The calculations I did for the track resistance came to about 16 Ohms for 60
feet. Since Prox Antenna's are normally wound out of wire with much less surface
area than a 10 mil track, I suspect the resistance (("Q" really) will not be an
issue, if anything, it might make it harder to tune. (it will have a lower
bandwidth around resonance. This also makes tuning to the correct resonant point
more difficult! )On some prox antenna stuff I did years ago, I found that the series tuning/coupling capacitor was the critical element. If I used a common "garden variety" SMD capacitor, there was about 70 volts across the coil. When I changed to a "Low dissipation" (IE: High "q" capacitor) the voltage on the coil went to about 220 volts. (9 times the original power) and the circuit reading/writing distance improved by about 4 times. So don't always blame the antenna inductance of you are having trouble ... Cheers Harry -----Original Message----- From: John C. Echols [mailto:[EMAIL PROTECTED] Sent: Saturday, April 03, 2004 10:42 AM To: Protel EDA Forum Subject: Re: [PEDA] Antenna coil The App Note looks interesting. Since I've never even wound a coil until last week I'm sort of winging it. Hadn't thought about the DC Resistance but I'm stuck with the 4 X 4 spacing to fit the room on the board. If it works I'll save $2-4 per assembly with the "free" antenna, so it's worth a try. Yes this is a 486 and in 3 or 4 years I've never had one piece of spam. My other computer that is part of the company's set-up get about 150 per day. That's been getting worse for years but last week they put in a filter and I'm down to 20 per day. Thank for everybody's input. When I get some proto boards I'll let you know if it worked. John Leo Potjewijd wrote: > At 29-03-2004 12:56, [EMAIL PROTECTED] wrote: > >In a message dated 2004-03-28 03:33:51 PM Eastern Standard Time, > >[EMAIL PROTECTED] writes: > > > > >......The coil is about 3.25 X 4.25", 700uHy and takes 60 turns of mag > > wire. Can I do this with traces?........ > > You can. EM does it in their proximity reader reference design, but use a > lower inductance. > They do 32 turns and swap layers every 4 turns. > > >I did something almost exactly like this a while back. Better do some > >calculations before you do those 4/4 design rules. I was very disappointed > >in the Q of the resulting coil; I needed a fairly high Q. > > But with prox readers, the Q has to be limited for bandwith reasons. > Depending on the type of datarate and modulation used you can end up with a > maximum Q of 1.5.......... Q's used with 2kb/s and ASK are in the range 10-25. > > >Should have done the calculations myself before layout, because it behaves > >as theory would dictate. I used 10/10 rules. With 1 oz copper (1.4 mils > >thickness), the cross-sectional area of a 10 mil trace is only 14 sq mils > >- roughly equivalent to #37 wire, which is about 2' per ohm. The coil you > >describe is about 60' long, so you've got at least 30 ohms with 10/10 > >rules. If you go to 4/4, the cross section drops to 5.6 sq mils, which > >puts you up around 90 to 100 ohms for 60' of coil. Now you need to bring > >the rest of the circuit into the picture to compute Q, if that's relevant, > >but you can at least say that you'll lose 1 volt of your drive for every > >10 mA of current through that coil. If I were doing it over again, I'd > >figure out a way to get some iron inside the coil and reduce the number of > >turns, and if possible use wider traces and thicker copper. > > For proximity cards you will need to maximise the current, after all that's > what powers the card. Some good computations can be found in Microchip's AN678. > > Leo Potjewijd > hardware designer > Integrated Engineering B.V. > > [EMAIL PROTECTED] > +31 20 4620700 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/[EMAIL PROTECTED] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
