|From Ocean Navigator #108 |
What might be the problems with placing a gimbaled radar mount on a backstay (insulated) that’s used as an HF (ham) radio antenna for the effective use of the radio and the radar operated simultaneously? Boat: 1939, 41-foot, wooden Alden marconi-rig sloop with a 60-foot mast. Radar: Simrad RA772UA LCD Radio: 150 watt SGC PowerTalk HF radio with auto tuner coupler and grounding to a very large dynaplate.
If I had a choice of putting the scanner unit on either the mast or the backstay, which would be best?
Since I need to step and unstep the mast often, I’ll need to cut the cable and junction box. Will I eventually have problems with the cable disconnect?
Larry CilleyBath, Maine Answer:
Placing a radar on an insulated backstay used as an SSB antenna will likely produce unsatisfactory results. Most radar set scanners must be connected to the vessel’s ground bus. A ground on the radar scanner will therefore place a ground on the backstay, unless the mount were specially insulated from the stay. The insertion of a ground at this point will make tuning the antenna difficult, if not impossible, and reduce the effectiveness of the antenna during transmission. In addition, the relatively high-voltage RF field surrounding the backstay during transmission may damage components in the radar scanner.
Repetitive connection and disconnection of the scanner/radar display cable for mast removal will require installation of either a suitable junction box or a special connector. Connection points are typically the weak link in any piece of marine electronics and should be avoided whenever possible.
Gimbaled mounts can cause problems with some radar scanner connecting cables. The constant motion of the scanner relative to the surface on which it is mounted can fatigue the cable, which is not designed to withstand this type of service.
It is likely that the best overall results will be achieved by mounting the radar on a short mast at the stern of the boat. It is unnecessary to mount the scanner at any great elevation; in fact, too high a mounting height can create problems when trying to see close-in targets (for fixed mounts and a somewhat heeled boat). I would mount the radar on a stern mast so that it clears the deck by about seven to eight feet. This will likely place the radar antenna about 10 to 11 feet above the water. At this height the radar horizon will be at least four miles distant. Targets at this height above the water will be visible at about eight miles, with higher targets visible at longer ranges. If you use this approach, do not mount a DGPS antenna adjacent to the radar scanner.