[Elecraft] Analog vs. Digital Front Ends

[Don Wilhelm]

I am going to go off on a wild tangent as a method of testing all 
receivers for the ability to copy signals in the midst of very crowded 
band conditions and/or the presence of noise.  Whether those receivers 
have analog front ends or an ADC.

An extremely crowded band could be simulated by broadband noise.
So take a medium strength single signal (say S-5) and inject it into the 
receiver under test.
Now add a low amplitude broadband noise signal, and increase it until 
the signal is buried in the broadband noise.

The receiver that can withstand the greater broadband noise level while 
still recognizing the single signal "wins".
That says nothing about the overload of the ADC for those receivers that 
put the ADC at the antenna - that is something for other test parameters.

73,
Don W3FPR

On 9/15/2015 6:28 PM, Jim Brown wrote:
> On Tue,9/15/2015 1:52 PM, Tony Estep wrote:
>> On Tue, Sep 15, 2015 at 3:36 PM, Joe Subich, W4TV <lists at subich.com> 
>> wrote:
>>
>>> ....noise power ratio testing hides the fact by not providing MDS 
>>> values under each test condition *and* fails to indicate that even 
>>> with *no preamplifier* the total noise signal is more than 10 dB 
>>> *less*...
>> =========
>> I take this to mean that the test results are not comparable across 
>> radios, and the SDRs are 10db worse than they show up on the 
>> comparison chart. If this is true, it ain't good.
>
> You've got the concept right -- the only difference is that 10 dB is 
> not a "hard" number -- it could be anything from 5 to 30 dB, depending 
> on how much test signal strength has been turned down, or preamp gain 
> removed, to get the input of the digital system out of clip!