I've owned a K-1 elecraft CW QRP radio for many years
Back in 2004 when hurricane after hurricane was blowing through Florida this little radio was a true friend. The first night of Francis at 18:00 my power went out and that was that. Earlier I had charged up a battery so I ran some coax from the station out to the family room where I was camped out. Soon enough darkness fell and it was play with the K-1 or listen to hour after hour of some weather man go "yea Charlie it's really blowing over here..." No kidding dude it was blowing over my head too, that's why I sent my family out of town. I flipped on the K-1 and started tuning around. Long story short I made dozens of contacts that night while 100 mph winds were coming ashore a mile from my house and it was damn nice to have the company of fellow hams.
I bought the KX3 because it's touted as a "SDR". In my opinion I'm not sure exactly what it is.
When I look over the diagram it ever so much reminds me of a SDR-1000 three card stack from a decade ago
Both radios use a direct conversion receiver to take RF and directly convert it to a baseband AF signal which is then fed into a ADC (analogue to digital converter) which digitizes the signal and then a "DSP" which performs various mathematical manipulations on now digitized signal. Instead of a PC which is used by the SDR-1000 to work the DSP and control magic the KX3 uses a Analogue device ADSP21479 DSP chip. I reviewed the specs of this chip and it's pretty impressive. Basically this chip replaces the "sound card" which was used by the SDR-1000. Instead of a PC the KX3 uses a pic18f87k22 8 bit PIC micro-controller for control. This is a good choice because it's easy on the batteries, and that is one good thing, the KX3 doesn't sip much power on RX.. useful in case of hurricanes!
One feature which severely hobbles the radio is the lack of a panadapter. The radio is one dimensional. It basically works like any other legacy radio. I guess to some that might be an advantage but I didn't care for it. To get a panadapter working you either have to buy an additional piece of hardware PX3 or a soundcard and additional software and a laptop or other computer. Or you can build a microcomputer/soundcard/screen outboard panadapter using a beagle bone black or raspberry pi computer In other words a lot of messing around to get what a Apache Lab Anan 10E does naturally for less money
I own the Anan-10 version of this radio and IMHO it is a far better choice than the KX3 UNLESS your goal is QRP in the woods, a hurricane, or something like that. The KX3 will run for a LONG time on a battery. The Anan-10 requires more power and a laptop as its minimal configuration but it is not at all out of the realm of a solar based power system.
The KX3 receiver is very good but not amazing as it is often touted to me. It is no more amazing than the SDR-1000 was in it's heyday in fact not as good.
Here are the KX3 specs from Sherwood's site
Note it says 65 dB dynamic range Here is what "v" says
All of these radios are phasing radios. What that means is their dynamic range is limited by the ability to null out the image. Flex in the SDR-1000 days created a routine that dynamically nulled out the image in the background in real time. It was an amazing feat. The image null degrades as you change bands and change frequencies. You have to null the image very close to the freq where you are operating to get best performance. The inability to null is a definite disadvantage and is probably why the optional "filter" is recommended since it is likely the PIC is not quite up to the task of dynamic nulling like the old SDR-1000. None the less the comments about the radio being the "best receiver I ever owned" are undoubtedly true! I said the same thing when I bought my SDR-1000 and sold my Orion and FT-1000D. As long as they don't overload SDR's are amazing.
I played with the built in decoders for RTTY, PSK and CW. Seemed to me these were very high maintenance compared to a program like WinWarbler or CW skimmer and they didn't work very well but they did work. If my goal was digital in the wild I would definitely be looking at the Anan 10 or 10E, plus maybe a Elecraft T-1 tuner.
So for me owning this radio is a mixed bag. I do not like the fact Elecraft charges you an arm and a leg for every extra cable and screw, like $30 for a mini manual or $30 for a USB cord which is required to update the firmware. I do not like the fact you have to
add a bunch of extra stuff to even approach something like the Anan 10E in terms of the real SDR experience (2 or 3 dimensions instead of 1). I like it's portability. I like its receiver and transmitter. Mine has the built in antenna tuner which is yet another accessory t o pay for and I really like that! I like how it operates on CW, but the old K-1 was very good on CW as well. I'm not much on the batteries being built in or the dorky little paddle on the front or the fact that if you are going to operate digital at full power you need add on heat sinks, because if you get the radio too hot the power cuts back. You can run the 10 at full power all day and it will continue to run at full power. I don't care for the BNC sticking out of the side. What can I say: it is what it is and it ain't what it ain't