Here is the page from The Use of Radar at Sea Here it’s called Second-trace echoes: [image] A quick check looks like 500 pulse/sec is typically ppr (or ppf pulse-repetition frequency). According to this if the rr is on 30 mile range second-trace echoes have to be beyond 162 miles. It does say i…

I assume that there is more sophisticated equipment out there now but we used a pinger on the same frequency as the echo sounder which gave a second trace so we could see how far the equipment was off the bottom.

[image] Hogsnort: pinger on the same frequency as the echo sounder which gave Clever. Echo sounder version of a RACON, or the transponders used to keep track of aircraft.

Does it randomly ping or answer the ping from the fishfinder?

It would have to answer, as it has to be synchronized to the outgoing pulse from the sounder. In effect it turns a little target into a big one.

So if the depth finder is set on the 10 meter scale and the depth is 11 meters the return from the bottom will show up on the display as if the depth was 1 meter. If the depth finder had a feature similar to the radar than on the 10 meter range one full rotation of the indicator would be 54.7 met…

[image] Kennebec_Captain: In other words on the 10 meters scale instead of sending a pulse the equivalent of every 10 meters the pules would be at intervals of 54.7 meters This won’t happen on a flasher-type echo sounder because the prf is always equal to the time taken by one revolution of t…

[image] dbeierl: This won’t happen on a flasher-type echo sounder because the prf is always equal to the time taken by one revolution of the light – it’s actually triggered by the light passing the zero point on the scale. Yes, agreed. [image] Kennebec_Captain: If the depth finder had a …

So the standard depth finder has no unambiguous range. However at the 100 meter range scale if the the pulse was sent at t = 0 only on every third revolution and the receiver was shut off for the next two revolutions than the unambiguous range would be 300 meters.

Radar Second -Trace / Unambiguous Range

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dbeierl January 31, 2020, 1:20pm 57

It’s still a thousand watts (joules per second) no matter how long or short the pulse. Total pulse energy of the above pulse would be 0.2 joules.

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Radar Second -Trace / Unambiguous Range

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