Hi Daniel
Cbus/SPI is easy, you dont need a library BUT
- but... if you need to ask about "what is SPI/Cbus, do I need a lib ?"
then you do not, in my opinion, have enough experience to make this
radio work properly..... these are very basic things and skillsets you
MUST have.
I'll be honest , while I think your endeavours are great, I dont think
you have the skillsets to execute a PRODUCT, without a lot more rubber
on the road..... Certainly, this is a very good way to learn about the
technology, but if you are planning to build and sell a radio, or have a
radio club project, you need much much more understanding and experience
to be able to execute such an endeavour successfully. Please dont take
this the wrong way....Maybe I have misunderstood your intentions..
Get yourself the eval board, or get some chips and build your own... you
will need to learn everything and understand everything about each
building block. This probably means bulding and prototyping each block
of your radio one by one, and connecting it all together before even
thinking about integrating it into one housing....
There will be many issues for you to overcome that are not documented
anywhere.
What do I mean ?
>>>>>I mean that the datasheets for a chip (this CMX chip and others) ,
and the application notes only ever have about HALF of what you really
need to get the thing working. The other half is required to be learnt
by the designer ! this requires alot of work and intuition.
DC offsets are no issue....they are servoed out.
I am certainly happy to continue to answer questions adlib.
cheers
On 16/02/2015 1:28 PM, Daniel Mundall wrote:
Thanks, Glen.
I agree we want to keep things simple.
Since you've used this IC, maybe you could answer two of David's
concerns. Is C-Bus a problem to interface to, or is it just something
like SPI? Are there already lib's out there?
And also has DC offset been an issue with your devices?
Thanks,
Daniel
Daniel Mundall
On Sun, Feb 15, 2015 at 6:19 PM, glen english <g...@cortexrf.com.au
<mailto:g...@cortexrf.com.au>> wrote:
Daniel , External VCO might be 80 cents.. but then it is something
that has to be tracked in production.
Don't set lofty goals for your 1st version, just use the internal
VCO.
Don't promise too much..
Over deliver.
David's route is different and not comparable- you are talking
about a standalone receiver.
A crystal filter, for this application type and performance, in
my opinion, is to be avoided .
They are expensive, need specific tuning/ production checks to get
the shape right (otherwise you are wasting your time) .
There is a place for crystal filters in receivers , but I can't
think why it would be here.
glen
On 16/02/2015 1:08 PM, Daniel Mundall wrote:
Hello Glen,
Thanks so much for your email!
I've been wondering which way to go with that, how much cost do
you think an external VCO adds to the BOM?
The dev boards I ordered should be here soon and I'll have to
play around with that.
David on the other hand is playing with a much more simple
approach, if he can get it to work well, we may go that route. He
has a basic mixer and xtal filter and then dealing directly with IF.
Anyway thanks again for the warning.
Daniel
Daniel Mundall
On Sun, Feb 15, 2015 at 12:24 AM, glen english
<g...@cortexrf.com.au <mailto:g...@cortexrf.com.au>> wrote:
Hi Daniel
I think the CMX994 is a good choice for your radio, overall.
But don't
expect anything magnificent out of the receiver for 1st 2nd
and 3rd
adjacent channels though- this should be strictly assumed as
a portable
radio receiver, or 'average' mobile radio receiver.
The reason for this is that the internal VCO is rather noisy,
and as an
integer N loop with a small step size, you are limited to
quite narrow
PLL bandwidths. (<2 kHz) This has the effect of not
correcting for the
rather noisy VCO away from channel.
An external VCO would improve it, and external LO again
improve it.
BUT !
it is more than adequate for a basic receiver that can 'do
all' at a
good price.
You would not do better for the same cost.
I am using this chip on another project, but with an external
local
oscillator- a DDS . (Not a portable application) (and at a
higher cost)
footnote
The advantage of an integer-N PLL is that is is relatively
free of PLL
generated spurs, whereas a fractional N PLL can operates at loop
bandwidths, typically for this application , up to 100kHz,
which often
translates into a very good adjacent phase-noise performance-
at the
expense of many (calculable) spurs. The integer N PLL will
also often
have much lower power consumption.
regards
glen english VK1XX
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CORTEX RF
&
Pacific Media Technologies Pty Ltd
ABN 40 075 532 008
PO Box 5231 Lyneham ACT 2602, Australia.
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&
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ABN 40 075 532 008
PO Box 5231 Lyneham ACT 2602, Australia.
au mobile : +61 (0)418 975077
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