components, capacitor, inductor, and resistor, connected to each other. But to accurately calculate the dimensions of an antenna you need to ensure the feed impedance equals the output impedance (relative resistance at a particular frequency) of the device connected to it, and that the capacitive reactance and inductive reactance are as close to zero as possible to ensure efficiency. So if you input 4.8GHz to your 2.4GHz antenna the feed impedance changes from 50 Ohm (ideal) to anything between 1.8K Ohm to 5K Ohm depending on the material used and the diameter, which would be like not attaching an antenna to your VTX in the first place.
Sorry to go all Tefal Toasterhead but some days I just can’t help myself.