Differences

This shows you the differences between two versions of the page.

--- projects:storm:antenna [2015/03/10 22:23] – storm
+++ projects:storm:antenna [2015/03/17 20:52] (current) – storm
@@ Line 1: / Line 1: @@
 ====== Antenna tuning ======
+Since I created this article rtl-sdr.com published a similar tutorial (http://www.rtl-sdr.com/rtl-sdr-tutorial-measuring-filter-characteristics-and-antenna-vswr-with-an-rtl-sdr-and-noise-source/) and mentioned rather cheap directional couplers, which I might acquire in the future.
 ===== Motivation =====
@@ Line 26: / Line 28: @@
 {{ :projects:storm:payload_step2_300-500.png?direct&600 |}}
+As all elements are longer then optimal a smaller resonance wavelength is expected. At around 375MHz a destinct drop in the return power can be seen. In this frequency range the antenna radiates a significant portion of the input power. All we now have to do is to incrementally cut the antenna elements and monitor the radiation spectrum.
+The following figure shows the spectrum for an antenna with a 17.5cm radiating element and 18.5cm radials:
 {{ :projects:storm:payload_step6_300-500.png?direct&600 |}}
+The last figure shows the spectrum for an antenna with a 164mm radiating element and radials of the same length, as described in the tutorial.
 {{ :projects:storm:payload_step10_350-500.png?direct&600 |}}
+Interestingly the bandwith goes up with the central frequency, while the maximum radiated signal strength slightly drops. To further investigate, I will have to do a proper compensation for the frequency dependence of the noise generator.
+It should also be noted, that I see a slight dependence on the orientation of the antenna. I suspect this is due to reflections of metallic surfaces in my rather cramped room. I will test outside and report back.