Hi Damien: When something has a 50 Ohm impedance the designer was expecting the port to be terminated with 50 Ohms. This means that the transmission line between the port and the final 50 Ohm load is 50 Ohms AND the actual load is 50 Ohms. It's possible to get a 50 Ohm trace on a double sided board if the back side is a ground plane and you use a "microstrip" design. You can also use a "stripline" design but this requires a ground plane both above and below the trace carrying the signal. As a prior poster has suggested you can also use what's called semi rigid 50 Ohm coax. But remember that you should also either end the 50 Ohm line in some other component that has a 50 Ohm impedance or in a connector that's 50 Ohms, like a BNC, TNC, N, SMA, etc. so that a 50 Ohm connector and coax like RG-58 can carry the signal to it's final 50 Ohm load. If the total distance between the source chip and the actual load is less than 1/10 of the wavelength of the highest frequency then all of the above may not be that important. For example for a 400 MHz signal a wavelength is 0.75 meters and 1/10 of that is 0.075 meters (3"). If you have a component on the board that has a 50 Ohm input impedance and the path is less than 3" the effect of a non 50 Ohm trace is not so big. Have Fun, Brooke Clarke, N6GCE http://www.PRC68.com >From: "Damien Cahill" >To: >Sent: Friday, February 20, 2004 12:55 AM >Subject: [EE]: RF Transmission Line PCB Routing > > > > >>Hi List, >> >>I have a reasonably simple question. I am currently routing an RF PCB >> >> >which > > >>uses a 1GHz DDS synthesiser. The RF signals on the board are up to 400MHz >>in frequency and obviously I must consider the impedance of any copper >>tracks I lay. What I am unsure of though is what impedance should I be >>aiming for with these tracks. Should it match the DDS outputs which are >> >> >all > > >>50ohm or should it be as low impedance as possible to reduce resistive >>losses. I eagerly await the lists omnipotent response. >> >>Cheers, >>Damien Cahill >> > > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics