3.1 Capacity

The EVN correlator has 32 correlator boards, each of which can currently handle a total of 4096 lags. The number of frequency points you will see is half the number of lags used in the correlation, so there is a total number of 65536 frequency points ( $4096\cdot 32/2$). This capacity must be divided among all the individual baseline/subband/polarization interferometers that belong to your experiment. The relevant formula is:

$$\frac{\mathcal{N}_{\rm sta}^2}{2} N_{\rm pol} N_{\rm SB} N_\nu \quad \le \quad 65536.$$ (4)

You can use eq.(4) to find the maximum number of frequency points you can get per baseline/subband/polarization product. However, due to the specifics of how the correlator is configured, there are some factors to keep in mind:

• $N_\nu$ can only be a power of 2.

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  Minimum value is 16.

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  Maximum value is 2048 (a baseline/subband/polarization product must fit onto a single correlator board).

• $N_{\rm pol}$ can only be 1, 2, or 4 (of course, $N_{\rm pol}$ can be 2 or 4 only if you scheduled a dual-pol experiment).
• The product of $N_{\rm SB}$ and $N_{\rm pol_{\Vert}}$ must be $\le 16$.
• $\mathcal{N}_{\rm sta}$ must be a multiple of 4, such that $\mathcal{N}_{\rm sta} \ge N_{\rm sta}$, your actual number of stations (hence its different font in eq.(4) to draw attention to this subtlety).

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  If $N_{\rm sta} > 16$, then we have to correlate your experiment in multiple passes. If $16 < N_{\rm sta} \le 24$ (3 passes required), then use $N'_{\rm sta} = \mathtt{ceil}( \frac{2}{3}N_{\rm sta})$ when determining the $\mathcal{N}_{\rm sta}$ to use in eq.(4).

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  Note that if all other parameters are powers of 2, then networks from 9-16 stations will all have the same maximum $N_\nu$. Thus, for example, dropping from $N_{\rm sta}=9\rightarrow 8$ would gain you a factor of 4 in maximum $N_\nu$, all other parameters remaining constant.

Table 1 summarizes some valid configurations that use the whole correlator.

Table 1: Some $N_{\rm sta}/N_{\rm SB}/N_{\rm pol}/N_\nu$ configurations that use the whole correlator.

	16sta	1SB	1Pol	512Frq	(Max. $N_\nu$ for 16 stations)
	8sta	1SB	1Pol	2048Frq	(Max. $N_\nu$ for 8 stations; also current max. possible $N_\nu$)
	4sta	2SB	2Pol	2048Frq	(with only 4 stations, you can get more SB/Pol)
	16sta	8SB	4Pol	16Frq	(opposite extremes: many SB/Pol with low $N_\nu$)
	8sta	16SB	4Pol	32Frq