Humminbird Side Imaging Forums
General => General Discussion => Topic started by: zaccaria on April 29, 2010, 04:05:50 AM
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Hello everyone, I am new to the forum, I'm building a towfish for my 797.
Can I get information about which cable to use and the maximum length you can use?
Thanks
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zaccaria,
Welcome to the forum.
You can use Belden 9730 or Alpha 6073C or any 12 to 15pf per foot.
22 or 24 gauge with 3 individually shielded twisted pairs.
I have heard of longer cables, but most seem to keep it around 150'. You have bump up the sensitivity quite a bit.
Good Luck and let us know how it turns out.
Robert
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Hi Zaccaria,
If you can't find the Belden or Alpha cables, or similar, or if you find them too expensive, it's possible to use ethernet cables like I do myself. I posted a detailed description on how that's done here: http://www.geotech1.com/forums/showthread.php?t=16307 (http://www.geotech1.com/forums/showthread.php?t=16307)
Here is an example that shows what you can expect with 50 m (150') ethernet cable. Small power boat at 30 m (90') depth:
[attachment=1]
Another example that shows an unknown vessel at 28 m depth. The towfish passed about 7 m over the seafloor.:
[attachment=2]
Regards,
Rickard
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Hey, good pictures. good tow.
question.
1) Do you have somne interference as I see a lot of short verticle lines. I have that occassionally on some motors since my unit is portable and is used on different boats?
Chuck
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Thanks and yes Chuck,
that's interference from the ignition system, I think. The vertical lines appear in both views simultaneously so they have to do with some common factor outside the SI channels. The lines can be eliminated by raising the noise setting in the instrument, but they do not disappear when you use a third part viewer like Humviewer or SiView. A long cable makes the system more sensitive to interference but I have got used to it so I do not notice the lines anymore until someone reminds me about them...
Rickard
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OK, thanks.
Sorry to remind you.................... when we run our unit on some boats I see the same lines. Wonder if I should filter or choke the power line. Or is this interference injected into the sonar cables?
Yes the lines show up on the viewers more so than the unit.
This was a more recent run. this boat had a 175 hp ourboard and near the transducer.
[attachment=1]
Thanks again. chuck
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I forgot the smiley after the reminder thing... ;)
I think the interference comes "through the air" - from sparkplugs or coils or something. I use a separate battery for the Humminbird to prevent from interference through the cables. That reduced interference alot but there are still lines and dots that seems impossible to get rid off.
Rickard
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Thats exactly the same here. The sonar unit is mounted in a box and that has its own battery inside. No connection to the boats system. I seem to get more interference with the larger motors and when the transducer is near the motor. ( mounted on the transom) :P This same boat had the transducer mounted in the front for a couple of runs and did not have the lines. The box unit was also in the front bow.
Maybe Greg can get in on this and talk about filters or chokes.
Appreciate the time to share your views and thoughts.
Chuck
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Thank you all, this week I try to assemble it all, I will keep you informed on how the tests.
Thanks
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Sorry to hijack your thread here zaccaria.
That’s probably RF interference Chuck. Radio Frequency interference does not need a metal to metal connection to get into something. Those transducer cables (and any other cable) acts like an antennae and can allow RF interference into the unit. Only way to know if it is coming in on the transducer or some other cable is to unplug it and see if the interference is still there. We have even seen it come in through the control head itself. Something to try on the extra transducer cable you have (even towfish) would be to counterwrap it. This is shown in the transducer installation guides and is supposed to help suppress RF interference.
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Yep we kind of screwed up Zaccaria post. I sent Robert a message asking how to split the topic so we could take the hijack out of the original post. maybe I can get that done tonight.
I want to get his original post back in line.
Chuck