[amsat-bb] Using DCI filters narrowband vs broadband

[Andrew Rich]

I get pagers on 148 making birdies on an RTL-SDR on 144 MHz

Hoping the funcube will be better

A


> On 15 Aug 2017, at 2:45 am, Robert Bruninga <bruninga at usna.edu> wrote:
> 
> Many people on AMSAT use DCI brand passband filters at their antennas to
> cut down on front end overload and splatter from other services.    These
> multi-resonator filters typically cover several MHz of bandwidth to cover
> entire sections of the Amateur Bands and block things out of band..
> 
> 
> 
> When I asked if they could be tuned narrower with all resonators favoring
> the same single frequency, their answer kept coming back YES, the bandwidth
> is 500 kHz.  But they did not define what the “bandwidth” meant.
> 
> 
> 
> Today, they sent me a revised spec sheet for their two meter filter when
> tuned to a single frequency.  Now they fully specify what the bandwidth
> is.  Here are the numbers:
> 
> 
> 
> - 3 dB  is 0.5 MHz
> 
> -20 dB is 1.25 MHz
> 
> -40 dB is 2.3 MHz
> 
> -60 dB is 4 MHz
> 
> 
> 
> This is useful information for those needing a single frequency filter.
> 
> 
> 
> Bob, WB4APR
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