For the section lengths I used the 1/2 and 3/4 wavelength for ADSB, and a .95 velocity factor for my plain 2mm copper wire (12ga plain wire from hardware store), but kept the ratio of the top to center sections the same (since the top is supposed to be slightly less than 3/4), and used approx 20mm diameter for each ‘loop’. Minor adjusting of the length of the top section and the vna shows a -40db to -45db logmag and an SWR of 1.01-1.03. So it -seems- like it should be fairly decent, but I don’t know if it has much gain (since I can’t measure that with the equipment I have).
Even a SWR =1 is worthless if any one or both of following happen:
(1) Gain is very low
(2) Radiation pattern is drastically different from lazy eight or infinity symbol ∞
The only practical way to find out without any sophisticated equipment is to conduct a side-by-side trial run with a standard antenna such as Flightaware or Jetvison, with two antennas at same location and not more than 3 feet horizontal seperation, same type & length of coax, same dongle & filter, and same gain setting. Compare Aircraft tracked, Messages received, and maximum range.
Interesting, is the simulation software free online? The page I was referring to mentioned that it should be a single loop. If that loop needs to be 1/4 wavelength, then maybe using a single 20mm diameter loop would turn out better.
But looks like the pattern isn’t nearly as nice as the V Stub anyway
So this is a close match to what I’ve built. My dimensions are slightly smaller after taking .95 of these values, but it seems that is required as building with the exact dimensions here doesn’t tune at all.
(1) Do not waste your time in trying to adjust dimensions of a 2.4 Ghz WiFi antena to receive1090 Mhz adsb.
(2) Do not blindly believe simulation results.
(3) Forget about simulation results, and forget about adjusting SWR by trimming. Make G7RGQ antenna using dimensions on Microtronics drawing, and put it to side-by-side trial run with a known antenna (FA or Spider). If side by side test show poor resuls, then try tweaking/trimming to improve SWR.
The loops are doing the time delay, needed to change the phase of the signal, for adding the waves.
That’s what the colinear antenna does with the normal shielded portions of coax.
@sigwx
Your best bet is to make both the antennas i.e. your design you have posted above and the G-7RGQ rev3 of Microtronics, and do a side-by-side test of each with a standard antenna of known perfoirmance (FA antenna or Spider antenna).
Note:
In your simulation while building the coil, you have used 20 mm dia of coil (10 mm radius). Since simulation uses mean diameter of coil, the inner dia will be mean diameter - diameter of wire = 20mm - 2 mm = 18 mm
When you actually build the antenna based on your simulation (2 mm dia wire, 20mm dia of coil), make the coils with inner dia = 18 mm.
The wire collinears are very sensitive to coil dimensions.
