The problem with the 24 bit ADCs out there is that they have a 24 bit output format, but don’t actually give 24 noise free bits. The AK5394A, for me in my use case could give 20.6 bits (192khz) and 21.5 bits (96KHz).
The 14 and 16 bit RF ADCs, in reality don’t even give signal to noise ratios close to the equivalent ENOBs, and oversampling doesn’t help enough. The fact that the ADC drivers potentially have hundreds of MHz bandwidth doesn’t help as the noise from aliases combines incoherently with the wanted signal and its noise floor.
The usual solution is to sell radios that run below 65MHz and count on atmospheric noise hiding your sins on HF amateur bands, or washing out the noise figure with pre-amplifier gain.
An alternative and increasingly useful way to look at things is using the noise power spectral density and ADC clip point and asking how much nearly noiseless RF gain must be added to achieve a certain equivalent noise figure and what the resulting dynamic range is(or other characteristics that matter).
-153dBm/Hz with no gain in front of it would be moderately impressive. The same with 30dB gain in front of it to get that, not so much.
________________________________
From:
[email protected] <
[email protected]> on behalf of Alan G4ZFQ via groups.io <alan4alan@...>
Sent: Sunday, December 29, 2024 10:24:59 AM
To:
[email protected] <
[email protected]>
Subject: Re: [softrock40] Costs of softrock units have skyrocketed
On 29/12/2024 15:00, David Underwood via groups.io wrote:
Maybe the Real value in going with the Softrock40 series is educational.
Dave,
I was thinking of modern SDRs recently.
It you can make do with a small frequency range then it could be said
modern ones have only just caught up with Softrocks:-)
A fair quality mid range soundcard gives 14 bits range, even simple
front ends keep things cleaner than putting everything from the antenna
into the mixer.
A high end sound device with 24 bits and Softrock mods makes it better..
73 Alan G4ZFQ
