I can't help but notice that you weren't able to come up with an example of a better SDR for my application. "cuteSDR" doesn't seem relevant because I write all my own code to control the radio, demodulate (FSK/NFM) the signals, correct the parity-checked bits so the CRC matches, decode the content, etc. It's really irrelevant, because I asked you to name a piece of SDR receiver hardware
which fits my bill and is cheaper than $400. I am all ears on that subject, but I don't need any pointers to software. I was asking you to substantiate your pooping on this project by providing an example of an SDR device that would be better for the fun I am having, not the fun you are having. You seemed to gloss over that for some reason.
So what's at 850-869 mhz of $400 worth of interest to you?
Public agencies trunked radio, with whom I am cooperating on a proprietary application. Sorry I can't say more than that, but the signal of interest is Motorola SmartNet in my case. The application sprang from having fun monitoring it, and observing the potential for an improvement to their system.
Re your success with FM, your dongle may have an FM broadcast band trap. Or your antenna system might be doing it for you.
No, none of the dongles have FM broadcast band traps, and the antennas are directly connected 800Mhz 1/4 wavelength dipoles. These are both purchased and home-built antennas, I have several of these dongles. I think you missed the part where I can easily pick up very weak and distant 120MHz signals (yes, using the 800Mhz antennas) which use the same front-end filter as broadcast FM, when we are talking about e4000-based dongles. The FM station nearby is so powerful that I owned several devices (telephones, computer speakers) which I've had to replace because the station was audible on their output. And yet, I can hear airplanes that are 50 miles out in the 120 MHz... I realize the 800MHz antenna is slightly antenuating the 95MHz FM signal, but it's also attenuating the 120MHz air band.
RF is somewhat tricky unless you're pretty knowledgable.
At this point, don't trip over your ego. I'm knowledgable enough to be sure there is no front-end filter of any sort reducing the FM broadcast stations. I understand there is a culture around talking up the trickiness of RF, but let's get past that for the sake of reality.
Dynamic range is one of the key specs we look at.
So, surely an expert amateur radio operator such as yourself will realize that 8 bits gives 50dB dynamic range? Which of course is awful. Yet this overload problem doesn't seem to be real.
That's aside from what happens if there's an RF front end in there, filter(s), a mixer, etc., which quite often, there is.
Are you aware the e4000 data sheet is "out there" on the web? Between the antenna and the A/D, I've got: an ESD diode with 6pF capacitance, the e4000 front-end filter and LNA, the e4000 mixer, 5 more amp stages, decoupling caps, then the A/D, then, the single worst part, a "mystery" (undocumented without NDA) FIR with 20 taps. Why you would imagine that a $20 dongle could arrive with an FM broadcast tap is beyond me. The dongles aren't even shielded, and I can easily pick up the FM broadcast with a shielded 50-ohm resistor connected across the antenna input...
I'll give you that it is likely that the FM station is always contributing to my noise floor, but, realistically, the noise floor of the e4000-based devices is already horrible, with an 8-11dB noise figure, lots of birdies around the multiples of 28MHz and 5/3 of that. If any signal were going to swamp the dongles, I would expect that to be 480MHz USB emanations -- in particular because there is no way to attenuate them via adjusting the front-end LNA gain -- the signal appears to intrude after that stage. Yet I can receive at 450MHz just fine, and that is in the same front-end filter band as 480MHz.