Yes I agree, I have built many colinear antennas with lots of failures. The one I use now is built to the formulas for wave-length and there is no guessing on the measurements as its not detuned by pvc pipe
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Originally posted by YWYY View PostYes I agree, I have built many colinear antennas with lots of failures. The one I use now is built to the formulas for wave-length and there is no guessing on the measurements as its not detuned by pvc pipe
http://forum.flightradar24.com/attac...0&d=1406435713
Antennas requiring phasing/tuning/matching are sensetive to dimensional accuracy and a nightmare for DIY hobbyist.
Any error in multi element antennas is multiplied by the number of elements. Collinears (coaxial collinear & franklin collinear) are example of this.
Antennas using tuning/phasing/matching/loading coils also present similar problem. Any error in diameter of coil , inter-turn spacing/length of coil creates an error in inductance & self capacitance of coil and affects performance.
What I am struggling for is to find a simple, repeatable design, whose performance does not appreciably deteriorate with dimensional errors common in DIY hobby situation.Last edited by abcd567; 2014-08-21, 23:23.
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Originally posted by abcd567 View PostWow! Looks great and very simple! That's what we need for DIY antenna.
Antennas requiring phasing/tuning/matching are sensetive to dimensional accuracy and a nightmare for DIY hobbyist.
Any error in multi element antennas is multiplied by the number of elements. Collinears (coaxial collinear & franklin collinear) are example of this.
Antennas using tuning/phasing/matching/loading coils also present similar problem. Any error in diameter of coil , inter-turn spacing/length of coil creates an error in inductance & self capacitance of coil and affects performance.
What I am struggling for is to find a simple, repeatable design, whose performance does not appreciably deteriorate with dimensional errors common in DIY hobby situation.
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Originally posted by abcd567 View Post@YWYY:
Is your CB band whip fed through loading coil?
Your antenna pucture shows a small cylinder between whip & coax (below circular ground plane plate), which looks like an enclosure for a loading coil.
With this antenna it can be built to the formulas with no adjusting for velocity and no loading effect from pvc radome. Its just wound around a fibreglass whipLast edited by YWYY; 2014-08-22, 11:14.
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Originally posted by YWYY View PostHi no, I use a uhf elevated feed for the whip, the disk is the groundplane.
With this antenna it can be built to the formulas with no adjusting for velocity and no loading effect from pvc radome. Its just wound around a fibreglass whip
I want to make this antenna and need following additional information:
(1) What is the diameter of fiberglass whip?
(2) Is 206 mm length of coil or length of wire in the coil?
Length of coil = distance between two ends of coil, measured in a straight line along the axis of whip.
Length of wire in coil = pi x dia of coil x number of turns.
.Last edited by abcd567; 2014-08-23, 01:05.
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Hi
1. the diametar of the whip is not important, its just a 27mhz cb whip. Make sure though that the fg whip is CLEAR fibreglass - Coloured will not work
2. 206.5 mm is the length of wire used to wind the coil. Th coil once wound, takes up 65 mm on the f/g
I used 2mm copper wire
I also made a shorter antenna with the same dimensions, only 4 elements,. I took a days plotting to get the range, then I covered it with heatshrink, leaving a couple of inches protruding out the top for trimming. I trimmed 1 mm at a time ...tested, then trimmed until it received the same as before I put the heatshrink on. It still receives exactly the same , I had to trim the top 137.5 mm (1/2 w ) down to 73 mm
I tried the same process on the longer antenna with 10 elements ( 1800mm) and couldnt get it to tune down. So I guess with a higher gain antenna, the detuning is much more severe. I use this antenna without a covering and it works fantastic, I get 270nm without a preamp, and I use 10 mtrs of LDF50 heliax coaxLast edited by YWYY; 2014-08-24, 05:30.
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Originally posted by peterhr View PostAbsolutely - but with the amplifier wrapped against the weather and a small bead of silicone caulk where the wires go into the coax to stop water ingress
1 of 4 - Half-wavelength Dipole - No Amplifier
2 of 4 - Range of Half-wavelength Dipole - No Amplifier - 2 hrs run
3 of 4 - Cantenna - No Amplifier
4 of 4 - Range of Cantenna - No Amplifier - 45 minutes run
WITH AMPLIFIER, THE DIFFERENCE BETWEEN TWO ANTENNAS WILL BE MUCH LESS DUE TO ADDED GAIN & AGC (Automatic Gain Control) OF AMPLIFIER.
Range Rings are 50 nautical miles apart
.Last edited by abcd567; 2014-08-24, 06:30.
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I have done several trial runs of Cantenna with 66mm dia Coke Can & 100mm dia Hot Chocolate can, but did not notice any improvement in range by using 100mm dia can.
The extra-ordinary range of 350+ nautical miles obtained few days ago did not occur again, and seems to be due to a very rare & favorable weather & atmospheric condition.Last edited by abcd567; 2014-08-24, 04:22.
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COMPARISON OF CANTENNA & HALF WAVELENGTH DIPOLE BY SIMULATION
1 of 2 - Simulation of Cantenna
Cylinder: 66mm dia x 69 high
Whip:69mm high
Please see the radiation pattern. Lobes are pulled down slightly.
The maximum gain of 5.5dBi is at 110 degrees i.e. 20 degrees below horizon.
Will get more of low flying & on the ground planes.
The horizontal (90 degrees) gain is 4.8 dBi
SWR is 2.28
================================================== ========================================
2 of 2 - Simulation of Half Wavelength Dipole
Upper & Lower Legs:68mm each
Please note the radiation pattern is symmetrical with maximum gain of 2.17 dBi in Horizontal direction.
SWR is 1.33
Last edited by abcd567; 2014-08-24, 07:23.
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.........And here is the Range of my Tiny Tot (half wavelength) antenna +AMPLIFIER
Compare with post #1524 for range without Amplifier. See how the range has increased drastically by use of Amplifier
1 of 2 - Half wavelength+AMPLIFIER
2 of 2 - Range of Half wavelength antenna + AMPLIFIER - 2 hrs run
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