If I have an SMA Antenna, what test/s can I perform to determine what frequency the Antenna is designed to operate at, other than plugging it in in seeing if it works.
Measure it and do some math.
Most antennas are designed to be 1/4 wavelength.
So measure, multiply by 4 to get 1 wavelength.
Frequency = speed of light/(antenna length x 4)
or
antenna length = (speed of light/frequency)/4
Example: 2.4GHz PCB trace antenna
299,792,458m/S / 2,400,000,000 Hz = 0.1249m, /4 = 0.031225m = 3.1225cm
Thanks Crossroads...
Can it also be designed for 50 Ohms?
It looks like the attached pic and the black part is 48mm long.
Pop off the black plastic covering and measure the length of the bare wire inside. That will be 1/4 wavelength. If it is a dipole antenna, there will be exposed shield braid, or a metal tube, extending in the opposite direction for 1/4 wavelength.
50 ohms would be the impedance of the PCB trace leading to the connector that the antenna screws onto. Generally something like 70mil wide 1 oz thickness copper on 1.6mm fiber glass PCB with ground plane next to the traces & on the bottom of the board, with lots of vias connecting the top & bottom layers. I don't recall how much trace to adjacent ground plane clearance, maybe 10mil was fine. There are online calculators to find dimensions.
jremington:
Pop off the black plastic covering and measure the length of the bare wire inside. That will be 1/4 wavelength. If it is a dipole antenna, there will be exposed shield braid, or a metal tube, extending in the opposite direction for 1/4 wavelength.
Excellent idea, although I discovered nothing exciting - other than a coiled wire with a rubber insulation at the base. Combining your advice and the calc info given by Crossroads ...
I could only count the 15 exposed coils, which spanned approx. 15mm - the rest were covered by the insulation. Anyway with an overall length of 23 mm, I estimate a total of 23 coils. Loop diameter centre/centre is about 3.4mm so I calculate single loop/coil length as 3.4 x 3.142 = 10.6828mm and overall length as 23 x 10.6828 = 245.7044. The right angle fitting adds about 22mm of length.
Based only on the coil length of 245.7044, I get a frequency of 305,033,668.51.
Allowing for errors in my estimated measurements, I would conclude it is probably a 315 MHz antenna.
CrossRoads:
50 ohms would be the impedance of the PCB trace leading to the connector that the antenna screws onto. Generally something like 70mil wide 1 oz thickness copper on 1.6mm fiber glass PCB with ground plane next to the traces & on the bottom of the board, with lots of vias connecting the top & bottom layers. I don't recall how much trace to adjacent ground plane clearance, maybe 10mil was fine. There are online calculators to find dimensions.
Thanks for clearing up my understanding of where the 50 Ohms design reference comes from.