Hi Paul
thanks for the link
I read through it. I disagree with the author's conclusion, but I think
this is because we've got different expectations of performance.
reading through it.....as I thought, it is a piece of junk, at least for
a receiver LO. Phase noise is not up toe scratch >10kHz. spurs look more
like a transmitter gone wild....
it is a very nice part for a digital pcb with lots of clocks required,
nothng really critical- that is what it is designed for...
no free lunches here.
cheers
On 26/02/2015 2:42 PM, Paul Warren wrote:
Glen,
nt7s has done some characterisation of the si531, has lots of graphs
and things that I don't quite follow (yet!), look for: Si5351A
Investigations in your favourite search engine, or via:
http://nt7s.com/tag/si5351/
May turn your 'potentially awful' into 'actually awful' but I'll let
you comment :)
--
Paul
VK1ATP
On Thu, Feb 26, 2015 at 2:25 PM, glen english <[email protected]
<mailto:[email protected]>> wrote:
the VHF softrock is clever ...
Si5351 is potentially awful
Si570 is OK. a bit noisy around the carrier +/- 500Hz
ADF4351 is probably your best bet for an IF receiver/LO. only 10
bucks.
like the Si570, knows how to drink the juice from your battery....no
free lunch....
Image rejection in practice- using an LMS algorithm is 60-90dB.
but if you design your digital voice algorithm to not have any DC
component, then you can put it slap bang in the middle and quadrature
matching matters little.....20dB would be sufficient for the demod....
Of course if you want to go off channel one side and reject the other
side, 60-80dB is what you need. In practice, you need to work very
hard
on other approaches (IF filters etc) to do be that good anyway on
adjacent channels, so don't get too worried about it....
the good thing is...IF there is a problem adjacent channel that is
higher than the image rejection you have, you can always change
your LO
and move that adjacent somewhere else so the image products do not
affect you....problem solved.
All this makes the integration of the CMX994 a bargain....I understand
the want though to roll your own. I often have my commercial hat
on when
I am talking about hobby stuff and it gets in the way (it is a big
hat).
glen
On 26/02/2015 1:46 PM, David Rowe wrote:
> Hi Glen,
>
> Thanks you for those suggestion, the VHF soft rock is very neat
and the
> front end might be just what I need.
>
> I wonder the if the Si570 might be a better choice that the Si5351.
>
> OK so a softrock style IQ SDR stage gives us IF (in our case)
> selectivity. However what sort of image rejection is possible in
> practice? Given the phase and amplitude variations of two separate
> analog channels? For example can it achieve 90dB?
>
> Thanks,
>
> David
>
> On 26/02/15 12:26, glen english wrote:
>> David
>> take a look at the soft-rock designs for quadrature demods.
>>
>> these are pretty good performers......
>>
>> the VHF particularly
>> this is a CLEVER design and I have built half a dozen...
>>
>> http://www.wb5rvz.com/sdr/ensemble_rx_ii_vhf/
>>
>> and this one
>> http://fivedash.com/resource/RXEnsembleIISchematic.pdf
>>
>>
>>
>> On 26/02/2015 11:51 AM, David Rowe wrote:
>>> Hi Glen,
>>>
>>> 1/ What characteristics should I look for to determine if the
S/H is
>>> good (or bad)? Is there test I should try, like perhaps two
signals at
>>> once in the ADC passband?
>>>
>>> The S/H RC time constant has a 3dB point of 7MHz.
>>>
>>> I'm not expecting sparkling performance, but would like to
experiment a
>>> bit more to see if it's a usable as a platform for our VHF FreeDV
>>> experiments.
>>>
>>> 2/ Thanks you for the comments on the blog. yes I enjoy
explaining
>>> things, and the blog is an outlet for the teacher in me :-)
Learning
>>> and helping others understand is something about open source
that I like
>>> and appreciate.
>>>
>>> 3/ Thanks for the IF filter spec. Yep, was going to push for
60dB on
>>> the next pass. It's those +/- 1MHz points that are critical,
as they
>>> alias on top of my wanted signals. A few kHz either side and
the DSP
>>> will nail it. So its likely to have better +/- 5kHz than +/-
1 MHz
>>> performance. But I guess every rx has its weak spots where
images or
>>> some equivalent pop up.
>>>
>>> Is it possible to get an xtal filter that has 100kHz 3dB BW
(or whatever
>>> we need for 2 channel diversity) and is > 60dB down at +/- 1 MHz?
>>>
>>> The other option is a few more coupled LC sections, they seem
to offer
>>> about 20dB extra attn per section. Not sure if there is a
more elegant way.
>>>
>>> Cheers,
>>>
>>> David
>>>
>>> On 26/02/15 08:55, glen english wrote:
>>>> and..
>>>> Using the ADC in the STM32 undersampling at 10.5 meg signal
at 2 Msps.
>>>>
>>>> Are you sure the STM ADC sample and hold is actually any
good at 10 MHz ?
>>>>
>>>> 1st adjacent channel performance (signals that get through
the crystal
>>>> filter) will be problematic for the ADC because the SFDR / IMD
>>>> performance of the ADC where the S&H is poor will be rather
awful.
>>>>
>>>> Additionally, the stopbands of the first IF filter for a
cheap radio
>>>> have got to be at least 60dB down, otherwise strong off channel
>>>> frequencies will be aliased down into the baseband... A good
radio would
>>>> be 120dB.....
>>>>
>>>> keep learning ! Nice work so far.
>>>>
>>>> Nicely explained in your blog. you should have been a teacher.
>>>>
>>>>
>>>> cheers
>>>>
>>>>
>>>>
>>>> On 26/02/2015 9:08 AM, David Rowe wrote:
>>>>> Hi Helmut,
>>>>>
>>>>> Can you please tell me how you worked that out? My next
step is to add
>>>>> gain to balance MDS and IP3 but not sure how you obtained
those numbers!
>>>>>
>>>>> Yes the radio as it stands requires another design pass. At
this stage
>>>>> it is a "proof of concept" to test the novel features: such
as the use
>>>>> of a uC for most of the tuning, and extreme hardware simplicity.
>>>>>
>>>>> Thanks,
>>>>>
>>>>> David
>>>>>
>>>>> On 26/02/15 08:09, Helmut wrote:
>>>>>> Hello David,
>>>>>>
>>>>>> a rough simulation of that SDR design predicts a rather
deaf radio: Total
>>>>>> noise figure = 38 dB, MDS=-95dBm @ 12,5kHz System BW, Input
IP3 = -20 dBm.
>>>>>> I would suggest at least a 20 dB preamp with high IP3
performance in front
>>>>>> of the ADC. So you will achieve a MDS of -114 dBm. Sure no
splendid value,
>>>>>> but will detect some VHF signals, hi.
>>>>>>
>>>>>> 73, Helmut, DC6NY
>>>>>>
>>>>>> -----Ursprüngliche Nachricht-----
>>>>>> Von: David Rowe [mailto:[email protected]
<mailto:[email protected]>]
>>>>>> Gesendet: Dienstag, 24. Februar 2015 22:16
>>>>>> An: [email protected]
<mailto:[email protected]>;
[email protected] <mailto:[email protected]>
>>>>>> Betreff: [Freetel-codec2] Simple SDR for VHF FreeDV
>>>>>>
>>>>>> Hello,
>>>>>>
>>>>>> To support VHF FreeDV developments I've been working on a
really simple and
>>>>>> very open SDR architecture for VHF radio:
>>>>>>
>>>>>> http://www.rowetel.com/blog/?p=3884
>>>>>>
>>>>>> Glen and Matt - would appreciate you suggestions on
appropriate input BPF
>>>>>> filtering and a VHF mixer. Also pls let me know if you see
any show
>>>>>> stoppers in this architecture.
>>>>>>
>>>>>> Cheers,
>>>>>>
>>>>>> David
>>>>>>
>>>>>>
----------------------------------------------------------------------------
>>>>>> --
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--
-
Glen English
RF Communications and Electronics Engineer
CORTEX RF
&
Pacific Media Technologies Pty Ltd
ABN 40 075 532 008
PO Box 5231 Lyneham ACT 2602, Australia.
au mobile : +61 (0)418 975077
------------------------------------------------------------------------------
Dive into the World of Parallel Programming The Go Parallel
Website, sponsored
by Intel and developed in partnership with Slashdot Media, is your
hub for all
things parallel software development, from weekly thought
leadership blogs to
news, videos, case studies, tutorials and more. Take a look and
join the
conversation now. http://goparallel.sourceforge.net/
_______________________________________________
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--
Paul Warren
p dot a dot warren at gmail dot com
pwarren.id.au <http://pwarren.id.au>
------------------------------------------------------------------------------
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by Intel and developed in partnership with Slashdot Media, is your hub for all
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news, videos, case studies, tutorials and more. Take a look and join the
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_______________________________________________
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-
Glen English
RF Communications and Electronics Engineer
CORTEX RF
&
Pacific Media Technologies Pty Ltd
ABN 40 075 532 008
PO Box 5231 Lyneham ACT 2602, Australia.
au mobile : +61 (0)418 975077
------------------------------------------------------------------------------
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by Intel and developed in partnership with Slashdot Media, is your hub for all
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news, videos, case studies, tutorials and more. Take a look and join the
conversation now. http://goparallel.sourceforge.net/
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