Re: airspy HF + availability to public #airspyhfplus


Leif Asbrink
 

Hi Yussef,

prog" <info@sdrsharp.com> wrote:

The 6 dB gain reduction might bring the analog noise below the
ADC noise in which case dynamic range would suffer.
This can never happen by design. Many AGC loops are involved
to ensure optimal SNR and available dynamic range. The real
concern is the DR of the analog chain.

The output is 768 KSPS IQ with 660 kHz alias-free.
The DDC and the analog filters can be configured to
output more bandwidth at the cost of much less usable
dynamic range.
I do not understand this statement. As a general statement
it is incorrect and it would be interesting to know
something about why the Airspy HF+ has thais peculiar
behaviour.

If you would double the sampling rate to 1536 kHz for
an alias-free range of perhaps 1260 kHz, dynamic range
as measured with a strong and a weak signal separated
by 25 kHz or 100 kHz should not change. Both signals
would be within the analog passband in both cases
which implicates that all AGC loops will have the
same state in both cases with only the single strong
signal affecting the AGC.

The same with an IM3 test where both signals as well
as the IM3 products are within the analog passband.

The drawback should be that with twice the analog
bandwidth, the peak signal level would be 6 dB
higher but the analog noise floor would be the same
so a 6 dB better IP3 would be required for for
the same performance in terms of freedom from
false signals caused by intermodulation.


73

Leif

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