Google searches dont give any good results on ground plane or vertical antenna projects for 978 MHz. Any ideas?
Glenn
Just build the coaxial colinear (CoCo) antenna for this frequency. https://www.engr.colostate.edu/~notaros/Papers/Generalized%20CoCo%20Antennas.pdf
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Interesting paper you linked to. There is, in section 4.2 an instance where they describe a CoCo that would approximate the gain of some wire designs. However, I cannot understand how they get to a 33.5 cm element length…their wire examples I presume use a wire with v/c .96 to arrive at a 45 cm element length, they state coax with a .67 v/c yet that would give an element length of 31.85 cm, not the 33.5 cm they use ?
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Use same design as 1090 mhz Cantenna or Spider. The only difference is that whip, radials, and food/drink can height to be 77mm instead of 69mm.
1/4 wavelength at 1090 Mhz = 69mm
1/4 wavelength at 1090 Mhz = 77mm
Above is based on speed of radio signal in vaccum. Since the speed in metal is slightly slower, you may use about 2 ~ 3 mm less than above figures.
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Velosity factor for RG6u is 0.659 ( one source just looked it up) so quarter wave sections should be 50.7mm theoretically…
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Easy and Reliable:
1. Commercial. Excellent Performer. Competetive Price.
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2. Home Brew. Good Performer (for 978 MHz, use 75 mm whip & radials)
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Too fun to homebrew antennas. My 8 element 1090 colinear antenna runs circles around the twinkie for ADSB, so I hope for the same result for 978MHz. Been using a 978MHz twinkie antenna for a couple of weeks now and getting really poor results. Was expecting to catch the odd plane flying overhead at least. Will build a UAT collinear for the slightly longer wavelength and see how that works.
My main receiver station uses the FlightAware 1090 antenna fopr ADSB and it works fine, as I would expect the 978 model would too.
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Pardon my ignorance but what is a twinkie antenna?
Thanks,
S.
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Post a picture of your antenna
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Yes that’s likely the easiest way to describe… but it is simply a quarter wave antenna with 4 ground-plane radials. I used a chassis mount SO-239 (female UHF connector) as I have a length of LMR-195 with an N on one end and a PL-259 (male UHF) on the other that was just the right length. It’s just sitting on the end of a pipe supported by the ground plane radials and the feedline runs down the pipe.
The term “twinkie” or “tweekie” is what we (some uf us) ham radio types call them… 
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No it isn’t (at least - probably not).
Making categorical statements like that is misleading to others and shows you don’t fully understand the subject.
The Velocity Factor (Vf) is a function of the materials use to construct the CoAx. As there is a variety of materials used, it follows that the Velocity Factor also varies.
Making definite statements like that (without specifying exactly the cable you are referring to) can be quite misleading.
Conrad 82%
Colman 78~81%
Wavenet 84%
Belden 1694 82%
Belden 1190 83%
Belden 3131 82% Note: this is 120Ω Cable (not 75Ω)
Pasternack RG6A/U 66%
Teletronik RG6 85%
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Yes you are absolutely right I should have worded that differently as that was only one source/type (Beldon rg6u). Good catch!
Out of curiosity, do you have any idea of the use your cable is intended? There are very few RG6 cables with a Vf that low - I was idly wondering ‘why’. There are plenty of exotic cables in Beldens catalogue (catenary wire, power lines, direct burial etc).
In thirty five years of amateur radio, I’ve never heard that term. You did say ‘some of us’ though.
I think the more generic term is ‘spider’.
Believe it’s a direct burial type for satellite/tvro. Cable is 8215. The dielectric could be poly or similar. Might have been part of an installer kit for a satellite TV. Nothing special about it really… just an example.
Probably a local ham dialect.
Had to do some serious reading in QST back in the day to learn that “spider” is the common name.
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I added 4 more ground plane radials yesterday and note I picked up one plane… or actually 0.4 of a plane according to the graph. Maybe it works better with the extra radials, or maybe a coincedence… I’ll leave it like this for at least a week before replacing it with a coco.
Now it looks like a real spider with it’s 8 legs!
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Made a F-type version of the 1/4 wave ground plane antenna for 978 & 1090 using RG-6 cable.
I bought one of the F-type wall plates rated for +2 GHz and removed the coax post with washer/nut. I then soldered 3 of the ground plane leads to the 4th lead that has a copper wire loop that fits over the coax post …
I installed the ground plane on the coax post between 2 large washers and tightened/locked it in place with the original washer/nut combo, bent the 4 leads down to a 45-degree angle, and then inserted the center antenna lead to complete the assembly.
The original clipped 1090 antenna was picking up planes ~50 miles away and this new F-type antenna has picked up a few planes 80 miles away.
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No, it is not a coincidence.
6 radials work better than 4 radials
8 radials work better than 6 radials
More than 8 radials, no significant improvement, law of diminishing returns.
8 legs for spiders is nature’s choice also
