[Ground-station] channelized FM SDR

[KENT BRITAIN]

 Way overkill on the filtering, but as Hannibal Smith of the A Team says...
"Over Kill is under rated"

Not bad for $15.
Kent


    On Monday, November 2, 2020, 5:42:26 AM CST, Mike Seguin via Ground-Station <ground-station at lists.openresearch.institute> wrote:  
 
 I keep one of these around when I need something to plug in for a quick 
test - even with it's limitations......

https://www.rtl-sdr.com/rtl-sdr-com-broadcast-fm-band-stop-filter-88-108-mhz-reject-now-for-sale/

On 11/1/2020 9:55 PM, KENT BRITAIN via Ground-Station wrote:
> Even a simile series tuned circuit to ground tuned to about 100 MHz can 
> take a lot of the energy
> out of the FM band.   This is a big problem we have been seeing with 
> indoor TV antennas.
> The switch to Digital greatly reduced the ERP limits from the FCC.   To 
> compensate most of the
> TV antenna companies increased the gain of their amps.  Lots of IP3 
> problems from FM stations.
> 
> A simple series  .22uH 12 pf notch filter across the input of the amp 
> does wonders.
> Not a brickwall filter, but does removes most of the FM Band energy from 
> the amp input.
> 
> Kent WA5VJB
> 
> 
> 
> On Sunday, November 1, 2020, 8:19:23 PM CST, Robert McGwier 
> <rwmcgwier at gmail.com> wrote:
> 
> 
> It is a real shame we can't purchase high quality FM bandstop filters. I 
> have purchased some I hoped would work and they attenuated the FM band 
> and much more. Next, as you well know, lots of people pretend every 
> piece of crap they hook to the antenna terminal is a 50 Ohm resistive 
> load at all frequencies from DC to light and doesn't crash the front end 
> filtering etc with their decidedly not 50 Ohm resistive loads.
> 
>   Cheers,
> Bob
> 
> 
> On Sun, Nov 1, 2020, 10:42 AM KENT BRITAIN <wa5vjb at flash.net 
> <mailto:wa5vjb at flash.net>> wrote:
> 
>    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 an
>    FM Band Notch filter   In with the rest of the TV accessories.  
>    Very little
>    loss outside 80-120 MHz.
> 
>    These days if you put up a broad band antenna in a urban area, about
>    2/3rds 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 overload
>    but 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
> 
> 

-- 

73,
Mike, N1JEZ
"A closed mouth gathers no feet"
  
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