[TG] [TG11] Pathfinder/C120 problem

[Bomber59]

My C120/4Kw Pathfinder radar has a 0.8 nm. totally blank area all around in all ranges. We swapped the radar to a 2Kw but with the same result. At this stage an internal diagnostic test was carried out and every component passed. The next step was to use another C120 but again with the same 0.8nm. blank area.
It was suggested that as the scanner is 10 metres above water level it would not pick up close in objects. I quickly dismissed this as basic navigation trigonometry shows the lower edge of the beam touches the surface at 46 metres.(10/tan12.5degrees).
Can anybody point me in the right direction or have a solution to my problem before I pull out what remaining hair I have left.

[Tom - Raymarine - Moderator]

Hello Bomber59,

Quite right about the range to the lower edge of the beam, that's not the cause of the problem.

Do the targets that you do see appear at the correct ranges, or is everything offset outwards? I am guessing that they are offset, and if so, that you either have an incorrect Display Timing setting or a problem with the PRI signal coming down the scanner cable to the display (I think the latter because I think that Display Timing is a display-side setup that would not affect both C120s.)

The Trigger pulse is what synchronises the time at which the scanner transmits with that at which the display starts drawing video: with a missing or incorrect Trigger pulse, the display gets the ranges wrong and everything ends up being offset outwards (I believe that the display draws the last 'spoke' when it receives the next azimuth pulse and realises that the scanner has moved on). The Display Timing is a fine-tuning of this synchronisation to compensate for different lengths of scanner cable and so video and PRI travel times, but it is only a fine-tuning: metres, not kilometres.

I'd check the ranges to identifiable targets and then check the scanner cable and connector at the scanner end for a broken wire or similar. You can also measure the resistance of the Trigger line up the cable and into the scanner using the info at http://forum.raymarine.com/showthread.php?tid=153. I think you'll see open-circuit.

Regards,
Tom

[Bomber59]

Thanks for your reply Tom,
I suspected the cable but as yet I havn' t done a continuity/ resistance test as per your link. Ranges of known objects check out. In the meantime I have just sourced a cable from our local Raymarine guru so I will jury rig my 4Kw unit up on the solar panels. Hopefully my problem will be solved with a replacement cable.
I have attached a shot of the radar screen with the VRM at 0.81 nm.
Thanks & Regards, Bomber59

[Tom - Raymarine - Moderator]

Hello Bomber59,

Having seen that image I am still thinking an open-circuit Trigger line, but I would recommend the simple resistance check before replacing the cable. These analogue radar cables are no longer made or available from us so I wouldn't consume a cable unless I knew it was required.

Regards,
Tom