Topic: Garmin vs Humminbird vs Lowrance Side Scan

[sonarbear]

Does somebody have images or experience to compare the resolution of HB and especially Garmin side scan? I can't seem to find much online. Does Garmin have higher resolution than the HB HD transducer?

[mike fish]

There was some talk about 30-45 days ago if you look back.  I'm not able to find it right now.

[Rickard]

If you ask for images, there are very few, if any, fair comparisons between Garmin and Humminbird on the web. One way to go is collecting specifications on the transducers, and then calculate beamwidths. You need data on element lengths and frequency. Then the horizontal beamwidht can be calculated. This feature is the most important factor that determines resolution. All other factors, like chirp or no chirp, element material etc are much less influental on the results.

You can find a discussion on Garmin transducers here: http://forums.sideimagingsoft.com/index.php?topic=7097.0

In the section on towfish construction there are several threads on the influence of various factors on resolution. I have built a number of experimental transducers using HB and Lowrance transducers to have better resolution. All of them were successful and used in my daily scanning since. I stick to HB head units, but often use transducers from other manufacturers to get better results.

Rickard

[sonarbear]

Hi Rickard,

thanks for the reply. I can't seem to find this data. Especially lowrance gives absolutely no info on specs.
What are typical beam angles?
Do you happen to know how the chirp works that garmin is advertising? Is it really a correlation based algorithm or do they just sweep the sent pulse?

[Rickard]

You never find any data on details in the sidescan transducers. Not even the beamwidth. In the beginning I had to estimate such features from the over-all dimensions of the transducers. The element array is of course always shorter than that. Some people have dismantled transducers, or x-rayd them. (I'm one of the dismantlers...) I think you need to ask around, and there are people who knows, at least some transducer models are well studied. I made some calculations and presented the results in graphs here: http://forums.sideimagingsoft.com/index.php?topic=8619.0
As you can see the beams vary betweem 1.5 and about 0.9 degrees in standard transducers at 455 kHz.

I'm not familiar with the details in the chirp systems.

Rickard

[rnvinc]

CHIRP is a different way to send the sound pulse into the water than normal fixed frequency Sonar (200kHz or 83kHz or 50kHz or 455kHz or 800kHz etc) ...

Fixed frequency Sonar sends a sound pulse (burst is actually a better moniker) of one single frequency ...

CHIRP Sonar sends a sound pulse (burst) of several different frequencies in the same burst ... This allows the sound pulse to actually collect more data thru the sound pulse travel than fixed frequency Sonar ... 

CHIRP in itself is defined as the "sounder" (transmitter) that can send this sound pulse of several frequencies in one burst ...

A CHIRP "system" is defined as a Sonar system that has a capable CHIRP "sounder" (transmitter) and a CHIRP capable xducer designed specifically to vibrate at all those varied frequencies that the CHIRP "sounder" is going to push thru it ...

A CHIRP "lite" or "Cheap CHIRP" system is a Sonar system that has a capable CHIRP "sounder" (transmitter) but does not have a CHIRP capable xducer ...and instead transmits the CHIRP multi-frequency CHIRP sound pulse thru a regular stock "fixed frequency xducer" that wasn't specifically designed to vibrate at the varied frequencies sent by the CHIRP sounder  ...but still vibrates well enough with the multi-frequency CHIRP sound pulse that the manufacturer feels it worthwhile to offer to the market as "CHIRP" ... Even tho it's only half of a complete "CHIRP Syatem" ...

And the simple marketing reason for manufacturers willing to offer this is cost ... Real CHIRP xducers - designed specifically to vibrate at all those multi frequencies that the CHIRP sounder is going to push thru it are very expensive ...Making a true "CHIRP System" too expensive for most of the market base ...

Fixed frequency xducers are not as expensive to make ...so manufactures can offer CHIRP technology to the market at a price point that more of the market can afford ... Even tho (once again) the market is not getting a true "CHIRP System" ... But only a CHIRP "Sounder" (transmitter) ...and a regular stock xducer... not really designed to CHIRP ...

Rickie

[newkid4si]

Rickie

    Thank you for that excellent explanation on CHIRP.

          Mike