Trial Run Results for Three Types of Whip Antennas

[majo]

Thank you for this great and easy to realize idea!

But before I cut my antenna allow one question:
If 1/2 wavelenght for 1090 MHz is 138 mm and I want my antenna to be 1/4 weavelenght (=69 mm) why should I make the cut at 67 mm (15 mm base + 52 mm whip)?

[CX6BX]

Great info abcd567, i will try this with my old antenna

[abcd567]

@Ben311

Hello Ben
There is another step to further improve: Enlarge the tiny ground plane provided by the 1 inch (25mm) dia mag mount base by placing it over a metallic surface like a metallic sheet, plate or a can.

Please see the following thread which demonstrates the boost when antanna was placed over a metallic surface (a food can), compared to when it was placed over a non metallic surface (inverted glass).

Trial Run Results for Four Sizes of Ground Planes

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[Ben311]

Hello all,

I just registered a new account to let everyone know, that this is a genius idea. As I already ordered a new antenna yesterday, I gave it a try and cut the old indoors-antenna. Now lots and lots of planes show up and my range increased by about 30-40 nm.

Thanks
Ben

[HNJAMeindersma]

So we may conclude; bigger is not always better. It's how you use your antenna.. :P XD haha

[abcd567]

Is the stock whip exactly 1/2 wavelength?

Yes, it is 1/2 wavelength.

The total length of whip is 115 mm removable part + 15 mm inside the base = 130 mm.
The 1/2 wavelength at 1090 MHz is 138 mm.
Therefore for all practical purposes, the stock whip is 1/2 wavelength.

However the impedance of 1/2 wavelength whip, even with ground-plane enlarged, is several hundred ohms. This gies a poor impedance match with 75 input impedance of the receiver (db-t usb dongle) and SWR is higher than 2.5

On the other hand, the impedance of 1/4 wavelength whip with ground-plane enlarged is between 50 and 75 ohms, and provides an almost perfect impedance match & SWR is 1.5 or less.

This is the reason the whip chopped to 1/4 wavelength performs better than full length whip.
Please note that 52 mm removable part + 15 mm inside base = 67 mm = 1/4 wavelength at 1090 MHz.

25164814131_839b1981bc_o.png. . . . 24872604509_2bc46a22db_o.png

[HNJAMeindersma]

Is the stock whip exactly 1/2 wavelength?

[dedicados]

very interesting, im going to try it

just to get a more info... why a trimmed antenna works better? did you start cutting little and test?

i found really interesting your tests and results. thanks for sharing with us!

If someone need space to upload a .iso .img or any kind of software i can help you, i have spare space in my servers.

[Oblivian]

So essentially, if you aren't using it for tv or any other frequency. Chop it!

[abcd567]

Please scroll down to see the test result graphs at the bottom.

(1) The three antennas under test were:

• (a) Coiled Whip
  (b) Stock Whip
  (c) Optimized Whip

(2) In order to minimize number of variables, only the removable parts of Whips were interchanged. All other hardware, location, and software/gain settings were identical. Even the same mag mount base & RG174 coax cable was used for all the three whips.

(3) In order to be sure that results are not influenced due to fluctuation in traffic, test were conducted twice.

• (a) First test between 2pm & 3 pm
  (b) Repeat test between 4pm & 5pm

Photo 1 - Three Antennas


Photo 2 - Test Setup


Photos 3 & 4 - Results of First Test






Photos 5 & 6 - Results of Repeat Test