I've been searching for an EXTIO DLL for the HackRF One that will work with HDSDR for years now.
Finally came across this today! AND BONUS! IT WORKS!
I contacted the author and asked him to add some smaller sample rates of 4 and 2 MSPS. He did that and posted the new release in just about 1-2 hours. This is useful for weak-signal stuff I most do. It allows the ability to get HDSDR's "Resolution Bandwidth" down to 7.6 hz when MSPS is @ 2. Which in my experience shows weak CW signals up very well!
A little about how I use HDSDR.
I use the 9 MHz IF OUTPUT from my Yaesu FTDX-5000 as the input source to whatever SDR I'm using to feed HDSDR. I've been using a TCXO based Nooelec RTL and an OCXO upconverter I built myself. Even with all that 'stability' the TCXO RTL drifts all the time. Which is a total pain in the butt for CW over the coarse of a day.
After swapping out the EXTIO for RTL in my HDSDR install I fired it up with HackRF. Although the HackRF has advertised a low range of 30 MHz or my experience has been that it works just fine down as far as 3.5 MHz in it's stock config. Mine is about 1.5 years old now with recent firmware installed.
Anyway I setup HDSDR initially to use 9,000,000 hz. HDSDR has a nifty option to display the VFO frequency of the Yaesu FTDX-5000 as it's frequency regardless of what input you're really using (9 MHz in my case).
There is also a way to automatically remove the DC Spike that would show up in the middle of the display if left as noted above. To accomplish this I set the OPTIONS > RF Front-end Frequency "IF frequency" to 9098000 and the Global Offset to 98067. This pushes the DC Spike well below my normal viewing area, and then the 'Auto RX DC Removal' notches it down to nothing.
In this way the DC spike goes away but everything stays lined up PERFECTLY for CW.
I also connected a GPSDO I've had around for a long time that I use with my Apache Labs "Hermes" SDR. Tee GPSDO emits a super stable 10 MHz signal that Hermes and now the HackRF lock onto.
In a 24 hour test just completed there was 0 hz drift noted on the HackRF. Which is what I had expected (and hoped for). This has been my experience with the GPSDO and Hermes so I didn't expect any difference.
So all of this Eliminates use of an RTL (which are drifty little bastards, but VERY VERY useful I've used them for over 5 years now with very good success), and because the RTL's are limited to 24 MHz I have always used an Upconverter which has the potential to add noise from it's OSC, and add drift to the resulting signal input to the RTL.
I'm using the HackRF because it's what I have currently and because this EXTIO is now FINALLY available.
I plan to also buy and test the AirSpy and SDRPlay at some point since I've read they hear better than the HackRF. BUT at this point I think I can actually relax after years of muxing around with RTL's that drift like crazy and spending way to much to make a $8 device do something it doesn't really wanna do LOL.
Time will tell, but for now I'm setting my upconverters and RTL's to the side to collect some MUCH NEEDED DUST.