Re: Rob Sherwood tests Perseus
- Hi Henry,
> Do you have a plot of the IMD response of the Perseus at 2nd, 3rd andI did not see any response to your posting.
> higher orders, with dithering and without, as per figs 4 and 5 in Lief
> Asbrink's QEX paper (IMD in Digital Receivers)?
Have you seen fig. 1 here?
I do not remember whether switching off dithering made any difference
on IM3 measurements, but it does affect IM2 slightly as you can see in fig 3.
Leif / SM5BSZ
- --- In perseus_SDR@yahoogroups.com, Henry <hjrech@...> wrote:
>Simulation (p. 21) via measurement (p. 22)?
> Can you explain the difference (viz. the level of the noise floor)
> between the plot with predistortion on p. 21 with the plot on page 22
> also with predistortion?
-90 dBc/Hz is so far from anything useable - -120 dBc/Hz is ugly, -140 dBc/Hz is acceptable and -160 dBc/Hz is good. At least in my metric (VHF driven) :-)
Maybe he really makes a direct feedback (in this low bandwidth, a concept called "Carthesian feedback loop" is viable) and picks up lots of noise from anywhere with the ADC. Instead of using an adaptive predistortion based upon a series approach with adjustable coefficients.
BTW do not expect too much from this radio - it has still the old generation ADC in the RX (like the SDR14 - see other thread). I could get one for testing since last year but did not yet find the time to prepare a competition.