[hpsdr] WG: New Hermes 2M Board

[H.A. Meijer]

Hi,

How to deal with  strong outband signals, for example in my situation
I have multiple of these "free radio stations" using 1 KW and more on 1.6/3.9/
6,2MHz 
Close to my qth.
With a mid-end class Icom using roofing filters I have no problems with them.
But with a 16bit Hermes, with no preselection I can hear them interfering with
allmost
every stronger signal.
So saying 16bit ADC is more then enough may not be case for all users.

> Op 10 juli 2017 om 17:38 schreef Helmut Oeller <oeller at freenet.de>:
> 
> 
> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hi Isaac,
> 
> thanks for your comments. This gives the chance to cancel some myths about
> ADCs. I'll try to do this comparing (my favorite) 75 USD dual 14 Bit, 125
> Msps AD9645 with the 300 USD dual 16 Bit, 310 Msps AD9652 you mentioned.
> Both ADCs are produced by Analog Device and the following data are gathered
> from their data sheet.
> It's not enough or tolerable to compare only the nominal number of bit of
> the ADC. You have to compare the effective number of bits (ENOB) specified
> in the data sheet. We'll find ENOB of AD9645 @70 Mhz 12,0 bits while the
> expensive AD9652 offers @70 MHz 12,1 bits, i.e. 0,1 x 6.02 dB = 0.6 dB more
> DR is no significant benefit.
> Let's compare the spurious free dynamic range SFDR at this frequency (middle
> of HF and considered undersampling bands 70/144 MHz): AD9645 is specified
> with 91 dBc, while the 16 bit AD9656 can only come up with 89 dBc.
> Same story occurs with SNR (74 dB both) and crosstalk between the two
> channels (-97 dB vs. only -90 dB of the AD9652!). Moreover the difference in
> power consumption is dramatically: the 14 bit AD9645 needs 0,24 W, while the
> fast AD9652 consumes 2,16 W.
> 
> It's evident that there is absolutely no reason for that fast, hot and
> expensive 16 Bit ADC.
> 
> 73, Helmut, DC6NY
> 
> 
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