A couple months ago I picked up a RTL2832U dongle to use with SDR#. I've been testing 433Mhz RF modules, and wanted to figure out what kind of wire antenna works best.
Antenna theory is rather complicated, and designing an efficient antenna involves a number of factors including matching the output impedance of the transmitter. Since I don't have detailed specs on the RF transmitter modules, I decided to try a couple different antenna designs, and use RTL-SDR to measure their performance.
I started with a ~16.5cm (6.5" for those who are stuck on imperial measurements) long piece of 24awg copper wire (from a spool of ethernet cable). One-quarter wavelength would be 17.3cm (300m/433.9Mhz), however a resonant quarter-wave monopole antenna is supposed to be slightly shorter. I started up SDR#, turned off AGC and set the gain fixed at 12.5dB. The signal peaked at almost -10db:
The next thing I tried was coiling the antenna around a pen in order to make it a helical antenna. This made the performance a lot (>10dB) worse:
I also tried a couple uncommon variations like a loop and bowtie antenna. All were worse than the monopole.
Have any other ideas on how to improve the antenna design? Leave a comment.
Last minute update: I tried a 1/4-wave monopole wire antenna on the RTL dongle, and got 2-3dB better signal reception at 433Mhz than the stock antenna. I tried a full-wave (69cm) wire antenna, and it performed better than the stock antenna, but slightly worse than the 1/4-wave monopole.