Switching spurii on 160m still present with latest Gateware

[Max]

I am running Gateware 71p1 but have had exactly the same issue with earlier versions.

I am still seeing what appear to be the strong switching spurii described in the "Options" section of the Wiki inside the 160m band, around 1.9MHz. This is with no antenna attached. I see them on both Spark SDR and also SDR Console, and they almost totally disappear when the filter board is disabled, as explained in the Wiki.

For some reason they are on very slightly different frequencies in each of the two programs, but they behave the same, strong with filters enable, almost totally absent without filter board enabled. Regarding the strength with filters disabled, any residual spurii with the antenna connected is totally swamped by natural band noise. Not so with the filter enabled.

Is it likely that for some reason the updated Gateware is not using the FPGA derived switching frequency as it should do? If so, what can I do about it? My HL2 board is Build 9 which I thought required no mods to enable this feature?.

Thanks

Max

[Steve Haynal]

Hi Max,

I checked a HL2 build9 board I have here and the option for FPGA-generated switching frequency is present. I checked the latest gateware and the PSSYNC option is still present and enabled by default. I checked with Quisk and am able to turn the option on/off and see the change in the spur frequencies. Can you try that? I checked with SparkSDR2 and see that the FPGA-generated switching frequency is on. 

Do you see a strong narrow spur at ~2.119MHz? This would be the FPGA-generated switching frequency if it is on. Maybe the other spurs are from noise at your QTH. Also, even though the FPGA provides the switching frequency, the charge pump is still on in the regulator ICs. Sometimes you can still see their spurs but at a diminished amplitude. Usually the noise floor is much higher than this and I've only seen them with a poor antenna or dummy load.

73,

Steve

kf7o

[Max]

Hi Steve

Thanks for reply. Yes, with Spark I do see the strong spur at 2119 but nothing at all on 2119 with SDRC. All my tests have been with no antenna connected. Does the PSSYNC option need enabling in the SDR program? So does Simon need to enable it in SDRC?

73

Max

[Steve Haynal]

Hi Max,

The FPGA-generated clock is enabled by default. Maybe Simon is disabling it (perhaps accidentally) or it is stuck at off due to software you were running previously. If you power cycle the HL2, and then first connect with SDRC, then you can see if SDRC is the one turning it off. See address 0 bit 12 below. Hopefully with an antenna any remaining spurs from the charge pumps will be well below the noise floor.

0x00

[12]

FPGA-generated power supply switching clock (0=on, 1=off)

73,

Steve

kf7o

[si...@sdr-radio.com]

Ah,

 

Looks like there was a change  with Address 0x00 and I missed it. I have bit 12 as Hardware AGC, and there’s an option to enable it.

 

So I’ll update tomorrow morning.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

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[Steve Haynal]

Thanks! The original thinking was to make this an on/off option in software so a user could reposition any spurs if they happened to be blocking the frequency of interest.

73,

Steve

kf7o

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[Max]

Thanks Steve and Simon for response. Clears up that mystery for me because I was convinced from the notes in Wiki that it was already enabled in the gateware independent of any action needed in the software.

73

Max

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[si...@sdr-radio.com]

Max,

 

Making a kit now (5:20 AM, Thursday) with the FPGA PSU clock on, can’t be switched off. I can make this user-selectable on/off if needed later. I’ll send you a direct link, please let me know if this should be user selectable.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

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[rhqq2yxrkt]

Steve,

To shift the 160m spur is it still necessary to do the 2 resistor mod mentioned in the wiki?  or is it just a matter of using the latest SparkSDR.

John
G3UGY

On 13/05/2020 20:18, Steve Haynal wrote:

Hi Max,

[Steve Haynal]

Hi John,

It depends on which build you have. Build9 units had the mod. Builds prior to 9 do not. You should be able to tell from the wiki pictures if you have the mod. The mod is necessary to shift the spurs.

73,

Steve

kf7o