yes and IC7300s with a transverter is a joy to use on VHF. But direct sampling on VHF is not so great as I will show below....so I wonder if the IC9700 will be any good.
The $1000 ADCs are items like 4 Gbps dual channel, 12 bit. Mainly used for oscilloscopes and fats digitizing, also small scale cellular base stations .
But the two tone performance (IMD) and SFDR (spurs that appear 'randomly' depending on what else is in the ADC) still top out at 90 to 100dB below full scale. See everywhere everything is referenced to full scale. In a pure analog receiver, many things are referenced to the minimum discernable signal.
That's why the hybrid analog front end/digital narrow band IF using 24 bit audio style converters making 120dB IMD /SFDR still rules the roost. But you have a hell of a job making the analog front end that good. You end up with a 7851....
Again it is about setting the full scale of your radio. With 90dB SDFR/IMD, If the radio is set at a full scale of say 0dBm, in most cases, on 80meters, the noise level on your dipole will be ~ -90dBm, so no problem.....
The performance on weak signal VHF is not so great.
If the full scale level is set at -30dBm, which actually might be a bit marginal because you can point your beams at stuff , the lowest usable level will be say 90dB below that. : -120dBm. That's where the spurs, the grass, the IMD will end up.
Remember from my first post - the IMD levels are all a fixed level below full scale regardless of the input level !
So if there are two OPs up the road and they are both -100 in your receiver, the IMD will still be -120dBm per the above case . terrible !!!
Oversampling means that is not the noise floor, the noise floor is more too do with the SNR and ratio of the ADC sampling rate to the final information rate. For SSB, a 122 MSps converter will yield an output SNR of about 111dB below full scale.
So, again, if the full scale is -30, the noise floor in a SSB bandwidth will be -30-111 = -141dBm. which is OK.
We satisfy SNR requirements, but if two OPs are next door on 144.15 and 144.2 that will throw -120dBm signal intermods on 144.1, 144.2
That's the limit of direct sampling VHF work...
did that make sense ?
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