Another variant Lower Radiator reduced from 137 mm to 60 mm
SWEEP- lower radiator length vs SWR & Gain
SIMULATION: Lower Radiator = 60 mm
SWR = 1.69
Gain = 4.98
Click on image to see larger size
You removed the feed match but appear to have replaced it with a ground plane. Could you explain the design change please.
Also, as it is the end of a half wave radiator in free space (ignoring the phase coil and second half wave) you would expect the impedance to be quite high.
The purpose of the impedance matching network is to transform the actual impedance to match the feed line impedance.
Thanks,
S
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True.
As the RF feed is on 2 wires, not on 1 wire, the other wire has to be connected somewhere. Ground plane is where 2nd wire is connected.
If the 2nd wire is connected to natural ground, then antenna being in free space, the single wire running from receiver up to antenna will itself become a radiator.
Taking RF feed on ladder line/twin wire/coax upto antenna requires a point where to terminate 2nd wire or shield, and that point is provided by the ground plane.
The purpose of removal of stub was to highlight its effect on radiation pattern/lobes. I knew very well that the impedance will be very high, but it was the lobes, and not the impedance, which was the object of this excersise.
True, and this is a well known and well utilised fact.
The 1/4 wavelength stubs are mainly used for two purposes:
- Impedance matching.
- phasing shifting, so that currents/voltages in two adjuscent 1/2 wavelength sections (connected through stub, and not directly) are in phase and do not cancel each other.
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Iâm afraid this doesnât clarify why you are including the feed and the impedance match in the antenna model.
If the feed and the match are affecting the performance of the antenna then you should reconsider your design.
If the feed and the match do not affect the antenna performance then I suspect that your modelling is seeing them as radiating elements and is skewing the output.
S
This is the requirement of simulation software. Without including the feed, the simulation fails.
Simulation of Super J-Pole with stub removed
Because in reality you always will have those two connected to a functional antenna.
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Looking to fix one of the FA 66cm ones to a round tubular mast - the supplied U bolts donât do a great job as there is only 1 saddle for each bolt. (So the figure 8 of the antenna/mast is clamped with circular/oval clamps.)
Anyone have some good suggestions how to fix the antenna to the mast?
Can you post a picture - I found the supplied clamp worked perfectly well with a round mast.
Agreed- my FA antenna is on a stand-off @
45 feet AGL on my tower and hasnât moved in the 1.5 years itâs been there; despite strong winds, ice, snow, rain and temperatures -30c to +30c. The supplied mount hardware works fine
Coiled Whip on Mag-mount
Note: Because of extremely reduced number of flights due to covid19 epidemic, the difference between graphs of two whips is not glaring. I will re-test after flights are normalized.
CLICK ON IMAGE TO SEE LARGER SIZE
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Hi guys, have a look at the link below. Itâs a collinear coaxial antenna for ADSB reception.
Iâve made one and receive positions of planes more than 500km away connected to an RTLSDR dongle and an LNA.
I used 8 elements as Iâve read that more elements will not necessarily result in improved range/performance. Works like a charm. At first could not believe my eyesâŚ
Just make sure that each element is cut as accurate as possible.
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Sorry for the delay, but lockdown put all my plans on hold for a while.
As you can see the clamps are WAY bigger than the base of the aerial - even tightened up it will move (note angle in 2nd picture.)
Those clamps are not what I would choose to clamp to round pieces together!
Mmh, arenât all FA antenna dark greenish in colour? Where did you buy it?
From AirNav Systems on Amazon.
AirNav ADS-B 1090 MHz Outdoor antenna with SMA connector
None of the UK outlets had the FA antenna in stock. I note that the clamp for that looks substantially better. Unfortunately, I canât find the clamp on it own anywhere.
Ah, ok. Maybe it works better when you use the ubolts around the pole instead of the antenna, then the other two parts are maybe thin enough to fit into the groves on metallic part of the atenna?
You can put thick rubber hose/tub around the base to make it more stable.
Like 1" fuel line piece or something.
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Doesnât work. The antenna has a couple of grooves - thatâs where I tried to get the U-bolts to sit. In any case, the pole is only 5mm bigger than the antenna!
Yeah, Iâve been thinking about something like that. Anyway - found some other clamp online that should be here in a couple of days - letâs see what gives.
But I wish I could get the one like the FA antenna uses.