Thanks for the info and the observation about 8-bit dongles. Contrary to Stanley, you're adding some value to my original question regarding choices to be made between a "true" SDR (e.g., QS1R, Perseus, SDR-IQ) vs a VHF/UHF dongle and an upconverter. Could provide some examples where an 8-bit dongle/upconverter would fall short vs. a true "SDR" for a panadapter application? The reason for asking is the Terratec T Stick Plus dongle I'm using with HDSDR as a panadapter for the Icom 7600 seems to be doing okay.
Well, again, if you want a pretty display you can just use the dongle, and so long as your just using it for a display only then you'll see most of your strong signals so in that case you can use the cheapo device.
Let's say though you want to use it as a true second receiver, or use it to help detect weak DX and actually listen to the output, then you get what you pay for and as a second receiver it's worse than the cheapest ICOM you can buy. You might for example use the 7600 for transmit and the SDR for receive. BTW, if you try to listen to both at same time on same frequency, your going to have a delay and hence nasty echo problem. So if your using the SDR as the receiver your listening to and transmitting with the ICOM then your going to have the receive volume off on the ICOM.
You can read the responses here for the technical details, no need for me to reinvent to technical explanation of differences in resolution based on bit depth.http://ham.stackexchange.com/questions/607/sdr-sampling-bandwidth-do-the-bits-per-sample-matter
Since you have a 7600 with a really good receiver, unless you want to improve upon your receiver either to get something quieter or better reception, then the dongle will be ok as a display only. If you want a superior receiver then you'll want one of the more expensive SDRs.
The whole debate about whether SDRs are better than traditional Riggs, well, that's not exactly been really quantified with the newer SDRs as you can't do apples to apples testing. Hence why the new Flex, Anan's ect are not on the receiver charts yet.
In my informal testing using a variable attenuator I give the Anan 100D a slight edge over the KX3, I own both still currently as well as the QS1R and a Ettus B200.
Up converters are lousy though, head to head though the Afedri beat the FunCube Dongle Pro Plus, also owned both those as well as a Flex 5000 which the Anan beat out as well. Depending on the upconverter you use and or the local interference you have in the upconverter frequency range, you may get stray signals on your display. Forget up conversion if your really want to use the SDR as a second receiver. A lousy upconverter makes a great SDR just as lousy as the cheap upconverter.
I have not had my hands on the new Flex Riggs, donut I will but have info that it's no better than the Anan or visa versa. Both have 16bit ADCs.
So it all comes down to what you really want.