Basic question concerning transducers

**hudnut** · 02-09-2015, 11:52 AM

Hey folks,
I have a basic question that for you guys that are really proficient with fish finders can answer
for me.
When the description refers to a dual frequency operation of 83 kHz to 200 kHz how does that
compute concerning the with of the beam under my boat and how far out to each side does it go
so I'll have some idea as to where the item that I'm looking at is actually located.
Thanks.

**Humminbird_Greg** · 02-09-2015, 12:08 PM

That depends some by brand and model. With a Humminbird unit that is using the 200/83kHz DualBeam sonar you are looking at 0.35 feet across for every foot of water depth when using the 200kHz 20 degree sonar. With the 83kHz 60 degree sonar beam you are looking at 1 foot wide for every foot of water depth. To figure how far out each side (and also frontwards and backwards) the beam goes you just need to figure the overall width of the beam and divide it by 2. So when using the 200kHz 20 degree sonar in 14 feet of water the unit is displaying sonar information that is up to about 2 ½ feet from the transducer (14 feet X 0.35 / 2). That same water depth using the 83kHz 60 degree sonar will be showing up to 7 feet away from the transducer.

Keep in mind too that the shape of the sonar beam is roughly conical (like an upside down ice cream cone), so while it may be 14 feet across at the bottom it is only a few inches across at the surface/transducer.

**CrappiePappy** · 02-09-2015, 05:23 PM

Originally Posted by hudnut

..... so I'll have some idea as to where the item that I'm looking at is actually located.
Thanks.

Remember, too .... that the "front edge" of your sonar cone depends on the "direction" your transducer is headed. You really won't know "exactly" where the images are coming from, as they will transmit from wherever they intersect within the width of the front edge of the cone shaped sonar ping. The deeper the water, the wider the sonar cone will get as it reaches bottom, so the "object" that displays on your screen could be anywhere within the leading edge of the cone. Don't matter to the unit whether the object is 10' to your right or left, it's going to show on screen as though it's right in front of you ... since the sonar ping only gives you the distance between the object and the transducer.

IMHO -
Side Imaging/Side Scanning is the only program that can tell you "location" (left or right of you) of objects under the water. Even my DI unit doesn't tell me "where" in the narrow fan shaped band of sonar pings that the object I'm seeing on the screen is actually located (as far as whether it's left or right of the tdx, or if I ran right over top of it).

... cp

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