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Topic: [solved] Receiving strong sigs 12.KHZ (Read 14191 times)
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F4HTX
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Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #75 on: 02. September 2018, 16:32:54 »
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Hi Andreas,
Thanks for checking the code, on my side I re-perform the process, and finally found that in 2.9.9 the birdies are there but very very low, even with volume fully cranked up. I only noticed them by moving around the frequency to notice it was there in the noise.
Very sorry for the false clue.
As you said ugly's the word.
73's
François
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F4HTX
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Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #78 on: 02. September 2018, 17:21:04 »
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Hi Andreas,
Good guess : on my mchf, with 2.5.57 it's there, almost unnoticeable, but definitely there.
Furthermore, on my ovi-40 with 2.9.50 and 2.9.9 it's also there. It is very faint and not obvious, but if you track it is definitely a birdy.
From my viewpoint this lead to an interesting conclusion : this issue might have been in our firmwares for a very long time but only surfacing in specific conditions. Most of users won't probably notice any birdies problem in real life use considering the usual HF background noise.
And also a second conclusion : the F1F3F5 reset do not get rid of the birdies problem but only make it to dive back in noise. So the parameters configuration might not be the problem, more a chemical revelator of a low noise illness. Not surprising that finally nothing surfaced in examining the backup files.
About my testing conditions : I used my Adret 7100D @ -73dBm, last time I checked it was correctly calibrated and the generator noise and spurs were very low (-136dB). Just to be sure, I'll check it later this week, in case something failed, and also redo the test with another generator (R&S SMT03). Just in case...
Best Regards,
François
Later PS : Crossed responses again 
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| « Last Edit: 02. September 2018, 17:22:41 by F4HTX » |
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DD4WH
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Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #79 on: 03. September 2018, 07:03:34 »
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Hi folks!
Sorry for being silent so long, I was busy with other things/hobbies ;-).
it is hard for me to understand the issue, because it is not present on my machine, but I try to summarize the main facts here and then I would like to pose some more questions which would be very nice if you could try to answer them/ carry out some more tests on your machines, thanks in advance!
SUMMARY of the 12kHz problem:
* a wanted signal is received
* you notice the presence of a copy of that wanted signal (called unwanted signal) which is 12kHz above and 12kHz below the frequency of the wanted signal
* the unwanted signal is audible, but not visible with magnify 1x [do not use other magnify modes while we are investigating this problem, please]
* that unwanted signal is well below the wanted signal [Francois reported: -73dBm wanted signal and -136dBm unwanted signal --> 63dB difference; Chuck reported: "there is no S-meter reading"]
* so I assume the unwanted signal is about 50-60dB lower than the wanted signal, is that correct?
* the unwanted signal(s) is/are much louder when using a filter bandwidth lower than 3k8, but they are still present with filter bandwidths higher than 3k6
* AGC ON/OFF has no influence on the presence of the unwanted signal
* NR ON/OFF has no influence on the presence of the unwanted signal
* NB ON/OFF has no influence on the presence of the unwanted signal
* Translate 0/6/12kHz has no influence on the presence of the unwanted signal
* has been present in the firmware since the very first versions by Chris & Clint (at least from 1.4.0 on)
FIRST THOUGHTS on the cause of the problem (from here on, this is massive speculation from my side):
* to me, it seems everything is pretty OK ;-):
* the filter suppresses unwanted signals by 60dB
* that is how the digital filters have been designed from the beginning of the making of the mcHF software: with 60dB stopband attenuation, so I would not expect better attenuation --> some filter details can be found here:
https://github.com/df8oe/UHSDR/wiki/How-does-your-UHSDR-software-DSP-work
* another question would be: are we happy with "only" 60dB: historically, the mcHF was not designed to be a high end TRX, it evolved more and more into that direction, but the filter design stayed the same and it would be a massive task to recalculate all the filters for higher stopband attenuation and on the F4 it would be very hard to achieve that because of memory and processor load constraints
* on the F7/H7 this is a totally different thing and we have to improve the filters there, that is clear
FURTHER QUESTIONS (please help me here):
* I assume the unwanted signal is about 50-60dB lower than the wanted signal, is that correct?
* could you carry out a test under defined conditions:
- 2k7 lowpass filter in USB
- IQ auto correction ON (because we have to eliminate the possibility that it is just a malaligned IQ phase/amplitude); alternatively you can show me on the video that your IQ phase and amplitude is perfectly manually calibrated at 7100kHz
- set frequency translation to +12kHz
- set display to spectrum display only
- wanted signal 7100kHz
- is the unwanted signal in LSB?
- which signal level does the unwanted signal have? is it approximately 60dB down? Please measure with the S-meter/dBm display with magnify 1x
It would be nice if you could do exactly the same test again with the 3k8 lowpass filter.
Thanks a lot for your efforts and tests so far and thanks in advance for helping exploring the cause of the issue!
73 Frank DD4WH
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| « Last Edit: 03. September 2018, 11:06:40 by DD4WH » |
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Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #80 on: 03. September 2018, 07:15:01 »
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could anybody post a video showing this problem or the results of your further tests?
Chuck: unfortunately your link does not work anymore (maybe its my dropbox account which is full ;-))
Thanks in advance!
73 Frank
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F4HTX
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Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #81 on: 03. September 2018, 07:25:15 »
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Hello Frank,
Thanks for trying to summurize, here are couple details to adjust :
1. * you notice the presence of a copy of did wanted signal (called unwanted signal) All which is 12 kHz above and 12kHz below the frequency of the wanted signal
It's 1x +/-12kHz ; 2x +/- 12kHz ; 3x +/-12kHz ; nx... I didn't check where n ends.
2. * That unwanted signal is well below the wanted signal [Francois reported: -73dBm wanted signal and unwanted signal -136dBm -> 63dB difference; Chuck reported: "there is no S-meter reading"]
My explaination was not clear : -73dBm is my test signal and -136dBm is the spurs level on my RF generator, not the mchf birdies
3. * so I assume the unwanted signal is about 50-60dB lower than the wanted signal, is did correct?
Definitely NO. In some of my test the +12 is almost as loud as the original signal. That's why people noticed in the first place and so started the issue.
So, no it's definitely not ok to hear a spur as loud as the main signal.
I'll try to find some spare time to set up the test you are asking for. Not easy to reach the 1Hz resolution in frequency. I have to think about a test setup. Do you need a +/-1Hz precision or more ?
73's
François
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| « Last Edit: 03. September 2018, 07:38:48 by F4HTX » |
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DD4WH
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Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #83 on: 03. September 2018, 07:54:27 »
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Salut Francois and thanks for the quick anwer!
Oh, thats not good to have an unwanted signal at that signal level! Then I have to think some more . . .
Dont worry too much about the test setup: it would be sufficient to inject a tone with your excellent signal generator and then zero beat the wanted and unwanted signal(s) with a one Hz resolution of the VFO. I just want to be sure that the difference of wanted and unwanted signal is exactly 12kHz/24kHz/36kHz etc.
73 Frank
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Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #84 on: 03. September 2018, 07:59:14 »
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Hmm, Andreas, now that is confusing . . .
Could it be that we are talking about two different things ? :
1.) the twinpeaks issue that is sometimes occuring with unwanted signals as loud as the wanted signal and
2.) the 12k issue reported here with 50/60dB suppressed unwanted signals?
Chuck, how loud are your unwanted signals? You stated that there is "no S-meter reading", so I assume they are not at all as strong as the wanted signal, is that correct?
Francois, is the issue with unwanted signals that are as loud as the wanted signal reproducible after doing a RESET CODEC from the menu (try it several times ;-))?
73 Frank
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Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #86 on: 03. September 2018, 08:05:09 »
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Andreas, I am not sure whether the twinpeaks issue can be totally omitted when using 0kHz translate, but you will not see it anymore (but probably still have the issue).(not totally sure about this)
To be safe, please use 12kHz translate for all tests, then the twinpeaks issue can be easily seen ;-).
73 Frank
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DD4WH
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Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #89 on: 03. September 2018, 09:02:51 »
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has anybody ever seen this problem in modes AM or SAM?
73 Frank
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. There is nothing what bothers in normal working conditions... All infected configs I have got show suppressions better than 40dB. That is slightly too bad - but not "as loud as wanted signal".
