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
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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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