From 1fc69d2b0e5c8da5c95a9e9355d786a9ede950d0 Mon Sep 17 00:00:00 2001 From: Michael Ossmann Date: Wed, 3 Jul 2013 21:34:55 -0700 Subject: [PATCH] Updated FAQ (markdown) --- FAQ.md | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/FAQ.md b/FAQ.md index f8cce12..db59dbf 100644 --- a/FAQ.md +++ b/FAQ.md @@ -34,6 +34,12 @@ Follow the instructions to [update your firmware](https://github.com/mossmann/ha ## What is this big spike in the center of my received spectrum? +### Q: + +I see a large spike in the center of my FFT display regardless of the frequency my HackRF is tuned to. Is there something wrong with my HackRF? + +### A: + You are seeing a DC offset (or component or bias). The term "DC" comes from "Direct Current" in electronics. It is the unchanging aspect of a signal as opposed to the "alternating" part of the signal (AC) that changes over time. Take, for example, the signal represented by the digital sequence: ``` -2, -1, 1, 6, 8, 9, 8, 6, 1, -1, -2, -1, 1, 6, 8, 9, 8, 6, 1, -1, -2, -1, 1, 6, 8, 9, 8, 6, 1, -1