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  1. #31
    Ausfish Silver Member 552Evo's Avatar
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    Melbourne
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    Re: Airmar TM165HW feedback wanted.

    Quote Originally Posted by scottar View Post
    The wide cone angle at 60 metres will make a pinnacle a much more rounded return due to the time it spends in the cone angle. Whether it's an issue or not will depend on the physical areas of reef and the species you are targeting and their tendency to move to a bait or stay tight on the structure.
    Thanks Scottar,
    So a wide cone with chirp would be good for locating reef and finding fish in and around reef in 10-40m ?

    Areas of reef along the coast hmmm, rocky, weedy, could be anything I guess.

    My main target fish off the coast are
    1 gummy which spend most their time along the bottom
    2 snapper anywhere in the water column
    3 kings above the bottom anywhere in the water column.

    I reckon generally all 3 of the above fish generally will be on the move, they won't hang for long.
    These are my observations happy to be corrected.
    Does this info help ?


    Sent from my iPad using Tapatalk

  2. #32

    Re: Airmar TM165HW feedback wanted.

    And THAT'S why you guys are lucky to have Scott around.

    Familiar with a Simrad setup and can cut straight through.

    Cheers, Scott.

    Ronje

  3. #33

    Re: Airmar TM165HW feedback wanted.

    552Evo

    Jamie

    Simply put, target separation (range resolution) is the ability to individually distinguish fish close together (like so). A screenshot on the LHS of a conventional pulse sounder with poor target separation/range resolution.

    The screenshot on the right is the same image but this time using CHIRP which shows the fish up as individual separate targets. THAT improvement is the main advantage of CHIRP.

    conventional pulse sounder.jpgChirp same image.jpg


    The screenshot below shows how individual targets can be clearly seen at 233 feet depth with Chirp. Also note that the sonar frequency in use is called High Chirp(lower left corner of image). That's simply a term used by the yanks to mean 200khz (which is what YOU want for deeper water excursions).

    Note that you can easily distinguish fish close to the bottom.


    200khz Chirp.jpg


    There is two important things to realize about CHIRP. Firstly you need to have a Chirp compatible transducer. Those Airmar ones we looked at are indeed Chirp compatible transducers for 200khz. One problem solved.

    Airmar is happy to advertise the technical aspects of its products. With the TM transducers we looked at, the technical graphs show that the transducers (centred on 200 khz) are capable of passing a Chirp signal that sweeps from 150 khz to 250 khz making it a sweep of 100khz. THAT'S very important because that potentially gives us a very good target resolution of 7.8mm

    What that means is that if the fish are more than 7.8mm apart, you'll see them as individual fish. OR if they are more than 7.8mm above the bottom, they show up separate from the bottom. Those are incredible figures for distinguishing between fish or between fish and the bottom.

    However, there is a drawback that's commonly encountered and that is that the sounder manufacturers are very secretive about how far their Chirp signal actually sweeps.

    Although the transducer may be technically capable of being swept from 150khz to 250khz (making 100khz of sweep), the sounder manufacturers don't always use full sweep and therefore the target separation/range resolution suffers and you don't get the full benefit of Chirp.

    Lets say they only set the sounder to sweep from 175khz to 225 khz (making 50 kz sweep). Then the target separation capability becomes 16mm.


    Still 16mm is pretty good anyway considering that a normal 200khz pulse sounder that uses a 1 millisecond pulse gives a target separation of 780mm. One hell of an improvement by using Chirp (even if it is "throttled back").

    Look up the specs on Humminbird Chirp sounders. Like other sounder manufacturers they are secretive about their sweep ranges.

    However, they quote a target separation/range resolution for ALL of their Chirp models as 63mm . We can work backwards from that to give us a sweep range of 13khz.

    So, although the transducer might be capable of 100 khz sweep, the Chirp sounder unit appears to be only sweeping it at 13kz (13% of its capability). So you'd have to ask yourself if its worth buying such a transducer if the sounder isn't going to drive it properly.

    Yell out if other queries.

    regards
    Ron

  4. #34
    Ausfish Silver Member 552Evo's Avatar
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    Jul 2016
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    Melbourne
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    Re: Airmar TM165HW feedback wanted.

    Quote Originally Posted by Ronje1 View Post
    552Evo

    Jamie

    Simply put, target separation (range resolution) is the ability to individually distinguish fish close together (like so). A screenshot on the LHS of a conventional pulse sounder with poor target separation/range resolution.

    The screenshot on the right is the same image but this time using CHIRP which shows the fish up as individual separate targets. THAT improvement is the main advantage of CHIRP.

    conventional pulse sounder.jpgChirp same image.jpg


    The screenshot below shows how individual targets can be clearly seen at 233 feet depth with Chirp. Also note that the sonar frequency in use is called High Chirp(lower left corner of image). That's simply a term used by the yanks to mean 200khz (which is what YOU want for deeper water excursions).

    Note that you can easily distinguish fish close to the bottom.


    200khz Chirp.jpg


    There is two important things to realize about CHIRP. Firstly you need to have a Chirp compatible transducer. Those Airmar ones we looked at are indeed Chirp compatible transducers for 200khz. One problem solved.

    Airmar is happy to advertise the technical aspects of its products. With the TM transducers we looked at, the technical graphs show that the transducers (centred on 200 khz) are capable of passing a Chirp signal that sweeps from 150 khz to 250 khz making it a sweep of 100khz. THAT'S very important because that potentially gives us a very good target resolution of 7.8mm

    What that means is that if the fish are more than 7.8mm apart, you'll see them as individual fish. OR if they are more than 7.8mm above the bottom, they show up separate from the bottom. Those are incredible figures for distinguishing between fish or between fish and the bottom.

    However, there is a drawback that's commonly encountered and that is that the sounder manufacturers are very secretive about how far their Chirp signal actually sweeps.

    Although the transducer may be technically capable of being swept from 150khz to 250khz (making 100khz of sweep), the sounder manufacturers don't always use full sweep and therefore the target separation/range resolution suffers and you don't get the full benefit of Chirp.

    Lets say they only set the sounder to sweep from 175khz to 225 khz (making 50 kz sweep). Then the target separation capability becomes 16mm.


    Still 16mm is pretty good anyway considering that a normal 200khz pulse sounder that uses a 1 millisecond pulse gives a target separation of 780mm. One hell of an improvement by using Chirp (even if it is "throttled back").

    Look up the specs on Humminbird Chirp sounders. Like other sounder manufacturers they are secretive about their sweep ranges.

    However, they quote a target separation/range resolution for ALL of their Chirp models as 63mm . We can work backwards from that to give us a sweep range of 13khz.

    So, although the transducer might be capable of 100 khz sweep, the Chirp sounder unit appears to be only sweeping it at 13kz (13% of its capability). So you'd have to ask yourself if its worth buying such a transducer if the sounder isn't going to drive it properly.

    Yell out if other queries.

    regards
    Ron
    Thanks Ronje1

    Very nice explanation, appreciate that.

    Iím still ( this morning ) browsing all the specs from airmar about the options on offer to make up my mind.

    Seems like the guts of the various transducers are common across the various mounting configurations- which makes obvious sense.
    So that clears up that issue - I ďwasĒ thinking the thru hull would be most likely to provide the best results. But after readings Scottars feedback iíd be happy to have a transom mount and save the effort of an enormous hole in the hull.

    So I think a transom mount.

    Yes a chirp version - for the best separation.

    Wide cone angle - I think because a majority of my fishing is done in less that 50m of water (say 20-40m) I think the wide option would be ok.

    600watt or 1000w - again I think because Iím in relatively shallow water the 600watt should be plenty.

    The TM165HW seems to tick all the boxes.
    For now

    Jamie


    Sent from my iPhone using Tapatalk

  5. #35

    Re: Airmar TM165HW feedback wanted.

    Good luck with it and I think you are heading the right way.

  6. #36

    Re: Airmar TM165HW feedback wanted.

    Jamie, i can't comment on the transom mount but i'm running a pair of through hull, one a high frequency wide angle and a another medium frequency both in 1kw 20 degree tilted elements in chirp to a pair of garmin 7410's. The high wide is a great bit of kit for getting over the heap of country out to about 80m when it becomes harder to triangulate the fish your seeing because of the width of the cone at that depth. To get the best value from the wide angle you need to be able to sound at speed, i recon thats the benefit of the through hull (for my boat anyway). Good flat day sounding at say 18knots you can cover some country.
    Scott

  7. #37
    Ausfish Silver Member 552Evo's Avatar
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    Melbourne
    Thread Starter

    Airmar TM165HW feedback wanted.

    Quote Originally Posted by Out-Station View Post
    Jamie, i can't comment on the transom mount but i'm running a pair of through hull, one a high frequency wide angle and a another medium frequency both in 1kw 20 degree tilted elements in chirp to a pair of garmin 7410's. The high wide is a great bit of kit for getting over the heap of country out to about 80m when it becomes harder to triangulate the fish your seeing because of the width of the cone at that depth. To get the best value from the wide angle you need to be able to sound at speed, i recon thats the benefit of the through hull (for my boat anyway). Good flat day sounding at say 18knots you can cover some country.
    Scott
    Always nice to have options. And youíve got awesome options. I like the idea very much of covering a lot of ground because here in Tijuana/Melbourne the bay can be a very sparse place. So to search at speed over a decent area for any lumps and bumps (or shopping trolleys) that hold fish has to be a good thing.
    Even when I venture outside the bay as I mentioned previously I havenít been far enough out to worry if my sounder will pick up a marlin at 300m half way down the water column
    Plenty of Kings and Tuna not that far out or deep. Not to mention my tub is shall I say - a fair weather craft
    Iím comfortable enough with Scottars advice about thru hull vs transom mount setup. So thatís all good.

    Cheers


    Sent from my iPhone using Tapatalk

  8. #38

    Re: Airmar TM165HW feedback wanted.

    I have to say with PPB being a bit of a soup bowl dessert. it does allow for side imaging sonar to play a more useful part than what salt water anglers would ordinarly use. especially the lower frequency side iamging "260khz-455khz" to cover a decent amount of ground.

    being able to pin point that natural or um "ehhhhh.. man made" reef among a sea of nothing is rather useful.

    Marine outfitting solutions
    www.moosemarine.com.au

  9. #39

    Re: Airmar TM165HW feedback wanted.

    "Through hull" transducers avoid the problems faced by turbulence caused by water flowing over/around the leading edge of the transducer when its in the water.

    Simply mount the transducer INSIDE the hull facing down on a bed of silastic or similar with NO air bubbles in the silastic.

    However, that means that the acoustic sounder signal has to pass through the silastic (or other bedding material), the hull itself and then the water. So there is going to be degradation of signal involved. That's just a simple fact of life.

    Actually the losses are DOUBLE because the signal has to go down to the target and being reflected back. THAT reflected signal also has to pass back through the water, the hull material and the silastic to reach the transducer again.

    The signal will be degraded both ways.

    However, if you've got sufficient signal to start with (sufficient power) , then a "through hull" mounting won't be a major problem despite losses PLUS it will be impervious to turbulence problems (unless you have existing turbulence on the underside of the hull already.

    Mostly, a "through hull firing" transducer works ok providing the hull is f/glass not metal.

    I put a "through hull firing" transducer in the bow of a 6m aluminium rescue vessel looking forward to give prior warning of obstacles ahead underwater in the treacherous river here for night work. Rockbars and remains of rock walls all over the place for 50km. The rescue guys didn't want to find fish or get lots of detail so it worked ok on the fw looking transducer despite the high losses.

    One complained that at speed at night the bow lifted up onto the plane and the forward looking signal was lost so he had to slow down. As the guy running the rescue unit, I told him that he wasn't to be doing planing speed at night with crew on board unless he was absolutely sure of where he was from his knowledge of the river. Installed a short range radar to help 'em do that accurately at night.

    So there's a good example of how to use something that DIDN'T work for what it was designed for (finding fish), but DID work for something that it WASN"T designed for. Thinking laterally.

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