Summary of backstay/SSB antenna radar mount posts:
Many thanks to all at the California Cape Dory Owners Association Information Exchange, at
rec.boats.cruising, and on the liveaboard list who responded to my post. The original post
concerned the advisability of a backstay radar mount where the stay was also the SSB antenna,
potential effects on compass deviation from mounting the display at the helm, and the need to
update or obtain a radio license to operte the radar in US waters.
The unanimous consensus is that mounting the radome directly from the backstay SSB antenna
is a BAD idea (some respondents suggested it mignt be possible to mount the radar below the
SSB antenna if the lower end of the stay was split into an inverted "Y", but advised against this).
The problems are evidently 1) coupling between the antenna and the radar interconnect cable
with possible damage to the radar display when the SSB is transmitting, 2) coupling of the radar
transmission into the SSB antenna and receiver masking ant SSB reception, and 3) problems
with the radar grounding interfering with both SSB transmission and reception. I am not well
versed in radio theory, so I can not be more specific but I will forward the original response to
any who want it.
Several responses addressed the issue of fixed vs. self levelling mounts in general. One
specifically mentioned problems with cable fatigue due to the constant motion of a levelling
mount. I plan to ask the radar manufacturers about this directly..
The responses on the question of compass deviation were mixed, with some people reporting no
apparent effect and others up to 5-7 degrees deviation which was adjusted out. One responder
specifically reported no difference if the radar was operating or not. The radar display will be
stamped with a minimum distance, beyond which it shound not affect the compass. One question
not addressed is the possible effect of heel inducing additional deviation.
The responses to the license question were also mixed. The best suggestion was to contact the
FCC directly.
Hope this is helpful, and once again, many thanks to all who responded.
Warren
wstringer@aristotle.net
Summary - Backstay radar mount and SSB antenna
Moderator: Jim Walsh