Hi,
I am building a frequency detector. It'll be able to detect frequency at 315MHz, 333MHz, 415MHz and 812MHz.
I designed the filters (Chebytchev) for each frequency I'm interested in. I know the impedance of my load and I assumed the Rs is 50ohms, which is a typical value for antennas.
My problem now is the following: if I use, let's say, a 50ohms 1/4 wave antenna for 315MHz, it will have 50ohms only at 315MHz. At 800MHz, the antenna won't act as a 1/4 wave anymore (fixed size antenna) and it will change the impedance and ultimately, screw my filter.
To solve this issue, I was thinking about using a telescopic antenna (like a car antenna). Also, my second idea was to use a transformer to make sure the Rs is always 50ohm, but it seems not to be the best idea at these frequencies. Another idea would be to have 2 antennas, but I am not happy with this solution.
Do you have any idea/advise to give me ?
Thanks,
c0
I am building a frequency detector. It'll be able to detect frequency at 315MHz, 333MHz, 415MHz and 812MHz.
I designed the filters (Chebytchev) for each frequency I'm interested in. I know the impedance of my load and I assumed the Rs is 50ohms, which is a typical value for antennas.
My problem now is the following: if I use, let's say, a 50ohms 1/4 wave antenna for 315MHz, it will have 50ohms only at 315MHz. At 800MHz, the antenna won't act as a 1/4 wave anymore (fixed size antenna) and it will change the impedance and ultimately, screw my filter.
To solve this issue, I was thinking about using a telescopic antenna (like a car antenna). Also, my second idea was to use a transformer to make sure the Rs is always 50ohm, but it seems not to be the best idea at these frequencies. Another idea would be to have 2 antennas, but I am not happy with this solution.
Do you have any idea/advise to give me ?
Thanks,
c0