Re: Some Si570 / mac / preferred SDR questions.
- Hi Barry,
The short answer is just get a full SRL+Xtal+USBV9.0 receiver. All this external USB vs. Si570 stuff goes away. And you have automatic filter switching. That said...
The long answer: I have a bunch of older SRL kits and Si570's and Si570 break-out boards. And it is very difficult (and expensive) to get a new kit to my QTH (I'm based in Indonesia). I have a pretty good junk box with a lot of parts I've collected over the years. Plus I have some Si570's, WB6DHW Si570 boards, ATtiny micro-controllers and the venerable AVR Dragon to program the ATtiny's So I make do...
I'll try to answer some of your questions...
"Is there a preferred SDR kit one should use with the various USB interfaces?"
By "various" USB interfaces I presume you're referring to the likes of the QRP2000 board from SDR-Kits? I am using both SRLV6.2 and SRL+XtalV8.3 with a WB6DHW Si570 board. I breadboarded the ATtiny45/85 Si570 controller from the SRL+Xtal+USBV9.0 schematic (didn't populate the ATtiny parts on the V8.3 board and tossed the crystal circuit on the V6.2 board) and programmed Fred's (PE0FKO) latest V15.10 firmare into the ATtiny85. It is working fine. I just capacitively couple the CMOS Si570 from the WB6DHW Si570 board (with capacitors included with the WB6DHW kit) to the quadrature clock divider input and bias the input to the divider flip-flop with two 10k resistors as per the SRL+Xtal+USBV9.0 or SRL+Xtal8.3 schematic (took a bit more work on the V6.2 board). I use a small piece of coax to interconnect the Si570's output with the SRL input. Works fine with the V8.3 and V6.2 receivers.
"I see large "spikes" akin to the image rejection issues we have all read about.
Is there a way to mitigate those "spikes"."
I presume you're referring to images that appear when you for-example tune a SRL receiver to 10.010MHz and look at a timing signal from the likes of WWV (etc.). Make sure you've got all sorts of 3D and "effects" disabled in your sound card setup software. Then in Winrad (for example) you have to go through the process of adjusting the I/Q timing delay and amplitude settings. In Winrad you'll have to iterated back and forth with the settings to null the image. Rocky will try to do this automatically, but it can take some time.
If you are having trouble nulling the images, (best done in Winrad) open the sound card mixer, switch to the record line-in settings and manually adjust the left-right balance control slightly to get left-right I/Q balance (in Winrad) to a point where can null the image. My experience with my the V8.3 receiver requires me to very slightly adjust the amplitude imbalance with the sound card mixer. The 30m V6.2 receiver is fine without this adjustment. So this indicates there are gain differences between the two receiver boards (op-amp stages) that are causing this. At 30m I can get really good image null on the V8.3 board with a cheap Audigy Value (not Audigy2 value) card in WinXP SP3+, significantly more than 70dB when I use a very low phase noise signal from a local 10MHz VCOCXO signal source.
"I've read somewhere that the "startup" frequency for the QRP2000 Si570 chip should be set to, I believe, 10 Mhz. Is this true?"
If you're running the PE0FKO V15.10 firmware and accompanying USB driver in your ATtiny instead of the original DG8SAQ firmware and USB driver, then I think you don't need to worry about the default startup frequency. I may be wrong though. I only have Si570's from the KM5H group-buy. They default to 56.32MHz startup frequency (56.32MHz/4=14.08MHz receive frequency).
I have both CMOS and LVDS Si570's P/N 570CAC000141DG and 570BBC000141DG respecitvely. In Winrad (latest and final V1.32) hit shift-h (upper-case H) and you will get the Si570 driver dialog. You can set some options in this dialog for startup frequency etc. Some of the reported parameters seem wrong for my Si570's in this dialog box (differences in the default Si570 register values - I've checked them via a direct i2c interface using a Parallax Propeller micro-controller with i2c firmware, but that's a different story), but they work correctly regardless both in Winrad and Rocky. Use my Si570 part numbers (stated above) and compare with your part numbers on the SiLabs Web site to determine your actual Si570 specifications. Link here:
Here's the link to Fred's (PE0FKO) latest ATtiny firmware:
Burning firmware and (required) changing fuse bits to the ATtiny micro-controllers is a different subject entirely. Refer to Fred's link immediatly above for links.
If you have a Si570 that doesn't have a 56.32MHz start-up frequency. I would like to know your actual part number and how Winrad in-particular with the PE0FKO firmware works (hit shift-h to see in Winrad 1.32).
"I have successfully completed 3 "6.2" boards and a 6.3 with xTall. So again, is one better than the other with regards to the USB interface ?"
Per the above information, I've been good with V6.2 and V8.3 SRL with the external WB6DHW Si570 board with CMOS Si570. I don't think it matters much V6.2 vs. V6.3. But in this respect but be careful with your cabling, keep cables short on the Si570 output side in particular. What we're talking about here is a hardware mash-up. But my results have been pretty good so far.
Best 73's David WB4ONA (GMT+7)