Glen,
Wow fantastic! Thanks so much for the info.
The thought of the LNA was to reduce the NF, but that doesn't sound like a
good idea. The noise figure of the receiver the way they have it setup is
4.5db.
The saw filter, can be positioned after the first internal LNA to help
reduce the NF. In any case it needs an LNA before the saw filter as the
loss is pretty high. I'm not bias to SAW filters, I'm actually very open to
any option as far as filtering goes. But there don't seem to be very many
low cost options out there. You seem to like the Helical filters, would you
recommend them over saw filters? Also any recommendation for a LPF? We're
going to have a TX power of around 30dbm.
Our current BOM is like $35, and $20 would be a pretty big chunk, are there
any lower cost options that would still work well? We're aiming to get this
out there for less than $150 all things included, hopefully for more like
$100.
I'm thinking for just getting version 1 on the road to go just single band,
but if there's some way that's not too complex, dual band would always be
nice.
Thanks both of you for the warning about harmonics, have to make sure
they're not too high. I'm thinking that a good LPF should for the most part
minimize this problem?
Thanks again for your input.
Daniel Mundall
On Sun, Feb 8, 2015 at 5:05 PM, glen english <g...@cortexrf.com.au> wrote:
> Daniel
>
> I've had a look at your block diagram, and I read the data sheets - That
> CMX994 is probably good enough without any sort of aggressive filtering.
> 3rd order input intercept of around -3dBm is very reasonable. You just
> need to keep out the FM stations...and pagers.
>
> BUT - the chip does really not need that extra LNA.
>
> That LNA you have ahead of the SAW filter could spell trouble for in band
> intermods (that is , strong signals that are in the SAW filter passband)...
> (unless the SAW has alot of loss)
>
> A TX low pass filter is not shown- I assume that is in there - all
> harmonics need to be below -30dBm , (preferably -36dBm if it is going to
> connect to a vehicle antenna and run more than 5W)
>
> You'll likely need TWO separate low pass filters for 2m/70cm operation.
>
> g
>
> On 9/02/2015 8:51 AM, Daniel Mundall wrote:
>
> Hello Glen and Matt,
>
> I've been going back and forth with David here about a very low cost SDR
> for 2M/70cm and a few concerns have come up. The main one has been dealing
> with strong interferers at a very near by frequency.
> Do you guys have any suggestions to to help mitigate receiver
> overload/desensitization?
> I've attached a block diagram of the radio we're working on.
> Here's a link for the datasheet of the RX IC we're using:
> http://www.cmlmicro.com/DesignSupport/resources/2012/11/23/CMX994-Datasheet
>
> What sort of specs should we aim for to have good strong signal
> performance?
> Any suggestions will be greatly appreciated!
>
> Daniel Mundall VA7DRM
>
>
>
> ------------------------------------------------------------------------------
> 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/
>
>
>
> _______________________________________________
> Freetel-codec2 mailing
> listFreetel-codec2@lists.sourceforge.nethttps://lists.sourceforge.net/lists/listinfo/freetel-codec2
>
>
> --
> -
> 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/
> _______________________________________________
> Freetel-codec2 mailing list
> Freetel-codec2@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/freetel-codec2
>
>
------------------------------------------------------------------------------
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/
_______________________________________________
Freetel-codec2 mailing list
Freetel-codec2@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/freetel-codec2
