Antenna Testing, Home Built super J pole or ¼ wave?
Introduction:
After building a few ¼ wave antenna and simple J poles I wanted to see if I could come up with a Super J which could be built multiple times to a given set of measurements. This little report includes a total failure and a nice success, it was tempting to hide the failure but the failure is included just so you can see how hard it can be to build some antenna types…….
I used a tuned up simple J as a starting point, which was made from 3mm brass rod (see Simple J results link https://discussions.flightaware.com/t/antenna-testing-home-built-simple-j-poles/33641.). I first tried adding a copper wire stub and second element to the Simple J to form a Super J pole.
I found the additional copper wire element and stub to be dimensionaly unstable and it wasn’t possible to make or measure 0.2mm changes; where as it had been possible to tune the simple brass J pole ± 0.1mm. Unfortunately I only had a small ammount of 3mm brass rod, so I had to find away to make a stable Super J pole from 1.6mm copper mains wire.
The solution I thought I would use was a simple wooden frame, with holes drilled in it to hold the J pole elements in a fixed position. After 21 runs of 24 hours I found the best coper wire simple J stub to single main element length, with a wooden frame to be.
I 201.0mm x 66.4mm or
II 199mm x 66.0mm
When compared to an air spaced J pole the wooden frame did effect the tuning a little but the effect was constant and the frame did limit the flex and thus the variation in reception. The patten for the best results appears to be to make the stub arround 0.5mm shorter than the theortical calculated length to match the stub and main; ie if the main is 201mm on paper the ¼ wave stub should be 67.0mm not 66.4.
The length of the main is not critical 201 to 199 seems fine but it is critical for the main and J to be a match.
The Failure:
After 21 tests the J pole on a wooden frame provided worse coverage than the first ¼ I had build. I didn’t give up at this point, I then tried to add additional elements and stubs to the frame, four in total. This was a total failure. It wasn’t posible to bend the wire so that the element lenghts where within 2mm of the desired length or drill holes in the wooden frame to within 0.5mm.
So if I wanted a J pole I would make it from brass rod and I wouldn’t bother trying to make a super J. A well tuned simple J pole made from brass rod will provide good coverage but it will take you several days to tune it up if you have no electronic test equipment.
The Come back kid:
After the total failure of the wooden framed Super J pole I went back to the ¼ wave I had first built. I decided that the best course of action was to try and optimize the simple ¼ because:
I The impedance matching is simple, just bend the radials to 45 degrees.
II The element length can easily be measured to within 0.1mm
III There are Only three variables, radial angle, radial length and element length
On the first test run the ¼ wave, with a untuned main element, out performed all the J poles I had made using copper wire!
First set of results were for ¼ Wave antenni; Antenna Testing, Home Built , ¼ waves.
The second set of results were for simple J Pole antenni; Antenna Testing, Home Built, simple J-Poles.
Dates:
Super J from 10 April 2018 to
Books:
“The Radio Communication Handbook” by RSGB ISBN: 1905086083,9781905086085 Chapter 16 “Practical VHF Antennas”.
Wave length to Frequency
Frequency to Wavelength convertion
F 1090 MHz
L 275.04 mm
L/2 137.52 mm
L/4 68.76 mm
====================================================
Tests:
All the tests where made using the same equipment, in the same location, over a 24 hour period. A control test using a ¼ wave cantenna is include below so that you can compare the performance to a know standard antenna.
===================================================
Best Results:
Coke Cantenna “CONTROL”
“Control Test”
¼ wave Coke Cantenna /
garage /
13-16/03/2018 /
Tues 20:00 – Friday 20:00
Arial element length: 68.5mm x 1.0mm brass wire
Diameter: it’s a coke can
Height: 69mm
Connector: F Type
===================================================
Best Brass, SIMPLE J pole
Test J19:
Best Brass, a SIMPLE J pole
garage /
1/04/2018 /
to Monday (24 hours 1 minute) Easter Monday
198.1mm * 6mm * 66.2mm and
feed 7mm from base
3.2 mm Brass rod element and J stub
Total messages / min : 11.519 x 10^3
Total messages: 16600,000
Max distance: 135 n miles (Azi 120deg)
Max dis 2nd lobe: 126n miles (Azi 200deg)
Max dis 3rd lobe: 109n miles (Azi 280deg)
===================================================
Best Brass and Copper Super J pole
Test SJ_3:
Best Copper wire and Brass rod Super J Pole.
08/04/2018 Sunday night to
10/04/2018 Tuesday night
All insulation removed and a reduced gap between the stub wires 5mm.
198.1mm * 6mm * 66.2mm and
feed 7mm from base
3.2 mm Brass rod element and J stub
and a 1.6mm copper wire secondary element and stub.
J stub separation to main was 6mm
(This design was dimensional flexible but it did prove I needed to control the flex of the copper wire stub and second element)
===================================================
Best Simple J Pole, using Copper wire on a wooden frame.
Test SJ_11
Simple J Pole, using Copper wire on a wooden frame
2018-04-18 20:43:37
to Thursday (1 day 51 minutes)
201.0mm
66.5mm
66.4mm
1.6 mm Coper wire main element and J stub. J stub separation to main was 6mm
feed 7mm from base
Range Maximum lobe: 104nm 290deg
Range Secondary lobe: 100nm 110deg
Contacts: 12909,358
Contact per minute: 8.658k
===================================================
Brass ¼ wave antenna
Test QW_09
Brass ¼ wave with 4 radials
2018-05-09
to Thur(1 day 9 hours 57 minutes)
main element length: 68.9mm
radial angle: 45 deg
radials length:
Main element and radials made from brass tube with an od of xxx mm and an id of yyy mm
Range Maximum lobe: 139nm 120deg
Range Secondary lobe: 112nm 270deg
Range Secondary lobe: 82nm 180deg
Contacts: 24689,000
Contact per minute: 12.120
image crop 6,6,5,3 and 68.2=68.9
===================================================
Conclusion:
The best resuls where obtained from a tuned simple J pole made from brass rodd but the results from a tuned ¼ wave where close. The time to build a tuned ¼ wave was approximaple 1/3 of the time to build a tuned simple J.
