Author Topic: Using the PCB Dipole on 915MHz  (Read 959 times)

raypat

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Using the PCB Dipole on 915MHz
« on: March 22, 2019, 10:18:23 PM »
Hi all,
I am a glider pilot from Australia looking to improve the flarm reception in my glider. Currently just have a approx. 3 inch stubby antenna protruding from the top of the instrument panel cover and range is not very good.I have purchased CHEM E's antenna element from the link on page 1 of this thread. 915 Mhz Rev 1. Australian Flarm operates on 921 Mhz. Have I bought the correct element and do I just follow the build instructions for 915 Mhz? Or do I need a different pigtail cable length? Can anyone put me on the right track Thanks. Cheers Ray.

Felix

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Re: Using the PCB Dipole on 915MHz
« Reply #1 on: March 23, 2019, 04:58:57 PM »
raypat,
Probably better as a separate thread.
You can trim the antenna to make it more resonant at higher frequencies than the current resonant frequency.
To measure where that point is you need an antenna analyzer.
Otherwise you can only guess how well the SWR is.

raypat

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Re: Using the PCB Dipole on 915MHz
« Reply #2 on: March 26, 2019, 02:35:29 AM »
OK Thanks Felix. When you say I can trim the antenna do I trim the pigtail or the actual antenna element? I have read some other posts and sighted a formula for the pigtail length for different frequencies. If that is what is required I think I can work it out but cutting the actual antenna to the correct length would be beyond my capabilities. I have neither an  analyser or the knowledge to use one.
Cheers Ray

Felix

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Re: Using the PCB Dipole on 915MHz
« Reply #3 on: March 26, 2019, 07:55:05 AM »
The PCB antenna has 2 elements, and their length (they should be equal whatever the length is) will determine what frequency the dipole resonates at.
The pigtail length determines how much of the signal is reflected back into the transmitter so you should make a bit of an effort to calculate that based on your RF/coax cable type, and its length from the TX output to the antenna center pin (including connectors). There are many calculators online for this.

raypat

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Re: Using the PCB Dipole on 915MHz
« Reply #4 on: March 26, 2019, 06:04:53 PM »
Thanks Felix. I have ordered four of the antenna so I will do the calcs for the pigtail length, install the antenna and test the reception with an online range analyser (The open Glider Network has one on their site). Then I will trim a small amount from the antenna and re test and repeat until there is either no improvement or a decline in reception.
Cheers
Ray