POSSIBLE REMEDY FOR V-STUB:
Add an external Filter between Dongle and V-Stub antenna.
With my V-Stub, I am using a Radarbox24 FlightStick (Green), which has a SAW filter chip between antenna SMA connector and front-end LNA / tuner chip R820T2. This is equivalent to adding an external filter to ProStick/ProStickPlus.
That’s what I already use. Are you sure the filter is at the front? I tried to ask RBOX support and never got an answer.
I am not sure as I have not checked it myself. I got this info from somewhere on web or in some forum where someone has opened the plastic cover of Radarbox 24’s green stick and physically found the SAW chip is connected between Antenna SMA and front-end LNA / Tuner.
Try to swap the Radarbox24 green dongle with another one (if you have a spare) to cover the (unlikely) case of defective SAW chip in that particular dongle.
Both the famous tracking sites which have 24 at the end of their names have lousy support 
How did those compare to real-time sweeps?
Don’t know as I did not perform real-time sweeps. Will do it when find time, as I will have to first built both the spider and V-stub (the V-stub I have made got damaged)
V-Lad’s symptoms are like this one:
https://discussions.flightaware.com/t/outdoor-antenna-works-indoor-only/69197
Yeah. As I was reading that post I was yelling “It’s overloaded!!” at my computer. 
Repaired the damaged V-Stub. The V-Stub is made of coax (no SO239), so was easy to fix. After repairs, ran a frequency sweep.
I dont have a spider, discarded long ago when purchased FA antena. Will make a Quick Spider soon and run a scan on it also.
Here is the snapshot of the scan of V-Stub Wire Collinear antenna 150 MHz ~ 2500 MHz:
Click on images to see larger size.
Scan range: 150 MHz ~ 2500 Mhz
Click on images to see larger size.
vs.
Results are pretty dang close when looking at the ~300Mhz, ~700Mhz and ~1100Mhz (every ~400Mhz or so). Obviously tough to decipher some of it with the wider resolution, but that’s irrelevant for a basic confirmation of the sim. Of course the N1201SA gets a little wonky > about 1800Mhz or so no matter how they have it spec’d, but for the money and ease of use it’s nice to be able to confirm some things.
Both avenues illustrate that the design would have a predisposition to pickup those ~400Mhz frequency increments, but not many designs are truly resonant at only one frequency.
Seeing that does contribute to more confidence in the simulation. Be neat to see more as time goes by. The simulation gain plot sure is interesting, too bad we cant confirm that with cheap equipment as well.
How meaningful is “Gain /FB” for an omni-directional antenna?
V-Lad is much happier on the roof with a FA 978-1090 filter on it. Stats and graphs tomorrow.
Just posted some results here…
This is a side-by-side comparison of FA ant vs V-stub on mag-mount base on metallic window sill (NOT the one with radials).
Both antennas were in same window with a horizontal spacing of 1 ft. (30 cm).
As I had only one ProStickPlus (blue), my previous comparisons used FA with ProStickPkus (Blue) and V-stub with FlightStick (Green)
Today I recieved my 2nd ProStickPlus (Blue), and replaced V-stub’s FlightStick (green) by ProStickPlus (blue).
Also set gain of both dongles to 49.6
https://flightaware.com/adsb/stats/user/abcd567#stats-76000
https://flightaware.com/adsb/stats/user/abcd567#stats-6396
| Time | Stn #76000 V-Stub Magmount |
Stn #6396 FA Antenna |
|---|---|---|
| 1600 ~1700 | 170 | 209 |
| 1700 ~1800 | 141 | 168 |
| 1800 ~1900 | 165 | 193 |
| 1900 ~2000 | 117 | 128 |
| 2000 ~2100 | 106 | 128 |
| TOTAL | 699 | 826 |
V-Stub/FA = (699/826) x 100 = 85%
| Time | Stn #76000 V-Stub Magmount |
Stn #6396 FA Antenna |
|---|---|---|
| 1600 ~1700 | 11431 | 14987 |
| 1700 ~1800 | 7260 | 9928 |
| 1800 ~1900 | 9955 | 13222 |
| 1900 ~2000 | 7123 | 7530 |
| 2000 ~2100 | 6742 | 8789 |
| TOTAL | 42511 | 54456 |
V-Stub/FA = (42511/54456) x 100 = 78%
Repeat comparison of V-stub Magmount vs FA antenna, using data of Sept 30, 2020 from Flightaware stats page.
(Previous was using data of Sept 29, 2020)
Results are consistant.
https://flightaware.com/adsb/stats/user/abcd567#stats-76000
https://flightaware.com/adsb/stats/user/abcd567#stats-6396
AIRCRAFTS
| TIME | V-stub Stn #76000 | FA Stn #6396 |
|---|---|---|
| 1 pm ~ 2 pm | 85 | 104 |
| 2 pm ~ 3 pm | 126 | 142 |
| 3 pm ~ 4 pm | 155 | 163 |
| 4 pm ~ 5 pm | 157 | 190 |
| 5 pm ~ 6 pm | 142 | 179 |
| 6 pm ~ 7 pm | 163 | 191 |
| 7 pm ~8 pm | 125 | 145 |
| 8 pm ~ 9 pm | 113 | 129 |
| TOTAL | 1066 | 1243 |
V-Stub/FA = 100(1066/1243) = 85.8%
MESSAGES
| TIME | V-stub Stn #76000 | FA Stn #6396 |
|---|---|---|
| 1 pm ~ 2 pm | 3883 | 6372 |
| 2 pm ~ 3 pm | 7701 | 9027 |
| 3 pm ~ 4 pm | 7635 | 8426 |
| 4 pm ~ 5 pm | 8373 | 11429 |
| 5 pm ~ 6 pm | 8292 | 11225 |
| 6 pm ~ 7 pm | 9699 | 12676 |
| 7 pm ~8 pm | 6835 | 9299 |
| 8 pm ~ 9 pm | 7432 | 9118 |
| TOTAL | 59850 | 77572 |
V-Stub/FA = 100(59850/77572) = 77.2%
Both antennas in same window. The V-stub Magmount placed on metallic window sill, while FA antena hanging from a string besides it at 30 cm horizontal seperation
| Average | Maximum | |
|---|---|---|
| V-Stub magmount | 190 nm | 250 nm |
| FA antenna | 200 nm | 265 nm |
Average = 190 nm
Maximum = 250 nm
Average = 200 nm
Maximum = 265 nm
(1) Forgot to mention the hardware details of two side-by-side setups:
| Antenna | Coax | Filter | Dongle | Gain |
|---|---|---|---|---|
| V-Stub Magmount | 3m RG174 | FA light blue | ProStick Plus Blue | 49.6 |
| FA Antenna | 2m RG174 | FA light blue | ProStick Plus Blue | 49.6 |
(2) If FA external filter is removed, performance of both antennas drops.
The V-Stub’s message rate/plane count drops to 80% of what it received with a filter.
The FA antenna’s message rate/plane count drops very severely to 20% of what it received with a filtrr.
Doesn’t RG174 cap out at 1000MHz?
Not sure if that’s an absolute, but it does dump about 1dB/m (The high quality stuff), so 3m will effectively half the signal. There are better options of course for a test of this sort, especially if using different length cable.
https://www.timesmicrowave.com/Calculator?Product=RG-174&RunLength=9&Frequency=1090
RG174 is standard cable used with magmount wip supplied with generic dvbt, as well as independently sold “5dBi” coiled magmount. Normally the length of this cable is 1 m only.
However I purchased a magmount whip with 3m RG174 because of distance between window sill and PC. From this magmount, I unscrewed the “5dBi” whip, and installed DIY V-Stub whip.
To make both side-by-side setups as similar as possible, I replaced the 30cm RG316 pigtail between FA antenna and dongle by a 2m RG174 coax which I already had.
