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<div dir="ltr" data-setdir="false">Way overkill on the filtering, but as Hannibal Smith of the A Team says...</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">"Over Kill is under rated"<br></div><div><br></div><div dir="ltr" data-setdir="false">Not bad for $15.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">Kent<br></div><div><br></div><div><br></div>
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On Monday, November 2, 2020, 5:42:26 AM CST, Mike Seguin via Ground-Station <ground-station@lists.openresearch.institute> wrote:
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<div><div dir="ltr">I keep one of these around when I need something to plug in for a quick <br clear="none">test - even with it's limitations......<br clear="none"><br clear="none"><a shape="rect" href="https://www.rtl-sdr.com/rtl-sdr-com-broadcast-fm-band-stop-filter-88-108-mhz-reject-now-for-sale/" rel="nofollow" target="_blank">https://www.rtl-sdr.com/rtl-sdr-com-broadcast-fm-band-stop-filter-88-108-mhz-reject-now-for-sale/</a><br clear="none"><br clear="none">On 11/1/2020 9:55 PM, KENT BRITAIN via Ground-Station wrote:<br clear="none">> Even a simile series tuned circuit to ground tuned to about 100 MHz can <br clear="none">> take a lot of the energy<br clear="none">> out of the FM band. This is a big problem we have been seeing with <br clear="none">> indoor TV antennas.<br clear="none">> The switch to Digital greatly reduced the ERP limits from the FCC. To <br clear="none">> compensate most of the<br clear="none">> TV antenna companies increased the gain of their amps. Lots of IP3 <br clear="none">> problems from FM stations.<br clear="none">> <br clear="none">> A simple series .22uH 12 pf notch filter across the input of the amp <br clear="none">> does wonders.<br clear="none">> Not a brickwall filter, but does removes most of the FM Band energy from <br clear="none">> the amp input.<br clear="none">> <br clear="none">> Kent WA5VJB<br clear="none">> <br clear="none">> <br clear="none">> <br clear="none">> On Sunday, November 1, 2020, 8:19:23 PM CST, Robert McGwier <br clear="none">> <<a shape="rect" href="mailto:rwmcgwier@gmail.com" rel="nofollow" target="_blank">rwmcgwier@gmail.com</a>> wrote:<br clear="none">> <br clear="none">> <br clear="none">> It is a real shame we can't purchase high quality FM bandstop filters. I <br clear="none">> have purchased some I hoped would work and they attenuated the FM band <br clear="none">> and much more. Next, as you well know, lots of people pretend every <br clear="none">> piece of crap they hook to the antenna terminal is a 50 Ohm resistive <br clear="none">> load at all frequencies from DC to light and doesn't crash the front end <br clear="none">> filtering etc with their decidedly not 50 Ohm resistive loads.<br clear="none">> <br clear="none">> Cheers,<br clear="none">> Bob<br clear="none">> <br clear="none">> <br clear="none">> On Sun, Nov 1, 2020, 10:42 AM KENT BRITAIN <<a shape="rect" href="mailto:wa5vjb@flash.net" rel="nofollow" target="_blank">wa5vjb@flash.net</a> <br clear="none">> <mailto:<a shape="rect" href="mailto:wa5vjb@flash.net" rel="nofollow" target="_blank">wa5vjb@flash.net</a>>> wrote:<br clear="none">> <br clear="none">> Hi Bob<br clear="none">> <br clear="none">> I covered this topic at my Def Con talk on the Care and Feeding of<br clear="none">> SDR's.<br clear="none">> <br clear="none">> A bit harder to get these days, but Radio Shack and several others<br clear="none">> sell an<br clear="none">> FM Band Notch filter In with the rest of the TV accessories. <br clear="none">> Very little<br clear="none">> loss outside 80-120 MHz.<br clear="none">> <br clear="none">> These days if you put up a broad band antenna in a urban area, about<br clear="none">> 2/3rds of the RF energy it picks up will be in the FM Broadcast band.<br clear="none">> (Quite a bit of local variation in that 2/3rd's)<br clear="none">> <br clear="none">> Amazing how many guys though they could eliminate the FM band overload<br clear="none">> but just telling the SDR to ignore 88-108 MHz in the software.<br clear="none">> <br clear="none">> 73 Kent WA5VJB<br clear="none">> <br clear="none">> <br clear="none">> <br clear="none">> On Sunday, November 1, 2020, 10:20:36 AM CST, Robert McGwier via<br clear="none">> Ground-Station <<a shape="rect" href="mailto:ground-station@lists.openresearch.institute" rel="nofollow" target="_blank">ground-station@lists.openresearch.institute</a>> wrote:<br clear="none">> <br clear="none">> <br clear="none">> A single strong FM transmitter anywhere near will collapse the front<br clear="none">> end. A FM bandstop filter also degrades 2 meter low end and has<br clear="none">> insertion loss that harms the sensitivity further.<br clear="none">> <br clear="none">> RTLSDR is great but you get what you pay for<br clear="none">> <br clear="none">> Bob<br clear="none">> <br clear="none">> <br clear="none">> On Sat, Oct 31, 2020, 2:10 PM Phil Karn via Ground-Station<br clear="none">> <<a shape="rect" href="mailto:ground-station@lists.openresearch.institute" rel="nofollow" target="_blank">ground-station@lists.openresearch.institute</a>> wrote:<br clear="none">> <br clear="none">> <br clear="none">> On 10/31/20 11:10 AM, Douglas Quagliana wrote:<br clear="none">> > Hi Phil,<br clear="none">> > Please let me know when the code is available. I would<br clear="none">> like to try<br clear="none">> > getting it to run off an RTLSDR dongle and try to have it<br clear="none">> identify the<br clear="none">> > callsigns of the repeaters that it receives.<br clear="none">> > 73,<br clear="none">> > Douglas KA2UPW/5<br clear="none">> ><br clear="none">> In principle I could use the RTL-SDR, but I haven't actually used it<br clear="none">> myself yet. It has a rather low dynamic range, so strong local<br clear="none">> repeaters<br clear="none">> could blank weaker signals on other channels within its bandwidth.<br clear="none">> Getting the most out it will probably require a lot of work on a<br clear="none">> good AGC.<br clear="none">> <br clear="none">> My favorite SDR used to be the AMSAT-UK Funcube dongle, but it has a<br clear="none">> very limited bandwidth (192 kHz). I'm now using the Airspy R2,<br clear="none">> which has<br clear="none">> a 10 MHz bandwidth and 12-bit sampling. This is enough to easily<br clear="none">> cover<br clear="none">> the entire 2m band. It can cover most of the 440-450 segment,<br clear="none">> but the<br clear="none">> actual coverage of SDR is a little less than 10 MHz because of<br clear="none">> anti-alias filtering ahead of the A/D. But it can easily cover<br clear="none">> the 5 MHz<br clear="none">> half of whatever segment used in your local area for repeater<br clear="none">> outputs<br clear="none">> (i.e., either 440-445 or 445-450).<div class="ydp1deea54fyqt4735362829" id="ydp1deea54fyqtfd56829"><br clear="none">> <br clear="none">> Phil<br clear="none">> <br clear="none">> <br clear="none"><br clear="none">-- <br clear="none"><br clear="none">73,</div><br clear="none">Mike, N1JEZ<br clear="none">"A closed mouth gathers no feet"<div class="ydp1deea54fyqt4735362829" id="ydp1deea54fyqtfd03159"><br clear="none"></div></div></div>
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