Hi Grant.
The 'standard' factory build for these vehicles was indeed a pair of these aerial roof mounts that were essentially flat with the two bent, flat, steel strap guards on either side of it. Early wireless equipment was basically HF only, using some form of sectional whip when installed in a vehicle. Although the CMPs were built to British standards with right hand drive, the designers were aware these vehicles would not always be driving on roads that conformed to British standards. This presented a problem for where the long whip aerials should be mounted on the vehicle roof. Roads often have trees, poles with wires, and lamps located along the shoulders creating a lot of overhead hazards for long aerials if they are close to the shoulder. Consider this the 'near side' of the vehicle as it is nearest the road shoulder. The far side of the vehicle, then becomes the side closest to the centre of the road and the side with typically fewer overhead hazards for the HF wireless whip aerial. Since from the designers perspective, they had no real idea in what locations the wireless vehicles would be operating, to solve their problem of where to place the aerial mounting plates, they installed two: one each side and left it up to the operators in the field where to put the aerial.
When the 19-Set was introduced with a VHF unit added to the mix, the dual mounts on the vehicle still worked as the one not occupied by the HF whip was adopted for the short VHF aerial which was at little risk on the near side of a vehicle as often as not.
Some HF sets with more output power than the 19-Set often had a special aerial base that did not lend itself well to the standardized roof mounts supplied with wireless vehicles so one sees the additional mounting assembles added to the sides of the vehicle roof to accommodate those wireless sets. A wireless vehicle might also be used as a Relay station between two separate radio nets: one using 19-Sets and the other net using other equipment (say a 52-Set), so the vehicle carried two different wireless sets with need for relevant aerial mountings.
Sorry for the natter.
By the way, Hannos post on this thread, #30, shows both factory aerial mounts on the roof, from a front left quarter view.
David
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