Antenna Testing, Home Built super J pole or ¼ wave?


#1

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 Antenna Testing, Home Built, simple J-Poles. 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.


#2

@g7pnu
Happy experimenting. :+1: :+1: :+1:
Thanks for sharing your experiments.

Try this one also:
QUICK SPIDER - No Soldering, No Connector


#3

Cheers. I was just wondering @abcd567 if a 1/2 wave element and a ground would work? ie the same ground base but double the length of the radiating element. I think it should work but cant see any examples. Any thoughts?


#4

How do you propose to impedance match your 1/2 wave vertical?


#5

It will have high gain of 15 dBi (VERY GOOD), but will also have very high SWR of 83 (TOO BAD). You will need an impedance matching arrangement to bring down SWR from 83 to less than 2. The Spider with 68mm Whip has SWR 1.65 without any impedance matching arrangement.

Simulation 1 of 2

68 mm x 8 Legs Spider With 1/4 Wavelength (68mm) Whip
Click on image to see larger size

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Simulation 2 of 2

68 mm x 8 Legs Spider With 1/2 Wavelength (138mm) Whip
Click on image to see larger size

Off the Topic:
Nature’s Selection: 8 Legs for all Species of Spiders :slight_smile:

spider%208%20legs%20-1 spider%208%20legs%20-2 spider%208%20legs%20-3 spider%208%20legs%20-4

.


#6

@g7pnu
@belzybob

ADS-B by PY4ZBZ: http://www.qsl.net/py4zbz/adsb.htm#e


#7

@abcd567
@g7pnu

I used the PY4ZBZ design for some time before switching to the FA 26" antenna. Worked well, better than a 1/4 GP, but the FA was a significant improvement over both.

15dBi for an end fed 1/2 wave (with or without GP) is a huge overestimation. How did you get that figure?


#8

From Radiation Curve of Simulation 2 of 2.

You are right, 15 dBi is too high for a 1/2 wave end-fed arial. Seems there is some bug in simulation. Will check it tomorrow.

HalfWave%20Whip%20Spider%20Simulation%20-%20Gain%20%26%20Radiation


#9

I’m so amused that we calculate the gain of a half wavelength dipole.

When i was at school a halfwave length dipole in free space had a maximum gain of 1 by definition. That is, it was the standard.

Every other antenna was measured relative to it and we used dBd .

For convenience in antenna design we used the mythical isotopic radiator which was defined as -2.15 dBd.

Somewhere along the way antenna manufacturers started to use dBi as the standard so their gain numbers looked better. (CB, Wi-Fi and phone antennae especially)

So long as a halfwave dipole is correctly fed it has a maximum gain of 1 dBd or 2.15 dBi.

S


#10

I was being polite :slight_smile:


#11

That would actually be a gain of 0 dBd. (no gain, no loss, with reference to unity)
1 dBd would be just a tad over unity.


#12

I will check the bug in simulation, but meanwhile as far as I know, the 1/2 wavelength mono-pole with ground-plane is equivalent of a full-wave dipole, not that of a half-wave dipole.

Quote from Wikipedia:
https://en.m.wikipedia.org/wiki/Monopole_antenna


#13

Gain of dipole & monopole antennas

Note that for monopole with ground-plane, length is 1/2 of dipole.

Dipole Length in wavelengths Monopole length in wavelengths Directive gain (dBi) Notes
≪0.5 ≪0.25 1.76 Poor efficiency
0.5 0.25 2.15 Most common
1.0 0.5 4.0 Not used
1.25 0.625 5.2 Best gain (5/8)
1.5 0.75 3.5 Third harmonic
2.0 1.0 4.3 Not used

#14

@g7pnu
@belzybob
@SweetPea11

Removed the bug in simulation.
Here are results.
Please note that these simulations are for antenna in free space. When I find time, I will simulate for antenna at 6 meters (20 feet) above real ground, and post results.

(1) Spider 1/4 wavelength Whip
Geometry: Whip = 68 mm, Radials = 8 x 68 mm, slanting 45 deg, Built on connector SO239
Gain = 1.31 dBi
Impedance = 66.1 + j 24.7
SWR 50 = 1.66

.
(2) Spider 1/2 wavelength Whip
Geometry: Whip = 138 mm, Radials = 8 x 68 mm, slanting 45 deg, Built on connector SO239
Gain = 0 dBi
Impedance = 511 - j 722
SWR 50 = 30.7

.

(1) Horizontal Ground-plane 1/2 wavelength Whip
Geometry: Whip = 138 mm, Radials = 8 x 68 mm, Horizontal, Built on connector SO239
Gain = 3.5 dBi
Impedance = 833 - j 658
SWR 50 = 27.1

.
SIMULATION 1 OF 3: Spider, 1/4 wavelength Whip
CLICK ON IMAGE TO SEE FULL SIZE IMAGE

.
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SIMULATION 2 OF 3: Spider, 1/2 wavelength Whip
CLICK ON IMAGE TO SEE FULL SIZE IMAGE

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SIMULATION 3 OF 3: Horizontal Ground-plane, 1/2 wavelength Whip
CLICK ON IMAGE TO SEE FULL SIZE IMAGE


#15

That’s nearer the mark; at these frequencies an antenna at any reasonable height is going to be effectively ‘free space’.


#16

Yes, a mistake in modelling caused it, possibly because I have prepared the model late in the night while I was feeling sleepy. :slight_smile:


#17

@g7pnu

Did you try PY4ZBZ antenna?
It is very simple and easy to make.


#18

Thanks for running the simulations and explaining why a 1/2 ground is a bad idea. I like the look of the py4zbz it looks like it could be made from ridged rod and be very stable. Thanks again @abcd567


#19

@g7pnu
One drawback if installed outdoor: Rain or dew drops will short the two sides of hair-pin (stub), and it will perform bad, till it dries.


#20

I used the core of some cellphone coaxial cable I had handy. About 4mm diameter. SO239 soldered directly to the matching section. The ‘chocolate block’ connectors were to allow quick changes to the antenna length.

Not pretty, but cheap and simple.