[hpsdr] Phoenix

[Helmut Oeller]

Steve,

the eval board DC854D-E is just matching the 50 ohms input to the ADC 
impedance and has no LPF, preamp or switchable attenuator on board, but 
that lack can be compensated with external components. When you are 
sampling with 61,44 MHz you need a LPF with 30 Mhz f_c. A simple 20 dB 
MMIC together with your elecraft AT1 will complete the 'line'. At least 
you'll be able to start first tests. I'll try to send  you tomorrow  
some additional info.

73, Helmut, DC6NY


> Helmut,
>
> ---
> 1: Would this work attached to the input of the DC854D-E ADC board?
>
> https://www.dxengineering.com/parts/dxe-z10046b-pm#overview
>
> You can find the DC854D-E schematic on my website: 
> https://ad0es.net/dfcADC/
>
> ---
> 2: I have an elecraft AT1 step attenuator, switched steps of: 1dB - 
> 1dB - 3dB - 6dB - 10dB - 20dB
>
> https://elecraft.com/collections/at1-model/products/at1-step-attenuator-kit 
>
>
> Would this go between the preamp and DC854D-E?
>
> ---
> 3: I believe the band pass of the DC854D-E is 1MHz - 70MHZ.  I am 
> sampling @ 61.44MHz for Nyquist 30MHz/10 meters.
>
> I think I can live with that for now?
>
> Eventually I expect to build a complete replacement board, but am 
> hoping the above 2 items will get me by till then?
> Any suggestions for an alternate COTS preamp?  Something I can buy now 
> for use during the real front end design cycle?
>
> tia,
> Steve AD0ES
> ps: thanks for the help, I can code the snot off a gorilla, but I'm a 
> complete analog nube...
>
> On 4/15/23 9:46 AM, Helmut Oeller wrote:
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> Hi Steve,
>>
>> You asked for  guidelines of a reliable frontend:
>>
>> 1. to lift the typical noise figure of the ADC around 40dB, at least
>> for  f>10 MHz a preamp with 20 dB gain is necessary.
>>
>> 2. on the other hand ADC clipping must be prevented due to too much
>> gain: 31dB step att like Hermes or 20 dB fix att like Mercury will help.
>>
>> 3. Antialiasing filtering is mandatory: LPF for 1. Nyquist. If the
>> concept allows undersampling, seperate BPF filters with reasonable
>> stopband attenuation are to provide.
>>
>> 73, DC6NY
>>
>
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