Below are two pictures of a test, first the standard SoftRock with a crystal and the second one using a SI570 chip. They are very similar with no appreciable extra spurs on added noise.

SoftRock connected to a dummy load using a crystal.

SoftRock connected to a dummy load using the SI570

12-25-2007

Some good news to day, below is an email from Mike Collins KF4BQ, he received his CMOS version of the SI570 and did some test on it, he reports very close results when compared to a crystal oscillator, that is really good news. The LVDS has even lower jitter so it should get even better results. Below is a copy of his email;

To: softrock40@yahoogroups.com
From: "mikecol2" <mikecol@tampabay.rr.com>
Subject: [softrock40] Si570 CMOS version performance

I was able to get one of my Si570 running at the startup freq
(56.32Mhz) and thought I would do some RX performance measurements
against the N2PK XTAL daughter board (56.2Mhz). Even though the freqs
were different I kept the two signal generators a constant from each
center.

One of the concerns folk had was the phase noise performance of the
CMOS version. I did some 1db Blocking RX measurements at different
signal generator spacings to reveal something about the overall phase
noise differences.

The results of the tests came out excellent for the CMOS Si570; almost
identical measurements against the N2PK XTAL oscillator. Example
measurements:

1dB Blocking (100 Khz spacing), 1.0uV(-107dBm) reference: Blocking
level = -7dBm (123dB Dynamic Range) on both Si570 and XTAL osc.

1dB Blocking (2 Khz spacing), 1.0uV(-107dBm) reference: Blocking level
= -40dBm (90dB Dynamic Range) on both Si670 and XTAL osc.

I will put a summary of my testing on a Softrock20MRXTX v6.2 (with
LT6231 in RX amp) in the files section. Also listed is 3rd order DR
IMD (at various spacings) and Noise floor/Sensitivity testing.

Now, if I can just get some I2C controls to work!!

Have fun, Mike Collins KF4BQ

Later he will use his Spectrum analyzer to compare the results of the crystal clock to the Si570.

Look for the link below for a PDF file with the SI570's specifications