In theory it's possible to receive on the third harmonic of the mixer injection frequency with a suitable bandpass filter to reject the fundamental response.
I recall doing this with the original Sentinel SDR receiver to reduce the spurious responses from the DDS synthesiser used in that receiver.
So applying the idea to the Sentinel 4 receiver design which covers up to 64 MHz it would be possible to extend the frequency coverage up to 192 MHz with extra relays and filters. This would cover the VHF air and marine bands.
It would need a completely new PCB design but it is technically possible.
Whether it's commercially viable is a different matter as most SDR receiver users today appear happy to use RTL-SDR or SDRPlay receivers with 8 or 12 bit receivers giving limited dynamic range compared to the 16 bit codec used in our receivers. In practice the receiver front end is suitable for use with 24 bit 192 kHz sound cards using the IQ output so wideband VHF FM reception is certainly possible.
The RF filtering on some of the SDR receivers barely meets the requirements to be called a filter.
If I was going to design a completely new SDR receiver I would go all out for a good RF design with excellent RF filtering and similar levels of isolation to the existing CCW receivers to give 24/7 all weather performance. However it wouldn't be cheap!
I expect that it would meet the needs of commercial and military customers but are enthusiasts looking for something like this?
I would be interested to hear opinions from everyone on this. Is it worth doing or are you all buying SDRPlay receivers?