26 February 2013

A container for 23cm biquad antenna

There is a bit of local activity on 23cm and the RTLSDR dongle allows me to receive that HAM band. An improvised indoor dipole brought in few interesting signals, increasing my interest for 1296 MHz. I have already built a biquad antenna, which needs a (cheap!) housing before being installed outside.

My biquad size is about 20x30x6 cm and I have had troubles locating suitable plastic containers in the kitchen department of local supermarkets.

During a visit to IKEA lower floor I spotted the SAMLA series of plastic transparent containers. The 11 litres one is large enough to host my biquad (38x28x14 cm) and it costs 1+1.75 = 2.75€ (lid+box).

The antenna will go on the internal side of the cover, which is easier to work on and cheaper in case the experiment fails. In that case the SAMLA container will be repurposed in the house.

13 February 2013

RTLUSB in VirtualBox virtual machine

Months ago I was advocating the creation and distribution of a Linux virtual machine image with pre-installed software for RTLSDR work (drivers and end user applications). The release of Zadig and SDR# for MS Windows has quickly obsoleted my idea. But how about running the whole SDR thing within a virtual machine? Would the "virtual USB" software layer be fast enough to pass through RTLSDR IQ samples?

A test within the virtual machine is quickly done with the rtl_test.exe utility distributed with RelWithDebInfo.zip file (google). My setup:
  • host computer i5 processor Win7 64bit
  • guest computer WinXP 32bit
  • R820T dongle
I have tried running rtl_test.exe at several sampling rates and always got lost bytes, even at the lowest value of 250 kSPS! And the CPU usage was not impacted at all, it remained low/idle.

My conclusion: unless you accept data loss in your RTLSDR decodes, a VirtualBox virtual machine does not guarantee enough "USB bandwidth" for successful reception within the VM itself.