High-pass filter characteristics for RTL-SDR.com ADS-B filtered amp?

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ExplodingLemur
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Joined: Wed Sep 02, 2015 12:28 am

High-pass filter characteristics for RTL-SDR.com ADS-B filtered amp?

Post by ExplodingLemur » Thu Oct 10, 2019 6:16 am

What are the characteristics of the highpass filter on the ADS-B amp from rtl-sdr.com? I've got a partial reel of 978MHz SAW filters that I can use to swap out the 1090MHz SAWs, but not if the HPF rolls off 978MHz.

snn47
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Joined: Tue Dec 27, 2016 11:00 pm

Re: High-pass filter characteristics for RTL-SDR.com ADS-B filtered amp?

Post by snn47 » Thu Oct 10, 2019 1:35 pm

SAW filter are Band-pass filter, to get an idea for a 978 MHz 6 MHz wide filter curve look here https://www.rfmw.com/products/detail/ta ... st/457856/

ExplodingLemur
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Joined: Wed Sep 02, 2015 12:28 am

Re: High-pass filter characteristics for RTL-SDR.com ADS-B filtered amp?

Post by ExplodingLemur » Thu Oct 10, 2019 4:32 pm

Yes, I understand that SAW filters are bandpass. That's why I plan to replace the 1090MHz SAW filters with 978MHz SAW filters (which I have a partial reel of). What I'm looking for is information on the highpass filter on the RF input of the rtl-sdr.com ADS-B filtered LNA, which is advertised as having a HPF in front of the first LNA stage, then SAW filters after the first and second LNA stages.
https://www.rtl-sdr.com/new-product-rtl ... ads-b-lna/
"In the LNA signal path there is first a low insertion loss high pass filter that reduces the strength of any broadcast FM, TV, pager or other similar signals that are usually extremely strong. Then in between the first and second stage of the LNA is a SAW filter tuned for 1090 MHz. A second SAW filter sits on the output of the LNA."

I want to know if THAT filter cuts off 978MHz, or if the passband includes 978MHz.

rtlsdrblog
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Re: High-pass filter characteristics for RTL-SDR.com ADS-B filtered amp?

Post by rtlsdrblog » Fri Oct 11, 2019 5:01 am

I don't have the exact numbers on me at the moment, but the 3dB is around roughly 900 MHz, so you should be fine with replacing the SAWs.

ExplodingLemur
Posts: 4
Joined: Wed Sep 02, 2015 12:28 am

Re: High-pass filter characteristics for RTL-SDR.com ADS-B filtered amp?

Post by ExplodingLemur » Fri Oct 11, 2019 5:15 am

Cool, thanks!

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