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Re: Si570 Set Frequency

Alfredo Mendiola Loyola
 

I got it.
Thank you for your help.
Alfredo Mendiola Loyola

On Wednesday, April 17, 2019, 2:31:00 PM GMT-5, Ambro_IW2FVO via Groups.Io <iw2fvo=yahoo.com@groups.io> wrote:

IF_offset is simply the value of the Intermediate frequency ( IF ) of your receiver .
If you want to receive 432.000 MHz and your receiver IF is 21.4 MHz then your SI570 shall output 432.000 MHz - 21.4 MHz for low side injection
or it shall output 432.000 MHz+ 21.4 MHz if you use the top side injection.
If you set the IFO_FRQ=0 in the code then the SI570 will output the frequency value received through the serial link ( from the IDE monitor ) without any offset.
73, iw2fvo

Re: Si570 Set Frequency

Alfredo Mendiola Loyola
 

Ambrogio,

What is the purpose of these variables:

#define MIN_FRQ_DCO 4850000000ULL // = 4850MHz
#define MAX_FRQ_DCO 5670000000ULL // = 5670MHz

They are used in the method CalcRFREQ()

Can I remove those variables from the logic of the code?

Thank you.

73
Alfredo Mendiola
OA4AJP

Re: Si570 Set Frequency

Ambro IW2FVO
 

Alfredo,
the DCO must stay in the frequency range provided in the si570 specification....
NO, you should not remove the limits from the code.
regards,
Ambrogio

Re: Si570 Set Frequency

Bob V
 

Hi Alfredo -

First off, let me admit to zero knowledge about the Si570.

I think it unlikely that the device could get anywhere near to 4850MHz
(=4.85 GHz). I suspect that is a typo.

I do note from https://ko7m.blogspot.com/2014/04/si570-programming.html
<https://ko7m.blogspot.com/2014/04/si570-programming.html>that the start up
frequency of the device is 56.320MHz, roughly a factor of ten off of this
number.

I suspect these numbers are critical but should really be 45500KHz to
56700KHz. Those would realistically reflect the frequency range of the
DCO.

73
Bob
WA2I

Re: Si570 Set Frequency

Jim Smith
 

Hi Bob/Alfredo,

Further down the KO7M link you provided he states:

"The internal DCO is constrained to 4.85 to 5.67 GHz determined by the internal crystal frequency multiplied by a reference frequency."

So not a typo, and not to be ignored.

73

Jim - G3ZQC

Re: Si570 Set Frequency

Ambro IW2FVO
 

I do suggest to read this document:
https://www.silabs.com/documents/public/data-sheets/si570.pdf
at page 14 figure 3.
I confirm that there is no errors:> the DRO must stay in the 4.8 GHZ to 5.6 Ghz frequency range.
As i told before the sketch is loaded on Arduino Nano and it is working as a VFO for my Two Meters FM receiver and for the APT ( around 137 MHz ) receiver.
The tuning information is provided to the Arduino Nano through a serial link : >> you could use the Arduino IDE Monitor to set the desired frequency.
I do really suggest to load the sketch as is, >> run it >> and then introduce the modification you need.
73, iw2fvo
ciao.

Re: Si570 Set Frequency

Ambro IW2FVO
 

for a better explanation have a look at this part of the code:

//--- First checks for N1=1 and HS_DIV between 4 & 11

i=1;

for (j = 0; j <= 5; j++)

{ f_dco = (uint64_t)Fout * (uint64_t)HS_Div_Vect[j];

if ( (f_dco >= MIN_FRQ_DCO) && (f_dco <= MAX_FRQ_DCO) )

{ found = TRUE;

N1 = 1;

HS_Div = HS_Div_Vect[j];

HS_Div_Reg = HS_Div-4; //the value to write in Si570reg must be subtracted by 4

break;

}

}
I do attach a spread sheet (if could be useful) .
73, iw2fvo, Ambrogio
North Italy

Re: Si570 Set Frequency

Ambro IW2FVO
 

Alfredo,
I do remember you that the sketch does not use any pre_computed value to generate any output frequency.
Just plug your Arduino to the Arduino IDE Monitor and command the frequency you want to have !
Of course your SI570 "type number" has to be able to generate it: >> look at the max frequency limit of your 570 .
You could have it by looking at the full part number printed on the chip.
73, iw2fvo
Ambrogio
North Italy

Re: Si570 Set Frequency

Alfredo Mendiola Loyola
 

On Fri, Apr 19, 2019 at 04:27 AM, Ambro IW2FVO wrote:


Ambrogio
Ambrogio,

I found the information about the DCO frequency range in the si570 Datasheet.
I understand how it works.

I created a repository with the Version 5 of the software at: https://github.com/oa4ajp/Si570_v5

Thank for your helps.
Alfredo
OA4AJP

Si570 LVDS Output Impedance

Alfredo Mendiola Loyola
 

Hello,

If I connect a Center Tap of an 1:4 Transformer (Secondary) to the LVDS outputs I will get a 50 Ohm output impedance on the Primary?

Schematic:
https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxhZTVwaHJhZGlvbm90ZWJvb2t8Z3g6NjA1OGNmZjAxNjQ5ZDhmNQ

I understand that the output impedance of each output of the si570 is 100 Ohm (LVDS), When I connect each output of the si570 to the transformer Secondary I will get 200 ohm and 50 ohm on the Primary (200 4 = 50 ohm).

Do I have to connect the center tap of the secondary to ground?

Transformer Datasheet:
https://www.coilcraft.com/pdfs/pwb.pdf
Model: PWB-4-BL

73
Alfredo Mendiola
OA4AJP

Re: Si570 LVDS Output Impedance

Clifford Heath
 

Check that you get the right impedance ratio - remember that it is the
square of the turns ratio.

I haven't checked the data sheet to see if the Si570 output is DC (ground)
referenced. If not, I would decouple the CT to ground with a capacitor
anyway. But check the data sheet.

Clifford Heath

On Mon, 22 Apr 2019, 02:29 Alfredo Mendiola Loyola via Groups.Io
<mendiola_loyola=yahoo.com@groups.io> wrote:

Hello,

If I connect a Center Tap of an 1:4 Transformer (Secondary) to the LVDS
outputs I will get a 50 Ohm output impedance on the Primary?

Schematic:

https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxhZTVwaHJhZGlvbm90ZWJvb2t8Z3g6NjA1OGNmZjAxNjQ5ZDhmNQ

I understand that the output impedance of each output of the si570 is 100
Ohm (LVDS), When I connect each output of the si570 to the transformer
Secondary I will get 200 ohm and 50 ohm on the Primary (200 4 = 50 ohm).

Do I have to connect the center tap of the secondary to ground?

Transformer Datasheet:
https://www.coilcraft.com/pdfs/pwb.pdf
Model: PWB-4-BL

73
Alfredo Mendiola
OA4AJP



Re: Si570 LVDS Output Impedance

Clifford Heath
 

The Si570 data sheet says: "Available LVPECL, CMOS, LVDS, and CML outputs".
So the correct output coupling depends on which one you use.

LVPECL (fastest) requires 50 ohms termination to Vdd-2.0V.
LVDS and CML require 100 ohm differential (not supply-referenced).
CMOS swings within about 0.4V of the rails.

Clifford Heath.

On 22 Apr 2019, at 12:39 pm, Clifford Heath via Groups.Io <clifford.heath=gmail.com@groups.io> wrote:

Check that you get the right impedance ratio - remember that it is the
square of the turns ratio.

I haven't checked the data sheet to see if the Si570 output is DC (ground)
referenced. If not, I would decouple the CT to ground with a capacitor
anyway. But check the data sheet.

Clifford Heath

On Mon, 22 Apr 2019, 02:29 Alfredo Mendiola Loyola via Groups.Io
<mendiola_loyola=yahoo.com@groups.io> wrote:

Hello,

If I connect a Center Tap of an 1:4 Transformer (Secondary) to the LVDS
outputs I will get a 50 Ohm output impedance on the Primary?

Schematic:

https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxhZTVwaHJhZGlvbm90ZWJvb2t8Z3g6NjA1OGNmZjAxNjQ5ZDhmNQ

I understand that the output impedance of each output of the si570 is 100
Ohm (LVDS), When I connect each output of the si570 to the transformer
Secondary I will get 200 ohm and 50 ohm on the Primary (200 4 = 50 ohm).

Do I have to connect the center tap of the secondary to ground?

Transformer Datasheet:
https://www.coilcraft.com/pdfs/pwb.pdf
Model: PWB-4-BL

73
Alfredo Mendiola
OA4AJP



Re: Si570 LVDS Output Impedance

Ambro IW2FVO
 

please see this document :>

https://www.sdr-kits.net/documents/PA0KLT_Manual.pdf

and look at fig. 7 on page 13/21 for impedance / transformer connections.

I am using the Si570 as a VFO for my airband AM receiver too with good results. I did try it last week !
Used also for : Two meters FM receiver and for APT (137 MHz ) 40 KHz IF FM receiver.
all the best !
73, iw2fvo
Ambrogio

Re: Si570 LVDS Output Impedance

Alfredo Mendiola Loyola
 

Hello:

My goal is to get a single channel output with exactly 50 ohms impedace.

By using a transformer 1:4 if the outputs of the si570 doesn't have exactly 50 ohm I will get at the output of the transformer an impedace higher or lower than 50 ohm.

I'm working with UHF sgnales 430 mhz.

73
Alfredo.
OA4AJP

Re: Si570 LVDS Output Impedance

Nick Kennedy
 

For that purpose, I'd try to assure 50 ohms by following the output with an
attenuator. I wouldn't assume a specific source resistance internal to the
Si570.

Another issue if you're trying to use the si570 in a signal generator type
of application is that the Si570 has a square wave output. However, if as
you say you are interested in a single channel use, you can LPF that signal
into a sine wave.

73-

Nick, WA5BDU


On Mon, Apr 22, 2019 at 6:28 AM Alfredo Mendiola Loyola via Groups.Io
<mendiola_loyola=yahoo.com@groups.io> wrote:

Hello:

My goal is to get a single channel output with exactly 50 ohms impedace.

By using a transformer 1:4 if the outputs of the si570 doesn't have
exactly 50 ohm I will get at the output of the transformer an impedace
higher or lower than 50 ohm.

I'm working with UHF sgnales 430 mhz.

73
Alfredo.
OA4AJP



Re: Si570 LVDS Output Impedance

Alfredo Mendiola Loyola
 

Hello,

I will use a 1:4 transformer with center tap to connect the output of the si570 (LVDS).
The secondary of the transformer (Center Tap) will be connected to the differential outputs of the si570
The primary of the transformer will be connected to a 3dB PI attenuator to get 50 ohm at the input and output of the attenuator.

The si570 datasheet states that the LVDS model has an output of 0.7 vpp {swing (diff)}

If I use a 1:4 transformer (Coilcraft PWB-4-BL) what will be the output peak to peak voltage at the transformer Primary?

73.
Alfredo Mendiola Loyola
OA4AJP

Re: Si570 LVDS Output Impedance

Clifford Heath
 

On 23 Apr 2019, at 11:12 am, Alfredo Mendiola Loyola via Groups.Io <mendiola_loyola=yahoo.com@groups.io> wrote:
I will use a 1:4 transformer with center tap to connect the output of the si570 (LVDS).
The secondary of the transformer (Center Tap) will be connected to the differential outputs of the si570
The primary of the transformer will be connected to a 3dB PI attenuator to get 50 ohm at the input and output of the attenuator.

The si570 datasheet states that the LVDS model has an output of 0.7 vpp {swing (diff)}

If I use a 1:4 transformer (Coilcraft PWB-4-BL) what will be the output peak to peak voltage at the transformer Primary?
1:4 impedance is 1:2 voltage ratio. 0.7Vp-p would reduce by 2:1 to 0.35Vp-p, which is 0.12Vrms.
Into 50 ohms that's about -5dBm.

Clifford Heath.

New to group

David Slipper <softfoot@...>
 

Hello all.

I am very interested in this project.

Dave

What is the difference between a DDS Type 1 and Type 2 ??

David Slipper <softfoot@...>
 

Are they different modules or chips ??

Rgds
Dave

Re: What is the difference between a DDS Type 1 and Type 2 ??

K5ESS
 

Dave,
They are different modules. Either might have either AD9850 or AD9851 DDS chips. See the attached file. The file also shows an adapter board that can be used when needed. The modules are becoming rather expensive particularly the Type I (three rows of seven pins).
Mike
K5ESS

-----Original Message-----
From: PHSNA@groups.io [mailto:PHSNA@groups.io] On Behalf Of David Slipper
Sent: Friday, April 26, 2019 12:09 PM
To: PHSNA@groups.io
Subject: [PHSNA] What is the difference between a DDS Type 1 and Type 2 ??


Are they different modules or chips ??

Rgds
Dave