The AOR AR5001D is the successor to the legendary AOR AR-5000+3 which has long been considered the best receiver money could buy.
The new AR5001D features the popular analog signal meter along with a large easy-to-read digital spectrum display. Up to three channels can be monitored simultaneously and its advanced signal detection capabilities detect hidden transmitters which may be operating illegally and also provide protection against eavesdropping by detecting miniature transmitters (bugs). Standard features include monitoring and storage of up to 2000 frequencies, 45 MHz IF digital signal processing, direct digital sampling, a high performance analog RF front-end, and a DDS local oscillator. The AR5001D can be operated by remote control using an optional LAN controller.
With an optional GPS unit, the internal reference oscillator of the AR5001D will be locked with the GPS frequency standard signal and provide 0.01 p.p.m. accuracy.
After 14 years of reliable service, my old AR5000+3 suffered a processor failure, a part long obsolete. This was just about the same time as the new 5001d was launched, but the price put me off. Then a silent key (the death of a fellow radio amateur) sale came up locally and I happened to get this receiver for a very low price, less than I'd paid for the 5000. It's very similar in operation to the previous model, but the technology is far in advance. Below 25 MHz it is a 'direct sampling SDR', which basically means the aerial signals are applied (after suitable filtering etc) to the input of a very fast A/D converter. This data stream is then handled by software. Above 25 MHz, the input signals are converted down via conventional tunable superhet techniques to an IF at 45 MHz, and again SDR methods do the donkey work. Plenty of front end filtering keeps the nasty stuff at bay, and the IF filters (which are software devices) are clean and steep-sided. Mine is an early model with some interesting 'quirks' in the operating system, so it's currently over at W&S in Essex being updated. Looking forward to getting it back!