Hello Glen,
Thanks for your thoughtful email, and I totally agree, I'm probably not
experienced enough to make a radio yet.
But I am familiar with SPI and have used it on other projects FlexScada. (
http://flexscada.com/)
As for the C-Bus, no where could I find it mentioned that it was SPI, but
by the looks of it it seemed to be, which was why I was asking about it.
And as you suggested, I am starting with the dev boards connected to some
STM32's once that's all working maybe move to a single PCB.
Anyway, I appreciate your patience and time answering my questions.
Daniel VA7DRM
PS. I've been doing over the air testing with David's Octave GMSK modem,
we're having some fun with multipath now. :) Nothing that can't be fixed,
but it's helping us prefect the demod. Multipath fades driving seem to be
anywhere from 5-20Hz. Interesting how on the fringe the fading is much less
(I assume that when the path losses are higher there are just less paths
even making it to the RX.)
Daniel Mundall
On Sun, Feb 15, 2015 at 7:09 PM, glen english <g...@cortexrf.com.au> wrote:
> 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>
> 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>
>> 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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>>
>>
>>
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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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>
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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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