Calibrating the Softrock Si570 USB Controller


This procedure only needs to be done once. When a Softrock controller is calibrated correctly NO SOFTWARE CALIBRATION IS NECESSARY. Just leave this at the default settings. If you HAVE tried software adjustments then you must set it back to zero. Depending on the software this may involve deleting  the configuration file to bring it back to default. This may need more than simply uninstalling the software.

The Si570 local oscillator frequency is set by an AVR ATTiny85 microcontroller. The original firmware for the AVR was written by DG8SAQ but Fred, PE0FKO modified and improved it. 
This firmware is in all Softrocks produced from 2009 so the PE0FKO configuration utility MUST be used. This is incorporated in the "ExtIO_Si570.dll used with HDSDR.

Initial calibration.

The tuning scale must have low frequencies at the left, high frequencies at the right. SSB should be on the correct sideband. If no other calibration has been made then frequency error could be +/- 20 KHz at 10MHz but is usually closer than that.   

The internal crystal of Si570s may vary +/-2000ppm. With NO calibration the frequency could be a long way out. When the Si570 is made a calibration figure is stored in each. This is  used in the initial calibration "Calibrate A". When this technique is used the frequency error should be  be less than +/- 1.5ppm. (Maybe a little more due to ageing?) 

 2012 INSTALL CFGSR Version 2.6  which you download from  with automatic installer and new guide on that web page. (Click on "msi" the correct msi file...) Note Fred details some other ways of calibrating. 
My screenshots show an earlier version but the tabs shown are almost identical.

Here is the Calibration tab similar to the one  on Fred's page.
To apply the preset factory calibration just click the top "Calibrate A" button.
This may be done with the stand-alone CFGSR or within HDSDR/Winrad as described below.
"Calibrate A" may be all you need. I recently setup a Softrock. Without any calibration it was 3.7KHz out at 10MHz. "Calibrate A" brought it within 36Hz.
Remember "Calibrate A" will always bring you back +/- 1.5ppm if a mistake is made.

To set the calibration to within 1Hz a reference signal needs to be accurately tuned.

But any SDR software that shows precise tuning may be used in conjunction with CFGSR.

HDSDR installation and operating procedure.
No manual but this should give you a start.

In Europe the RWM signals on 4996, 9996, and 14996KHz  are often heard. It uses a variety of modulation types, wait until the plain carrier appears. Eight minutes of carrier starting at 00 and 30 minutes past an hour.  There is no hurry! The Softrock needs to be left for as long as possible so the frequency has stabilised.  Other signals to use might be 5, 10, 15, 20MHz from WWV or BPM. CHU on 3330 kHz, 7850 kHz, 14670 kHz. 

A trick that Juan EA2KQ uses to ease the fine tuning of the AM signal:- Use ECSS mode and let the system autotune until the phase "circle" changes from blue to green. Then push H to calibrate following the normal procedure. 

Another way, easier when the calibration signal is weaker, is to use CW mode, tune close and use "CW Zap" maybe a few times to bring the signal dead on tune.

Below, HDSDR, 2.60 March 2013.

This has had the phase indicator reinstated. BUT be careful how you use it!

FOR SOFTROCKS DO NOT USE HDSDR's LO FREQUENCY CALIBRATION! This is for SDRs without the Softrock's one-time calibration facility.

Tune in your standard, 10.000 MHz shown below. Set to ECSS, bring up the phase indicator  - options - RF front End.....   Wait for the ring to go green then click "ExtIO" to bring up the Si570 calibration utility.
Ensure that the CFGSR Calibrate B tab shows the "Tuned" frequency. If not, click "Close" then "Open" . Type in the Real frequency of your standard and click "Calibrate"
In the example above I'm only 2Hz out, not worth getting any closer.

Always remember "Calibrate A" will bring you back very close if a mistake is made.

For other SDR radios where the LO is not able to be set independently then HDSDR'S Front End calibration tab should be used in a similar fashion. But never use it for a Softrock!

Note that the Startup and Crystal frequency shown may be unique to your Si570.

It is unlikely that your Si570 will be absolutely stable. With temperature changes it may drift +/- 10Hz at higher HF frequencies but for most uses it will be close enough. 

I do not know the purpose of the "Reset" button but do not use it. It makes the calibration a very long way out! 

I think this just resets the AVR to default - no calibration. If you do use this then "Calibrate A" must be the next step.

"Ctrl-C" copies the displayed Crystal frequency to the clipboard for special use.

This page is based on Bob, G8VOI's advice often  posted in the "Softrock40" Yahoo group. Eg.
Bob helped Fred when testing the firmware, he knows how to do it!

"I always find doing that within Winrad (or the advanced development HDSDR) is the simplest method. If you use
something like 10MHz WWV or one of the other time standards, select AM mode and
fine tune until the 'phase' display slows down or stops rotating. If you then
press 'H' to call up the configuration screens and go to the 'Calibration' tab,
you can type in the frequency in the 'Real' box, i.e. 10000000 and press 'Save' (Calibrate)
and 'Read'. That should accurately calibrate the Si570 frequency."
Note the phase display has moved, it is on HDSDR's calibration window. But do not use HDSDR's calibration with a Softrock.

The Si570 in a Softrock-type SDR:-

This is supplied with a start-up frequency of nominally 56.32MHz. Divided by 4 gives an operating centre frequency of 14.08MHz +/- any calibration error.

If it is controlled by the AVR ATTiny85 microcontroller then by default  it will be set to 28.2MHz, giving a centre frequency of 7.05MHz. The operator may reset this to his own preference with CFGSR.

Accuracy:- With no compensation the factory preset start-up frequency is not particularly accurate. The reference crystal is 114.285MHz +/- 2000ppm. However the manufacturer aids calibration by setting registers inside each device that allow easy correction. CFGSR "Calibrate A" reads these registers and applies the factory calibration, to +/- 1.5ppm.  +/- 15Hz at 10MHz.

CFGSR's "Calibrate B" enables calibration to the nearest Hz.

More notes about CFGSR

Other SDRs and devices use the DG8SAQ firmware. To the best of my knowledge this does not have this frequency calibration facility. Thought should be given to change the AVR for one with Fred's firmware. Cecil sells pre-programmed ones here "Re: FA-SDR TRX - does it work? Hi, Just received the ATtiny last chip with 15.14 release from Fred, and it works now well inside the FA-SRD without any click on frequency step. ( yes, ABPF has to be disabled in CFGSR screen to get the PTT line working ) - so I recommend to FA-SDR users to change the original chip provded by funkamateur, by the last release from PE0FKO. Pascal F6EHP" In fact the FA-SDR will work properly BUT only with PSDR. A special DLL is used with this SDR. Using Fred's AVR will enable the FA-SDR to be tuned correctly whatever software is used. 

G4ZFQ March 2011
alan4alan at googlemail com
More of my pages related to SDR
Setting up CFGSR for different versions of the Softrock

Using an Ensemble with a conventional transceiver as a panadaptor. My preferred way for HF. Ideally take the Ensemble antenna connection from the transceiver.
Using with a conventional receiver or transceiver as an IF panadaptor. 
Using HDSDR with a RTL dongle And using the dongle as an IF panadaptor with a conventional rig.

All aspects of the Softrock SDR a big page with lots of links but you should find answers to most questions.

 1 The Si570        
2 Getting and Making Softrocks What computer?          
3 Building a Softrock. Or look at        
4 For Information Surrounding the Softrock  VHF converter, MOBO, PAs, Panadapter for use with conventional rigs etc.    
5 Soundcards Setting up, USB, problems.      
6 PIC/PICAXE control of the  Si570, Tony's first method. switched control without a computer. Reprogramming the PIC (and PICAXE)          
7 Parallel Port Control of the SI570.        
8 USB Control of the SI570  Information, driver installation. BPF control.       
9 Serial (COM) Control of the Si570.         
10 Some Stand-alone Controller Kits Control the Si570 independently. Links to other SDR kits. Notes and links for all soundcard SDR software I know. 
Including Modes not yet Supported by these SDR Programs.  Audio Files to Test Software Without a SDR And a few links to some of the many SDRs on the web. Check them out without owning one.