| ??? 12/28/05 01:44 Modified: 12/28/05 01:49 Read: times |
#106064 - Relay Responding to: ???'s previous message |
Shaharyar said:
will this work for antenna switching? You can use a relay, theoretically. But you must use a RF relay. Why? Assume your relay shows a stray capacitance of 5pF to the contact, that is left open. Then, this will result in an impedance of 1 / (2 x pi x f x C)= 76 Ohm at 418MHz! This means, that a heavy impedance mismatch will occur. Only a relay, which shows a stray capacitance of less than 0.5pF, according to a stray impedance of more than about 760 Ohm might work to some extent, but will still result in a relevant impedance mismatch at 418MHz. Another issue is the ultra small input voltage at reciever input in the range of a few µV. This means for the relay, that a "dry" load is to be switched. Only special relays with massive gold contacts, ideally protected by an inert gas chamber will allow the switching of dry loads. So, you would have to buy a special and expensive RF relay for your task. Something like DX-relay from SDS or better. I think, the relay is not realy a remedy for your problem. Any other methode which does not solve the above stray capacitance problem will not be a remedy either. Kai |
