Charleston master oscillator & misc

[Terry Fox]

Here are updates on a few items:

1.  I finally got around to replacing my temporary replacement of the 
76.8MHz programmed oscillator on the Charleston Receiver board.  I had 
ordered a couple custom CMOS SI570 running at 76.8MHz.  I am PLEASED TO 
REPORT that the phase noise issues that I had been trying to fix for 
quite a while ARE COMPLETELY GONE!  Those of you following the SoftRock 
saga know about the SI570, a programmable oscillator from SI Labs.  You 
can order the SI570 to come at your own start-up frequency, plus it can 
be programmed to any frequency in its range via an I2C bus interface.

If you want to order SI570s to replace your older oscillators, they are 
about $13 each, plus shipping.  I suggest group orders wherever 
possible.  The custom part number that SI Labs assigned to my SI570 
setup is: 570AC000729DG.  It usually takes about 4-6 weeks for custom 
orders, which can be placed via the SI Labs website.

I installed my SI570 in the same place as the original oscillator.  The 
SI570 has some extra pads, two of which are the I2C lines.  In order to 
connect wires to them, I used some small SMT zero-ohm resistors as small 
standoffs to put the oscillator above the board.  I actually soldered 
the four 0-ohm resistors to the four corner pins of the SI570, and then 
a couple small wire-wrap wires to the I2C pads.  Then, I placed the 
oscillator with the resistors on top of the original oscillator pads, 
and soldered it in place.  I then ran the extra wires to a small 
four-pin header, with the two outside pins bent over and soldered to the 
ground plane on the underside of the board.

2.  James Ahlstrom, author of Quisk, has a nice article in the latest 
QEX regarding a digital SDR HF transceiver.  It uses an FPGA, A/D, D/A, 
and other stuff.  This is the type of radios that I am interested in, in 
the long run.

3.  I've been messing around more with FPGA programming, learning this 
stuff.  I have a 12-bit A/D & D/A system passing data through 
themselves.  Next, I plan to tap the A/D samples and feed them into a 
buffer and graphics converter.  I also have the VGA output of the Nexys2 
board creating a 640x480 display with a 10x10 grid inside it, like an 
oscilloscope.  The hope is to create a simple oscilloscope using just 
the FPGA board and a fast A/D.  That is the first "end-product" toward 
building a panadaptor using the Charleston receiver.

3.  Toward the oscilloscope project, I also purchased a quad 8-bit A/D, 
100MHz board from Joe Rothweiler of Sensicomm.  It actually has only two 
of the four A/D positions populated, but it appears to work.  His 
software is geared toward PC display using Linux & Octave.  It only does 
a single-shot grab & display right now.  While that is interesting, I 
want to use the FPGA VGA output instead.  His board plugs into the 
Nexys2 large FX2 connector, so the hardware is compatible.  He is also 
finishing up a design that has two 8-bit A/D & a smaller FPGA on a 
single board.  Google Sensicomm if interested.

4.  I also have been playing with small TFT LCD displays.  I have a 
4.3inch 480x272 display running with the Nexys2, it's plugged into the 
FX2 connector.  More recently, I found a 5.6inch, 640x480 TFT LCD on 
ebay, and have successfully made it work with the Nexys2 FPGA board, 
also interfaced via the FX2 connector.  The 10x10 'scope-like display 
works with it in addition to a standard VGA monitor.  The "Truly" 
480x272 display was less than $50, but you can also buy replacement 
480x272 PSP displays for about $25 on ebay.  The 640x480 TFT LCD costs 
more, about $50, plus another $25 for shipping (I think).  Most of these 
displays come from China.

5.  I also purchased a Xilinx-compatible USB JTAG programming cable on 
ebay, also from China.  It costs about $59.  I can use it to program the 
Sparkfun Xilinx FPGA board, or the Digital Shortcut FPGA board.  I no 
longer need to worry about finding parallel ports to do taht jtag 
programming.  I tried to buy it from "hummingosand", but it never showed 
up.  Thank goodness Paypal has protection against that type of thing.  
Beware of this vendor, check the feedback!  I ended up buying one from 
hongkong_electronics, and it showed up promptly.

6.  Is anybody else doing FPGA work?  Is there interest in creating a 
group of simple sessions to help beginning FPGA programming?

73s
Terry