[linrad] Linrad, MAP65, and SDR-IQ

[Joe Taylor <Princeton.EDU; joe@xxxxxxxxxxxxxxxx>]

Hi Leif and all,

I have been thinking about ways to make MAP65 available to 
those using the SDR-IQ (or SDR-14).  Last evening I re-read 
your very informative email of July 2 to Fletch, K3JYD.

As I understand it, the SDR-IQ always samples at 66.6667 MHz 
at its input.  Its on-board AD6220 digital down-converter 
divides the sample rate by a number N that is the product of 
three integers: CIC2 * CIC5 * RCF.  By reading the AD6620 
spec sheet I find that CIC2 must be in the range 2-16, CIC5 
and RCF in the range 1-32.  I think Linrad allows one to 
choose these integers, and I understand that some trade-offs 
concerning location and attenuation of spurs will be 
involved in the choice.

MAP65 presently requires an input sample rate of 96000 Hz.

The ratios 66,666,667/694 = 96061.48... and
66,666,667/695 = 95923.26... are probably "close enough", 
but they are not usable because 694 = 2 * 347 and 695 = 5 * 
139, and both 347 and 139 are prime.

So it seems that to provide a usable bandwidth of about 90 
kHz with the SDR-IQ, MAP65 must provide an option to use 
input data sampled at some new rate commensurate with 
66.6667 MHz, with an integer divisor somewhere around 700. 
The divisor must be factorable into three integers 32 or 
smaller.

Several good possibilities for the divisor, and their 
factors, would seem to be:

684: 2 2 3 3 19      ==> 19*6*6, 19*9*4
690: 2 3 5 23        ==> 23*5*6, 23*10*3
693: 3 3 7 11        ==> 11*9*7
696: 2 2 2 3 29      ==> 29*8*3, 29*6*4
700: 2 2 5 5 7       ==> 10*10*7
702: 2 3 3 3 13      ==> 13*9*6
704: 2 2 2 2 2 2 11  ==> 11*8*8
714: 2 3 7 17        ==> 17*7*6
715: 5 11 13         ==> 13*11*5

Am I thinking about this correctly?  Is the present Linrad 
set up so that it can command the SDR-IQ to do these things?

	-- 73, Joe, K1JT

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