Daniel, the easiest way to deal with the real world on a low power small
chipset radio is to put a whoppign filter in front of the receiver. The
mini chipsets will rarely have decent strong signal performance
For a narrow range like 144-148, this is not hard
In a commercial grade radio, this problem is more difficult.
Something like this from Temwell will do the job .
http://www.temwell.com.tw/
type :
TT67709B-146M USD$18 in singles and only 22mm x 7mm x12mm tall.
you really need the 3 pot, not the two pot filters.
However, it will still suffer from 3rd order IMD in band, and adjacent
until the filter has about 20dB in the way....so nasties plus or - 5-10 MHz.
there is no free lunch.....and a digital radio it is MUCH more critical
because unlike an analog system you can't hear when you cope
interference, the signal just drops out. (another advantage of
frequency diversity)
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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look and join the conversation now. http://goparallel.sourceforge.net/
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