I understand that if I offset my radio tuning by (say) 1500 Hz from a received carrier, I will hear a 1500 Hz note in the audio. If you use USB mode, then the tuning should be offset in a negative direction. For LSB mode, the tuning should be offset in a positive direction. Both methods should produce the exact same beat note with a properly-aligned radio. I was doing this sort of test with my new IC7610 - with its GPS sync'd oscillator - and eventually found that the two methods produce frequencies that differ by 0.1 Hz. It looks like USB/LSB are offset by equal amounts: 0.05 Hz in opposite directions. This seems independent of the frequency being measured. Since this is an SDR-based radio, I suppose that the cause may be some sort of round-off error in the frequency synthesis. Perhaps due to resolution limitations of the scheme. Or maybe its an actual programming error? I was wondering if others have seen this type of thing with SDR radios? Is it common? Ken/KE2N

IC7610s are not test instruments..... the Icoms have fixed offset errors.. I told them about this and their response was "its good enough" On 7/12/2024 2:38 pm, ke2n--- via time-nuts wrote: > I understand that if I offset my radio tuning by (say) 1500 Hz from a > received carrier, I will hear a 1500 Hz note in the audio. > > > > If you use USB mode, then the tuning should be offset in a negative > direction. > > For LSB mode, the tuning should be offset in a positive direction. > > > > Both methods should produce the exact same beat note with a properly-aligned > radio. > > > > I was doing this sort of test with my new IC7610 - with its GPS sync'd > oscillator - and eventually found that the two methods produce frequencies > that differ by 0.1 Hz. It looks like USB/LSB are offset by equal amounts: > 0.05 Hz in opposite directions. This seems independent of the frequency > being measured. > > > > Since this is an SDR-based radio, I suppose that the cause may be some sort > of round-off error in the frequency synthesis. Perhaps due to resolution > limitations of the scheme. Or maybe its an actual programming error? > > > > I was wondering if others have seen this type of thing with SDR radios? Is > it common? > > > > Ken/KE2N > > > > > > _______________________________________________ > time-nuts mailing list --time-nuts@lists.febo.com > To unsubscribe send an email totime-nuts-leave@lists.febo.com

Hi, There are a couple of factors in how a receiver creates offsets: 1) Timebase offset - internal reference oscillator not perfect on nominal frequency 2) Synthesis offset - For practical reasons, synthesis is not engineered to necessarily give exactly 100 Hz steps (or whatever) with perfect 0 Hz offset from nominal. The synthesis offset comes from implementation and forms a scaling of the timebase. The timebase can be locked up in some receivers, and then synthesis offset remains. With a bit of care, these can be characterized for the particular receiver dial frequency, but indeed, this is not test instruments, they are not built for it, so you will have to learn how they work and compensate for it. Cheers, Magnus On 2024-12-07 07:34, glen english LIST via time-nuts wrote: > IC7610s are not test instruments..... the Icoms have fixed offset > errors.. I told them about this and their response was "its good enough" > > > On 7/12/2024 2:38 pm, ke2n--- via time-nuts wrote: >> I understand that if I offset my radio tuning by (say) 1500 Hz from a >> received carrier, I will hear a 1500 Hz note in the audio. >> >> >> If you use USB mode, then the tuning should be offset in a negative >> direction. >> >> For LSB mode, the tuning should be offset in a positive direction. >> >> >> Both methods should produce the exact same beat note with a >> properly-aligned >> radio. >> >> >> I was doing this sort of test with my new IC7610 - with its GPS sync'd >> oscillator - and eventually found that the two methods produce >> frequencies >> that differ by 0.1 Hz. It looks like USB/LSB are offset by equal >> amounts: >> 0.05 Hz in opposite directions.  This seems independent of the frequency >> being measured. >> >> >> Since this is an SDR-based radio, I suppose that the cause may be >> some sort >> of round-off error in the frequency synthesis. Perhaps due to resolution >> limitations of the scheme. Or maybe its an actual programming error? >> >> >> I was wondering if others have seen this type of thing with SDR >> radios? Is >> it common? >> >> >> Ken/KE2N >> >> >> >> _______________________________________________ >> time-nuts mailing list --time-nuts@lists.febo.com >> To unsubscribe send an email totime-nuts-leave@lists.febo.com > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

What really irks me is that the manufacturers virtually never admit to the existence of synthesis offset errors in their data, and that they do not display the amount of synthesis offset error in the course of normal operation. Nor, as a rule, do they show sufficiently detailed info on the overall design that one could compute that error for himself. Dana On Sat, Dec 7, 2024 at 3:58 AM Magnus Danielson via time-nuts < time-nuts@lists.febo.com> wrote: > Hi, > > There are a couple of factors in how a receiver creates offsets: > > 1) Timebase offset - internal reference oscillator not perfect on > nominal frequency > > 2) Synthesis offset - For practical reasons, synthesis is not engineered > to necessarily give exactly 100 Hz steps (or whatever) with perfect 0 Hz > offset from nominal. > > The synthesis offset comes from implementation and forms a scaling of > the timebase. The timebase can be locked up in some receivers, and then > synthesis offset remains. > > With a bit of care, these can be characterized for the particular > receiver dial frequency, but indeed, this is not test instruments, they > are not built for it, so you will have to learn how they work and > compensate for it. > > Cheers, > Magnus > > On 2024-12-07 07:34, glen english LIST via time-nuts wrote: > > IC7610s are not test instruments..... the Icoms have fixed offset > > errors.. I told them about this and their response was "its good enough" > > > > > > On 7/12/2024 2:38 pm, ke2n--- via time-nuts wrote: > >> I understand that if I offset my radio tuning by (say) 1500 Hz from a > >> received carrier, I will hear a 1500 Hz note in the audio. > >> > >> > >> If you use USB mode, then the tuning should be offset in a negative > >> direction. > >> > >> For LSB mode, the tuning should be offset in a positive direction. > >> > >> > >> Both methods should produce the exact same beat note with a > >> properly-aligned > >> radio. > >> > >> > >> I was doing this sort of test with my new IC7610 - with its GPS sync'd > >> oscillator - and eventually found that the two methods produce > >> frequencies > >> that differ by 0.1 Hz. It looks like USB/LSB are offset by equal > >> amounts: > >> 0.05 Hz in opposite directions. This seems independent of the frequency > >> being measured. > >> > >> > >> Since this is an SDR-based radio, I suppose that the cause may be > >> some sort > >> of round-off error in the frequency synthesis. Perhaps due to resolution > >> limitations of the scheme. Or maybe its an actual programming error? > >> > >> > >> I was wondering if others have seen this type of thing with SDR > >> radios? Is > >> it common? > >> > >> > >> Ken/KE2N > >> > >> > >> > >> _______________________________________________ > >> time-nuts mailing list --time-nuts@lists.febo.com > >> To unsubscribe send an email totime-nuts-leave@lists.febo.com > > _______________________________________________ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe send an email to time-nuts-leave@lists.febo.com > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

If the frequency error is always the same, it is consistent with the synthesis design that is not meant to be accurate, otherwise it can be a discontinuous adjustment, like the IC9700. In the IC9700 it is "on demand" and you have to start manually the adjustment procedure, the IC7610 has no manual start but maybe is not a real lock to external reference. On Sat, Dec 7, 2024 at 12:18 PM Dana Whitlow via time-nuts < time-nuts@lists.febo.com> wrote: > What really irks me is that the manufacturers virtually never admit > to the existence of synthesis offset errors in their data, and that they > do not display the amount of synthesis offset error in the course of > normal operation. Nor, as a rule, do they show sufficiently detailed > info on the overall design that one could compute that error for > himself. > > Dana > > > On Sat, Dec 7, 2024 at 3:58 AM Magnus Danielson via time-nuts < > time-nuts@lists.febo.com> wrote: > > > Hi, > > > > There are a couple of factors in how a receiver creates offsets: > > > > 1) Timebase offset - internal reference oscillator not perfect on > > nominal frequency > > > > 2) Synthesis offset - For practical reasons, synthesis is not engineered > > to necessarily give exactly 100 Hz steps (or whatever) with perfect 0 Hz > > offset from nominal. > > > > The synthesis offset comes from implementation and forms a scaling of > > the timebase. The timebase can be locked up in some receivers, and then > > synthesis offset remains. > > > > With a bit of care, these can be characterized for the particular > > receiver dial frequency, but indeed, this is not test instruments, they > > are not built for it, so you will have to learn how they work and > > compensate for it. > > > > Cheers, > > Magnus > > > > On 2024-12-07 07:34, glen english LIST via time-nuts wrote: > > > IC7610s are not test instruments..... the Icoms have fixed offset > > > errors.. I told them about this and their response was "its good > enough" > > > > > > > > > On 7/12/2024 2:38 pm, ke2n--- via time-nuts wrote: > > >> I understand that if I offset my radio tuning by (say) 1500 Hz from a > > >> received carrier, I will hear a 1500 Hz note in the audio. > > >> > > >> > > >> If you use USB mode, then the tuning should be offset in a negative > > >> direction. > > >> > > >> For LSB mode, the tuning should be offset in a positive direction. > > >> > > >> > > >> Both methods should produce the exact same beat note with a > > >> properly-aligned > > >> radio. > > >> > > >> > > >> I was doing this sort of test with my new IC7610 - with its GPS sync'd > > >> oscillator - and eventually found that the two methods produce > > >> frequencies > > >> that differ by 0.1 Hz. It looks like USB/LSB are offset by equal > > >> amounts: > > >> 0.05 Hz in opposite directions. This seems independent of the > frequency > > >> being measured. > > >> > > >> > > >> Since this is an SDR-based radio, I suppose that the cause may be > > >> some sort > > >> of round-off error in the frequency synthesis. Perhaps due to > resolution > > >> limitations of the scheme. Or maybe its an actual programming error? > > >> > > >> > > >> I was wondering if others have seen this type of thing with SDR > > >> radios? Is > > >> it common? > > >> > > >> > > >> Ken/KE2N > > >> > > >> > > >> > > >> _______________________________________________ > > >> time-nuts mailing list --time-nuts@lists.febo.com > > >> To unsubscribe send an email totime-nuts-leave@lists.febo.com > > > _______________________________________________ > > > time-nuts mailing list -- time-nuts@lists.febo.com > > > To unsubscribe send an email to time-nuts-leave@lists.febo.com > > _______________________________________________ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe send an email to time-nuts-leave@lists.febo.com > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

Note that DDS synth blocks don't always give the "nice round numbers" that humans would see on a dial, and they should also block out divider values that cause even moderate phase noise, substituting a nearly equivalent divisor with much less phase noise. If the net result is a fraction of a Hz off nobody but a time-nut would ever notice. Your suggestion of a rounding inconsistency that happens at 0 - say floor() vs round() - is certainly possible too. If you are going to be doing FMT entries you'll map these out beforehand for the frequency you actually dial into your rig. Tim N3QE On Sat, Dec 7, 2024 at 1:16 AM ke2n--- via time-nuts < time-nuts@lists.febo.com> wrote: > I understand that if I offset my radio tuning by (say) 1500 Hz from a > received carrier, I will hear a 1500 Hz note in the audio. > > > > If you use USB mode, then the tuning should be offset in a negative > direction. > > For LSB mode, the tuning should be offset in a positive direction. > > > > Both methods should produce the exact same beat note with a > properly-aligned > radio. > > > > I was doing this sort of test with my new IC7610 - with its GPS sync'd > oscillator - and eventually found that the two methods produce frequencies > that differ by 0.1 Hz. It looks like USB/LSB are offset by equal amounts: > 0.05 Hz in opposite directions. This seems independent of the frequency > being measured. > > > > Since this is an SDR-based radio, I suppose that the cause may be some sort > of round-off error in the frequency synthesis. Perhaps due to resolution > limitations of the scheme. Or maybe its an actual programming error? > > > > I was wondering if others have seen this type of thing with SDR radios? Is > it common? > > > > Ken/KE2N > > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com >

Hi Building a synthesizer that is *exact* at *any* frequency you come up with is pretty much impossible. You can build one that will tune to 10 Hz steps over 1 to 30 MHz. That’s not going to hit 1,000,001 Hz exactly. It will jump from 1,000,000 Hz to 1,000,010 Hz. It simply can’t get to something below it’s minimum resolution. On HF a resolution of 0.01 Hz (or anything close to that) is indeed doing very well. It wasn’t a long time ago that 0.1 Hz or even 1 Hz was considered “plenty good”. Now, how does the firmware handle this and what arbitrary output frequency does it pick? Time to dig into that source code and see what decisions they made. Best guess: They did it so it tunes quickly without a lot of CPU cycles going into decision making. Folks complain a lot more about tuning lag than some of the rest of this stuff. Is this just an issue with HF radio? Very much not. It’s simply a great example of how a lot of DDS based stuff works these days. There are a lot of signal generators out there that have the same sort of weird “base step” somewhere deep down inside the beast. You can get all sorts of odd things just like this popping up as a result ( = I though I moved exactly 1.5 KHz and it’s not …). Bob > On Dec 7, 2024, at 9:35 AM, Azelio Boriani via time-nuts <time-nuts@lists.febo.com> wrote: > > If the frequency error is always the same, it is consistent with the > synthesis design that is not meant to be accurate, otherwise it can be a > discontinuous adjustment, like the IC9700. In the IC9700 it is "on demand" > and you have to start manually the adjustment procedure, the IC7610 has no > manual start but maybe is not a real lock to external reference. > > On Sat, Dec 7, 2024 at 12:18 PM Dana Whitlow via time-nuts < > time-nuts@lists.febo.com> wrote: > >> What really irks me is that the manufacturers virtually never admit >> to the existence of synthesis offset errors in their data, and that they >> do not display the amount of synthesis offset error in the course of >> normal operation. Nor, as a rule, do they show sufficiently detailed >> info on the overall design that one could compute that error for >> himself. >> >> Dana >> >> >> On Sat, Dec 7, 2024 at 3:58 AM Magnus Danielson via time-nuts < >> time-nuts@lists.febo.com> wrote: >> >>> Hi, >>> >>> There are a couple of factors in how a receiver creates offsets: >>> >>> 1) Timebase offset - internal reference oscillator not perfect on >>> nominal frequency >>> >>> 2) Synthesis offset - For practical reasons, synthesis is not engineered >>> to necessarily give exactly 100 Hz steps (or whatever) with perfect 0 Hz >>> offset from nominal. >>> >>> The synthesis offset comes from implementation and forms a scaling of >>> the timebase. The timebase can be locked up in some receivers, and then >>> synthesis offset remains. >>> >>> With a bit of care, these can be characterized for the particular >>> receiver dial frequency, but indeed, this is not test instruments, they >>> are not built for it, so you will have to learn how they work and >>> compensate for it. >>> >>> Cheers, >>> Magnus >>> >>> On 2024-12-07 07:34, glen english LIST via time-nuts wrote: >>>> IC7610s are not test instruments..... the Icoms have fixed offset >>>> errors.. I told them about this and their response was "its good >> enough" >>>> >>>> >>>> On 7/12/2024 2:38 pm, ke2n--- via time-nuts wrote: >>>>> I understand that if I offset my radio tuning by (say) 1500 Hz from a >>>>> received carrier, I will hear a 1500 Hz note in the audio. >>>>> >>>>> >>>>> If you use USB mode, then the tuning should be offset in a negative >>>>> direction. >>>>> >>>>> For LSB mode, the tuning should be offset in a positive direction. >>>>> >>>>> >>>>> Both methods should produce the exact same beat note with a >>>>> properly-aligned >>>>> radio. >>>>> >>>>> >>>>> I was doing this sort of test with my new IC7610 - with its GPS sync'd >>>>> oscillator - and eventually found that the two methods produce >>>>> frequencies >>>>> that differ by 0.1 Hz. It looks like USB/LSB are offset by equal >>>>> amounts: >>>>> 0.05 Hz in opposite directions. This seems independent of the >> frequency >>>>> being measured. >>>>> >>>>> >>>>> Since this is an SDR-based radio, I suppose that the cause may be >>>>> some sort >>>>> of round-off error in the frequency synthesis. Perhaps due to >> resolution >>>>> limitations of the scheme. Or maybe its an actual programming error? >>>>> >>>>> >>>>> I was wondering if others have seen this type of thing with SDR >>>>> radios? Is >>>>> it common? >>>>> >>>>> >>>>> Ken/KE2N >>>>> >>>>> >>>>> >>>>> _______________________________________________ >>>>> time-nuts mailing list --time-nuts@lists.febo.com >>>>> To unsubscribe send an email totime-nuts-leave@lists.febo.com >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@lists.febo.com >>>> To unsubscribe send an email to time-nuts-leave@lists.febo.com >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@lists.febo.com >>> To unsubscribe send an email to time-nuts-leave@lists.febo.com >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe send an email to time-nuts-leave@lists.febo.com > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

Yes, my thinking exactly.  A little more checking required, but the .05 Hz offset seems independent of rx frequency.  It's a USB/LSB thing. Sent from AOL on Android On Sat, Dec 7, 2024 at 10:52 AM, Tim Shoppa<tshoppa@gmail.com> wrote: Note that DDS synth blocks don't always give the "nice round numbers" that humans would see on a dial, and they should also block out divider values that cause even moderate phase noise, substituting a nearly equivalent divisor with much less phase noise. If the net result is a fraction of a Hz off nobody but a time-nut would ever notice. Your suggestion of a rounding inconsistency that happens at 0 - say floor() vs round() - is certainly possible too. If you are going to be doing FMT entries you'll map these out beforehand for the frequency you actually dial into your rig. Tim N3QE On Sat, Dec 7, 2024 at 1:16 AM ke2n--- via time-nuts <time-nuts@lists.febo.com> wrote: I understand that if I offset my radio tuning by (say) 1500 Hz from a received carrier, I will hear a 1500 Hz note in the audio. If you use USB mode, then the tuning should be offset in a negative direction. For LSB mode, the tuning should be offset in a positive direction. Both methods should produce the exact same beat note with a properly-aligned radio. I was doing this sort of test with my new IC7610 - with its GPS sync'd oscillator - and eventually found that the two methods produce frequencies that differ by 0.1 Hz. It looks like USB/LSB are offset by equal amounts: 0.05 Hz in opposite directions.  This seems independent of the frequency being measured. Since this is an SDR-based radio, I suppose that the cause may be some sort of round-off error in the frequency synthesis. Perhaps due to resolution limitations of the scheme. Or maybe its an actual programming error? I was wondering if others have seen this type of thing with SDR radios? Is it common? Ken/KE2N _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com

The NCOs in my Elad FDM-DUO SDR radios have an inherent but predictable error at each 1Hz tuning step, but if I set both radios to the same frequency, the outputs are phase-coherent when fed from the same 10 MHz source. I've measured the phase error over periods of hours and there is no drift detectable between the two radios. Andy G4JNT carried out tests on his DUO to determine the errors and I've confirmed some of the offsets, which are often better than 5 mHz, but some are over 25 mHz. Great when I'm running something needing phase coherence to another DUO or a radio with mHz resolution and precision. The errors appear consistent with the use of a 32 bit NCO. Knowing *exactly* how wrong you are is often almost as good as being right. Neil G4DBN > On 7 Dec 2024, at 18:17, Bob Camp via time-nuts <time-nuts@lists.febo.com> wrote: > > Hi > > Building a synthesizer that is *exact* at *any* frequency you come up with is pretty much impossible. > You can build one that will tune to 10 Hz steps over 1 to 30 MHz. That’s not going to hit 1,000,001 Hz > exactly. It will jump from 1,000,000 Hz to 1,000,010 Hz. It simply can’t get to something below it’s > minimum resolution. > > On HF a resolution of 0.01 Hz (or anything close to that) is indeed doing very well. It wasn’t a long time ago > that 0.1 Hz or even 1 Hz was considered “plenty good”. > > Now, how does the firmware handle this and what arbitrary output frequency does it pick? Time to > dig into that source code and see what decisions they made. Best guess: They did it so it tunes > quickly without a lot of CPU cycles going into decision making. Folks complain a lot more about > tuning lag than some of the rest of this stuff. > > Is this just an issue with HF radio? Very much not. It’s simply a great example of how a lot of DDS based > stuff works these days. There are a lot of signal generators out there that have the same sort of > weird “base step” somewhere deep down inside the beast. You can get all sorts of odd things just > like this popping up as a result ( = I though I moved exactly 1.5 KHz and it’s not …). > > Bob > >> On Dec 7, 2024, at 9:35 AM, Azelio Boriani via time-nuts <time-nuts@lists.febo.com> wrote: >> >> If the frequency error is always the same, it is consistent with the >> synthesis design that is not meant to be accurate, otherwise it can be a >> discontinuous adjustment, like the IC9700. In the IC9700 it is "on demand" >> and you have to start manually the adjustment procedure, the IC7610 has no >> manual start but maybe is not a real lock to external reference. >> >>> On Sat, Dec 7, 2024 at 12:18 PM Dana Whitlow via time-nuts < >>> time-nuts@lists.febo.com> wrote: >>> >>> What really irks me is that the manufacturers virtually never admit >>> to the existence of synthesis offset errors in their data, and that they >>> do not display the amount of synthesis offset error in the course of >>> normal operation. Nor, as a rule, do they show sufficiently detailed >>> info on the overall design that one could compute that error for >>> himself. >>> >>> Dana >>> >>> >>> On Sat, Dec 7, 2024 at 3:58 AM Magnus Danielson via time-nuts < >>> time-nuts@lists.febo.com> wrote: >>> >>>> Hi, >>>> >>>> There are a couple of factors in how a receiver creates offsets: >>>> >>>> 1) Timebase offset - internal reference oscillator not perfect on >>>> nominal frequency >>>> >>>> 2) Synthesis offset - For practical reasons, synthesis is not engineered >>>> to necessarily give exactly 100 Hz steps (or whatever) with perfect 0 Hz >>>> offset from nominal. >>>> >>>> The synthesis offset comes from implementation and forms a scaling of >>>> the timebase. The timebase can be locked up in some receivers, and then >>>> synthesis offset remains. >>>> >>>> With a bit of care, these can be characterized for the particular >>>> receiver dial frequency, but indeed, this is not test instruments, they >>>> are not built for it, so you will have to learn how they work and >>>> compensate for it. >>>> >>>> Cheers, >>>> Magnus >>>> >>>> On 2024-12-07 07:34, glen english LIST via time-nuts wrote: >>>>> IC7610s are not test instruments..... the Icoms have fixed offset >>>>> errors.. I told them about this and their response was "its good >>> enough" >>>>> >>>>> >>>>> On 7/12/2024 2:38 pm, ke2n--- via time-nuts wrote: >>>>>> I understand that if I offset my radio tuning by (say) 1500 Hz from a >>>>>> received carrier, I will hear a 1500 Hz note in the audio. >>>>>> >>>>>> >>>>>> If you use USB mode, then the tuning should be offset in a negative >>>>>> direction. >>>>>> >>>>>> For LSB mode, the tuning should be offset in a positive direction. >>>>>> >>>>>> >>>>>> Both methods should produce the exact same beat note with a >>>>>> properly-aligned >>>>>> radio. >>>>>> >>>>>> >>>>>> I was doing this sort of test with my new IC7610 - with its GPS sync'd >>>>>> oscillator - and eventually found that the two methods produce >>>>>> frequencies >>>>>> that differ by 0.1 Hz. It looks like USB/LSB are offset by equal >>>>>> amounts: >>>>>> 0.05 Hz in opposite directions. This seems independent of the >>> frequency >>>>>> being measured. >>>>>> >>>>>> >>>>>> Since this is an SDR-based radio, I suppose that the cause may be >>>>>> some sort >>>>>> of round-off error in the frequency synthesis. Perhaps due to >>> resolution >>>>>> limitations of the scheme. Or maybe its an actual programming error? >>>>>> >>>>>> >>>>>> I was wondering if others have seen this type of thing with SDR >>>>>> radios? Is >>>>>> it common? >>>>>> >>>>>> >>>>>> Ken/KE2N >>>>>> >

I'll need to recheck about USB/LSB offsets in the FDM-DUO. There is definitely evidence that it rounds down in the NCO, but I didn't record my findings about offsets in LSB mode. Neil G4DBN > On 7 Dec 2024, at 20:00, Ken via time-nuts <time-nuts@lists.febo.com> wrote: > > Yes, my thinking exactly. A little more checking required, but the .05 Hz offset seems independent of rx frequency. It's a USB/LSB thing. > > Sent from AOL on Android > > On Sat, Dec 7, 2024 at 10:52 AM, Tim Shoppa<tshoppa@gmail.com> wrote: Note that DDS synth blocks don't always give the "nice round numbers" that humans would see on a dial, and they should also block out divider values that cause even moderate phase noise, substituting a nearly equivalent divisor with much less phase noise. If the net result is a fraction of a Hz off nobody but a time-nut would ever notice. > Your suggestion of a rounding inconsistency that happens at 0 - say floor() vs round() - is certainly possible too. > If you are going to be doing FMT entries you'll map these out beforehand for the frequency you actually dial into your rig. > Tim N3QE > On Sat, Dec 7, 2024 at 1:16 AM ke2n--- via time-nuts <time-nuts@lists.febo.com> wrote: > > I understand that if I offset my radio tuning by (say) 1500 Hz from a > received carrier, I will hear a 1500 Hz note in the audio. > > > > If you use USB mode, then the tuning should be offset in a negative > direction. > > For LSB mode, the tuning should be offset in a positive direction. > > > > Both methods should produce the exact same beat note with a properly-aligned > radio. > > > > I was doing this sort of test with my new IC7610 - with its GPS sync'd > oscillator - and eventually found that the two methods produce frequencies > that differ by 0.1 Hz. It looks like USB/LSB are offset by equal amounts: > 0.05 Hz in opposite directions. This seems independent of the frequency > being measured. > > > > Since this is an SDR-based radio, I suppose that the cause may be some sort > of round-off error in the frequency synthesis. Perhaps due to resolution > limitations of the scheme. Or maybe its an actual programming error? > > > > I was wondering if others have seen this type of thing with SDR radios? Is > it common? > > > > Ken/KE2N > > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com >