Bias Tee powerd LNA suggestions

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Hoshen_Kadosh
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Joined: Sat Sep 08, 2018 11:15 pm

Bias Tee powerd LNA suggestions

Post by Hoshen_Kadosh » Thu Sep 26, 2019 9:42 am

Hi.
I currently have a 30m RG-58 coax going to my antenna (Nagoya NL-770S) on my roof. I am mostly using it for Radiosonde reception (400-406Mhz),and because of the long cable and the lose, I would like to add an LNA to the setup. Since I don't have any available power on my roof to power a LNA the only option of power is the bias tee from the RTL-SDR V3 dongle.

I thought about getting the RTL-SDR Blog LNA, how will it work with the long cable?
Or maybe different type of LNA?

rtlsdrblog
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Re: Bias Tee powerd LNA suggestions

Post by rtlsdrblog » Thu Sep 26, 2019 11:28 am

Voltage drop over 30m RG-58 should be minimal assuming you have good quality RG-58 without any kinks/broken high resistance areas in the cable.

Inner conductor would be roughly 40 Ohms/km so 1.2 Ohms for 30m. Double it for back and forth = 2.4 Ohms (actually should be less since the outer conductor usually has less resistance).

Current draw of the SPF5189Z is 90mA, so V_drop = 0.09 * 2.4 = 0.22V. It can work down to about 3.3V, so 4.5-0.22 = 4.28V, it will be fine.

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