Thread: On A Tight Budget

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Originally Posted by Bill_in_SC

The more I dig into these depth finders the more confused I get trying to understand the whys and wherefores of their design specs. It seems that the frequency is somehow related to the the cone angle of the beam but maybe not. I am looking at the Piranhamax 153 and comparing it to the Garmin Echo 150 (yeah I know, I originally asked about the Echo 100). They both seem to operate on similar dual frequencies. But the Piranhamax has cone angles of 60 and 20 degrees. The Garmin reports cone angles of 120 and 60 degrees. The wider cone angles would seem to be better for shallower waters and slow moving canoes but is there a trade off? If I look at the Piranhamax 175, which is priced like the Echo 150, I find even narrower cone angles of 28 and 16 degrees.

I am also finding a number of models in my under $100 budget with some significant differences with just a $10 or $20 price point difference. Since I am not in a position to be buying a different model every year to correct a buying mistake I'd sure like to make the right decision on this.

Bill,
Narrow or wide sonar beam angles both have their advantages and disadvantages. The narrower the sonar beam the better the more accurate the bottom detail can be but at the cost of not showing a lot of the water/bottom that is under your boat. With a wide angle sonar beam you can cover a wider area of the water and bottom but at the cost of not being able to display the detail that a narrow sonar beam can. Narrower beam units can also work to greater water depths but this is usually hundreds of feet deep and does not affect most freshwater fishermen. Example: if you are on a flat area and there is a small depression in the bottom; the narrow beam unit might be able to show this to you but the wider beam unit would not. With a narrower beam unit you are mostly just showing what is directly under the transducer but with a wider beam unit you would be able to see those fish that were off to the right of the boat… So Dual Beam units were developed that have the best of both worlds.

Frequency is related to the width of a transducer beam. Inside the transducer are what some call “elements”. These are what change the electrical signal from the sonar unit to the acoustical (sound) pulse that is required for sonar to operate. They also take the returned sonar signal and convert it back into an electrical signal for the sonar unit to process and display for the user. If you had a sonar element that could be used at more than one frequency; you would find that typically the higher the frequency; the more narrow the sonar beam it produces is. The lower the frequency the wider the sonar beam it produces is.

Frequency will also play a part in the possible resolution of the sonar and how deep it will work in the water. The higher the frequency the better the sonar resolution but the less deep it will work. Lower frequencies work to a lot deep water depth but at the cost of sonar resolution.

What you should probably look at more is the area covered by a particular unit’s sonar beam at the water depths you will be using it at. Oh, and get a dual beam sonar unit so you will have the best of both the narrow and wide sonar beams.

Thanks for the insights. There seems to be some differences from manufacturer to manufacturer as far as the relationship between frequency and beam width. Different manufacturers seem to produce slightly different beam widths for the same frequency. But generally speaking the relationship you describe seems to hold up. For use on a canoe or kayak in relatively shallow water it seems as though I am going to be happier with the wider beam units. Something with a 120/60 dual beam capability should be nice.

Originally Posted by Bill_in_SC

Thanks for the insights. There seems to be some differences from manufacturer to manufacturer as far as the relationship between frequency and beam width. Different manufacturers seem to produce slightly different beam widths for the same frequency. But generally speaking the relationship you describe seems to hold up. For use on a canoe or kayak in relatively shallow water it seems as though I am going to be happier with the wider beam units. Something with a 120/60 dual beam capability should be nice.

The difference in sonar beam widths in different brands is usually attributed to the fact that the different brands "measure" their respective beam angles differently...

HB measures (and advertises) their beam angles measured at the -10db value...

I think Lowrance measures their beam angles at the -3db value...

Rickie