[Ground-station] channelized FM SDR

[KENT BRITAIN]

 Hi Bob
I covered this topic at my Def Con talk on the Care and Feeding of SDR's.
A bit harder to get these days, but Radio Shack and several others sell anFM Band Notch filter   In with the rest of the TV accessories.   Very littleloss outside 80-120 MHz.
These days if you put up a broad band antenna in a urban area, about2/3rds of the RF energy it picks up will be in the FM Broadcast band.(Quite a bit of local variation in that 2/3rd's)
Amazing how many guys though they could eliminate the FM band overloadbut just telling the SDR to ignore 88-108 MHz in the software.
73 Kent WA5VJB



    On Sunday, November 1, 2020, 10:20:36 AM CST, Robert McGwier via Ground-Station <ground-station at lists.openresearch.institute> wrote:  
 
 A single strong FM transmitter anywhere near will collapse the front end.  A FM bandstop filter also degrades 2 meter low end and has insertion loss that harms the sensitivity further. 
RTLSDR is great but you get what you pay for 
Bob

On Sat, Oct 31, 2020, 2:10 PM Phil Karn via Ground-Station <ground-station at lists.openresearch.institute> wrote:


On 10/31/20 11:10 AM, Douglas Quagliana wrote:
> Hi Phil,
>    Please let me know when the code is available. I would like to try
> getting it to run off an RTLSDR dongle and try to have it identify the
> callsigns of the repeaters that it receives. 
> 73,
> Douglas KA2UPW/5
>
In principle I could use the RTL-SDR, but I haven't actually used it
myself yet. It has a rather low dynamic range, so strong local repeaters
could blank weaker signals on other channels within its bandwidth.
Getting the most out it will probably require a lot of work on a good AGC.

My favorite SDR used to be the AMSAT-UK Funcube dongle, but it has a
very limited bandwidth (192 kHz). I'm now using the Airspy R2, which has
a 10 MHz bandwidth and 12-bit sampling. This is enough to easily cover
the entire 2m band. It can cover most of the 440-450 segment, but the
actual coverage of SDR is a little less than 10 MHz because of
anti-alias filtering ahead of the A/D. But it can easily cover the 5 MHz
half of whatever segment used in your local area for repeater outputs
(i.e., either 440-445 or 445-450).

Phil



  
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