Garmin introduces the Ultra High-Definition Scanning Sonar System

[Astrochris]

I've seen them on Facebook. Very uninspiring. The range is somewhere around 30 foot. Resolution is great close to boat and seems on par with Megaimaging but no signal remains even a few meters out on the bottom.

That is not 30 feet that is 20 meters it’s more than 60 feet, from what I see here, the range seems to be on par with the mega.

[Wayne P.]

That is not 30 feet that is 20 meters it’s more than 60 feet, from what I see here, the range seems to be on par with the mega.

I assume the Garmin 1200 kHz will perform like the Humminbird 1200 kHz. What I see is the sensitivity is very high and concentrated, so any particles in the water or the thermocline will be affecting the images.

The thermocline is affecting this screen shot:

[mdj]

EchoMap Plus 93 is like $900, plus the $600 for this add-on, or you could get a Humminbird Helix 9 Mega SI w/ transducer for $1100.

If you want to stick with Garmin and add it on, sure, might be worth it. If you're in the market for a new unit with Mega imaging I don't see the value. Unless Garmin starts bundling it with a 9" unit for around $1100.

Helix 9 doesn't have touchscreen, active captain, and the 2d transducer options are better with Garmin

[Mobi]

Garmin appear to have reduced the range resolution (target separation) ability of the GCV20 from what its capable of.

Using 1115 kHz gives very small target resolution down to < 2mm. However, if range resolution isn't equal to or less than that, bait schools will simply appear as a solid blob/ball.

Nobody really wants to chase individual targets that small (< 2 mm) but do want to see target definition improvement particularly on structure and more importantly on fish shape (to identify species).

Throttling back the CHIRP bandwidth to only 110khz at 1115 kHz centre frequency cancels a lot of any definition improvement provided by the higher frequency.

Anybody got any info on that, please?

[LWINCHESTER2]

Throttling back the CHIRP bandwidth to only 110khz at 1115 kHz centre frequency cancels a lot of any definition improvement provided by the higher frequency.

I don't have a clue what you are saying. 110khz at 1115 kHz.

[Mobi]

Hi

Target resolution (ability to see smaller target sizes)= 5118/freq = 5118 / 1115 khz = less than 2 mm. The unit can see targets just under 2 mm in size.

However, CHIRP range resolution ( ability to separate targets) @ 1115 kHz = 5118/ 2 x bandwidth = 5118/2 x 110khz = 6.8 mm.

So there is no resolution advantage in using CHIRP MEGA because the unit can't distinguish between targets that are less than 6.8mm apart (even though the targets are only 2mm long).

The CHIRP bandwidth has apparently been throttled back.

Question is why?

[LWINCHESTER2]

Ok. Now I see where you got the 110 and 1115. I had not investigated the technical specs of the GT34UHD. What I had seen was the promotion stating 1200 kHz. After your post I went back and saw the chirp frequency spread as 1060-1170 that gives the 110 spread and you took the midpoint to get 1115 kHz. Your math looks a little unusal to me but I'm quite a novice on these calculations. 5118? Where did that come from? I would have expected to see a formula with the speed of sound in water around 1500 m/s and the 110 bandwidth range or alternatively if calculating using a fixed frequency, some estimate of the pulse width to do calculations.

[Mobi]

Thanks for the reply.

5118 is the speed of ultrasonic in salt water in ft per second.

I used ft per sec as that's the nomenclature used in the US.

It translates to 1560 metres/sec.

So if you divide 1560 by 2 x 110 you get a range resolution of 6.8 mm.

That range resolution does zip for the target resolution of 1.3mm that 1115 kHz is capable of.

What's the point of having a device that can see targets as small as 1.3mm when the range resolution can't separate them 'cos its been throttled back. Target definition which allows species identification is important. A popular species here has a certain shape and another has a forked tail which should be easy to see.

Estuarine crocodiles under the boat are easy to identify 'cos range resolution and target resolution don't matter. Its simply huge and takes up half the screen.

So why throttle the bandwidth?

Its so easy to turn up the swept bandwidth at those freqs of 800 khz and nominally 1200 khz (to say 200kz or 250 kHz) giving a range resolution that allows the user to gain real advantage of CHIRP. Not this pretend tupperware marketing hype.

Humminbird has done a similar thing except they've nominated 65 mm as a common range resolution on ALL of the freqs on which they employ CHIRP. Unsure if that's simply a marketing convenience or if H/bird actually performs better than that.

At the moment Garmin is attempting to play "ducks and drakes" about the issue. I'm guessing that H/bird will do similar.

The loser in this is the user(you and I).

[Wayne P.]

Thanks for the reply.

5118 is the speed of ultrasonic in salt water in ft per second.

I used ft per sec as that's the nomenclature used in the US.

It translates to 1560 metres/sec.

So if you divide 1560 by 2 x 110 you get a range resolution of 6.8 mm.

That range resolution does zip for the target resolution of 1.3mm that 1115 kHz is capable of.

What's the point of having a device that can see targets as small as 1.3mm when the range resolution can't separate them 'cos its been throttled back. Target definition which allows species identification is important. A popular species here has a certain shape and another has a forked tail which should be easy to see.

Estuarine crocodiles under the boat are easy to identify 'cos range resolution and target resolution don't matter. Its simply huge and takes up half the screen.

So why throttle the bandwidth?

Its so easy to turn up the swept bandwidth at those freqs of 800 khz and nominally 1200 khz (to say 200kz or 250 kHz) giving a range resolution that allows the user to gain real advantage of CHIRP. Not this pretend tupperware marketing hype.

Humminbird has done a similar thing except they've nominated 65 mm as a common range resolution on ALL of the freqs on which they employ CHIRP. Unsure if that's simply a marketing convenience or if H/bird actually performs better than that.

At the moment Garmin is attempting to play "ducks and drakes" about the issue. I'm guessing that H/bird will do similar.

The loser in this is the user(you and I).

Humminbird's band width is 1125-1300 kHz.

[TroyBoy30]

[Riccochet]

did you take those screenshots?

[LWINCHESTER2]

Probably not. The map coordinates look to be in Australia. But he could have went there. Troy gets some shots off Facebook at times and posts them for our benefit that might not go there to see them. It's a good thing. I really don't care who took them. Sure some may have been cherry picked but for comparison purposes we need to compare cherry picked with cherry picked. Troy is also straight up about where they come from. If you go back through his posts, whether you agree with him or not, and you may not, his comparisons and evaluations of performance of whatever product he is discussing are his own.

[fishin couillon]

So what is the max range on sidevu with the UHD?

[Nikonian]

A few more UHD images on the Australian Mr Sonar Facebook page link here: https://www.facebook.com/MrSonarAU/p...38729979644356

Mr Sonar states the images are straight out of the unit and taken in saltwater.

[ring fry]

So what is the max range on sidevu with the UHD?

Maximum depth	200' Ultra High-Definition ClearVü 125' to each side Ultra High-Definition SideVü, 250' total, at a maximum depth of 30'

From the spec sheet on Garmin website.

SE Kansas grass grower

[TroyBoy30]

i didnt take em. got them from facebook

[Mobi]

Humminbird's band width is 1125-1300 kHz

Thanks Wayne. Yep, 1125 - 1300 is what their marketing says.

. That gives a target separation of 4.6mm. Yet their marketing spec says 65mm which is 1/15 of that.

As a matter of fact, Humminbird says that ALL of its units (including non-CHIRP ones) have a target separation of 65 mm which is 1/15th of what the CHIRP ones are capable of.

So is the bandwidth of the unit throttled back to produce such a lousy target separation figure or is the transducer itself producing the throttling by not having the necessary bandwidth? Its NOT a low Q transducer?

Three choices I guess.

1. Frequency sweep (bandwidth) reduced in generator unit;

2. Bandwidth limitations in transducer ( not a low Q transducer; or

3. Simply fill in all the target separation specs with 65mm just to fill the gaps in the specs. Customers wont notice and if they did, then they wouldn't understand anyway.

[Wayne P.]

Thanks Wayne. Yep, 1125 - 1300 is what their marketing says.

. That gives a target separation of 4.6mm. Yet their marketing spec says 65mm which is 1/15 of that.

As a matter of fact, Humminbird says that ALL of its units (including non-CHIRP ones) have a target separation of 65 mm which is 1/15th of what the CHIRP ones are capable of.

So is the bandwidth of the unit throttled back to produce such a lousy target separation figure or is the transducer itself producing the throttling by not having the necessary bandwidth? Its NOT a low Q transducer?

Three choices I guess.

1. Frequency sweep (bandwidth) reduced in generator unit;

2. Bandwidth limitations in transducer ( not a low Q transducer; or

3. Simply fill in all the target separation specs with 65mm just to fill the gaps in the specs. Customers wont notice and if they did, then they wouldn't understand anyway.

The only "LowQ" transducer that is advertised is the 2D crystal in the new Dual Spectrum DI transducer.
Have not seen any mention of LowQ Imaging crystals.

Are Garmin's Vu crystals LowQ?

[LWINCHESTER2]

Sometime back there was a discussion about the "Q" of various Garmin transducers among some that claimed to know how to calculate the "Q". This did not come from Garmin. I'm not saying this is accurate, but it may be. I don't know about the new GT34UHD but perhaps Mobi can calculate and post it and perhaps verify or dispute these numbers.

XD Q
GT8 2.21
GT15 1.56
GT52 2d 2.17
GT52 800 13.67
GT52 455 7.58
GT51 2d 1.50
GT51 260 8.67
GT51 455 22.75
GT50 2d 1.56
GT50 455 7.58
GT50 800 13.67

I really don't get the reliance on this calculation in judging the quality of the return. For example, the GT52 on 455 is stated as 425-485 giving it a "Q" of 7.58. Without changing anything about the transducer, but in the unit changing the chirp frequency to 400-500 then it would appear to have a Q of 4.50. So all of a sudden its a better transducer giving better imagery? So what about the performance at 400 and 500? This kind of thing was done with non-chirp designed transducers but sending a chirp pulse through them. At the time, this performance was critized as not being anywhere close to a transducer engineered for a specific chirp range. Don't we need to see a graph of the FOM vs frequency to get some idea as to where to limit the range for the best performance? I don't think it would be appropriate to describe Garmin or Humminbird chirp transducers as throttled back. I would suggest that the engineers looked at the performance well beyond the final published range to determine what range gave the best performance.

[Mobi]

Fellas the Q of a transducer refers to the pass bandwidth.

Its calculated by dividing the centre frequency by the "useable" bandwidth. The "useable" bandwidth is the width either side of the centre frequency where the intensity/power of the frequency pass has dropped by half.

For example, take Humminbird's spec of 1125 kHz - 1300 kHz as pointed out by Wayne P. That gives a centre freq of 1212 kHz. (halfway between the 2).

If the lower and upper frequencies of 1125 and 1300 are the half intensity/power points then the bandwidth is 1300 - 1125 = 175 kHz.

THEREFORE the Humminbird transducer Q @ 1212 khz= Centre frequency (in kHz) divided by bandwidth (in kHz) = 1212 /175 = 6.9

For the Garmin GCV20, the swept range is 1060 - 1170 kHz. The centre freq = (1060 + 1170)/2 = 1115 kHz (sound familiar?)

And bandwidth = 1170 - 1060 kHz = 110 kHz (also familiar).

Therefore transducer Garmin Q = Centre freq / bandwidth = 1115 /110 = 10

Normal Q for narrow band pulse unit is 30 or so (high Q)

Normal Q for a real CHIRP transducer is 2 - 3 (low Q).

A Q of 7 - 10 is neither your backside nor your elbow for CHIRP.

But not everything is as it seems.

You'd think that the Humminbird transducer (having a lower Q) would work better on CHIRP.

The reality is that Humminbird enhance the figures. But they do it up front and openly declare it. Most don't pick it up though.

Humminbird measure their bandwidths at 1 tenth power and not 1 half power. In technical speak Humminbird measures -10 db points (you'll see them quoted up front) on their specs. Others measure theirs at -3 db (half power) points.

So Humminbirds bandwidths will appear wider and consequently ( with a greater divide by figure) the transducer Q will appear lower, better and more acceptable when in reality it's probably in the same performance ballpark.

Humminbird does the same thing on their beamwidth specs. That's why they seem broader than competitors.

If I knew how to draw a diagram on here I'd show you easily how its done.

I'll have a look at those figures you put up above.