On Jul 5, 2006, at 7:05 AM, Palaniappan C wrote: > On Wednesday 05 July 2006 17:20, Vasile Surducan wrote: >> On 7/5/06, Wouter van Ooijen wrote: >>>> The input signal is 20v peak-to-peak (-10v to +10v) ac 14Mhz >>>> rf signal. >>>> and i want to shift it to ( -15v to +5v ). I looking for a >>>> way to do it >>>> without using additional power supply. >>> >>> a suitable transformer, with the 0 of the secondaryt at -5V? >> +10v - (-10V) = 20V swing >> +5V - (-15V) = 20V swing too >> Pass the signal via a capacitor and fixe the DC level at the right >> value(ie -5V). >> The question is how you've get 20Vpp/14Mhz RF signal (meaning >> sinusoidal) >> and what you're doing with it. >> Vasile > > Thanks for your replies, > The actual problem is , i am modifying a rf transceiver board (rf > id) , for > more power. There is low power transceiver ic (TI S67 00) on the > board, which > do all the modulation and demodulation (only for low power output). > I need to modify it to get more power output and more range for rf > id tag. > I added a power amplifier on transmitter path. > > For the receiver path, the rx pin of IC is limited to 5V, so i need to > attenuate the rx signal, without losing the data on its envelope. > direct > resistance attenuation will affect the signal strength (envelope). > so i > thought of shifting down the signal and feeding it to the IC. > > I am trying the methods you suggested. Thanks. > > regards, > palani. Most RFID systems I've seen were already running at their maximum legally allowable power limits. Are you sure your modification is legal where you live? Are you going to end up turning the RFID system into an RF noise generator that someone will have to come hunt down to keep it from interfering other radio services? -- Nate Duehr nate@natetech.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist