Receive Filters
Posted: Sat Sep 16, 2017 8:46 pm
I went out /P out Portsdown Hill today, which is a very challenging site RF-wise. I managed to receive some pictures from G4GUO on 146.5 MHz. The receive filter I used has a 3dB bandwidth of about 700 KHz, a 20dB bandwidth of 1.75 MHz and a 40 dB bandwidth of about 4 Mhz.
Despite this, I still had problems from a co-located APRS TX (should be 40 dB down) and some other transmitters. I could have done with a sharper filter! The preamp+filter response plot below is centred on 146.5MHz, 500KHz/div and 10 dB/div.
Interestingly, the leandvb receiver in the Portsdown build (RTL-SDR and Raspberry Pi with touchscreen) performed better than a MiniTiouner because it was able to lock-up faster when the interfering signals went off. A lot of the time, the interferers started transmitting again before MiniTioune had locked.
Dave, G8GKQ
Despite this, I still had problems from a co-located APRS TX (should be 40 dB down) and some other transmitters. I could have done with a sharper filter! The preamp+filter response plot below is centred on 146.5MHz, 500KHz/div and 10 dB/div.
Interestingly, the leandvb receiver in the Portsdown build (RTL-SDR and Raspberry Pi with touchscreen) performed better than a MiniTiouner because it was able to lock-up faster when the interfering signals went off. A lot of the time, the interferers started transmitting again before MiniTioune had locked.
Dave, G8GKQ