DFF3D 165khz harmonics

[mattology]

Which is more painful for interference regarding DFF3D?

a chirp sweep through 165khz, like in the B175H and B175HW

or

a chirp sweep through 82.5khz, like in the B175M ?

I much prefer heaving compensation to keyphasing so for me, it's all about effective interference management through either acceptable levels of interference rejection built into the TZT3 software or a pre-defined reduced bandwidth sweep on transducers to minimize and/or eliminate interference.

 

[Quitsa]

Have you experimented with custom sweep bands? I tried using the preset frequencies to do that as a way to eliminate interference between the DFF-3D and my B175H. To my surprise, it did not seem to be effective. I used a variety of settings for the B175H with bands above 165Hz as well as CW fixed frequencies above 165Hz.

If I turned off the interference rejection filters, I saw more or less the same pattern of vertical bars as would appear with auto CHIRP sweeping the full range on the B175H. I have no idea why that would be the case but that was my experience.

So the only thing that really works for me is setting the interference rejection to "High" on both the DFF-3D and the internal sounder with the B175H. It doesn't seem to visibly affect the performance of either sounder.

Maybe one of the Furuno guys can explain why the limited bands did not eliminate the interference.

I agree with you that heaving compensation is too big a sacrifice to justify installing the KP cable.

 

[mattology]

I'm going to go to the B175M sometime soon. It will be interesting to see if I can get it to operate without any interference.

 

[Quitsa]

I'm going to go to the B175M sometime soon. It will be interesting to see if I can get it to operate without any interference.

Unless you want the B175M for other reasons, I would definitely connect it and drop it over the side to see how much interference it creates before committing to an installation. I have a feeling that what is happening is that the sounder is controlling the frequencies at which it transmits but that the transducer element resonates across a wider range of frequencies and those additional signals get displayed as the interference noise we see when the filters are off. That's the only reason I can think f for why limiting the preset frequencies to ranges outside 165Hz would not eliminate the interference.

Thus I think the B175M will "hear" the 165Hz transmission of the DFF-3D and show noise too just like the B175H.

 

[hillman]

i plan to buy 165T/265LH-PM488 DFF3D CHIRP Combo Pocket Mount Transducer, High—CHIRPS from 130 kHz to 210 kHz,
will that be ok with DFF3D operating frequency 165 kHz?
Thanks in advance!

 

[Johnny Electron]

Yes, it is fine. You will get some slight noise but many times that can be filtered with interference rejection filter. If you really get a lot of cross talk a KP (key pulse) kit could be added between the two sounders so they can't interfere but it does slow the transmissions down a bit. Most don't find a KP is needed.