997 SI Towfish and Beldan 9730

Anything Related to the Humminbird 11xx, 9xx, 8xx, 7xx also known as CORE series Units
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drinkalot
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Joined: Sat Jul 19, 2008 8:46 pm

997 SI Towfish and Beldan 9730

Post by drinkalot » Wed Jul 30, 2008 3:06 pm

Has anyone here actually build a towfish using Beldan 9730 or similar low impedance cable. I would like to know before I go down this path. I am trying to pick up small wrecks, in the 250' range in saltwater. yes, I laready bought the 262 KHZ transducer.

Sherman

Humminbird_Greg
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Post by Humminbird_Greg » Thu Jul 31, 2008 2:11 pm

Sorry, did not see your other post with Wbrusate.
Greg Walters at Humminbird
gwalters@johnsonoutdoors.com
I help because I can

rk_diver
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Joined: Sun Aug 24, 2008 5:22 pm

Post by rk_diver » Sun Aug 24, 2008 5:33 pm

http://www.alphawire.com/pages/228.cfm

The 6010C is the cable suggested by the person I spoke to at Humminbird some time ago, 50' max. The towfish I built works better in shallow water for some reason. I was out looking for a drowning victim in 50 FOW last week and the images weren't what I expected. The link below shows a shot of an intake station as scanned @ 455khz in 20+ FOW. Depth doesn't show correctly since when I did the snapshot I was using the towfish which was obviousloy closer to the bottom.

Rick

Image

drinkalot
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Joined: Sat Jul 19, 2008 8:46 pm

Post by drinkalot » Tue Sep 02, 2008 4:56 pm

Well here is the DIY towfish....video

http://vimeo.com/1635082

Problem is we added 240' of low impedance cable, and either we screwed up a splice or it is just not working...like not working at all.

No depth and the sidescan is scrolling super slow...

rk_diver
Posts: 10
Joined: Sun Aug 24, 2008 5:22 pm

towfish woes

Post by rk_diver » Tue Sep 02, 2008 7:01 pm

I did two dives last Friday afternoon on two different lakes here in Madison, WI. Viz was less then a foot in both places. Watching your video made me sick! I wouldn't know what to do with myself if our water was that clear! :P Oh well, at least I can go ice fishing! 8)

I'm going to take the transducer off the towfish and mount it on the transom to see how it works there. If it still has problems I'll cut out the extra 50' of cable and see if it works then.

240' of cable is awful long. You have to be concerned with the cable resistance and impedance as well as it's capacitance. For grins did you try setting your power level to manual and stepping thtough the different levels? You also have to remember that you have to consider transmit power and receive sensitivity. You may be able to send enough power through 240' of cable, but you may not be able to receive the returned echo. I'm guessing if your connections are good that this would be the issue. It may be worthwhile to cut the cable in half and see if there's any improvement...

Rick

onfloat
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Post by onfloat » Sat Sep 20, 2008 4:39 pm

At 240' the cable has 7 ohms of resistance. How much line loss can the unit stand and still have a useable result?

rk_diver
Posts: 10
Joined: Sun Aug 24, 2008 5:22 pm

Post by rk_diver » Sat Sep 20, 2008 9:26 pm

This may be a boring response...I honestly don't know what the max length can be. I was told 50' but I'm making some assumptions on how they (Humminbird) came up with that distance. If you left all your settings on defaults possibly 50' would be the distance that you're able to get consistent, reliable returns. If you tweak your receive senstivity and other settings I'm sure you could exceed the 50' max. Keep in mind though that the term "resistance" refers to a straight resistive load, it doesn't take into account other variables which are always present (capacitance and inductance) that can/will affect the input and output signals. This loss is "impedance", which can vary considerably from strictly resistive loads (which don't really exist in the "real" world). If you consider a basic "resistive" circuit of a battery, wire and an incadecent lamp, one would assume it would be strictly resistive. But it's not...the filament of the lamp has inductance and capacitance, as does the battery itself, and the wire. A cool example of this is when I'm diving with my underwater metal detector. If I turn on my dive light I can hear the load having current applied to it through my headset (just like a motor circuit, a lamp has it highest current draw the instant power is applied).

Combining resistance, capacitance and inductance in the proper setup will filter out (or pass) certain frequencies. So if the cable you use has the correct values you can pretty much kill your return signal (or transmitted signal). That's why if you have 200' of cable you may have terrible results, but with a little less you might be OK (which also means it might be OK with a little more cable since you're changing the filtering values). Look at it this way, a short piece of cable, because of it's internal impedance, could (can) give you a worse target return then a longer one.

Like I said, probably boring. Trial and error is what's used to get the best possible return. The mathematics will get you close, but the "proof is in the pudding"! Hopefully this will explain a little bit why you just can't look at the resistance. Rick

Chessyman
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Location: Minnesota

Thanks, great reply rk_diver. (no text)

Post by Chessyman » Tue Oct 14, 2008 11:41 am

.

phowarth
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Joined: Tue Sep 30, 2008 9:25 pm

50 Limit

Post by phowarth » Wed Nov 05, 2008 11:12 pm

One possible reason for the 50' recommendation is if the transducers communicate with the head unit using the RS232 standard. If that is the case there may be line drivers that can improve the transmission characteristics for longer runs.

Paul

rk_diver
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cable

Post by rk_diver » Thu Nov 06, 2008 11:47 am

No, it's not RS232. Different technology. There's no "electronics" in the transducer which would be necessary for serial communications. Rick

LutherRay
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Post by LutherRay » Sun Jan 24, 2010 6:39 pm

I know it has been a while since this was posted but to help anyone who needs it...

First, Amazing video. Thank you for taking the time to record and post it.
Second, cable splices can be sealed effectively using 3M "130C Linerless Rubber Sealing Tape" and put 3M "Super 88" tape over the top, wound in the opposite direction to cap it off. Make sure when you are applying the sealing tape that you keep firm, slightly stretching, pressure on the tape as you apply it and that you half lap your tape. Heat the splice up with a hair dryer after you are done to set the adhesive in the tape.
I use this method at work on low voltage (30mV max) cables submerged in 2' of water for years with no leakage.
Also, if you think you may have water in a cable, the only sure way of determining for sure is to use a megohmmeter to test it with. You test all of the inside wires twisted together to the shield wire. cables will dry out if you leave them in a warm well ventilated area for... (some period of time)
I taped up a pencil to show what I am talking about. The loose tape is there for reference only.
Hope this helps...
Image
[/img]

drinkalot wrote:Well here is the DIY towfish....video

http://vimeo.com/1635082

Problem is we added 240' of low impedance cable, and either we screwed up a splice or it is just not working...like not working at all.

No depth and the sidescan is scrolling super slow...
Luther

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RGecy
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Post by RGecy » Sun Jan 24, 2010 8:10 pm

The longest cable I have seen is 150' and the sensitivity had be jacked all the way up. I am not sure what cable was used, but it is listed somewhere here on the forum. Just do a search for towfish.

We need some engineers to come up with a device to extend the signal out further so we can use a longer cable.

Robert

RimaMoricca
Posts: 1
Joined: Tue Jul 29, 2014 8:47 pm

Re: 997 SI Towfish and Beldan 9730

Post by RimaMoricca » Tue Jul 29, 2014 8:53 pm

If you want to know the things under the water, you can buy an underwater metal detector, and it can help you to solve the proble that you have encountered.

PattiHych23
Posts: 1
Joined: Wed Sep 24, 2014 12:56 am

Re: 997 SI Towfish and Beldan 9730

Post by PattiHych23 » Wed Sep 24, 2014 12:59 am

underwater metal detector is especially designed for the underwater performances, here it provide with these kind of derectors of high-tech manufacturing, hope it can help!

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