Antenna question regarding wireless transceivers.

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farmosh203
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Posted by farmosh203: Mon. Sep 7, 2009 - 06:24 PM
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Hello, I started a wireless transceiver project to send one byte of data and receive it with a separate wireless transceiver.

I bought an antenna off Digikey,

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ANT-315-SP_-ND

From the datasheet, it looks like I connect pin 1 of the antenna to the output of my transceiver. Pins 2-6 of the antenna should go to ground. When I ohm'ed out pin 1 of the antenna to pins 2-6, they were direct short circuits. When I hooked up the antenna with pin 1 to the transceiver output and pins 2-6 to ground, the circuit started to smoke (3.3V was shorted to ground).

I ended up cutting the trace to the Splatch antenna and using a simple wire. This worked, although the range was about 2 feet at most.

Does anyone know why the Splatch antenna didn't work and how to make it work? Why is pin 1 of the antenna connected to ground?

Does anyone have a recommendation for an antenna that would work well? I am using 315 MHz for the wireless transmissions. The two possibilities I found on Digikey were:

http://www.antennafactor.com/documents/ANT-315-PW-LP_Data_Sheet.pdf

http://www.antennafactor.com/documents/ANT-315-HETH_Data_Sheet.pdf (if I were to connect this horizontally, would both ends of the antenna wire go to the same node of L3? Or would one end have to go on RF_1 and the other end on RF_2?)

Thanks for any help, I can't wait to get my wireless working over longer distances!

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Learning and Information, General Electronics
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ka7ehk
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Posted by ka7ehk: Mon. Sep 7, 2009 - 06:33 PM
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Yes, that antenna will have a DC path to ground. At the operating frequency, it will appear quite different.

Your radio cannot tolerate a DC short circuit to ground. You will need to add a capacitor in series with the antenna. That capacitor needs to go between the antenna and the junction of C2 & L3. Maybe 10-100pf, smt (100pf if it is 430MHz, 30pf if its 900MHz, 10pf if its 2.4GHz). The precise value is not critical as long as its reactance at the operating frequency is less than an ohm or so.

Jim

 

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leon_heller
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Posted by leon_heller: Mon. Sep 7, 2009 - 06:35 PM
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Some antennas need a ground, if only so that the matching network will function properly.

Leon

Leon Heller G1HSM

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