On 5/11/07, Gerhard Fiedler wrote: > > Peter P. wrote: > > >>>> buy nH inductor kit > >>> > >>> Yeah. Get the kit where you also get a complimentary bridge in the > >>> desert included. > >> > >> I didn't understand this... I guess you mean it's not worth it? > > > > Yup. It would be a box with pieces of wire and instructions to avoid > > bending them or putting them near any metal or dielectric ... > > I thought about SMD inductors, and about repeatability. Keeping a tight > PCB > layout with short traces to reduce dependency on the PCB and using > inductors that come with reasonable tolerances would make it more probable > that the next device works like the one before -- I thought. Did I think > wrong? You are correct. It may be that you can get 5% tolerances with a PCB coil, but you'll have to do some calculations to figure it out for sure. > [...] they cannot predict the real situation. As I said, small details > > can pull the frequency off 1-3%. That's 10 MHz at 433 MHz (way too > > much). > > I have to continue discussing this... When I look at a typical keyfob, > they > seem to use standard SMD capacitors and inductors -- with tolerances > probably more than 3% (at least 5%). And yet they seem to work fine, > probably without individual adjustment. From this, I gather that the > frequency of the LC resonance being off 3% can't be that crucial... Again, > am I wrong? Resonant frequency is F=1/(2*pi*sqrt(L*C)), so if the inductance goes up by 3%, the frequency goes down by ~1.5%. For a key fob transmitter, that's pretty good, they are really simple and sloppy. > Try very hard to locate a place where they have a specan. Any lab that > > does cell phones or handy phones (UHF) should have one. Or try to rent > > from an equipment supplier. > > Good idea; I'll see what I can find. > > Thanks, > Gerhard > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist