A Few Words on Receivers
From The RadioReference Wiki
If you decide to get into digital, you will need better equipment than a simple portable. While some portables will work with reasonably stronger signals, the more complex the signal (or conditions), the more a portable will fall short.
While the number of newer desktop receivers has plummeted, a sharp eyed listener can often find such receivers at hamfests. Do your homework - use the Receiver Reviews category to begin your research. Even though most of the reviews do not specifically refer to digital capabilities, keep an eye on tuning accuracy (10hz resolution is necessary for some modes), tools that enhance selectivity (to be able to isolate one signal out of crowded conditions) and stability (little or no drift). Those folks with a modern ham transceiver have an advantage - they often have a general coverage receiver built in.
The big push these days is in the development of Software Defined Radios (SDRs). Many are very capable at HF; one of their biggest advantages is being able to see a large swath of frequencies, all at one time. For modes like ALE, which show up for a few seconds and are sometimes gone, this is a big plus for capturing data quickly.
Pay close attention to the calibration of your receiver. Many of the more modern modes such as STANAG4285 and MIL-STD-188-110A/B require a high degree of frequency accuracy. Decoding can be affected or completely prevented with more than +/- 50 Hz of error. Some of the more sophisticated decoding programs can compensate for errors within this tolerance with some form of automating tuning tracking but even they cannot cope with greater frequency errors. SDRs, for all their technical wizardry are often the most prone to large frequency errors. Checking any receiver by tuning to WWV or a similar frequency standard and calibrating is strongly recommended.
There are some digital decoding programs that natively support SDRs (or with the installation of a few DLLs). This can make routing audio to the application easier, without the need of installing a separate app such as Virtual Audio Cable. See our SDRs and Digital Decoding article for videos that demonstrate this capability.
Unfortunately, many lower end communications receivers, as well as Software Defined Radios, may be overloaded by local MW and/or FM stations, causing noise and other artifacts in the HF spectrum. You may need to add some front-end filtering - see our Improving HF Reception article.