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[FlexRadioSmartSDR] SDRs and harmonics


Kermit Lehman
 

Thanks, Al. 

I also asked Flex directly, but no reply yet.

The issue is audio harmonics and whether I need to use the WSJT-X so-called "Split" option, really "Shift", with my 6500. 

73,
Ken, AB1J


-----Original Message-----
From: Al Groff via groups.io <al.k0vm@...>
To: FlexRadioSmartSDR@groups.io
Sent: Fri, Oct 16, 2020 2:28 pm
Subject: Re: [FlexRadioSmartSDR] SDRs and harmonics

Ken,
  If TX level meter is kept below 0db, no audio harmonics are generated ( TX EQ off ).  Its all digital.
ALL RF amplifiers produce RF harmonics. And intermod products on multitone waveforms.

AL, K0VM


On 10/15/2020 7:38 PM, kb5ve wrote:
Ken I would think they would since Harmonics are a normal thing but the strength would be the issue. On that level I believe the flex is very good.

Dale Hankins 


On Oct 15, 2020, at 6:44 PM, Kermit Lehman via groups.io <ktfrog007@...> wrote:



Does an SDR, for example my 6500, generate AF or RF harmonics like an analog transceiver?

73,
Ken, AB1J




Bill Somerville
 

Hi Ken,

all digital audio paths can produce unwanted audio harmonics. in general it should only happen if gain is applied at some stage, in fact any digital gain is very likely to cause audio harmonics with WSJT-X. WSJT-X produces full swing audio sample values if the "Pwr" slider is at the top, i.e. 0 dB Full Scale (FS). If a later stage adds *any* gain then the signal will be clipped and rich in harmonics, particularly odd harmonics. You can demonstrate this if you use VAC to route audio between applications, by default VAC passes audio samples without any amplitude changes, which is good. In the VAC Control Panel you can enable volume controls for the channels, please *don't* enable that option for on-air operation. With volume controls enabled about 16 dB of digital gain is available, and you should find that even the tiniest amount of gain above 0 dB (FS) will introduce considerable distortion in the form of harmonics.

73
Bill
G4WJS.

On 16/10/2020 16:21, Kermit Lehman via groups.io wrote:
Thanks, Al. 

I also asked Flex directly, but no reply yet.

The issue is audio harmonics and whether I need to use the WSJT-X so-called "Split" option, really "Shift", with my 6500. 

73,
Ken, AB1J


-----Original Message-----
From: Al Groff via groups.io <al.k0vm@...>
To: FlexRadioSmartSDR@groups.io
Sent: Fri, Oct 16, 2020 2:28 pm
Subject: Re: [FlexRadioSmartSDR] SDRs and harmonics

Ken,
  If TX level meter is kept below 0db, no audio harmonics are generated ( TX EQ off ).  Its all digital.
ALL RF amplifiers produce RF harmonics. And intermod products on multitone waveforms.

AL, K0VM


On 10/15/2020 7:38 PM, kb5ve wrote:
Ken I would think they would since Harmonics are a normal thing but the strength would be the issue. On that level I believe the flex is very good.

Dale Hankins 


On Oct 15, 2020, at 6:44 PM, Kermit Lehman via groups.io <ktfrog007@...> wrote:



Does an SDR, for example my 6500, generate AF or RF harmonics like an analog transceiver?

73,
Ken, AB1J



Al Groff
 

Ken,
  I have been using None in WSJT-X for the last 6 years ( WSJT-X FT8, & FLex 6500/6600 ).  As long as the TX level meter is less than 0db there will be no audio harmonics.. WSJT-X Generates a digital signal, DAX transports a digital signal and it remains a digital signal until it is converted to RF in a digital process.

I run with the SSDR RF power control at 100% ( except for when I have the amp on ) and control the output with the WSJT PWR control and DAX GUI TX Gain. The level meter at -7  to -8 gives about 40 watts output. No audio harmonics.

AL, K0VM



On 10/16/2020 10:21 AM, Kermit Lehman via groups.io wrote:
Thanks, Al. 

I also asked Flex directly, but no reply yet.

The issue is audio harmonics and whether I need to use the WSJT-X so-called "Split" option, really "Shift", with my 6500. 

73,
Ken, AB1J


-----Original Message-----
From: Al Groff via groups.io <al.k0vm@...>
To: FlexRadioSmartSDR@groups.io
Sent: Fri, Oct 16, 2020 2:28 pm
Subject: Re: [FlexRadioSmartSDR] SDRs and harmonics

Ken,
  If TX level meter is kept below 0db, no audio harmonics are generated ( TX EQ off ).  Its all digital.
ALL RF amplifiers produce RF harmonics. And intermod products on multitone waveforms.

AL, K0VM


On 10/15/2020 7:38 PM, kb5ve wrote:
Ken I would think they would since Harmonics are a normal thing but the strength would be the issue. On that level I believe the flex is very good.

Dale Hankins 


On Oct 15, 2020, at 6:44 PM, Kermit Lehman via groups.io <ktfrog007@...> wrote:



Does an SDR, for example my 6500, generate AF or RF harmonics like an analog transceiver?

73,
Ken, AB1J