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OA47

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Joined: 11/04/2012
Location: Australia
Posts: 926

Posted: 03:54am 07 Apr 2023

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As mentioned earlier I am using a number of these units in a micromite network and was wondering if there is a simple way of measuring the reflected power from the antenna. I am cutting the antenna at 173.1mm to suit 433Mhz 1/4 wave length and was wondering if I was doing it correctly.

I have SWR meters in the shed but with FSD settings of 1KW,10W & 1W I cannot get enough power from the low power units to measure the reflected power.

Any suggestions greatly appreciated.

0A47

morgs67
Regular Member

Joined: 10/07/2019
Location: Australia
Posts: 75

Posted: 04:22am 07 Apr 2023

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The nanoVNA, VNA = vector network analyzer can check antenna resonance.

nanovna.com is one of many versions found on searching "nanoVNA"

Tony

TassyJim

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Joined: 07/08/2011
Location: Australia
Posts: 6102

Posted: 05:15am 07 Apr 2023

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It all depends on your ground plane and antenna diameter but I would usually cut mine to 16.5cm (0.95 * quarter wave)

The nanoVNA is good but a bit expensive of a one time use.

Jim

VK7JH
MMedit MMBasic Help

OA47

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Joined: 11/04/2012
Location: Australia
Posts: 926

Posted: 05:42am 07 Apr 2023

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Jim, I initially used factory made plastic covered antenna but the birds with the bent beaks found them too attractive and destroyed them very quickly. I decided on this format which does win the battle with the birds.

My measurement is taken from the plate to the tip of the antenna.

0A47

TassyJim

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Joined: 07/08/2011
Location: Australia
Posts: 6102

Posted: 06:43am 07 Apr 2023

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Birds can be a big problem.
Rocking chair and shotgun helps...

I wouldn't get too worried about the dimensions. Either will work well enough.

IF you want to try something that doesn't need a ground plane/bird perch, look up J-pole.

Jim

VK7JH
MMedit MMBasic Help

Mixtel90

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Joined: 05/10/2019
Location: United Kingdom
Posts: 6812

Posted: 07:29am 07 Apr 2023

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I used a J pole on 2m for years. Quite effective and compact. :) It's still up there on the chimney stack, unused for many years now and I'm no longer agile enough to go up there to take it down.

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

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