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Technical Topics => Equipment => Topic started by: RobRich on September 12, 2023, 1808 UTC

Title: Low-pass + Shelving Filter by Turn Island Systems
Post by: RobRich on September 12, 2023, 1808 UTC

Spotted this double-purpose filter board via NextGenSDRs@groups.io (https://groups.io/g/NextGenSDRs/topics):

https://turnislandsystems.com/sdr-front-end-filter/
https://turnislandsystems.com/test-results-shelving-low-pass-filter/

It is a four-section 30MHz elliptic low-pass filter and a two-stage 10MHz shelving filter on a single board. The shelving filter(s) can be bypassed if desired.

$30 shipped inside the USA. That was a decent enough price IMHO for me to order one for evaluation.

Title: Re: Low-pass + Shelving Filter by Turn Island Systems
Post by: RobRich on September 25, 2023, 2106 UTC

Received the filter today. First impression of the filter response is good. Build quality looks good, too. I might toss it in some type of enclosure later.

It did what I wanted between the Tecsun PL-330 nightstand radio and an active miniwhip antenna. Yeah, I am feeding a portable radio with an active antenna, which it not exactly ideal IMO.

Now gain on lower frequencies has a some roll-off, but it is nowhere near enough act like a highpass. The roll-off under 10MHz is enough to help lower the noise floor under 10MHz while preserving gain above 10MHz. That should help with potential overload on the lower bands, too. Any actual SNR benefits remain to be seen, but I am only using one of the two integrated shelving filters for testing at the moment, so there is a little wiggle room for further testing.

On the high side of HF, that active miniwhip tends to considerably roll-off above 30MHz anyway, but the included lowpass filter could be useful with a different antenna setup.