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Bitx40 75KHz Spurious, How to solve it. #bitx40

Skip Davis
 

Great work Akira, thanks for the pictures.

Skip Davis, NC9O

On Jul 5, 2018, at 05:12, jj1epe@... wrote:

Akira

jj1epe@...
 

Dear Jerry aa1of,

The modification for suppress the spurious of this time is as follow.
I hope this would be useful for you.
 

1) Add 3.3uF electrolytic capacitor and 0.1uF x 2 bypass capacitor to VCC line of Arduino board =>PIC1-1a  PIC1-2a
2) Insert high frequency choke of about 100 uH in the power line of Arduino =>PIC2a
3) Connect the minus line of power supply line to the ground =>PIC3-1a  PIC3-2a
4) Connect the minus line of BITX40s to the ground
5) Add 0.1 uF × 2 bypass capacitor to VDD of BITX 40 board=>PIC5a
6) To prevent common mode noise, add 0.01uF x 2 bypass capacitor to the power connector=>PIC6a

73!
Akira
JJ1EPE

Jerry Gaffke
 

Recommendation:  Use Allard's v2 firmware and associated hardware mods:
    https://github.com/amunters/bitx40-raduino-v2
Moving to a high side vfo using Allard's firmware should fix this spur.

When operating at 7.2 mhz with a low side vfo,
that vfo is at 12-7.2 = 4.8 mhz.
The fifth harmonic of the vfo mixes with the second harmonic
of the 12mhz bfo:    4.8*5 = 24  = 2*12
PA4Q (Cor) figured this one out:  https://groups.io/g/BITX20/message/21996

The bfo and vfo have no reason to mix, except that this rig is not shielded.
Also, both are being generated inside the si5351, there may be crosstalk there.

Going to a high side VFO should work, the vfo is now at 12+7.2 = 19.2
To operate lower sideband as is customary on 40m,
the bfo must now be moved down a few khz to the other side of the 12mhz crystal filter.
The easiest way to do all of this is to use Allard's v2 code for the Bitx40,
he uses the si5351's clk0 to drive the bfo instead of the 12mhz crystal oscillator.

Curiously enough, 19.2*5 = 96 = 12*8
So their might still be a slight birdie when operating at 7.2 mhz with a high side vfo
but much reduced from the stock low side vfo.

Jerry, KE7ER


On Sun, Jul 1, 2018 at 10:53 pm, Raj vu2zap wrote:
OK! connected up the bitx40 with Raduino.

Yes, there are spurious as reported. The spurious distance from carrier varies with frequency.

All the spurs all come together and disappear at near 7.2 Mhz. This is mixing of harmonics but
cant remember the maths.. Jerry and others had worked it out.

I will try out a filter that I had wired on some board but donno where I kept it!

Jer Tres
 

Dear Akira,
Please share with us the specific details about modifications you used that successfully solved the spurious output problems.
Thank you very much and
73
Jerry aa1of

Allard PE1NWL
 

Hi Akira san,

thanks for your update:

He said the cause of spurious was the noise of VCC around 19 MHz of 0.15V.
As the result of the modifications of Bitx40 to reduce the noise, such as adding the big condenser and choke coil etc , the spurious level went down below of the criteria.
That's good news, congratulations!
This issue may also be related to the strong "birdie" that can be heard at 7199 kHz when the radio is in LSB mode (almost no birdie in USB mode).
It was found that the strength of the birdie greatly depends on the VFO drive level. Default drive level is 4 mA. In the SETTINGS menu, you can try different drive levels (2,4,6,8 mA). The optimum level may be different for each BitX40 radio.
The VFO drive level setting may also have an effect on the spurious signals you observed. Perhaps it is possible to fix this issue just by adjusting the drive level setting (in that case, extra hardware modification such as adding capacitor or choke could be avoided).

Could you try it out?

73 Allard PE1NWL

jj1epe@...
 

Hi!

Thank you for your comment and advice.

My friend have found the cause of spurious of 75 KHz.
He said the cause of spurious was the noise of VCC around 19 MHz of 0.15V.
As the result of the modifications of Bitx40 to reduce the noise, such as adding the big condenser and choke coil etc , the spurious level went down below of the criteria.

By this modification, my Bitx40 meets the criteria of the spurious of Japanese regulation.
So I am going to submit the application for obtaining the certification of Bitx40 from the relevant authority.

There are two criteria for the spurious.
   1)  Baseband area :  under -40db of power of fundamental frequency
            This frequency range is the 2.5 x  occupied band of frequency of TX mode.
   2) Spurious area :  under -50db of power of fundamental frequency.
           This frequency range is the out of Baseband area for super harmonic spurious.

The attached files are
  1) The picture of noise of VCC
 2) The picture of Spurious of 50KHz/div after the modification.
 3) The picture how the modification were added.

73!
Akira
JJ1EPE






 

OK! connected up the bitx40 with Raduino.

Yes, there are spurious as reported. The spurious distance from carrier varies with frequency.

All the spurs all come together and disappear at near 7.2 Mhz. This is mixing of harmonics but
cant remember the maths.. Jerry and others had worked it out.

I will try out a filter that I had wired on some board but donno where I kept it!

Raj

At 02-07-18, you wrote:
Raj,
thanks for testing, but the issue that Akira san reported, is with BitX40,
not ubitx.
If possible, could you please repeat the same check with BitX40 and let us
know the results?

Many Thanks, 73
Allard PE1NWL

On Sun, July 1, 2018 15:59, Raj vu2zap wrote:
Correction 500KHz span!

At 01-07-18, you wrote:
Akira,

I just put my uBitxr4 on the spectrum analyzer and found nothing +-250
Khz. That is 500 Khz BW.

I think your measurements are being affected by switch mode power supply
in one of the items.

Raj

At 25-06-18, you wrote:
Hi!

I built Bitx40 about 2 weeks ago.

I measured the spurious of Bitx40 by using the spectrum analyzer.
The level of spurious of harmonics were under 50db. So this is fine.
But the spurious at 75KHz was observed.
The spurious might be the multiple of 25KHz.
It would be much appreciated if you could advise me the cause and
solution of this spurious of Bitx40.

In Japan, we must prove to the authority that the spurious of the
transceiver meets the criteria to obtain the certification of the
transceiver from the authority.
So if i could not resolve this spurious, I will not be able to use
Bitx40 in Japan.

Thanks in advance,
Akira
JJ1EPE



 

Thanks Allard, goofed there. Will re-hookup the bitx40 later today and see.

At 02-07-18, you wrote:
Raj,
thanks for testing, but the issue that Akira san reported, is with BitX40,
not ubitx.
If possible, could you please repeat the same check with BitX40 and let us
know the results?

Many Thanks, 73
Allard PE1NWL

Allard PE1NWL
 

Raj,
thanks for testing, but the issue that Akira san reported, is with BitX40,
not ubitx.
If possible, could you please repeat the same check with BitX40 and let us
know the results?

Many Thanks, 73
Allard PE1NWL

On Sun, July 1, 2018 15:59, Raj vu2zap wrote:
Correction 500KHz span!

At 01-07-18, you wrote:
Akira,

I just put my uBitxr4 on the spectrum analyzer and found nothing +-250
Khz. That is 500 Khz BW.

I think your measurements are being affected by switch mode power supply
in one of the items.

Raj

At 25-06-18, you wrote:
Hi!

I built Bitx40 about 2 weeks ago.

I measured the spurious of Bitx40 by using the spectrum analyzer.
The level of spurious of harmonics were under 50db. So this is fine.
But the spurious at 75KHz was observed.
The spurious might be the multiple of 25KHz.
It would be much appreciated if you could advise me the cause and
solution of this spurious of Bitx40.

In Japan, we must prove to the authority that the spurious of the
transceiver meets the criteria to obtain the certification of the
transceiver from the authority.
So if i could not resolve this spurious, I will not be able to use
Bitx40 in Japan.

Thanks in advance,
Akira
JJ1EPE


 

Correction 500KHz span!

At 01-07-18, you wrote:
Akira,

I just put my uBitxr4 on the spectrum analyzer and found nothing +-250 Khz. That is 500 Khz BW.

I think your measurements are being affected by switch mode power supply in one of the items.

Raj

At 25-06-18, you wrote:
Hi!

I built Bitx40 about 2 weeks ago.

I measured the spurious of Bitx40 by using the spectrum analyzer.
The level of spurious of harmonics were under 50db. So this is fine.
But the spurious at 75KHz was observed.
The spurious might be the multiple of 25KHz.
It would be much appreciated if you could advise me the cause and solution of this spurious of Bitx40.

In Japan, we must prove to the authority that the spurious of the transceiver meets the criteria to obtain the certification of the transceiver from the authority.
So if i could not resolve this spurious, I will not be able to use Bitx40 in Japan.

Thanks in advance,
Akira
JJ1EPE

 

Akira,

I just put my uBitxr4 on the spectrum analyzer and found nothing +-250 Khz. That is 500 Khz BW.

I think your measurements are being affected by switch mode power supply in one of the items.

Raj

At 25-06-18, you wrote:
Hi!

I built Bitx40 about 2 weeks ago.

I measured the spurious of Bitx40 by using the spectrum analyzer.
The level of spurious of harmonics were under 50db. So this is fine.
But the spurious at 75KHz was observed.
The spurious might be the multiple of 25KHz.
It would be much appreciated if you could advise me the cause and solution of this spurious of Bitx40.

In Japan, we must prove to the authority that the spurious of the transceiver meets the criteria to obtain the certification of the transceiver from the authority.
So if i could not resolve this spurious, I will not be able to use Bitx40 in Japan.

Thanks in advance,
Akira
JJ1EPE

Tim Gorman
 

Raj,

What then are the exact beginning and ending of the scan?

If the center frequency is 7.029Mhz then a 500khz scan would run from
6.779Mhz to 7.279Mhz.

I can come up with no spurious products that would result in an
harmonic progression increasing in amplitude as you move away from the
carrier frequency, especially as close in as 75khz.

The bitx40 uses a 12Mhz oscillator and a 5Mhz oscillator. I can't think
of a combination of these two frequencies that will give you a signal
at 7.104Mhz or 6.954Mhz as well as the carrier of 7.029Mhz.

I am still suspicious that something else is going on here besides
spurious products from the bitx40 itself.

tim ab0wr

On Tue, 26 Jun 2018 16:37:08 +0530
"Raj vu2zap" <@Raj> wrote:

Tim.

That is the marker M 7.049 , its very low in level and not seen.

Raj

At 26-06-18, you wrote:
It shows scanning from 7.029Mhz to 7.049Mhz. That's only a 20khz
scan, not 50khz. And certainly not 50khz per division on the screen.

The funny thing is that those unknowns are *increasing* in amplitude
as you move away from the carrier instead of decreasing. I'm not
sure what would generate this.

Could these be products from overdriving the spectrum analyzer?

tim ab0wr


 

Tim.

That is the marker M 7.049 , its very low in level and not seen.

Raj

At 26-06-18, you wrote:
It shows scanning from 7.029Mhz to 7.049Mhz. That's only a 20khz
scan, not 50khz. And certainly not 50khz per division on the screen.

The funny thing is that those unknowns are *increasing* in amplitude as
you move away from the carrier instead of decreasing. I'm not sure what
would generate this.

Could these be products from overdriving the spectrum analyzer?

tim ab0wr

Tim Gorman
 

It shows scanning from 7.029Mhz to 7.049Mhz. That's only a 20khz
scan, not 50khz. And certainly not 50khz per division on the screen.

The funny thing is that those unknowns are *increasing* in amplitude as
you move away from the carrier instead of decreasing. I'm not sure what
would generate this.

Could these be products from overdriving the spectrum analyzer?

tim ab0wr

On Tue, 26 Jun 2018 04:30:56 +0530
"Raj vu2zap" <@Raj> wrote:

Allard,

The pic attached is in 50Khz horizontal display.

Raj

At 26/06/2018, you wrote:
Hi Akira san,

But the spurious at 75KHz was observed.

I guess you mean 75 MHz (not kHz)?

The spurious might be the multiple of 25KHz.

In that case it could be a harmonic of 25 MHz (not kHz). Perhaps it
comes from the 25 MHz crystal in the Raduino?

73 Allard PE1NWL

Tim Gorman
 

Your carrier is at 7.029Mhz. Did you have your mode set to CW?

If so, you aren't seeing "spurious" mixer products at 75khz, 150khz,
and 225khz. They are something else. Since their appear on both sides
of the carrier I would have called them some kind of IMD products but
I've never seen IMD go up as you move away from the carrier.

If you were in CW mode, the mixers aren't used to generate the carrier
frequency so you wouldn't see any spurious mixer products.

There is something else going on here.

Since harmonics are based on the carrier frequency the closest one you
would have would be at 14.058Mhz. It wouldn't show up on your scan.

It's very obvious that you are picking up something that is
harmonically related at multiples on both sides of the carrier.

I have to admit I'm not sure what your screen is telling me. It appears
it is scanning from 7.029Mhz to 7.049Mhz. That's only 20khz total from
screen-edge to screen-edge, not the 500khz that would be required to put
your unknown 75khz away from the carrier.

If your total scan is 20khz then your unknowns are at 3khz, 5khz, and
8khz. They wouldn't even be harmonically related.

Are you sure your "50.0KHZ/" on the screen isn't the video bandwidth or
something?

tim ab0wr

On Mon, 25 Jun 2018 00:09:11 -0700
jj1epe@... wrote:

Hi!

I built Bitx40 about 2 weeks ago.
 
I measured the spurious of Bitx40 by using the spectrum analyzer.
The level of spurious of harmonics were under 50db. So this is fine.
But the spurious at 75KHz was observed.
The spurious might be the multiple of 25KHz.
It would be much appreciated if you could advise  me the cause and
solution of this spurious of Bitx40.

In Japan, we must prove to the authority that the spurious of the
transceiver meets the criteria to obtain the certification of the
transceiver from the authority. So if i could not resolve this
spurious, I will not be able to use Bitx40 in Japan.

Thanks in advance,
Akira
JJ1EPE


jj1epe@...
 

Hi Allard san,

I am glad I can contact with you on this group too.
As Raj san mentioned, unit of the frequency of spurious is KHz.

Akira
JJ1EPE 

jj1epe@...
 

MVS Sama,

Thank you for your prompt reply.
My friend measured the spurious.
I will ask my friend to check whether cause of spurious is the power supply.

Regard,
Akira
JJ1EPE

 

Allard,

The pic attached is in 50Khz horizontal display.

Raj


At 26/06/2018, you wrote:
Hi Akira san,

But the spurious at 75KHz was observed.

I guess you mean 75 MHz (not kHz)?

The spurious might be the multiple of 25KHz.

In that case it could be a harmonic of 25 MHz (not kHz). Perhaps it comes from the 25 MHz crystal in the Raduino?

73 Allard PE1NWL

Allard PE1NWL
 

Hi Akira san,

But the spurious at 75KHz was observed.
I guess you mean 75 MHz (not kHz)?

The spurious might be the multiple of 25KHz.
In that case it could be a harmonic of 25 MHz (not kHz). Perhaps it comes from the 25 MHz crystal in the Raduino?

73 Allard PE1NWL

MVS Sarma
 

how did you power it - by smps wall wart mor linear  or just a battery?

regards
sarma
 vu3zmv

Regards
MVS Sarma
 

On Mon, Jun 25, 2018 at 12:39 PM, <jj1epe@...> wrote:
Hi!

I built Bitx40 about 2 weeks ago.
 
I measured the spurious of Bitx40 by using the spectrum analyzer.
The level of spurious of harmonics were under 50db. So this is fine.
But the spurious at 75KHz was observed.
The spurious might be the multiple of 25KHz.
It would be much appreciated if you could advise  me the cause and solution of this spurious of Bitx40.

In Japan, we must prove to the authority that the spurious of the transceiver meets the criteria to obtain the certification of the transceiver from the authority.
So if i could not resolve this spurious, I will not be able to use Bitx40 in Japan.

Thanks in advance,
Akira
JJ1EPE