Hi Robby, Below is what Mike Collins posted a number weeks ago in testing a v8.1 Lite+Xtall board that used a CMOS Si570. I think Mike's tests show that the CMOS part works well with quite reasonable RX performance.
Tony sent me the new V8.1 Lite+XTALL last weekend to play with. Below is a summary of testing and overall impression: The first thing I noticed is the excellent layout of the new receiver. The PIC and Si570 integrated nicely into the design. The flexible BPF approach is very nice, it allows the users decide if they want a local or remote band switching filter design. Also the frequency selection switch can be remote mounted. Good power supply design, stepping down from the 5V for the 3.3 with single 12V input. Initial power up showed 12V current around 88mA. Tests were run using PowerSDR-sr40 and EMU1212M sound card. Some concern initially on overall noise floor shape across the 192Khz passband. It ended up being some common mode noise from the signal generator. This design seems to have less rejection of common mode noise at the antenna compared to other "Softrock" designs. Tony is revising the BPF ground plane to minimize the "size" of the connection to the +2.5 reference. Using the provided BPF and a simple external 1:1 balun for connection to my signal generator showed excellent RX sensitivity. On 40M measured MDS was around -128dBm and on 20M it was around -131dBm (@500Hz bandwidth). One thing I noticed right away is the center freq is very balanced and never noticed it at all (this is quite unique from all my other Softrocks where I always see a huge spike). Likely due to the "synchronous" flip flop design and overall layout. Overall DR and IMDR numbers were very good. With my EMU1212M card they would be even better if the OP amp gain reduced, but most users with "average" sound cards the gain is probably about right. Some spurs seemed to be PIC related and moved when touching the top of the device (around -115dBm). I put a (additional) .1 cap from pin 8 to 1 on the PIC and spurs disappear. One minor drawback to the design is the moderately high oscillator leakage into the antenna (approx -37dBm). Those who want to integrate into an existing radio will probably use some kind of buffer amp to get better reverse isolation. My initial on air RX tests were using the 40M and 20M BPF boards (Tony supplies several boards, parts for various bands you want). Later in the weekend, just for fun I replaced the BPF board with a homebrew balun (with center tapped secondary) and connected it to my antenna. Realizing the drawbacks of the "aliasing" using no filter it was sure a lot of fun jumping from 80M to 40M to 20M with just the DIP switch freq select. Of course "you" shouldn't do this but I ended up using it this way for several days as my "main" receiver :)) Overall from my view, it is a real winner. I have several softrock Lites and RX/TX models but real happy to have this one. I think Tony is going to start shipping soon and make sure you get your Si570 (CMOS) chip from Tom. The performance vs cost can't be beat!! 73, Mike Collins KF4BQ ----- Original Message ----- From: R R Robson To: [email protected] Sent: Saturday, May 03, 2008 12:22 PM Subject: [softrock40] Re: SRLite+Xtall V8.3 Dimensions? What are the considerations in deciding whether to go with the CMOS vs the LVDS version of the SI570? Tx es 73 de Robby WB5RVZ
