Total posts : 45366
Thanks for the offer Neil, I might take you up on that crystal. I found a couple of crystals at Allied that will get me 1638.x including one that will work with the mentioned divide by N in the AM-100 plans (4.xxx Mhz), and it was only about $2.00.
Now to make for more choices, I was looking over the Maxim site, and found some goodies that have a .5% error which is what they say you get from a crystal. These are serial programmed devices, and the first is in a TO-92 case so it is easy to work with. I’ll be contacting Maxim to see what they can do for me. Here are the URLS (again no linky)
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2616
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3359
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3491
The DS 1077 and DS1085 would be nice in a microcontroller based transmitter because of the separate data pins. Note that the DS1085 has a minimum of 8.2Mhz on one output which means that either the internal divide by N could be used, or an external div-N device (at least for me). I’ll probably check on the DS1065 since it is easier to solder.
One thing I need to check on is what happens to the error when you start dividing the frequency… It should also be reduced by the same amount as the division because the error is at the oscillator not the output, so these might make a very tightly controlled transmitter if you are dividing by 8 or more (0.0625 %). Either that or I’m thinking backwards and the error gets worse after division.
It’s looking like I can put one of these together for about $15 plus shipping and should have a power supply kicking around to use with it. The antenna will still need some scrounging, but we might have everything on campus to maintain the buildings (it is plumbing stuff after all).
