Click the “max” button and let her run awhile 
Also, mess with the “autoscale” button, it will help as mentioned prior.
Yes, the external filter removes out-of-band signals BEFORE these strong signals reach the ProSticks’s LNA and saturate it. These strong out-of-band signals also cause cross-modulation.
It will be worth trying your V-Lad with a FA external filter added between Antenna & Dongle.
1 Like
Yep. The filters are due in tomorrow.
OK, fresh scans following above instructions
(1) FlightAware Pro Stick Plus (Blue)
Scan 1.1:
V-Stub with FA Pro Stick Plus (Blue) 
CLICK ON IMAGE TO SEE LARGER SIZE
Scan 1.2:
V-Stub with FA ProStickPlus (Blue)+FA Filter (Light Blue) 
CLICK ON IMAGE TO SEE LARGER SIZE
(2) Radarbox24 Flight Stick (Green)
Scan 2.1:
V-Stub with RB24 Flight Stick (Green) 
CLICK ON IMAGE TO SEE LARGER SIZE
Scan 2.2:
V-Stub with RB24 FlightStick (Green)+FA Filter (Light Blue)
CLICK ON IMAGE TO SEE LARGER SIZE
That last one is interesting but TBH, I prefer the fixed scales. It’s easier to compare. 
Actually I’m finding it difficult to decipher. How is stuff getting through the FA filter when used with the RB24 stick?
Important is the last scan (RB24 FlightStick Green + FA Filter). Even without fixed scale, following is my observation:
The signal has passed through FA Light Blue Filter, then SAW Filter of RB24 Green, then passed to LNA, and still there is some strong signal at lower frequencies. It shows there is some internal strong signal genertation (cross modulation???) in the RB24 Green stick.
Yeah. The only other thing I can think of is inadequate shielding. Are the FA sticks shielded at all?
No.
Both FA and RB24 sticks are un-shielded
Well, this explains a lot. This is the FA 1090 antenna with a RBOX 1090 SDR…
Notice the gain is set to 0 !!!
This with the gain set to 45 and the addition of the RBOX filter.
This is the Mutant Spider with gain at 45 with the RBOX SDR and the RBOX filter.
A RTL-SDR v3 with FA antenna, gain=0 no filter:
A RTL-SDR v3 with FA antenna, gain=45 with RBOX filter:
Tomorrow: V-Stub, the FA Filter, noise source (not antennas of course).
Maybe we need a new topic just for Spektrum Testing Results of various components.
Good idea! Please create a new thread dedicated to testing by Spektrum.
Alternatively you can use an existing thread which I have created in January 2020. I have created this dedicated thread for testing various components using noise source and software rtlpan (rtl-sdr dongle panorama).
Make it easier: Here is an example of a PCB antenna stabbed into an FA Orange, and the filled graph is result after plopping a cavity filter between the antenna and radio. Don’t think it can get easier to decipher this way for a direct comparison
Same scale as above, this time FA Blue, then with the cavity:
EDIT: The takeaway? FA Blue shows about -3dB attenuation @1090Mhz as opposed to FA Orange with same filter inline. Interesting me thinks. So (here comes the caveat), for my testing location which happens to be on my computer desk, FA Blue is sufficient enough and doesn’t need the external filter since the SNR is decent enough without. FA Orange, totally different story as anyone could see.
This is why we test. I guarantee a different outcome when tapping into the normal feed line with a better antenna that’s up high above the roofline.
2 Likes
How do you create a filled graph?
You didn’t do your homework mister! Supposed to be pushing buttons until your thumbs and eyes bleed! 
1 Like
If I’ve got time this week, I’ll be submitting some enhancements to Spektrum… Showing SDR serial numbers in the selection dropdown, being able to switch SDRs without shutting down, saving SDR with profiles.
@abcd567 Good idea to use your other thread. Will start doing so.
2 Likes
How about simultaneous display of two SDR spectrums (eg, before and after a filter)
A dual channel SpecAn sound cool.
With a ground plane antenna, does the length of the ground plane legs effect the R of the antenna? I’ve built a V-Stub, and it looks pretty good on the graphs, but the R is a little low and I was wondering what I’d adjust to improve it. Thanks!
This requires two things
-
Running simulation sweep of radial length vs Z (R+jX)
-
Making a prototype, trim radials, and measure Z (R+jX) for each length of radial to determin optimum length of radials.
Couple of years ago (March 2016), I have run simulation of a similar (but not identixal) design to find optimum radial length. Due to differebce in design, and using system impedance of 75 ohm instead of 50 ohm, It will not fit to V-stub, but will give an idea that reducing the length of radials improves performance.
https://discussions.flightaware.com/t/why-are-all-wireantennas-differnt/18160/9
Your measurements of the V-Stub antnna you have made show a SWR nearly 1 and impedance nearly 50 ohms. These are excellent results for a DIY antenna. Why you want to change R?
However if you are keen to find, make radials a bit longer, say 75mm, and start trimming say by 2mm each time several times, and repeat measurement at each radial length to see the influence of radial length on SWR and Impedance
