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extra physical 'shield' on antenna.. what does it do?
#1
Hi folks, 

I've seen this kind of 'terminator' piece on 2.4ghz and 5.8ghz antennas but have no idea what their function or added worth is. I have no idea how to google for this and haven't been able to find anything on it. Can anyone here shed some light on this? Like.. does it actually play a role in the quality of the signal? Does it apply gain? Does the length of the cylinder matter?

[Image: 0GByCcm.jpg]
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#2
If you referring to the metal sleeve, it is to make your antenna into a dipole antenna. Someone correct me if I am wrong.
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#3
I'm referring to the sleeve indeed. Aha, dipole. This just drove me to research a bit what that means. This is what I love about this hobby Smile

Just to share and see if I got it even remotely right: what I learned is that a dipole has a more favourable omnidirectionality compared to the monopole which is dependent on a flat ground plane and emits only 'upwards' (not sure about this one) and which has a higher gain, resulting in a radiation pattern with high yield to the sides but a pretty big hole straight above it. The dipole is more omnidirectional, has a lower gain and a much more ideal 'apple' shape radiation pattern.
I got this info from cobbling together these resouces:
- https://en.wikipedia.org/wiki/Dipole_antenna
- https://www.digikey.com/en/articles/tech...ed-designs
- http://www.antenna-theory.com/

So ok, if the sleeve serves the purpose of making the antenna a dipole then it's crucial that the sleeve is of equal length to the exposed core of the coax cable, ie. a quarter wavelength or 12.9mm. Is that correct?
This would actually explain well why this vtx was giving me grief because the sleeve was totally loose from the cable.
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