Try attenuate RF entry level on SDR Dongle 73, lu7abf, Pedro On 12/28/20, Jean Marc Momple <jean.marc.momple(a)gmail.com> wrote:

Hi Andy, Because you have 1 MHz between two signals, then you can try to do something yourself. HAM radio is an experiment ;). If I would be you I will try to make two quarter-wave impedance transformers using a cable, as the frequency trap. As a consequence, you can reach a different ratio between both signals on 144 and 145 MHz. Sorry for my not professional/technical English words in this case. I hope people who know technical English better than me and catch my idea can write to you more (some keywords). Another similar solution is the notch filter from cable, eg. http://dl4xav.sysve.de/coax.filter/coax-filter.html Here is another solution https://www.pa0nhc.nl/IMDfilter/EN/CableNotchFilter145MHz/KabelNotchFilterV… If the trap/notch filter will be too wide (wider than 1MHz), then you can try to move the maximum of the resonance/attenuation much more outside both frequencies 144 and 145 and you can try to operate on the slope. 73, Armand SP3QFE W dniu 2020-12-28 19:29, Andy Brian napisał(a):

LNAs are good, but they also raise the noise power in the pass band, right? From my experience, too much amplification is a bad thing when seeking lower power RF signals. Why not consider better (industrial/lab quality) components at the RF front ends taking out the components supplied with the cheap dongles? Use the back end, but reengineer the front end. Those parts are probably the cheapest quality so if one could get a 0.5 or 1 dB increase .... and I learnt of a tip: older radio operators (WWII to 1960s) used tube front ends in RX boards for weak signal VHF. Amazing technology that should still be interesting. Narrow-Q but high dynamic range! Like an audio pre-amp with tube circuits. Discussion and criticism welcome. Samudra N3RDX -----Original Message----- From: Armand SP3QFE <kontakt(a)sp3qfe.net> Sent: Monday, December 28, 2020 3:14 PM To: Mathison Ott <mathisono(a)gmail.com> Cc: Andy Brian <briaandy(a)gmail.com>om>; AMSAT-BB <amsat-bb(a)amsat.org> Subject: [AMSAT-BB] Re: SSTV with SDR RTL2832 Hi, I think that the LNA will boost both 144 and 145 MHz signals. Armand W dniu 2020-12-28 21:11, Mathison Ott napisał(a): ----------------------------------------------------------- Sent via AMSAT-BB(a)amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! View archives of this mailing list at https://mailman.amsat.org/hyperkitty/list/[email protected] To unsubscribe send an email to amsat-bb-leave(a)amsat.org Manage all of your AMSAT-NA mailing list preferences at https://mailman.amsat.org Disclaimer: The information contained in this communication may be privileged, and is intended for the use of the above named addressee(s). If you are not the intended recipient(s), do not use or rely upon it. Instead, please inform the sender and then delete it. Thank you.