Topics

#ubitx-help Strong Audio Tones in and outside audio receive passband #ubitx-help

John <passionfruit88@...>
 

Hello group,

I need help after spending over a week trying to figure out an issue I have with my uBitx. 

First let me thank Farhan and team for such a great kit. I have built my uBitx around a manpack configuration (External side mounted heatsink, no connection at the back, room for an autotuner).

The issue I have is that I have strong audio tones inside and outside the passband on receive, typically up to 15khz.

I have attached an audio recording and took some audio spectrum snapshots made by placing the phone's microphone near the uBitx speaker. Using this method the dB value of the different FFT frequencies need to be taken with a grain of salt since there are not measured with an oscilloscope. Nevertheless the relative value are of interest here.

As you can see in the spectrums the tones are often near or above the level of the decoded signal which makes them impossible to ignore.

I have observed the following:

1. The tones frequency DO NOT change significantly with tuning up or down, or going through the menu items except when passing over the "CW Speed" option (this can be heard in the recording).

2. Changes in tones frequency DO occur when: 
   2.1 The unit BFO frequency is changed (the most significant variation)
   2.2 When the calibration is changed (this changes the BFO frequency too)
   2.3 When I touch the pins of the SI5351 crystal
   2.4 When I touch the pins of the Arduino's crystal

I have re-done the factory alignment and BFO adjustment several times and always come back to a +16 alignment number and a BFO frequency of 11,996.8Khz.

I have checked or tried the following:

A. Three different power supplies (one Lipo direct, one Lipo through a filtered 12V UBEC, a noise free 13.8V commercial power supply). No change except a small shift in tone frequency).

B. Checked the voltage on the Radiuno: 5.01VDC.

C. Added capacitors from the Radiuno 5V rail to ground (470uF, 0.1uf mica, no change), power supply rail to ground (470uF, no change), 1nF between casing of Arduino crystal to ground (produces a shift in tone, but no reduction in amplitude).

D. I tried a modified software where I would shift the frequencies of both the first and second oscillators by the same amount, thereby leaving the received frequency the same. The result was no change in tones frequency. So only a BFO frequency change produces a shift in tones. 

C. I noticed that when I shift the tones frequency (through BFO adjustment for example), the amplitude of the tones seem to follow the filters passband. This would indicate that they are produced before the sideband filter.

So I have thought of some mixing of the Arduino's crystal frequency with the BFO's one, but this seems to be contradicted by the fact that going over some menu items changes SOME tones.

Needless to say I am out of ideas right now, so your input is welcomed.

Best regards,

John (VK2ETA)


Bill Bates
 

I would be interested in recommended android apps for audio spectrum analysis, there are lots out there but what is a good one (preferably free 😊) God bless, Bill. G6ATO


From: John
Sent: ‎24/‎01/‎2018 08:54
To: BITX20@groups.io
Subject: [BITX20] #ubitx-help Strong Audio Tones in and outside audio receive passband

Hello group,

I need help after spending over a week trying to figure out an issue I have with my uBitx. 

First let me thank Farhan and team for such a great kit. I have built my uBitx around a manpack configuration (External side mounted heatsink, no connection at the back, room for an autotuner).

The issue I have is that I have strong audio tones inside and outside the passband on receive, typically up to 15khz.

I have attached an audio recording and took some audio spectrum snapshots made by placing the phone's microphone near the uBitx speaker. Using this method the dB value of the different FFT frequencies need to be taken with a grain of salt since there are not measured with an oscilloscope. Nevertheless the relative value are of interest here.

As you can see in the spectrums the tones are often near or above the level of the decoded signal which makes them impossible to ignore.

I have observed the following:

1. The tones frequency DO NOT change significantly with tuning up or down, or going through the menu items except when passing over the "CW Speed" option (this can be heard in the recording).

2. Changes in tones frequency DO occur when: 
   2.1 The unit BFO frequency is changed (the most significant variation)
   2.2 When the calibration is changed (this changes the BFO frequency too)
   2.3 When I touch the pins of the SI5351 crystal
   2.4 When I touch the pins of the Arduino's crystal

I have re-done the factory alignment and BFO adjustment several times and always come back to a +16 alignment number and a BFO frequency of 11,996.8Khz.

I have checked or tried the following:

A. Three different power supplies (one Lipo direct, one Lipo through a filtered 12V UBEC, a noise free 13.8V commercial power supply). No change except a small shift in tone frequency).

B. Checked the voltage on the Radiuno: 5.01VDC.

C. Added capacitors from the Radiuno 5V rail to ground (470uF, 0.1uf mica, no change), power supply rail to ground (470uF, no change), 1nF between casing of Arduino crystal to ground (produces a shift in tone, but no reduction in amplitude).

D. I tried a modified software where I would shift the frequencies of both the first and second oscillators by the same amount, thereby leaving the received frequency the same. The result was no change in tones frequency. So only a BFO frequency change produces a shift in tones. 

C. I noticed that when I shift the tones frequency (through BFO adjustment for example), the amplitude of the tones seem to follow the filters passband. This would indicate that they are produced before the sideband filter.

So I have thought of some mixing of the Arduino's crystal frequency with the BFO's one, but this seems to be contradicted by the fact that going over some menu items changes SOME tones.

Needless to say I am out of ideas right now, so your input is welcomed.

Best regards,

John (VK2ETA)


Jerry Gaffke
 

Farhan has said that the uBitx uses a low side BFO, below the crystal filter passband,
because with a BFO about 3khz higher on the high side of the crystal filter 
the harmonics of the 12mhz BFO beat with the harmonics of the 16mhz oscillator on the Nano
and create havoc.    I'd guess that you have an especially low 16mhz crystal on the nano,
and/or a pick of 12mhz crystals that happen to be especially high.

Your best bet might be to either replace the nano or replace the 16mhz crystal on the nano.
It might be possible to shield and filter the nano sufficiently somehow, but that would be tough.
Could be that hfsignals would consider replacing your Raduino, you might ask them.
Do you have somebody nearby you could swap out the Raduino with,
see if the problem follows the Raduino?
 
The ideal would be to buy or build an Arduino of some sort with the oscillator far removed from 16mhz.
That would allow us to choose high side second local oscillator injection (currently low side when operating LSB),
which might help improve opposite sideband rejection (we can choose the sharper 12mhz filter skirt)
and perhaps avoid some birdies.

Jerry, KE7ER


On Wed, Jan 24, 2018 at 12:49 am, John wrote:
2. Changes in tones frequency DO occur when: 
   2.1 The unit BFO frequency is changed (the most significant variation)
   2.2 When the calibration is changed (this changes the BFO frequency too)
   2.3 When I touch the pins of the SI5351 crystal
   2.4 When I touch the pins of the Arduino's crystal

Gordon Gibby
 

​maybe he could measure those two oscillators with a communications receiver and come back with some numbers and we could verify your hypothesis?



From: BITX20@groups.io <BITX20@groups.io> on behalf of Jerry Gaffke via Groups.Io <jgaffke@...>
Sent: Wednesday, January 24, 2018 11:07 AM
To: BITX20@groups.io
Subject: Re: [BITX20] #ubitx-help Strong Audio Tones in and outside audio receive passband
 
Farhan has said that the uBitx uses a low side BFO, below the crystal filter passband,
because with a BFO about 3khz higher on the high side of the crystal filter 
the harmonics of the 12mhz BFO beat with the harmonics of the 16mhz oscillator on the Nano
and create havoc.    I'd guess that you have an especially low 16mhz crystal on the nano,
and/or a pick of 12mhz crystals that happen to be especially high.

Your best bet might be to either replace the nano or replace the 16mhz crystal on the nano.
It might be possible to shield and filter the nano sufficiently somehow, but that would be tough.
Could be that hfsignals would consider replacing your Raduino, you might ask them.
Do you have somebody nearby you could swap out the Raduino with,
see if the problem follows the Raduino?
 
The ideal would be to buy or build an Arduino of some sort with the oscillator far removed from 16mhz.
That would allow us to choose high side second local oscillator injection (currently low side when operating LSB),
which might help improve opposite sideband rejection (we can choose the sharper 12mhz filter skirt)
and perhaps avoid some birdies.

Jerry, KE7ER

On Wed, Jan 24, 2018 at 12:49 am, John wrote:
2. Changes in tones frequency DO occur when: 
   2.1 The unit BFO frequency is changed (the most significant variation)
   2.2 When the calibration is changed (this changes the BFO frequency too)
   2.3 When I touch the pins of the SI5351 crystal
   2.4 When I touch the pins of the Arduino's crystal

 

Bill : 

I am using "Spectroid" which is free. It works quite well and was very useful in setting the BFO frequencies on my BITX40 
running Raduino V2.03.

Cheers

Michael VE3WMB 

Jerry Gaffke
 

John reports audio tones up around 15khz.
That is not in the normal SSB passband and may be perfectly normal for this rig.
Best solution here may be shielding and perhaps audio filtering.

Farhan's fix for interference between the 16mhz nano oscillator and the 12mhz bfo was to move the bfo down by perhaps 3khz.
The harmonics involved here are the 3rd and 4th respectively, to give 48mhz.
Moving the bfo down 3khz would only move the tones down by 12khz.
I don't think replacing the raduino is going to fix a 15khz tone.
If it is loud enough to be objectionable, this particular rig may have some sort of extra coupling between the two
due to loose wires or something.
 
The Bitx40 also had a 16mhz nano and 12mhz bfo, I don't recall this issue ever coming up,
so perhaps some sort of shielding or filtering is the answer.
The uBitx has the Raduino mounted directly on the main board, the nano very near the modulator/demodulator 
That's good and bad, we want the 12mhz clk0 connection to be very short.

So still some open questions here.

Dave Bottom <ars.kd6az@...>
 

I have the same issue that oddly is getting worse over time with no change to the Radio other than firmware.

I’ve started replacing critical leads with shielded cable but agree that audio filtering might help if early enough. My headphones already roll off at 6000 so it way down but still annoying.

Work continues...

Dave WI6R

Sent from my iPhone

On Jan 24, 2018, at 8:54 AM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:

John reports audio tones up around 15khz.
That is not in the normal SSB passband and may be perfectly normal for this rig.
Best solution here may be shielding and perhaps audio filtering.

Farhan's fix for interference between the 16mhz nano oscillator and the 12mhz bfo was to move the bfo down by perhaps 3khz.
The harmonics involved here are the 3rd and 4th respectively, to give 48mhz.
Moving the bfo down 3khz would only move the tones down by 12khz.
I don't think replacing the raduino is going to fix a 15khz tone.
If it is loud enough to be objectionable, this particular rig may have some sort of extra coupling between the two
due to loose wires or something.
 
The Bitx40 also had a 16mhz nano and 12mhz bfo, I don't recall this issue ever coming up,
so perhaps some sort of shielding or filtering is the answer.
The uBitx has the Raduino mounted directly on the main board, the nano very near the modulator/demodulator 
That's good and bad, we want the 12mhz clk0 connection to be very short.

So still some open questions here.

Bill Bates
 

Thanks for the reply Michael 😃, God bless, Bill.


From: Michael Babineau
Sent: ‎24/‎01/‎2018 17:40
To: BITX20@groups.io
Subject: Re: [BITX20] #ubitx-help Strong Audio Tones in and outside audio receive passband

Bill : 

I am using "Spectroid" which is free. It works quite well and was very useful in setting the BFO frequencies on my BITX40 
running Raduino V2.03.

Cheers

Michael VE3WMB 

Dave Bottom <ars.kd6az@...>
 

For Audio Spectrum Analysis I use RTA Audio.  
There is a Free version and a inexpensive purchase version for both iOS and Android.
I've found it very useful.

Dave WI6R

On Wed, Jan 24, 2018 at 5:42 AM, Bill Bates <billy.bates@...> wrote:
I would be interested in recommended android apps for audio spectrum analysis, there are lots out there but what is a good one (preferably free 😊) God bless, Bill. G6ATO

From: John
Sent: ‎24/‎01/‎2018 08:54
To: BITX20@groups.io
Subject: [BITX20] #ubitx-help Strong Audio Tones in and outside audio receive passband

Hello group,

I need help after spending over a week trying to figure out an issue I have with my uBitx. 

First let me thank Farhan and team for such a great kit. I have built my uBitx around a manpack configuration (External side mounted heatsink, no connection at the back, room for an autotuner).

The issue I have is that I have strong audio tones inside and outside the passband on receive, typically up to 15khz.

I have attached an audio recording and took some audio spectrum snapshots made by placing the phone's microphone near the uBitx speaker. Using this method the dB value of the different FFT frequencies need to be taken with a grain of salt since there are not measured with an oscilloscope. Nevertheless the relative value are of interest here.

As you can see in the spectrums the tones are often near or above the level of the decoded signal which makes them impossible to ignore.

I have observed the following:

1. The tones frequency DO NOT change significantly with tuning up or down, or going through the menu items except when passing over the "CW Speed" option (this can be heard in the recording).

2. Changes in tones frequency DO occur when: 
   2.1 The unit BFO frequency is changed (the most significant variation)
   2.2 When the calibration is changed (this changes the BFO frequency too)
   2.3 When I touch the pins of the SI5351 crystal
   2.4 When I touch the pins of the Arduino's crystal

I have re-done the factory alignment and BFO adjustment several times and always come back to a +16 alignment number and a BFO frequency of 11,996.8Khz.

I have checked or tried the following:

A. Three different power supplies (one Lipo direct, one Lipo through a filtered 12V UBEC, a noise free 13.8V commercial power supply). No change except a small shift in tone frequency).

B. Checked the voltage on the Radiuno: 5.01VDC.

C. Added capacitors from the Radiuno 5V rail to ground (470uF, 0.1uf mica, no change), power supply rail to ground (470uF, no change), 1nF between casing of Arduino crystal to ground (produces a shift in tone, but no reduction in amplitude).

D. I tried a modified software where I would shift the frequencies of both the first and second oscillators by the same amount, thereby leaving the received frequency the same. The result was no change in tones frequency. So only a BFO frequency change produces a shift in tones. 

C. I noticed that when I shift the tones frequency (through BFO adjustment for example), the amplitude of the tones seem to follow the filters passband. This would indicate that they are produced before the sideband filter.

So I have thought of some mixing of the Arduino's crystal frequency with the BFO's one, but this seems to be contradicted by the fact that going over some menu items changes SOME tones.

Needless to say I am out of ideas right now, so your input is welcomed.

Best regards,

John (VK2ETA)





--
73 Dave WI6R

Bill Bates
 

Spectroid app loaded Michael & looks good 😊, many thanks 😊.


From: Michael Babineau
Sent: ‎24/‎01/‎2018 17:40
To: BITX20@groups.io
Subject: Re: [BITX20] #ubitx-help Strong Audio Tones in and outside audio receive passband

Bill : 

I am using "Spectroid" which is free. It works quite well and was very useful in setting the BFO frequencies on my BITX40 
running Raduino V2.03.

Cheers

Michael VE3WMB 

John <passionfruit88@...>
 

Thank you for your replies.

I will check the frequencies of the Arduino and BFO with another transceiver.

I have tried to move cables around but this had no influence on the tones.

Please note that the strongest tone is at 5,426Hz and with more up to 15KHz. So if I go the audio filter way it will have to be pretty steep I suspect.

In desperation I have thought of cutting the traces of the BFO line and one of the two other oscillators and wire swap them around, then changing the sketch accordingly. Would this prove/disprove a coupling issue?

I could buy another Raduino, my only issue is then what if this is on the main board?

So if the frequency test does not show anything out of the ordinary I will buy a header-less Arduino Nano and attempt the swap.

How do you de-solder the arduino? Is a de-soldering braid effective?

To Bill: I used "Spectrum Analyzer"  from Rasberrywood (the free version seems fine for radio audio analysis).

All the best,


73, John (VK2ETA)

Jerry Gaffke
 

Weird that you have a range of frequencies between 5khz and 15khz, I would expect a single tone.
Will be interesting to know if you hear some warble when listening to the 16mhz Nano and the 12mhz bfo.

I doubt switching the clk0 bfo out of the si5351 with one of the other si5351 outputs would help.

You might try wrapping most of the Raduino and display in insulating tape and then tinfoil
to keep the Nano's 16mhz from radiating.
But leave the LM7805 regulator sticking out the side cuz it needs airflow to keep cool 

Ultimately, I think we may need either better shielding, or move the 16mhz clock frequency
of the Raduino to something else.  We've heard from two with this problem, are there others?



On Wed, Jan 24, 2018 at 01:44 pm, John wrote:
Thank you for your replies.

I will check the frequencies of the Arduino and BFO with another transceiver.

I have tried to move cables around but this had no influence on the tones.

Please note that the strongest tone is at 5,426Hz and with more up to 15KHz. So if I go the audio filter way it will have to be pretty steep I suspect.

In desperation I have thought of cutting the traces of the BFO line and one of the two other oscillators and wire swap them around, then changing the sketch accordingly. Would this prove/disprove a coupling issue?

I could buy another Raduino, my only issue is then what if this is on the main board?

So if the frequency test does not show anything out of the ordinary I will buy a header-less Arduino Nano and attempt the swap.

How do you de-solder the arduino? Is a de-soldering braid effective?

To Bill: I used "Spectrum Analyzer"  from Rasberrywood (the free version seems fine for radio audio analysis).

All the best,


73, John (VK2ETA)

James Lawrie
 

Hello,

Get good quality braid and use extra flux. I have done this to several shields and clones, use toothpick to put a little extra flux along pins and use a 40 watt iron. I start with a inch of braid along pins place iron on braid when solder starts to melt I slowly pull braid towards me while moving iron away. 

Usually works first time round and when done use alcohol to cleanup mess just don’t hold iron in one spot to long the plastic and pins can separate. It’s kinda a skill you have to learn but a little extra flux pull melted solder all the way through the hole.

James Lawrie

On Jan 24, 2018, at 15:44, John <passionfruit88@...> wrote:

Thank you for your replies.

I will check the frequencies of the Arduino and BFO with another transceiver.

I have tried to move cables around but this had no influence on the tones.

Please note that the strongest tone is at 5,426Hz and with more up to 15KHz. So if I go the audio filter way it will have to be pretty steep I suspect.

In desperation I have thought of cutting the traces of the BFO line and one of the two other oscillators and wire swap them around, then changing the sketch accordingly. Would this prove/disprove a coupling issue?

I could buy another Raduino, my only issue is then what if this is on the main board?

So if the frequency test does not show anything out of the ordinary I will buy a header-less Arduino Nano and attempt the swap.

How do you de-solder the arduino? Is a de-soldering braid effective?

To Bill: I used "Spectrum Analyzer"  from Rasberrywood (the free version seems fine for radio audio analysis).

All the best,


73, John (VK2ETA)

John <passionfruit88@...>
 

Thank you again for the inputs you provided and thank you James for the de-soldering technique (I will need it).

Results of further investigations based on your inputs. Stock firmware loaded in Raduino. 

I checked also the 3.3V supply of the Arduino and found 3.62V. Stable even when changing menu items and tuning in frequency.

I placed an FT-817 in USB mode with it's rubber antenna near the Raduino (in place in the uBitx). Signals were around S8-S9.

1. Arduino 16Mhz crystal: Measured as oscillating on 15,995.27KHz. Tone would shift slightly and of a similar amount to the Rx audio when tuning the encoder and selecting menu items (see attached recording).

2. BFO was found on 11,996.70KHz which is consistent with the calibration value of 11,996.8KHz. No shift or noise present in the signal received.

3. First oscillator found at 52,090.72KHz for an Rx frequency of 7,100.00KHz. Again no shift or noise present in the signal received when changing the menu items. Change of Rx frequency by turning the encoder would result in a stepped but clean change in tone as received in the FT-817.

4. Second oscillator found at 32,993.95KHz as uBitx was in LSB mode. Clean, stable signal.

So the only clock that resembles the tuning noise but not the multiple tones of the Rx signal is the 16MHz Arduino clock.

I tried to wrap a ground connected shield around the Arduino (from the "top"), but did not find any difference in tones apart from a slight shift as when I place my finger near the Arduino's crystal.

So as proposed above I have ordered a new Arduino and will attempt its replacement on the Raduino.

Attached is the Rx of the 16Mhz Arduino clock.

John <passionfruit88@...>
 

Problem solved.

Just to re-state the issue: strong tones within the passband, mostly fixed in ferquency. Some slight variation in frequency when scanning through the menu items. Also strong tones outside the passband (near 6400Hz and 14900Hz). These were fixed in frequency and would change with BFO frequency adjustments.

I also had noises when turning the tuning encoder each time the frequency was changed. I thought these were normal as they were mentioned in the Bitx40 rig.

I bought a cheap Arduino on eBay and after some struggle I changed the Nano, re-programmed it and all came good. The tones within the passband are gone and the ones outside the passband can be eliminated with a careful choice of BFO frequency.

Also the tuning noises have disappeared. 

So it must have been a bad Arduino in all logic.

As an interesting aside, when chasing this issue I changed the first two mixers VFOs thereby changing the alignment between the 45Mhz filter and the 12Mhz one. I noticed that the default values produced a signal around 8dBs lower than when "re-aligning" the two passbands.

If anyone is interested I can share the code for this test (I simply re-assigned the RIT menu item and had an extra variable which was added to the first two VFOs so that the net received frequency stayed the same, but the first IF was shifted correspondingly).

Please note that I found the removal of the Arduino a challenge and resorted to cutting the edges out of the Arduino board with a
Dremel and cut the plastic spacer between each pin to be able to de-solder each one individually. I have not mastered James technique obviously!

Since I have mounted the display remotely and have space towards the front of the Raduino, I opted to put some female headers so that I can plug/unplug the Arduino, just in case.

Hope this helps,

73, John (VK2ETA)

Jerry Gaffke
 

Very cool, good job!
Thanks for the update, this may come up again.

Could be that the old arduino had a faulty 16mhz crystal.
But that thing is tiny, swapping in a different crystal would be tough.
Could also be that the ATMega382P processor had a faulty oscillator.

Jerry


On Thu, Feb 1, 2018 at 10:03 pm, John wrote:
I bought a cheap Arduino on eBay and after some struggle I changed the Nano, re-programmed it and all came good. The tones within the passband are gone and the ones outside the passband can be eliminated with a careful choice of BFO frequency.

John <passionfruit88@...>
 

Jerry, I am not sure which is the problem, but I can't tell now that I destroyed the Arduino.

The key pointer was when I connected a 1nF capacitor to one side of the Arduino crystal to ground, effectively stopping the clock of the cpu, the tones within the passband would disappear (as well as any control of course).

Cheers, John

Dave Bottom <ars.kd6az@...>
 

John,

Thanks for your hard work.  My uBITX has the same exact issue with the "squeal".  Mine did not originally have this issue until a couple of weeks ago (received Dec 22) and now it has gotten worse over that time.

It is interesting that the HFOs were off far enough to effect the signal by 8dB. Something to check and maybe this should be part of alignment for each radio?  At least with a spectrum analyzer this won't be too hard.
Yes interested in your code for this test.  

So now when I have time I know what to try, although it doesn't sound like much fun changing the Nano.

Dave WI6R

On Thu, Feb 1, 2018 at 10:03 PM, John <passionfruit88@...> wrote:
Problem solved.

Just to re-state the issue: strong tones within the passband, mostly fixed in ferquency. Some slight variation in frequency when scanning through the menu items. Also strong tones outside the passband (near 6400Hz and 14900Hz). These were fixed in frequency and would change with BFO frequency adjustments.

I also had noises when turning the tuning encoder each time the frequency was changed. I thought these were normal as they were mentioned in the Bitx40 rig.

I bought a cheap Arduino on eBay and after some struggle I changed the Nano, re-programmed it and all came good. The tones within the passband are gone and the ones outside the passband can be eliminated with a careful choice of BFO frequency.

Also the tuning noises have disappeared. 

So it must have been a bad Arduino in all logic.

As an interesting aside, when chasing this issue I changed the first two mixers VFOs thereby changing the alignment between the 45Mhz filter and the 12Mhz one. I noticed that the default values produced a signal around 8dBs lower than when "re-aligning" the two passbands.

If anyone is interested I can share the code for this test (I simply re-assigned the RIT menu item and had an extra variable which was added to the first two VFOs so that the net received frequency stayed the same, but the first IF was shifted correspondingly).

Please note that I found the removal of the Arduino a challenge and resorted to cutting the edges out of the Arduino board with a
Dremel and cut the plastic spacer between each pin to be able to de-solder each one individually. I have not mastered James technique obviously!

Since I have mounted the display remotely and have space towards the front of the Raduino, I opted to put some female headers so that I can plug/unplug the Arduino, just in case.

Hope this helps,

73, John (VK2ETA)




--
73 Dave WI6R

Jerry Gaffke
 

HFO's being off suggests the 25mhz crystal at the si5351 might be the problem on this one.
Regardless, it is probably a matter of 3'rd harmonic of the 16mhz nano oscillator
beating with the fourth harmonic 1.9985mhz bfo.
Tone should change when you bring your finger close to the very very dinky crystal near the nano's processor.
Will likely change when you bring your finger near the 25mhz ref crystal near the si5351 also.

I'd take a calibrated SW receiver, listen for the 16 and 25mhz oscillators, see if one is off frequency
then maybe try swapping out just that crystal.    Especially if that signal seems somewhat unstable.
A crystal in an entirely different package will probably work  if you keep the wires short.

If the 25mhz reference oscillator were unstable, that would make the ubitx receiver unstable also,
which I assume is not the case.  So best guess is John's 16mhz crystal near the Nano.

What exactly do you mean by "HFOs were off far enough to effect the signal by 8dB."
So, perhaps your BFO as shipped from HFSignals was far enough from the 12mhz crystal ladder filter
that signals were down by 8dB?  Or perhaps you updated your firmware, and lost the HFSignals calibration?

Jerry


On Fri, Feb 2, 2018 at 02:04 pm, Dave Bottom wrote:
John,
 
Thanks for your hard work.  My uBITX has the same exact issue with the "squeal".  Mine did not originally have this issue until a couple of weeks ago (received Dec 22) and now it has gotten worse over that time.
 
It is interesting that the HFOs were off far enough to effect the signal by 8dB. Something to check and maybe this should be part of alignment for each radio?  At least with a spectrum analyzer this won't be too hard.
Yes interested in your code for this test.  
 
So now when I have time I know what to try, although it doesn't sound like much fun changing the Nano.
 
Dave WI6R
 

Ashhar Farhan
 

Since we noticed these problems, we do check for the presence of these tones. Our pass test includes viewing the audio spectrum at 5v/db, 625 hz per division setting of FFT on rigol. We set the carrier so that the audio passband is inside two cursors at 300 hz and 3000 hz. Then we check for any spurs upto 15 khz that are above the noise floor. If these tests pass, we move to the next test of transmit outputs on 3.5, 7, 14 and 28 mhz. These tests are a part of the firmware being shipped.

I suspect the 16 mhz crystal must have aged. There are two things you can try. First is go into the bfo settings and move it slightly so the spurs go away. Second is to add some capacitance to the 25 mhz crystal, about 10 pf. There is a third way too, which is to program the si5352 initialization code to enable a different load capacitance on oscillator. I havent tried the third method myself.

Very often, closed commercial designs tend to ignore or bury design faults. Open source proceeds with acknowledgment and fixing these to make the system better. As the saying goes, given enough eyeballs, all bugs are shallow.

- f

On 3 Feb 2018 4:19 am, "Jerry Gaffke via Groups.Io" <jgaffke=yahoo.com@groups.io> wrote:
HFO's being off suggests the 25mhz crystal at the si5351 might be the problem on this one.
Regardless, it is probably a matter of 3'rd harmonic of the 16mhz nano oscillator
beating with the fourth harmonic 1.9985mhz bfo.
Tone should change when you bring your finger close to the very very dinky crystal near the nano's processor.
Will likely change when you bring your finger near the 25mhz ref crystal near the si5351 also.

I'd take a calibrated SW receiver, listen for the 16 and 25mhz oscillators, see if one is off frequency
then maybe try swapping out just that crystal.    Especially if that signal seems somewhat unstable.
A crystal in an entirely different package will probably work  if you keep the wires short.

If the 25mhz reference oscillator were unstable, that would make the ubitx receiver unstable also,
which I assume is not the case.  So best guess is John's 16mhz crystal near the Nano.

What exactly do you mean by "HFOs were off far enough to effect the signal by 8dB."
So, perhaps your BFO as shipped from HFSignals was far enough from the 12mhz crystal ladder filter
that signals were down by 8dB?  Or perhaps you updated your firmware, and lost the HFSignals calibration?

Jerry

On Fri, Feb 2, 2018 at 02:04 pm, Dave Bottom wrote:
John,
 
Thanks for your hard work.  My uBITX has the same exact issue with the "squeal".  Mine did not originally have this issue until a couple of weeks ago (received Dec 22) and now it has gotten worse over that time.
 
It is interesting that the HFOs were off far enough to effect the signal by 8dB. Something to check and maybe this should be part of alignment for each radio?  At least with a spectrum analyzer this won't be too hard.
Yes interested in your code for this test.  
 
So now when I have time I know what to try, although it doesn't sound like much fun changing the Nano.
 
Dave WI6R