Dug out my copy of "The Enemy is Listening", so for the OP and, in particular, Cordwainer's Post #19 the full text of that section reads:
"Apart from our responsibility for monitoring Luftwaffe R/T, we also had the task of investigating what we called 'Noises'. These included beam and pulse transmissions from enemy radar, and such signals as high-speed Morse transmissions. In this Reggie Budge and Jonah Jones, who were particularly interested in signals developments in the higher frequencies, worked in close collaboration with No. 80 Wing, TRE and the naval signals specialists. As these higher frequency transmissions have a strictly limited range, we opened up a new HDU at Capel, near Dover, and an attempt was even made in July 1941 to set up a listening watch in a man-carrying balloon to cover decimetre band transmissions which we thought might be connected with the setting up of the beams.
The balloon which was used was an R-type Cacquot of the kind used during the First World War for observation purposes. The ascents were made at night under the expert guidance of Squadron Leader Lord Ventry and Flight Lieutenant John Evason. The principal radio operators involved in this hazardous venture, who spent many airsick hours in a gondola slung beneath the swaying balloon 3000 or 4000 feet above Dover, with air-raids in progress beneath them, were the then Flying Officer Jimmy Mazdon and Pilot Officer Basil Sadler. By coincidence, Sadler was the great grandson of the early English balloonist of the same name. (He was to be killed later during an investigational flight over Western Europe.) The venture was short-lived, as the Air Ministry considered it was too expensive in manpower and they had found a way to operate the receivers in the gondolas by remote control."
Also, for those really interested in early Radar, can I recommend the "Technical History of the Beginnings of Radar" by S.S. Swords, published by the IET.
Messy