Re: Softrock Image rejection build 277


Dom Baines M1KTA
 

Further.... from a note/thread on the Softrock40 group so I do not claim to be the originator of the idea...

I investigated a bit more and at work I have a simple Softrock V9.0 and simple a wire antenna I can hang out of a window. The current  Rocky 3.6 install (I have a number of SDR programs installed not just SDR-Radio) when configured forIQ balance auto-collect  the software holds the data in a file in the C:\Program Files (x86)\Afreet\Rocky\Bal folder  starting 'IQBalance this contains the values for the gain and phase for each centre frequency Rocky was used with, for this installation and setup. These numbers do alter slightly as the SDR and Rocky are left running. If you change the sound card leads the numbers can change.

This is how on a restart Rocky will appear, if nothing else has changed to automatically have done the IQ balance every time.

If you use  a Softrock for TX too there is another file TxBalance.ini that contains the TX phase data as well.

I might look at the data and see if it corresponds with the phase and balance with the SDR-Radio too.

72

Dom
M1KTA


From: Dominic Baines
To: sdr-radio-com@...
Sent: Wed, 2 June, 2010 13:00:51
Subject: Re: [sdr-radio-com] Softrock Image rejection build 277

 

Hi Simon et al...

Apologies been out of contact as leaving current job soon and daytime access is now severely restricted.
I'll be on Skype in shack tonight and tomorrow night.

I am melting solder on a MOBO V4.3 and Si570/SR V6.3 setup, with 4x20 LCD etc for you and will have that with me when visit just before Friedrishafen 2010 so you'll have that for Softrock TX development end June.

The image rejection issue...
As you know Rocky software etc does this as an 'in band' calculation sampling all the strong stations in the current IQ bandwidth so the image rejection gets better the longer the SDR is on the air. Which is what was implemented in the link you mention. By altering the phase and amplitude with SDR-Radio you can deal with image rejection for one specific hardware set up as we have already tested and that will reduce by 30dB any images but this is not always consistent when frequency changes (especially to another band). The same effect occurs with Rocky if you change frequency as well. The Genesis SDR radios have an interesting image rejection method that balances the I & Q signals through the RX op amps.

As the problem is Softrock specific it might be worth suggesting this is worth studying:
http://www.wb5rvz.com/sdr/RXTX_V6_3/image_rejection_hints.htm

A lot of image problems can be attributed to poor connections/constructions resulting in an imbalance in the IQ, poor leads and sockets can also be an issue. I have a couple audio leads with a 'ring' where the sockets have scored them.

The loosing USB connection during the process I have not seen yet. Loosing connection to a Softrock V9.0 seems to be an issue with the libusb driver & AVR Softrocks all seem to 'do this' from time to time if using Vista but not with XP, especially if anything changes on the USB bus (e.g. plug in a USB pen, or a USB drive goes to sleep). The radio will seem to work, then change bands and the radio carries on but the frequency hasn't changed.... I had not looked at this exhaustively yet so time to test needed. This does happen more often if the USB port is not a powered hub or a direct connection. I will have V9.0 and an Ensemble RXTX up on 40m and 80m.

72

Dom
M1KTA

>
>From: Simon HB9DRV <simon@...>
>To: sdr-radio-com@...
>Sent: Wed, 2 June, 2010 11:18:21
>Subject: RE: [sdr-radio-com] Softrock Image rejection build 277
>
> >
>>
>
>>
>
>
>
>
>>
>Hi Alan,
>
>I haven't really got the soundcard image rejection working too
>well. I'll be working with Dom M1KTA very soon and together we'll get it sorted
>out. I now have a SoftRock v9.0 and the Cross Country Wireless SDR so have all
>I need for testing.
>
>I am surprised that you lose USB control - I assume this is the
>Si570 chip? I can test this myself, let me know if this is what you mean by USB
>control please.
>
>There's some excellent theory in Rocky http://www.dxatlas. com/Rocky/ Advanced. asp >which I must implement.
>
>>
>Simon Brown, HB9DRV
>http://sdr-radio. com


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