DRS4D-NXT Display Fades Intermittently

[Loy]

While U/W in ICW (low lying Marsh country) the radar contacts intermittently fade completely, then, after a minute or so, return. Waterways banks will show bright and then disappear. This fluctuation doesn't happen while in a slip.

Additionally, small (15' to 28') fast closing targets show red, switch to green, then disappear completely irrespective of range from own boat.

It's as if the gain is being reduced to zero and then restored.

Setup as follows:
- 2-TZT2-12 Displays
- Single Range at 0.5 mile
- Target Analyzer on
- Rezboost Enhanced 3
- No Sector Blanking
- ARPA targets

 

[Flatline]

Loy,
Thank you for your inquiry.
Your description of targets fading and then re-appearing makes me believe that its possible that these targets are in fact passing below or under the beam of the radar, but as they gain distance re-appear because they are once again within the beam of the radar. The stated minimum range of the 4DNXT is 20m (65'). That being said however we have routinely witnessed excellent target returns on objects much closer than this distance.
A few things to note here; the vertical beam width of the DRS4DNXT radar is 25 degrees. So in theory if the radar is mounted on a perfectly horizontal plane 12.5 degrees of the radar beam is pointed "skyward" and 12.5 of the radar beam is pointed "downward" toward the water surface. Knowing this geometry it is possible that targets that are close to the vessel & radar antenna will eventually pass beneath the radar beam (which accounts for the disappearance) but as the vessel moves away from the target and the distance between the two increases the target re-enters the beam and as such re-appear on the radar.
This effect can be exacerbated by the trim of the vessel. If you vessel tends to ride or plane out with the bow pointed even just a few degrees skyward and not at a perfectly horizontal plane, you've now increased the distance that targets could pass beneath the radar beam. Many installers will counter this effect by slightly shimming the backside of the radar antenna when mounting. This gives the appearance on the radar antenna pointing ever so slightly downward when the vessel is sitting level (like when in your slip).
My recommendation would be to try to readjust the angle of the mounting of the radar antenna itself to see if this corrects the anomaly that is occurring.

 

[Loy]

Thank you for the response Flatline. Entirely plausible; I wish that were the answer. But......
The Radome is essentially parallel with the horizon while running at the displacement speeds where the fading is experienced. As noted, this has happened when on the 1/2 mile scale. The fading is over the entire range, from own ship out to the edge of the display. All contacts & land fade uniformly. It is as if the gain is reduced.
Maybe significant: the fading has not [yet] occurred if Target Analyzer is NOT engaged.

 

[Loy]

Nothing has changed since my last post 3Nov.
Any other ideas?
Help!

 

[Johnny Electron]

Do you have a photo of the boat showing the mounting location and surrounding items?

 

[Loy]

PDF file of photos of my two panels is attached.

On the interior panel a Class B AIS [VESPER XB-6000] is mounted behind the TZXT2 display along with a VHF antenna splitter tying the AIS to the antenna of the station's VHF radio [seen to stbd of the TZX2 display]. Also behind the panel is FURUNO Hub along with a NEMO GATEWAY Multiplexer. The NEMO ties the Autopilot Control Box [J300X] with other NMEA 0183 devices with NMEA 2000 and a WIFI router, again behind the panel or immediately adjacent below the engine instrument pane..
The VHF handset to port is the remote for the AIS-capable [receive-only AIS] VHF radio located at the FB panel.

On the flybridge panel, the equipment is self-evident. Nothing fancy located on the back side.

Mike

 

[Johnny Electron]

Sorry, I should have been more specific. It would be useful to see the radar antenna and the surrounding items. Many times what you are reporting is related to the radar mounting and what is around it. You have very nice layout.

 

[Loy]

Johnny,
Thanks for the quick response; I sure misinterpreted you instructions! Hah.
Attached are 2 photos of the setup on the Radar Arch.
The NXT is centerline.

To port, there is a VHF antenna 72" from c/l serving a radio with AIS receive-only.

To stbd:
--outboard is a duplicate VHF antenna 72" from c/l serving a radio and AIS transmit via antenna splitter
--A GPS mushroom antenna is 32" from c/l
--A WiFi Ubiquiti-type antenna is 32" from c/l
--A cell phone amplifier is 31" from c/l
--A TV antenna is 18" from c/l
--A Hailer speaker horn is 11" from c/l

Mike

 

[Loy]

It looks like my two small pdf files [from my photos] did not upload.
I looked thru FAQ about attachments and couldn't see what I am doing wrong.
One pdf was 142KB, the other was 77KB. Are these really too large?
Are only jpg files accepted?
Mike

 

[Loy]

Alright, I've played around with files to try and reduce size.
Let's see if the 2 upload this time.
Mike

 

[Johnny Electron]

Looking at the radar placement, I suspect you need a wedge mount. There have been several others on the forum that mounted the NXT straight like that and when the boat hull pulls up during operations the radar beam is not digging in and it is over shooting. I would be also a bit concerned about some of the transmitting antennas near the dome. It is hard to tell by the photo but one looks about a foot and a half way. Furuno recommends VHF/AIS antennas be at least 3 foot or better away. Based on your description, it sounds more like a wedge mount is needed. You might try taking the boat out and running the radar at idle and see if it works well. If it does, then later the problem develops running; it really sounds like the issue. I assume you haven't got any settings setup like sweepfade, echo average, target trails setup. When troubleshooting it is best to go with the basics.

 

[Loy]

Johnny
Re: wedge/radar mount angle -- see my post this topic 3Nov. Bow does not rise at displacement speed.
same post mentions that fade not seen if target analyzer is engaged

Specific distances are detailed my post 26Dec 5:29PM. VHF [and AIS] antennas are 72" outboard of c/l.

Mike

 

[Johnny Electron]

I don't see anything that would cause radar reflections to tune it down. The unit might need to be evaluated by your dealer or local Furuno distributor.