On Wednesday 05 July 2006 22:58, Nate Duehr wrote:
> 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 <wouter@voti.nl> 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) =3D 20V swing
> >> +5V - (-15V) =3D 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?
>

The one i am working on is a low power board, and i am trying to modify
it for high power (within legally allowable power limits).

>On the high end, but what about the other end? =A0Are you really sure it c=
an
>handle -15V?

You are correct, the IC can't handle negative peak. I thought of limiting it
after shifting.  On the other hand, limiting the waveform first and then =

shifting is also fine, I thinking of trying both.


regards,
palani.

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http://palam.blogspot.com

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