Ground plane antenna implementations

[Charles Webb - SnkMtn]

I've used home made ground plane antenna's with great success for both rf22 and rf69.  The other day one of my ceramic GPS antennas had dangled a bit too much from it's unsupported tiny coax line.  Yep, it broke.  No easy way to get that soldered back on.  Made a ground plane antenna out of 30 gauge hook up wire tuned to 1500 MHz.  The "coax" and solder point for the 4 ground radials was copper tape.  My rough calculations for the coax with two turns of copper foil tape was about 50 ohms!  The antenna calculates about 50 ohms.  No, I have no SWR measurements to verify.  Empirically I observed satellite lock within about 3 minutes and can see 9 satellites from an east window, upside down!  Much lighter than the original ceramic antenna.  Cost next to nothing.  Just thought I would share.

[James Coxon]

Hi Charles

Yeah I think with the newer GPS modules they are so sensitive that they don't need fancy antennas and you can get away with a wire antenna. I have a feeling that some of the round the world pico balloons use a 1/4 wave GP to save weight.

James

On 18 January 2017 at 22:37, Charles Webb - SnkMtn <cewe...@gmail.com> wrote:

I've used home made ground plane antenna's with great success for both rf22 and rf69.  The other day one of my ceramic GPS antennas had dangled a bit too much from it's unsupported tiny coax line.  Yep, it broke.  No easy way to get that soldered back on.  Made a ground plane antenna out of 30 gauge hook up wire tuned to 1500 MHz.  The "coax" and solder point for the 4 ground radials was copper tape.  My rough calculations for the coax with two turns of copper foil tape was about 50 ohms!  The antenna calculates about 50 ohms.  No, I have no SWR measurements to verify.  Empirically I observed satellite lock within about 3 minutes and can see 9 satellites from an east window, upside down!  Much lighter than the original ceramic antenna.  Cost next to nothing.  Just thought I would share.

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[Phil Crump]

Hi All,

One of the key features of a typical GPS antenna such as a patch or helix, is that it's designed for Right-Hand Circular Polarisation. The GPS transmissions are also Right-hand, but when bounced off a building or other obstruction they reflect into Left-Hand Circular. The Right-Hand circular antennas strongly reject Left-Hand signals, therefore providing an effective countermeasure against simple multipath, such as that often experienced in cities or canyons, as well as rejecting any reflection off the ground.

When you've got a good direct view of the sky however, as you always do at high altitude(!), a 1/4 wave whip will only receive the Circular signals ~3dB weaker than an ideal antenna, and so performs quite well!

Phil

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