[Skimmertalk] The Red Pitaya 122.8-16 -- an important lesson learned.

[Bob Wilson, N6TV]

According to the specs and graphs on this page:

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


"Outside of the pass band the insertion loss is practically zero below 500
MHz, less than 0.5 dB from 500 MHz – 1 GHz"


So you may be seeing loses in the patch cables or something.

I highly recommend this filter for all owners of the Red Pitaya 122.88-16
SDR, especially if you're within a few miles of one or more FM broadcast
stations.  It may also help the older Red Pitaya boards in some cases.

73,
Bob, N6TV


On Thu, Aug 15, 2019 at 6:30 AM N4ZR <n4zr at comcast.net> wrote:

> Sure, Jeffrey -  I also have no precise idea what the insertion loss of
> the two series filters is, but they cleaned up my 15 and 12-meter issues.
> Some rough-and-ready tests with an Elecraft XG-3 Signal Source and HDSDR's
> S-meter suggest it's a few dB, and more than made up by the 11-dB Norton
> preamp.
>
> I am confident that a high-quality set of band-pass filters would be
> preferable, but since I'm trying to skim 8 bands simultaneously, that would
> be pretty clumsy to implement - imagine an 8-way splitter, 8 filters, an
> 8-way combiner and an amplifier to make up for the losses.  Actually,
> that's what W3LPL uses at his station, as described on the RBN blog
> recently - reversebeacon.blogspot.com
>
> 73, Pete N4ZR
> Check out the Reverse Beacon Network
> at <http://reversebeacon.net> <http://reversebeacon.net>, now
> spotting RTTY activity worldwide.
> For spots, please use your favorite
> "retail" DX cluster.
>
> On 8/14/2019 9:39 PM, Jeffrey Pawlan wrote:
>
> The partial schematic shows what is in the front end between the SMA
> connector and the A/D converter.  He even removed some components that
> should be there for optimal performance. There is definitely no filter.
>
> I modified one of my Perseus radios to have a similar unfiltered input.  I
> carried it will me all over the US, Canada, and Israel to give lectures on
> SDR. I took a simple signal generator with me to show that the untuned SDR
> radio would receive very well up to almost 500MHz and demonstrated how
> alternating Nyquist bands would change tuning direction.
>
> Perhaps you might find limited performance with the purchased external
> filters. That would come as a result of the reflections of the signals and
> the noise from the A/D sample and hold being reflected back by the filters
> into the A/D input. To maximize performance one would need to buy or build
> what are called non-reflective (aka absorptive) filters for your specific
> bands of interest.
>
> 73,
>
> Jeffrey Pawlan  WA6KBL
>
>
>
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