Date   
Re: ubitx circuit, wiring, source code on github

Jerry Gaffke
 

Looking over the sketch, not quite sure what all is going on yet with si5351_set_calibration()
Here's what I would expect to see:

Place the BFO (clk0) somewhere near the middle of the crystal filter passband so we can hear a zero beat.
An uncalibrated BFO frequency of 11997000 hz should be close enough.

Place clk1 (the local oscillator into the second mixer) at 45mhz + 12mhz = 57mhz  (the 45mhz filter is fairly wide, should not be critical)

Have the user tune clk2 (the VFO into the first mixer) till the display shows the exact frequency for a signal of known frequency.
This signal could be from a calibrated signal generator or an AM station such as WWV, or a CW transmitter with a brick on the key.
The displayed frequency should be exactly   sig = clk2-(clk1-clk0),
where clk0, clk1, clk2 are the value provided in the second parameter to si5351bx_setfreq(clknum, fout)
Given a signal frequency, we can compute the VFO frequency as   clk2 = sig+(clk1-clk0).

For example, assume we are tuned to WWV at 15mhz, with clk0=11.997mhz, and clk1=57mhz
Then clk2 (the VFO) should have a value of    clk2 = sig+(clk1-clk0) = 15mhz+(57mhz-11.997mhz) = 60.003mhz
when the display reads 15000000 hz.

Ask the user to turn the tuning knob until zerobeat is achieved, the tuning knob controls the value
of the calibration factor si5351bx_vcoa
The granularity with which si5351bx_vcoa can be varied should be down in the low single digits.
This accuracy will be very useful in some digital modes.  Perhaps use Don Cantrell's shuttle tuning
scheme, with increments/decrements of 1 for si5351bx_vcoa near the middle of the tuning range.  
The display should somehow indicate how far si5351bx_vcoa is from its nominal value of 875mhz.

For each change in the value of si5351bx_vcoa, do the following three function calls:
    si5351bx_setfreq(0, FREQclk0)
    si5351bx_setfreq(1, FREQclk1)
    si5351bx_setfreq(2, FREQclk2)

Note that the values for those three frequencies do not change.
In our example, they remain fixed at 11.997mhz, 57mhz, and 63.003mhz respectively.
However, as the calibration value si5351bx_vcoa changes between calls,
the frequency emitted by the three clock outputs will change proportional to that calibration constant.

When the user hears zerobeat, they press a button to save that value of si5351bx_vcoa
At this point, the Si5351's 25mhz reference oscillator is exactly calibrated, and any frequency we
program into clk0, clk1, or clk2  should be correct to within a fraction of a hz.
 
Once the si5351 is calibrated using the above procedure, then the user is asked to position the BFO
for the upper and lower sideband settings.  One way would be to have an incoming SSB signal of
known quality, and then set the BFO for best audio clarity.  An alternative would be to scan clk2 and clk0
through the crystal filter passband such that a constant frequency audio beat note is heard, and have the
user identify where the amplitude falls off at each edge of the 12mhz crystal filter passband. 

Jerry, KE7ER



On Wed, Dec 6, 2017 at 09:02 pm, Ashhar Farhan wrote:
i have uploaded the sketch for the ubitx, wiring diagrams and the circuit on github. ou can see it on https://github.com/afarhan/ubitx
 

Re: Any problem to have 2 sources powering the Raduino??

Jerry Gaffke
 

I'm not so sure.

First off, there is no 5v regulator on the Nano board.  
The Nano's 5v rail is wired directly to the Raduino's LM7805, no protection diode there.
The Nano's 5v rail can also be powered from the USB connector through a protection diode.
 The 3.3v Si5351 is operating off that same 5v rail by way of a 3.3v regulator hidden inside the USB chip on the Nano.

The protection diode on the Nano is an SS1P31 schottky diode, according to this schematic:  
    https://www.arduino.cc/en/uploads/Main/Arduino_Nano-Rev3.2-SCH.pdf
Here's the diode datasheet:
    https://www.vishay.com/docs/88915/ss1p3l.pdf
Forward voltage drop through the diode is somewhere between 0.1 and 0.4 volts, depending on how much current and how hot it is.
The LM7805 datasheet is here (one of many manufacturers), output voltage could be as low as 4.75v.:
    https://www.fairchildsemi.com/datasheets/LM/LM7805.pdf

Let's assume we have Bitx40 power on while the Nano has a USB cable in place.
If the host computer supplies a bit more than 5v to the USB port, or if the LM7805 output voltage is near the low end of their spec,
we may be powering the Nano plus the Si5351 from the USB port.
But that's no worse than the situation when we have the Raduino unplugged from the Bitx.
More typically, we'd get 5v from the LM7805 to power the Nano and Si5351, no current would be coming from the USB host.

If we power down the Bitx40 and Raj's diode is not in place, we might have 100ma of 5v going backwards
through the LM7805 into the Bitx40, and perhaps powering up the receiver.  
But an extra 100ma through the protection diode probably won't fry anything.
However, if you somehow kick the Bitx40 into transmit mode, current could go much higher
and you may fry that protection diode.  

So a good idea to add Raj's diode.

Some have seen Nano's blown when powering the Raduino from the Bitx while plugged into a USB host.
We don't really know for sure what's on the $2 Nano clones, and we don't know exactly what fried on those Nanos.

So I'd add Raj's diode, and also shut down power to the Bitx when plugging in a USB cable to the Nano.
Not exactly sure why you would need to power down the Bitx, but then we don't know exactly what happend
in those few cases where the Nano got fried.  My guess is that Raj's diode would have prevented such trouble.

Jerry, KE7ER

 

On Thu, Dec 7, 2017 at 09:40 am, RCBoatGuy wrote:
When plugged into the Raduino board, the Nano is powered externally by a regulator on the Raduino board, which also has no protection diode.  So if you put 12V on the Nano Vin supply pin, you are shorting the outputs of the Nano's regulator to the Raduino's regulator, which in turn are connected via a diode to the USB supply.  The diode on the USB supply cannot provide adequate protection from the other supplies unless diodes exist on the other supplies, so when connecting the Nano via USB to a computer, the other supplies should be disconnected.

Re: Any problem to have 2 sources powering the Raduino??

Jack, W8TEE
 

Jerry:

Are you sure about this:

First off, there is no 5v regulator on the Nano board.

The specs say it can be powered by:
    1) the USB port
    2) a 6-20V DC source (pin 30)
    3) a regulated 5V source (pin 27).

Jack, W8TEE



From: Jerry Gaffke via Groups.Io <jgaffke@...>
To: BITX20@groups.io
Sent: Thursday, December 7, 2017 2:15 PM
Subject: Re: [BITX20] Any problem to have 2 sources powering the Raduino??

I'm not so sure.

First off, there is no 5v regulator on the Nano board.  
The Nano's 5v rail is wired directly to the Raduino's LM7805, no protection diode there.
The Nano's 5v rail can also be powered from the USB connector through a protection diode.
 The 3.3v Si5351 is operating off that same 5v rail by way of a 3.3v regulator hidden inside the USB chip on the Nano.

The protection diode on the Nano is an SS1P31 schottky diode, according to this schematic:  
    https://www.arduino.cc/en/uploads/Main/Arduino_Nano-Rev3.2-SCH.pdf
Here's the diode datasheet:
    https://www.vishay.com/docs/88915/ss1p3l.pdf
Forward voltage drop through the diode is somewhere between 0.1 and 0.4 volts, depending on how much current and how hot it is.
The LM7805 datasheet is here (one of many manufacturers), output voltage could be as low as 4.75v.:
    https://www.fairchildsemi.com/datasheets/LM/LM7805.pdf

Let's assume we have Bitx40 power on while the Nano has a USB cable in place.
If the host computer supplies a bit more than 5v to the USB port, or if the LM7805 output voltage is near the low end of their spec,
we may be powering the Nano plus the Si5351 from the USB port.
But that's no worse than the situation when we have the Raduino unplugged from the Bitx.
More typically, we'd get 5v from the LM7805 to power the Nano and Si5351, no current would be coming from the USB host.

If we power down the Bitx40 and Raj's diode is not in place, we might have 100ma of 5v going backwards
through the LM7805 into the Bitx40, and perhaps powering up the receiver.  
But an extra 100ma through the protection diode probably won't fry anything.
However, if you somehow kick the Bitx40 into transmit mode, current could go much higher
and you may fry that protection diode.  

So a good idea to add Raj's diode.

Some have seen Nano's blown when powering the Raduino from the Bitx while plugged into a USB host.
We don't really know for sure what's on the $2 Nano clones, and we don't know exactly what fried on those Nanos.

So I'd add Raj's diode, and also shut down power to the Bitx when plugging in a USB cable to the Nano.
Not exactly sure why you would need to power down the Bitx, but then we don't know exactly what happend
in those few cases where the Nano got fried.  My guess is that Raj's diode would have prevented such trouble.

Jerry, KE7ER

 
On Thu, Dec 7, 2017 at 09:40 am, RCBoatGuy wrote:
When plugged into the Raduino board, the Nano is powered externally by a regulator on the Raduino board, which also has no protection diode.  So if you put 12V on the Nano Vin supply pin, you are shorting the outputs of the Nano's regulator to the Raduino's regulator, which in turn are connected via a diode to the USB supply.  The diode on the USB supply cannot provide adequate protection from the other supplies unless diodes exist on the other supplies, so when connecting the Nano via USB to a computer, the other supplies should be disconnected.


Re: ubitx circuit, wiring, source code on github

Jerry Gaffke
 

To scan the 12mhz filter passband, I'm thinking we drive CW-KEY high to unbalance the first mixer,
freeze clk1 at 57mhz, then scan clk2 and clk0 around 45mhz and 12mhz respectively,
monitoring the resultant audio beat note with scope or AC voltage meter.

Since the first mixer is unbalanced, anything on clk2 will continue on through to the second mixer
where it mixes with the 57mhz clk1 to create something near 12mhz. 
If clk0 varies from 12.000mhz down to 11.990mhz while clk2 varies from 45.000mhz to 45.010mhz, we should hear a constant
1khz audio tone that varies in intensity according to the 12mhz crystal filter's response to the 57mhz-clk2 frequency that
is passing through it.  This could be plotted on graph paper while reading the AC audio voltage and the frequency
of 57mhz-clk2 from the display, 

At any rate, nothing I am bringing up today should slow hfsigs down in building those rigs.
They will likely work fine as shipped, and all these minor adjustments will give the tinkerer's among us something to do.

Jerry, KE7ER


On Thu, Dec 7, 2017 at 10:09 am, Jerry Gaffke wrote:
An alternative would be to scan clk2 and clk0
through the crystal filter passband such that a constant frequency audio beat note is heard, and have the
user identify where the amplitude falls off at each edge of the 12mhz crystal filter passband.

Re: Any problem to have 2 sources powering the Raduino??

Jerry Gaffke
 

You are correct, there is an LM1117 5v regulator between the Vin pin (Nano pin 15) and the Nano's 5v ral.
However, in my defense, the Raduino does not tie anything to pin 15, so this regulator is not used 
and should have no effect on what's going on with the Raduino.

Jerry KE7ER


On Thu, Dec 7, 2017 at 11:29 am, Jack Purdum wrote:
Jerry:
 
Are you sure about this:
 
First off, there is no 5v regulator on the Nano board.
 
The specs say it can be powered by:
    1) the USB port
    2) a 6-20V DC source (pin 30)
    3) a regulated 5V source (pin 27).
 
Jack, W8TEE
 

Re: Any problem to have 2 sources powering the Raduino??

Jack, W8TEE
 

Correct. I was just pointing that out in case there are any Nano experimenters out there. Also, while the spec says 6-20V on input using the regulator, it gets a little flaky when the voltage is below 7V and the chip gets pretty toasty at voltages above 15V.

Jack, W8TEE



From: Jerry Gaffke via Groups.Io <jgaffke@...>
To: BITX20@groups.io
Sent: Thursday, December 7, 2017 2:50 PM
Subject: Re: [BITX20] Any problem to have 2 sources powering the Raduino??

You are correct, there is an LM1117 5v regulator between the Vin pin (Nano pin 15) and the Nano's 5v ral.
However, in my defense, the Raduino does not tie anything to pin 15, so this regulator is not used 
and should have no effect on what's going on with the Raduino.

Jerry KE7ER


On Thu, Dec 7, 2017 at 11:29 am, Jack Purdum wrote:
Jerry:
 
Are you sure about this:
 
First off, there is no 5v regulator on the Nano board.
 
The specs say it can be powered by:
    1) the USB port
    2) a 6-20V DC source (pin 30)
    3) a regulated 5V source (pin 27).
 
Jack, W8TEE
 


Re: ubitx circuit, wiring, source code on github

Ashhar Farhan
 

Jerry, 
Earlier, the calibration routine put out a 10 MHz signal out the antenna (by unbalancing the diode mixer and setting the first oscillator to 10 MHz). I chucked it because it assumed that everybody had a dummy load or a 10 MHz antenna. 

On the other hand, it is easier for a ham to call up someone and ask them to call CQ on a particular frequency. The way the present calibration works is like this. I call up  friend to call CQ from his calibrated radio exactly at 7050 KHz. I set the dial to 7050 KHz, Then you switch on the calibration and tune until it goes dead zero beat.  If only life was that simple. 

First, the crystal filter has a steep skirt. We would ordinarily celebrate this. But in our case, that means, unless the signal is a 30 db over S9, you are not going to hear the zero beat, much less the swing to the other sideband.

Second issue with this is that as we recalibrate the VCO and reset the oscillators, the BFO too is corrected by an equal amount and the zero-beat will go away. To compensate for this, this is what I came up with, bear with me...

The VCO frequency is at 875 MHz. We generate any needed frequency by dividing the PLL by a fraction. So, to generate 1 Mhz, it is divided by 875. Now, suppose our reference that we are trying to align with is at 1 MHz, we need to nudge the 875 MHz VCO. If the VCO moves by 875 Hz, we can see the 1 MHz move by 1 Hz. To move the 1 MHz by 10 Hz at  time, we have to move the VCO by 8750 Hz at a time. Our BFO is at 12 MHz, if we push the VCO up or down by 875 Hz, the 12 Mhz will be  moved by 12 Hz. If we push the VCO around by 8750 Hz, the 12 Mhz BFO has to be corrected by 120 Hz. This is what the code does. 

- f

On Fri, Dec 8, 2017 at 1:14 AM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
To scan the 12mhz filter passband, I'm thinking we drive CW-KEY high to unbalance the first mixer,
freeze clk1 at 57mhz, then scan clk2 and clk0 around 45mhz and 12mhz respectively,
monitoring the resultant audio beat note with scope or AC voltage meter.

Since the first mixer is unbalanced, anything on clk2 will continue on through to the second mixer
where it mixes with the 57mhz clk1 to create something near 12mhz. 
If clk0 varies from 12.000mhz down to 11.990mhz while clk2 varies from 45.000mhz to 45.010mhz, we should hear a constant
1khz audio tone that varies in intensity according to the 12mhz crystal filter's response to the 57mhz-clk2 frequency that
is passing through it.  This could be plotted on graph paper while reading the AC audio voltage and the frequency
of 57mhz-clk2 from the display, 

At any rate, nothing I am bringing up today should slow hfsigs down in building those rigs.
They will likely work fine as shipped, and all these minor adjustments will give the tinkerer's among us something to do.

Jerry, KE7ER


On Thu, Dec 7, 2017 at 10:09 am, Jerry Gaffke wrote:
An alternative would be to scan clk2 and clk0
through the crystal filter passband such that a constant frequency audio beat note is heard, and have the
user identify where the amplitude falls off at each edge of the 12mhz crystal filter passband.


Re: Any problem to have 2 sources powering the Raduino??

RCBoatGuy
 

Jerry,

Please look in the lower left corner of the Nano schematic you linked to above.  That LM1117IMPX-5.0 device in the section labeled '+5V REG' is a +5V regulator that exists on the Nano's board.  Right beside it in the schematic is the SS1P3L Schottky diode for the USB power supply protection that you mentioned.  In addition, the Nano documentation itself clearly lists the on-board regulator as being supplied by the Vin 7-12V supply pin.

So, if you connect 12V to the Vin supply, you are shorting the Nano's regulator and the Raduino's regulator outputs together.  Neither device puts out a perfect 5.0V, so there is always some fighting going on.  Regulators typically have a +/- 5% variance over temperature, if properly filtered.  That's 4.75V to 5.25V, or a 0.5V (10%) swing with good filtering, more than enough to make the schottky diode conduct with its 0.1V - 0.4V forward voltage range.  And the filtering on both the Nano and Raduino boards is sub-optimal, at best, so the overshoot can exceed 5.25V and the undershoot can go below 4.75V.

Same is true for the USB supply, especially if you are using a cheap, unshielded USB cable -- it, too, can have significant noise, and the low forward voltage of the schottky diode means it doesn't take a lot to make it conduct.  When one supply is overshooting while another is undershooting, the problem is multiplied, and you can end up frying something.  The Nano's regulator is a tiny one, not meant to provide a lot of current.  Doesn't take much to overstress it.

The USB protection diode was an poor attempt to allow powering the USB and either the Nano's on board regulator or an external 5V regulator (never both!).  A proper attempt would have had a protection diode on the Nano's regulator output, too. 

BTW, I do think it's reasonable for an external supply to provide its own protection, so I don't fault them for not adding an on-board protection diode to the Nano's external 5V supply connection.

Gordon,

If you are using the Raduino's 5V regulator to power the Nano, I would recommend putting a switch in the line so you can fully power the Nano via USB when attached to a computer.  Either that, or add diode protection between the Raduino's regulator and the Nano to provide extra protection.  Above all, put the extra filtering on the Raduino 5V supply that has been suggested in this forum before.

I personally don't recommend connecting 12V to the Nano's Vin supply.  For one thing, 12V at the extreme range of what the Nano's regulator can handle.  Exceeding 12V will damage the Nano's regulator.  I think the power filtering on the Nano is inadequate, and it's not easy to add filtering to that tiny board given that the Raduino PCB connects the pin to the Raduino's 5V supply.  If you do add 12V to the Nano's Vin supply, I recommend the following:

1) That you put a diode in the 12V supply line as mentioned earlier

2) That you add a 9V regulator with decent filtering between the 12V supply and the Nano Vin pin to avoid overstressing the Nano's regulator.  This is especially true if you plan to run with a 13.8V supply any time in the future...

3) That you put a switch in the line to the Nano's Vin so you can disconnect the Vin supply when programming. 

4) That you disconnect the Raduino's 5V supply to the Nano when powering the Nano via the Vin supply.  Either that, or add the diode protection to the 5V supply, but disconnecting it is safer.

73,
Carl  K0MWC

 

Re: Any problem to have 2 sources powering the Raduino??

RCBoatGuy
 

Oops, sorry, the 7-12V range is recommended, but the overall range is 6-20V.  So there may not be much point in adding the 9V regulator I suggested. 

73,
Carl  K0MWC

Re: Any problem to have 2 sources powering the Raduino??

Gordon Gibby <ggibby@...>
 

Thanks everyone for so much information.  I may have missed stated, it was never my intention to provide +12 to the nano, only to the raduino.   Adding the diode resistor and filtering is a next step.  

Thanks again!

Sent from my iPhone

On Dec 7, 2017, at 15:18, RCBoatGuy via Groups.Io <ijnfan-HamRadio@...> wrote:

Jerry,

Please look in the lower left corner of the Nano schematic you linked to above.  That LM1117IMPX-5.0 device in the section labeled '+5V REG' is a +5V regulator that exists on the Nano's board.  Right beside it in the schematic is the SS1P3L Schottky diode for the USB power supply protection that you mentioned.  In addition, the Nano documentation itself clearly lists the on-board regulator as being supplied by the Vin 7-12V supply pin.

So, if you connect 12V to the Vin supply, you are shorting the Nano's regulator and the Raduino's regulator outputs together.  Neither device puts out a perfect 5.0V, so there is always some fighting going on.  Regulators typically have a +/- 5% variance over temperature, if properly filtered.  That's 4.75V to 5.25V, or a 0.5V (10%) swing with good filtering, more than enough to make the schottky diode conduct with its 0.1V - 0.4V forward voltage range.  And the filtering on both the Nano and Raduino boards is sub-optimal, at best, so the overshoot can exceed 5.25V and the undershoot can go below 4.75V.

Same is true for the USB supply, especially if you are using a cheap, unshielded USB cable -- it, too, can have significant noise, and the low forward voltage of the schottky diode means it doesn't take a lot to make it conduct.  When one supply is overshooting while another is undershooting, the problem is multiplied, and you can end up frying something.  The Nano's regulator is a tiny one, not meant to provide a lot of current.  Doesn't take much to overstress it.

The USB protection diode was an poor attempt to allow powering the USB and either the Nano's on board regulator or an external 5V regulator (never both!).  A proper attempt would have had a protection diode on the Nano's regulator output, too. 

BTW, I do think it's reasonable for an external supply to provide its own protection, so I don't fault them for not adding an on-board protection diode to the Nano's external 5V supply connection.

Gordon,

If you are using the Raduino's 5V regulator to power the Nano, I would recommend putting a switch in the line so you can fully power the Nano via USB when attached to a computer.  Either that, or add diode protection between the Raduino's regulator and the Nano to provide extra protection.  Above all, put the extra filtering on the Raduino 5V supply that has been suggested in this forum before.

I personally don't recommend connecting 12V to the Nano's Vin supply.  For one thing, 12V at the extreme range of what the Nano's regulator can handle.  Exceeding 12V will damage the Nano's regulator.  I think the power filtering on the Nano is inadequate, and it's not easy to add filtering to that tiny board given that the Raduino PCB connects the pin to the Raduino's 5V supply.  If you do add 12V to the Nano's Vin supply, I recommend the following:

1) That you put a diode in the 12V supply line as mentioned earlier

2) That you add a 9V regulator with decent filtering between the 12V supply and the Nano Vin pin to avoid overstressing the Nano's regulator.  This is especially true if you plan to run with a 13.8V supply any time in the future...

3) That you put a switch in the line to the Nano's Vin so you can disconnect the Vin supply when programming. 

4) That you disconnect the Raduino's 5V supply to the Nano when powering the Nano via the Vin supply.  Either that, or add the diode protection to the 5V supply, but disconnecting it is safer.

73,
Carl  K0MWC

 

Re: ubitx circuit, wiring, source code on github

Henning Weddig
 

Jerry,

a similar situation will happen under "nromal conditions: the first mixer never is fully balanced resulting that receiving 12 MHz, tehre will be an attenuated 57 Mhz signal from the frist LO at the output of the first mixer besides the wanted  45 MHz... we will have a big spur at 12 MHz antenna signal?!


Am 07.12.2017 um 20:44 schrieb Jerry Gaffke via Groups.Io:

To scan the 12mhz filter passband, I'm thinking we drive CW-KEY high to unbalance the first mixer,
freeze clk1 at 57mhz, then scan clk2 and clk0 around 45mhz and 12mhz respectively,
monitoring the resultant audio beat note with scope or AC voltage meter.

Since the first mixer is unbalanced, anything on clk2 will continue on through to the second mixer
where it mixes with the 57mhz clk1 to create something near 12mhz. 
If clk0 varies from 12.000mhz down to 11.990mhz while clk2 varies from 45.000mhz to 45.010mhz, we should hear a constant
1khz audio tone that varies in intensity according to the 12mhz crystal filter's response to the 57mhz-clk2 frequency that
is passing through it.  This could be plotted on graph paper while reading the AC audio voltage and the frequency
of 57mhz-clk2 from the display, 

At any rate, nothing I am bringing up today should slow hfsigs down in building those rigs.
They will likely work fine as shipped, and all these minor adjustments will give the tinkerer's among us something to do.

Jerry, KE7ER


On Thu, Dec 7, 2017 at 10:09 am, Jerry Gaffke wrote:
An alternative would be to scan clk2 and clk0
through the crystal filter passband such that a constant frequency audio beat note is heard, and have the
user identify where the amplitude falls off at each edge of the 12mhz crystal filter passband.

Re: ubitx circuit, wiring, source code on github

Jerry Gaffke
 

Farhan,

You've actually done this stuff, and I'm just engaging in armchair punditry.
So take my suggestions with a grain of salt.

But I think the procedure I outlined should work well, no trouble with hearing a zerobeat right off
if the si5351 25hz reference crystal and the 12mhz crystals are all within 50ppm or so.
If crystal tolerances exceed that, we may need to go to a two step procedure.

And should work with any known signal source that is within the capabilities of the receiver, 0-30mhz.
I'll play with the code if and and when I get my hands on a ubitx, see if I'm right about that.
I'd much prefer to zerobeat a time standard such as WWV than some random ham's 7050khz signal.
If not a time standard, then perhaps one of those nasty 41m broadcast stations that others tell us
is accurately on frequency.  

It's not a disadvantage that all three clocks are locked to vcoa.
If we set the display to a known frequency then nudge vcoa around till the signal is correctly
received, the math is such that vcoa has exactly the frequency at which the vco is operating at.
And thus compensates for any error in the 25mhz reference crystal.
I'm assuming we call setfreq() for each of the three clocks each time we nudge vcoa.

One minor hack that might be fun to try on the Raduino:  
Measure the temperature around the si5351 and the 25mhz crystal using a Nano analog pin
and a diode junction.  Or perhaps a proper temperature sensor with i2c interface.  
Adjust vcoa as a function of the temperature we sense using a piecewise linear fit stored in flash
that characterizes how the measured frequency of the 25mhz reference changes with temperature.
A cheap way to give us a very stable TCXO.

Jerry, KE7ER
 


On Thu, Dec 7, 2017 at 12:15 pm, Ashhar Farhan wrote:
Earlier, the calibration routine put out a 10 MHz signal out the antenna (by unbalancing the diode mixer and setting the first oscillator to 10 MHz). I chucked it because it assumed that everybody had a dummy load or a 10 MHz antenna. 
 
On the other hand, it is easier for a ham to call up someone and ask them to call CQ on a particular frequency. The way the present calibration works is like this. I call up  friend to call CQ from his calibrated radio exactly at 7050 KHz. I set the dial to 7050 KHz, Then you switch on the calibration and tune until it goes dead zero beat.  If only life was that simple. 
 
First, the crystal filter has a steep skirt. We would ordinarily celebrate this. But in our case, that means, unless the signal is a 30 db over S9, you are not going to hear the zero beat, much less the swing to the other sideband.
 
Second issue with this is that as we recalibrate the VCO and reset the oscillators, the BFO too is corrected by an equal amount and the zero-beat will go away. To compensate for this, this is what I came up with, bear with me...
 
The VCO frequency is at 875 MHz. We generate any needed frequency by dividing the PLL by a fraction. So, to generate 1 Mhz, it is divided by 875. Now, suppose our reference that we are trying to align with is at 1 MHz, we need to nudge the 875 MHz VCO. If the VCO moves by 875 Hz, we can see the 1 MHz move by 1 Hz. To move the 1 MHz by 10 Hz at  time, we have to move the VCO by 8750 Hz at a time. Our BFO is at 12 MHz, if we push the VCO up or down by 875 Hz, the 12 Mhz will be  moved by 12 Hz. If we push the VCO around by 8750 Hz, the 12 Mhz BFO has to be corrected by 120 Hz. This is what the code does. 
 

Re: CAT control of the bitx frequency

RCBoatGuy
 

On Thu, Dec 7, 2017 at 06:23 am, Karl Heinz Kremer, K5KHK wrote:
Ashhar, here is information about how the Arduino's are getting reset by the serial port: https://playground.arduino.cc/Main/DisablingAutoResetOnSerialConnection

The DTR line is connected (via a capacitor) to the Arduino reset input (you an see this on the Nano schematic: https://www.arduino.cc/en/uploads/Main/ArduinoNano30Schematic.pdf). Based on the "Reset" information from above, you should be able to prevent this reset by adding a resistor between "Reset" and +5V - this will however also prevent the Arduino from being programmed automatically, and you will have to trigger a normal reset by pushing the reset button on the Nano board. 
Most of the "Disabling Auto Reset" discussion was related to Uno's.  If you look at the Nano schematic, you will see that there is already a 1K resistor between "Reset" and +5V (it's connected at the "Reset" pushbutton switch).

The DTR output of the USB chip connects to "Reset" thru C4.  Tombstoning C4 should disable the Auto Reset.  Adding an SPST switch between the now open C4 pad and the now unconnected terminal on the tombstoned C4 will allow you to get the Auto Reset back later if you want it.  Switch open - no AutoReset, switch closed - AutoReset enabled.

73,
Carl  K0MWC

Re: ubitx circuit, wiring, source code on github

Jerry Gaffke
 

I'm not quite sure what this means.
Is this only a problem when attempting to receive a 12.000 mhz signal?
I can see where receiving 12mhz may be problematic, though I don't plan to be operating there much.

Yes, there are all kinds of unwanted products from the mixers flying about, especially since we don't have any shielding.
I'm willing to live with a few birds given the likely price point and capabilities and hackability of this rig.
Should be a fun to try to figure out where they are coming from.

Jerry, KE7ER


On Thu, Dec 7, 2017 at 12:35 pm, Henning Weddig wrote:

a similar situation will happen under "nromal conditions: the first mixer never is fully balanced resulting that receiving 12 MHz, tehre will be an attenuated 57 Mhz signal from the frist LO at the output of the first mixer besides the wanted  45 MHz... we will have a big spur at 12 MHz antenna signal?!

BITX QSO Night, Sunday, December 10, 7pm Local Time, 7277 kHz in North America, 7177 kHz elsewhere

John P
 

BITX QSO Night, Sunday, December 10, 7pm Local Time, 7277 kHz in North America, 7177 kHz elsewhere

Join us as we make contacts from BITX40 to BITX40 on 7.277 MHz in 40 meters!

This is a worldwide event for BITX40 stations starting at 7pm in each time zone. To participate, call CQ BITX on Sunday, starting at 7pm your local time. The BITX QSO Night continues through the evening and conditions usually improve after sunset, so it is worthwhile to participate later in the evening.

Suggested Best Operating Practices:

Work at QRP power levels unless conditions require more power.
Call and listen for CQ BITX on the hour and every quarter hour.
It is helpful if you call CQ BITX with your callsign, name and location. 
Repeat your callsign a number of times during your CQ BITX and during QSO's.
Start a QSO by confirming the callsign, location, name and signal report of the other operator.
Say the callsign, name and location of the other operator so others can hear.
If the frequency is busy, avoid long conversations.
After your initial QSO is complete, ask if there are any other stations who would like to contact.

Report your QSO's, discuss propagation, noise, signal reports, audio reports, antenna type, etc. in this thread.

This is an undirected, scheduled event.  The BITX QSO Night relies on you to call CQ BITX to initiate contacts with other stations, so warm up that final and transmit a few calls on Sunday evening.  Talk to you then!
--
John - WA2FZW

Re: BITX QSO Night, Sunday, December 10, 7pm Local Time, 7277 kHz in North America, 7177 kHz elsewhere

John P
 

I'll try to be on again at 3PM EST (2000 UTC). Hopefully I won't fall asleep on the couch this week and actually make it on the air by 3! That worked out well last week!
--
John - WA2FZW

Re: ubitx circuit, wiring, source code on github

Jerry Gaffke
 

You may not hear the beat frequency right off if the 25mhz si5351 reference is off significantly,
since it is creating signals up to 45+30=75mhz.  And 100ppm at 75mhz is an error of 50*75=7500hz
But if you slew around the vcoa calibration factor enough, you should eventually hear the audio beat.

Even if the 12mhz crystals are off by 100ppm, creating a second IF that is 12*100=1200hz away from where we expect it.
Will likely be able to faintly hear zerobeat on the filter skirt even at that extreme. 
A slam dunk if the crystals are +/- 50ppm.
So should work as a single pass calibration procedure.

Jerry,  KE7ER

 

On Thu, Dec 7, 2017 at 12:49 pm, Jerry Gaffke wrote:
But I think the procedure I outlined should work well, no trouble with hearing a zerobeat right off
if the si5351 25hz reference crystal and the 12mhz crystals are all within 50ppm or so.
If crystal tolerances exceed that, we may need to go to a two step procedure.

Re: Any problem to have 2 sources powering the Raduino??

John Backo
 

That shouldn't be a problem, Gordon.

The real danger of 2 power sources, one of them USB,
is possibly allowing 12v into the USB port, and frying
your motherboard. Of course, that should not be allowed
for the ATMega chip either.

Be sure EVERY actual circuit you use has NO connection,
or possible connection to the USB port if it is over 5v.

There is no harm in sing any Arduino with 2 sources,
as all of them are adequately separated. However, sometimes
it will be noted that only the USB power should be attached for
programming purposes.

john
AD5YE

Re: ubitx circuit, wiring, source code on github

Gordon Gibby <ggibby@...>
 

​I've measured four Raduinos now and every one of them has been roughly 4 kHz ABOVE  25.000000   when commanded to go right to 25.0000000 MHz.   A few hundred hertz upper at times, but always about 4 kHz above 25.00000000


Gordon



From: BITX20@groups.io <BITX20@groups.io> on behalf of Jerry Gaffke via Groups.Io <jgaffke@...>
Sent: Thursday, December 7, 2017 4:54 PM
To: BITX20@groups.io
Subject: Re: [BITX20] ubitx circuit, wiring, source code on github
 
You may not hear the beat frequency right off if the 25mhz si5351 reference is off significantly,
since it is creating signals up to 45+30=75mhz.  And 100ppm at 75mhz is an error of 50*75=7500hz
But if you slew around the vcoa calibration factor enough, you should eventually hear the audio beat.

Even if the 12mhz crystals are off by 100ppm, creating a second IF that is 12*100=1200hz away from where we expect it.
Will likely be able to faintly hear zerobeat on the filter skirt even at that extreme. 
A slam dunk if the crystals are +/- 50ppm.
So should work as a single pass calibration procedure.

Jerry,  KE7ER

 
On Thu, Dec 7, 2017 at 12:49 pm, Jerry Gaffke wrote:
But I think the procedure I outlined should work well, no trouble with hearing a zerobeat right off
if the si5351 25hz reference crystal and the 12mhz crystals are all within 50ppm or so.
If crystal tolerances exceed that, we may need to go to a two step procedure.

Re: ubitx circuit, wiring, source code on github

Jerry Gaffke
 

Curious.
That's off by 1e6*(4khz/25mhz) = 160 parts per million.

The cheapest 25mhz crystal on Mouser is $0.10 in quantities of 1000.
Claims a tolerance of 30ppm, stability of 50ppm.
Perhaps the Si5351 is not configured for a load capacitance (an i2c register setting)
that matches the crystal used?

Jerry, KE7ER


On Thu, Dec 7, 2017 at 05:44 pm, Gordon Gibby wrote:

​I've measured four Raduinos now and every one of them has been roughly 4 kHz ABOVE  25.000000   when commanded to go right to 25.0000000 MHz.   A few hundred hertz upper at times, but always about 4 kHz above 25.00000000