The SWR will improve gradually from > 2 to < 1.5 as the tilt is reduced from 45 deg to 0
What’s with negative tilt? 
Here you go. Sweep from tilt -70 degrees to +70 degrees.
(-) is tilt UP
(+) is tilt DOWN
Nice chart, based on some work I did years ago, the radial angles affect radiation angles of the reception. Do you have a similar gain chart? or radiation pattern. For those not as familar with antennas, radiation pattern from the side also implies gain pattern. Not much gain is needed at the high angles overhead, and trades that for higher gain primary lobe near the horizon. Nice work on your antenna, I particularly like the sliding top sleeve to adjust the top length.
Cutting was a nuisance. If I cross the sweet point, then I have to solder a piece of wire. Sliding sleeve allows tuning without cutting the wire, and is pretty easy. Once sweet point is found, solder the sliding piece in position.
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Interesting plot. you have about 4db gain with your configuration. The V notch is much easier to control than a coiled wire configuration. Nice and innovative design. Well Done.
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This is exactly the reason I have gone for V-Stub.
Coil is extremely dimension sensitive, and hence unsuitably for DIY, just like the CoCo is. It is best made using industrial techniques & test instruments. I have tried several coiled antennas, but all failed to perform better than standard 1/4 wavelength Spider, some even performed worst.
The advantage of V-stub design is that you can keep dimensions of lower wire and V-Stub fixed, and just adjust the length of upper wire to tune the antenna to minimum SWR.
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Has anyone build & tried this DIY antenna?
SWR = 1.23 (measured)
Gain = 3.8~4.3 dBi (calculated by simulation)
Comparison of V-Stub QuickSpider with Bench Mark Antenna (FA Antenna)
FA Antenna >> 30cm RG316 pigtail >> FA light Blue Filter >> FA ProStickPlus (blue) >> OrangePiPC
V-Stub Antenna >> 100cm RG174 pigtail >> Radarbox24 FlightStick (green) >> RPi4
Flightaware 26" Antenna on left side of window
V-Stub Quick Spider on right side of window
Horizontal spacing between antennas = 30 cm
NOTE: The paper behind V-Stub was placed while taking snapshot, as without it the thin wire of V-Stub was not clearly visible in the photo.
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Did you use this gain to advantage in doing the above comparison?
S
I dont understand what do you mean by “using the gain to advantage” while comparing two antennas. These are compared “as is”.
If you are referring to gain setting of dongles, then both dongles were set at gain 48.0
The FA antenna is omni-driectional.
The wire antenna is not omni-directional.
Did you orient the wire antenna to maximize the gain in the direction of interest?
S
Both the FA and V-Stub antennas are omni directional.
The FA antenna being geometrically symetrical around 360°, its radiation pattern is also perfectly symetrical around 360°, i.e. a perfect circle in horizontal plane.
The V-Stub antenna being geometrically unsymetrical around 360°, its radiation pattern is also unsymetrical around 360°. However this unsymetry is not big. The maximum is 4.3 dB in direction of mouth of V, while minimum is 3.8 dB in the direction of tip of V. In all the other directions it is between 3.8 and 4.3. Although the radiation pattern is not a perfect circle in horizontal plane, it is not very far from a circle.
I have tried with the mouth of V in different direction, but as flights here are all around, there is no noticeable advantage. For locations with flight paths in one direction only, pointing the mouth of V in that direction may give some advantage, but not much, as the difference between best direction (4.3 dB) and worst direction (3.8 dB) is not big.
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The diagram in post #59 had wrong dimension of upper wire. I cannot edit that post now (older than 2 months). I am therefore posting the corrected diagram here:
The table you have listed above had the 84/141 line highlighted and for an 82 lower wire it lists 143 for the upper wire. With a 150 combined tuning/fixed upper section, do you find that you’ve ‘tuned’ it down to near the 143 expected length?
Right now I have one built with the 84 lower/141 upper and it seems to be doing as good or better than my spider, mostly in that I’m seeing more reports with approximately the same number of aircraft.
Thanks!
The initial dimensions (in the tables) were from simulation. I tried several combinations of Lower and Upper wires and opening of V. Therefore you will find many sketches with different dimensions.
The final dimenions I got by making a prototype and tuning it, which is shown in my last post above.
Lower wire =82 mm
V = 69 mm x 69 mm x 45 mm wide
Upper wire = I got best SWR (1.148) at 150 mm (adjusted by sliding the sleeved piece of wire at top of the upper wire). It may vary by few mm for different pieces.
If you add a piece of wire to upper wire, thereby increasing the total length of upper wire from 141 mm to 150 mm, you will most likely see further improvement. Try different total upper wire lengths between 145mm & 150mm by sliding up / down the short piece of wire.
As you do not have a VNA, use aircrafts & message rate as a measure of performance at each setting of upper wire length.
Will do, Thanks! Also thinking about 3D printing some sort of support for the V so I keep it from changing shape when I’m adjusting.
I’m thinking some inexpensive VNA is in my future
(Hence I started a conversation in another thread on suggestions)
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Scan of V-Stub Quick Spider with & without Filter
Following settings were used for both these scans
Gain = 25.5
Vertical range = -53 ~ 0 dB
Horizontal range = 24 MHz ~ 1800 MHz
Scan 1 of 2: V-Stub Antenna + FA ProStick Plus (Blue)
CLICK ON IMAGE TO SEE LARGER SIZE
Scan 2 of 2: V-Stub Antenna + FA ProStick Plus (Blue) + FA Filter (Light Blue)
CLICK ON IMAGE TO SEE LARGER SIZE
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Wow! The FA ProStick Plus (Blue) has the filter after the LNA which is why it benefits from the external filter, yes?