Author Topic: Antenna Impedance  (Read 2539 times)

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Offline James Nilton

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Antenna Impedance
« on: June 01, 2015, 10:09:47 pm »
I have to remove the antenna from my Multi-Rotor to get it into the boot of my car, this has on a couple of occasions led to me almost powering up with no antenna attached. this would obviously lead to my transmitter frying, so I made a 'remove before flight' flag to remind me.
But i'd like to make a flag to replace the antenna with the same impedance as the antenna, just in case the flag doesn't remind me.
how would I measure the impedance and what could I use to replicate its impedance?
 

Online Howardlong

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Re: Antenna Impedance
« Reply #1 on: June 01, 2015, 10:54:11 pm »
I assume that this is for the video downlink?

You can measure the impedance with a network analyser.

However, it's almost certainly 50 ohm.
 

Offline calexanian

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Re: Antenna Impedance
« Reply #2 on: June 02, 2015, 12:56:33 am »
I would use an appropriate small dummy load. What bands and what power are we talking here?
Charles Alexanian
Alex-Tronix Control Systems
 

Offline Melt-O-Tronic

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Re: Antenna Impedance
« Reply #3 on: June 02, 2015, 01:45:55 am »
Pending answers to the above questions, you can almost certainly solve your problem with a 50 ohm terminator off of eBay.  I'm guessing RP-SMA or SMA.  Once you get one, dip it in red Plasti-Dip or paint it a bright color as a visual reminder.
 

Offline calexanian

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Re: Antenna Impedance
« Reply #4 on: June 02, 2015, 06:13:16 am »
http://www.diamondantenna.net/dl30a.html

Something like this perhaps. Also most modern digital rigs have high SWR cutout to save the power amp. MOST do. Not all, and it should in no way be used as a fail safe in that manner.
Charles Alexanian
Alex-Tronix Control Systems
 

Offline Dago

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Re: Antenna Impedance
« Reply #5 on: June 02, 2015, 07:29:56 am »
Are you sure your transmitter would fry? Most low power transmitters can handle full reflection.
Come and check my projects at http://www.dgkelectronics.com ! I also tweet as https://twitter.com/DGKelectronics
 

Offline SeanB

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Re: Antenna Impedance
« Reply #6 on: June 02, 2015, 05:36:26 pm »
50R dummy load on a N connector, and attach the red flag to it as well, so you are less likely to lose it.
 

Online T3sl4co1l

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Re: Antenna Impedance
« Reply #7 on: June 02, 2015, 05:53:28 pm »
Note that the terminator has to be rated for at least some fraction of full transmitter power, or else both will end up smoked.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
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