[Ground-station] channelized FM SDR

[Mike Seguin]

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"