deploying their own AN/ARC-1 ten-channel VHF-AM set in increasing numbers, but hedged their bets with the AN/ARC-5 VHF sets in certain aircraft. This experimentation even caused them to contract for and officially nomenclature a continuously tunable AN/ARC-5 VHF capability from Aircraft Radio Corporation for evaluation purposes, shown in the above chart, but by that time (latter part of 1944) channelized equipment became the preferred technology to reduce aircrew "fiddling" with controls, so it was not pursued beyond the evaluation quantities. By late war, the discovery of "ducting" in the lower VHF band (that allowed Japanese tactical radio intercepts over long distances under certain conditions) drove development of the AN/ARC-12 (UHF version of the AN/ARC-1) and AN/ARC-27 sets in currently-used UHF-AM military aircraft band. However, it is important to understand that this gradual movement to VHF was not accomplished overnight, and there were still pockets of documented HF command set employment through war's end, especially in smaller aircraft. In terms of longevity, the AN/ARR-2 continued into service well into the 1950s, and the beacon band R-23A/ARC-5 receiver was still to be found in some older US Navy aircraft as late as the 1970s. Amateur radio use After World War II, surplus HF receivers and transmitters of the AN/ARC-5 family were extensively used in amateur radio stations. According to CQ magazine publisher Wayne Green, they first appeared for public purchase in March 1947, with thousands eventually becoming available, making them "by far the most popular surplus item to appear on the market." Green's magazine alone published some 47 articles on converting command sets to amateur use over the following 10 years, reprinting them in a compendium in 1957. Interest has continued into the 21st century. Other users The T-16 and T-17 transmitters which operated in the standard broadcast band were very hard to find on the surplus market but were used by some as low power "pirate" AM stations with the addition of a modulation transformer in the B+ line and a suitable audio amplifier which was often a 50 watt 'HI-FI home entertainment amplifier. The tuning system would allow the rig to be loaded into almost any kind of vertical antenna for neighborhood and beyond AM broadcasting. The on air fidelity of the unit was very good. One T-17 was used on 1580 at three locations in Chicago as a pirate station in the 1960s with the local FCC office raiding