EMRFD Message Archive 10333

Message Date From Subject
10333 2014-10-03 15:45:51 Chris Howard w0ep from I to I/Q
Hi,

Instead of working on the projects I already have, today
I am thinking about something else.

I was wondering about making I/Q from a cheap DDS based on
the AD9850 module I got from ebay.

I understand one can use a pair of D-flip flops to make
I/Q but it is divide by four of the original frequency.

I did a search and TI makes this thing which says it
is a SN65LVDS150 MuxIt PLL Frequency Multiplier.
Mouser sells them for about $12. The datasheet says
it will do programmed multiples from 4x to 40x using
input between 5 and 50 MHz.

I'm thinking I could turn my cheap 1-15 MHz DDS into an
I/Q DDS that would cover multiple ranges.

Any experience with this multiplier thing?

Chris
w0ep

(Still working on the VHF antenna idea.. will let you know
if I get some progress there.)
10334 2014-10-03 16:01:15 Dave Re: from I to I/Q
Chris:
  It's possible to create I/Q by  using an exclusive OR gate to produce 2 outputs 180 degrees apart and feeding them to a pair of  flip-flops.  You could also use a line receiver in stead of the exclusive OR..  This only requires a divide by 2 frequency.  I do this on my 995X board.

Dave - WB6DHW


10335 2014-10-03 18:33:07 Will Re: from I to I/Q
Hi Chris,

Why not buy another cheap module, take the oscillator can off it. Then
link the modules together and common the oscillator.

Program them with one leading/lagging by 90 degrees.
That is my intention - when time allows.

Will
ZL1TAO

10336 2014-10-03 18:34:17 DuWayne KV4QB Re: from I to I/Q
I have seen an older design using  a ICS511M LOCO PLL CLOCK MULTIPLIER.
The App note on  the 9850 shows using 2 configured to run on the same frequency with a phase shift.
If you do a search on ad9850 phase shift there are several examples of this

73  DuWayne   KV4QB

 


Hi,

Instead of working on the projects I already have, today
I am thinking about something else.

I was wondering about making I/Q from a cheap DDS based on
the AD9850 module I got from ebay.

I understand one can use a pair of D-flip flops to make
I/Q but it is divide by four of the original frequency.

I did a search and TI makes this thing which says it
is a SN65LVDS150 MuxIt PLL Frequency Multiplier.
Mouser sells them for about $12. The datasheet says
it will do programmed multiples from 4x to 40x using
input between 5 and 50 MHz.

I'm thinking I could turn my cheap 1-15 MHz DDS into an
I/Q DDS that would cover multiple ranges.

Any experience with this multiplier thing?

Chris
w0ep

(Still working on the VHF antenna idea.. will let you know
if I get some progress there.)


--  Of all the things I lost, I miss my mind the most.
10337 2014-10-03 21:58:59 farhanbox@gmail.c... Re: from I to I/Q

the ad9850 has terrible phase noise. that would itself be the limiting factor of your radio. the jitter of the digital phase generator wouldnt be as much a factor. 

i would recommend Si5351.it is inexpensive at 2 dollars a pop. the specs look impressive.

- f

------ Original message------

10338 2014-10-04 01:29:48 Dennis Anderson Re: from I to I/Q
Hi Chris

Look at Paul M0XPD's Blog, I think he may answer some of the questions your asking


Regards

Dennis G6YBC


10339 2014-10-05 09:37:26 kb1gmx Re: from I to I/Q
I've played with the 9850 DDS and the phase noise is not bad...  Assuming the phase 
noise of the reference is also good.  This is not always true.  With a good reference 
source they are ok for phase noise but the SFDR is still limited.

Its limitation is SFDR (spurious free dynamic range) is limited partly due to the low clock 
frequency and the 10bit (memory test) DAC inside.  For its capabilities its a fair part.

I would not multiply its output.  That degrades all parameters by the multipication factor.
So things like drift, phase noise and spurs tend to get a bit worse.

For an IQ radio I'd use a Si570 or a later Analog Devices part (some even supply I and Q
directly).  Its phase noise (jitter) is fairly low and its easily divided by 4 to get I/Q signals.


Allison