DanOverlappingChannels < ColdFeedback

---+ Overlapping DAN channels

Overlapping DAN channels

Motivation

Using DAN at 195 kHz with channels separated by less than 195 kHz may be an option we consider. Here, I show some of the effects associated with DAN channels that overlap in frequency space.

Digitization Noise

The following plot shows the nuller amplitude. Note that the dominant noise source is larger than 1/sqrt(12). Since the only type of noise that could be greater than 1 bit in the standard dongle setup is due to digitization, this shows that the digitization at the accumulator is ~15x larger than the digitization noise due to the FIR.

Fig. 1: Timestream of nuller amplitude.

Noise Shaping

Since the accumulator has an "extra" bit that is not being fed back on, we see some noise shaping. The following plot shows the PSD of Fig 1.

Fig. 2: PSD of nuller amplitude.

Only some of this noise makes it through the feedback loop.

Fig. 3: PSD of residual signal.

-- TijmenDeHaan - 09 Aug 2010

Attachments

Topic attachments
I	Attachment	Action	Size	Date	Who
png	dan_digitization_noise.png	manage	14.0 K	2010-08-09 - 16:13	TijmenDeHaan
png	dan_digitization_tod.png	manage	13.0 K	2010-08-09 - 16:13	TijmenDeHaan
png	dan_low_gain_nulling.png	manage	12.1 K	2010-08-09 - 16:13	TijmenDeHaan
png	dan_separation_spike.png	manage	10.2 K	2010-08-09 - 16:13	TijmenDeHaan

This topic: ColdFeedback > WebHome > DanOverlappingChannels Topic revision: r1 - 2010-08-09 - TijmenDeHaan