Planar Disk Antennas...

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andyk
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Joined: Wed Sep 21, 2016 11:49 am

Planar Disk Antennas...

Post by andyk » Thu Sep 22, 2016 11:55 am

Hi all - first post on RTL-SDR

Having just received my R820T/R820T2 SDR dongle with its not-very-good antenna I am thinking of making a Planar Disk Antenna as a relatively cheap way of improving signal reception. From what I have read it seems that the diameter (larger=lower) of the discs dictates the lower frequency limit and the size of the gap (smaller=higher) decides the upper frequency and that these type of antenna broadly resemble 1/4 wave dipole - so two 24" dishes would reach down to about 120MHz? I am not sure how the size of the gap relates to the upper frequency though......
Anyway my question is - do the 'disks' have to be solid ie could the 'diameter' be, say, a bike wheel rim or similar and then be covered in, say, chicken wire or other similar metallic mesh? The thinking was that the wheel rim/chicken wire may be cheaper but also offer less resistance to wind if mounted outside?
Any links to these type of antenna would be appreciated.......

Andy

rtlsdrblog
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Re: Planar Disk Antennas...

Post by rtlsdrblog » Fri Sep 23, 2016 4:32 am

I think it should work with a mesh, but there would be probably some unknown effects on the frequency range and gain pattern. If you're looking for wind resistance, it would probably be better to build yourself a discone antenna, which is a fairly wind resistant design.

jmcc
Posts: 4
Joined: Mon Jan 30, 2017 12:59 am

Re: Planar Disk Antennas...

Post by jmcc » Mon Jan 30, 2017 1:17 am

andyk wrote:I am not sure how the size of the gap relates to the upper frequency though......
The size of the mesh gap, from memory (working with satellite TV antenna design years ago) is related to the wavelength and has to be less than a quarter wavelength (sometimes a tenth) of the highest frequency in use. However these are reflector antennas.
Anyway my question is - do the 'disks' have to be solid ie could the 'diameter' be, say, a bike wheel rim or similar and then be covered in, say, chicken wire or other similar metallic mesh? The thinking was that the wheel rim/chicken wire may be cheaper but also offer less resistance to wind if mounted outside?
Any links to these type of antenna would be appreciated.......
It is worth experimenting as chicken wire mesh or even the kind of metal mesh used for doors is cheap. The advantage of a solid element is that it doesn't necessarily need support whereas a mesh antenna does. As this is not a reflector antenna like a satellite TV dish, the performance of a mesh type planar disk antenna might not be the same as that of a solid planar disk antenna. Depending on how you cut the mesh, you may have a set of wires at the edges of each disk but you could always electrically short them by soldering a length of wire to each of them around the circumference of the disk. My antenna theory is a bit rusty though so I'm not exactly sure of how a mesh version would compare with a solid version.

Regards...jmcc

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