Comparing USB dongles. Stability on 432 MHz.
(Jan 9 2014)
Figure 1 is a photo of the four dongles that have been compared in this experiment. Figure 2 is a screen dump with all the dongles running. All dongles sample at 1.6 MHz and all processing parameters are identical between the dongles. Figure 3 is a screen dump when the room temperature has been disturbed by an opened window. (Note that the frequency scale is contracted compared to figure 2.)

In figures 2 and 3 the same signal is routed to the four domgles through a 7 port resistive splitter to which a HP8970A and a HP8970B is connected. The two signal generators are locked to independent 10 MHz frequency standards. Even in the best dongle the frequency drift of the two signals is perfectly correlated which means that the noise modulation visible for the Logitec dongle is entirely due to the dongle and not due to the signal generators.

The dongles are arranged the same way in all three images.

    Lifeview LV5TDeluxe
    Manufacturer: Realtek
    Product id: RTL2838UHIDIR
    Tuner: E4000 (Elonics)
    Interface: RTL2832 (Realtek)

    Manufacturer: Logitec
    Product id: none
    Tuner: MSi001 (Mirics)
    Interface: MSi2500 (Mirics)

    ezcap USB 2.0 DVB-T/DAB/FM dongle
    Manufacturer: Realtek
    Product id: RTL2838UHIDIR
    Tuner: R820T (Rafael)
    Interface: RTL2832 (Realtek)

    Terratec NOXON DAB/DAB+ USB dongle (rev 1)
    Manufacturer: NOXON
    Product id: DAB Stick
    Tuner: FC0013 (Fitipower)
    Interface: RTL2832 (Realtek)

It is obvious that the frequency stability differs significantly between the dongles.

Fig. 1. USB dongles for digital TV and FM radio.

Fig. 2. The dongles have very different noise sideband characteristics in the close range. The frequency instability might affect the performance of narrowband modes such JT65.

Fig. 3. USB dongles for digital TV and FM radio. Here the room temprerature is unstable. A window was opened.