In the early days of DF, most of the transmitters were crystal controlled valve types that were home made, until the advent of Amateur commercial radios in the 60’s. The advent of these transmitters and transceivers tempted the foolhardy affluent types to use them at hidden sites. This was fine whilst the sport was still run in a gentlemanly manner, ie, hides were not too vicious, just a table and deck chairs under some trees way off the road. The disadvantage of the early amateur sets was that they only had one filter for TX and RX on all AM type modes, thus when switching from CW to AM as is required, the carrier frequency moves quite a lot to keep it in the filter passband. This meant that a competitor could be receiving the CW with a beat on one side of the carrier, and the TX switched to pseudo AM (inserted carrier SSB) and moved its carrier out of the receiver pass band. Salisbury used to do this for some years , until newer purpose built TX’s were built.