I just saw the Raymarine Dragonfly 4DV on sale below $130. I know this is downvision only and chirp I believe. I currently have a Humminbird Helix 5 SI GPS. The downvision on this unit isn't that great and I believe it is a computer simulation and certainly not chirp. I would put this unit right next to it and use it just for downvision and put a full screen side imaging or map on the humminbird. Does anyone have the 4DV only? I can't find many screen shots online. Is it big enough to see? Is this an old discontinued model? Is it worth the price? Any other input?

The Humminbird Helix SI units produce a Down Imaging view by blending the two SI pulses. 

Right Wayne. So it that good or bad? Better or worse than the Raymarine chirp downvision?

Dedicated down looking imaging produces sharper images than the blended Side Imaging.

The Raymarine DV is better, well any brand with dedicated down looking imaging is better, even the DI that Humminbird ONIX SI units have.

Do you think I can run both units at the same time with both transducers on my transom? Or will the transducers produce signals that will confuse each other?

Have not researched the Raymarine products.

Simple rule is if any units are operating at the same time on the same frequencies, when their sonar pulses overlap, they will cross-talk. Overlapping for sonar pulses on transom mounted transducers is pretty much a sure thing.

The Helix broadcasts 200 kHz 2D all the time no matter which frequency (83 kHz or 200 kHz) you choose to view. You can select either 455 kHz or 800 kHz for Imaging.

If the Raymarine has a 2D frequency that is independently selectable and a DV frequency that is independently selectable, you can use the one that doesn't match the Helix and won't get cross-talk much. Harmonics of a frequency will cross-talk a little but usually not noticeable.

The dual Image screenshot I posted has some cross-talk since SI and DI are using the same frequencies. I typically do not use Down Imaging at all so that is either turned off or I set it to 800 kHz for demo screen shots. Just did that screen shot for demo.

 

 

Thanks for your input Wayne. I guess I just need a second job so I can afford adult size electronics....

The two units you have in mind will do just fine independently.

You can pay $10,000 or more each for sonar/GPS units and they will still cross-talk if they are using the same frequencies.