Sector blanking DRS4D

[colemj]

I'm installing a DRS4D on a bracket on the front of our mast. I assume it will need a sector blank for the portion of its sweep that includes the mast. How wide should this sector blank be? Is setting it for just 180* enough, or set the range to cover the center of the antenna sweeping past the 6" of mast section, or does it need a large range that includes the whole 24" of antenna sweep across it? If the latter, then it seems like there will be no radar transmit/return for ~50% of the antenna sweep, and the blind spot will be huge. Even setting a range to clear 6" of mast section, the trig works out to a 30* blank sector.

Mark

 

[C-Bass]

Colemj,

Thank you for your inquiry.

Typically it is must a small sector blank that is needed. The good news is it is an easy procedure to do so you can fuss with the blanking sector a couple of times to make sure you achieving the results for a good performing radar. You could start really small and work your way up or start larger and work your way down to find the best value.

C-Bass.

 

[colemj]

Thank you for the reply. I guess my question is how do I know how large of a sector I should blank? With no blanking, I don't see any problem with the radar return. Even at a very close scale, I see objects behind the mast past the main bang suppression distance. Playing with blanking angles just makes those objects disappear when they are in the blanked sector. Since the mast itself doesn't show up, I don't know how much sector to blank.

Is sector blanking required at all for a radar mounted on a 6" mast section? Many, many sailboats have radars mounted in this position, and when I ask about how they set up sector blanking, I just get blank stares.

 

[Taniwani]

There is the remote possibility, that the strong return signal from the mast could blow your mic. Though that would only be the case if you had a timing problem and the mic was opened way to early, (or not closed at all). That would mean a smaller fault could cause a bigger damage.

On the other hand preventing a strong return form the mast would require a blanking sector of almost 180 degrees, given that some part of the antenna would still aim at part of the mast for most of the aft sector.

A certain blanking sector may help reducing false echoes, from beams that are reflected off the roundish mast profile, though I found this really hard to do.

I had helped a number of friends with mast mounted domes and found that none had blanking set and when trying it out, I wasn't able to get a better performance. Without a blanking sector the radar usually works fairly ok in the aft direction, as the antenna is wider than the mast, so that at least part of the signal passes left and right of the mast (and comes back that way). It's just weaker and it 'sees' less far in the aft sector.

 

[colemj]

My concern is from this Furuno thread: viewtopic.php?f=5&t=5252

Our setup is identical, although our mast section is a bit narrower than that shown.

The manual only briefly mentions sector blanking, but doesn't provide much guidance.

So what is the sector degree needing blanking for a 6" mast section immediately behind the dome?

Mark

 

[Taniwani]

Just looked at the thread you mention above. Seems a rather small dome on a really fat mast.
So firing at it really makes not much sense, whether it hurts the unit or not.

I think your 24" radar is a different story and I would think that you should 'see' targets right astern of your boat. The 6" mast section would only block about 25% of the radar beam.

On the other hand, as your antenna is fairly wide, it will send into the mast for a rather wide sector. For a normally close to the mast dome, this would be some 80 degrees on each side, so that the blanking sector would have to be 160 degrees if you want to avoid a strong return signal coming back at the antenna. The strength of the reflected signal would be the same as long as part of the antenna still covers the full mast section. But as the mast has a roundish profile, the reflected energy will be spread and that spread signal will only be covered wholly when pointing straight aft.

So there may bee some advantage avoiding the maximum return using a smaller sector.

But as I said before, the radar is designed to clamp the receiver input of the MIC and the expectation of a strong close return is part of the design brief.