What the seller forgot to mention #6 – the Vexilar SP200, the first sonar in this series that hands you a measurement
This is part six of the series in which I check how much of what you see on a fish finder screen is a measurement and how much is a drawing. In the previous episode the PUPOPAN turned out to be a device that gets one depth number from the water and paints the whole bottom with a ready-made picture baked into the display.
Today the Vexilar SP200 SonarPhone. An American brand, a price several times higher than the balls from the previous episodes. The sonde sets up its own Wi-Fi network and the phone connects to it and receives the data.
After four episodes about cheap balls it was time to check whether more expensive hardware really does it differently. It does. And not by a few percent, but by a whole class.
What comes out of the water is 300 echo samples, not 120
The frame is 330 bytes: a header, 300 echo samples and a checksum. It arrives five times per second.
The header carries depth to within 0.1, temperature to within 0.1 degree, supply voltage every 0.01 volt, the current range, the selected frequency and the unit the sonde counts in. The demo material shipped with this sonde’s app is 1402 consecutive frames and all 1402 have a correct checksum, computed over the whole frame including the echo.
That sounds trivial, but in the cheap sondes from the previous episodes the checksum either does not cover the echo at all, or it is verified only after the reply has been sent, so a corrupted frame ends up on the screen anyway.
| Sonde | What comes out of the water | Echo samples |
|---|---|---|
| Lucky FF918 | four numbers | 0 |
| PUPOPAN | one depth number | 0 |
| Black ball XJ02B | echo cross section | 120 |
| Erchang XF07C | echo cross section | 120 |
| Vexilar SP200 | echo cross section | 300 |
There is not a single fish field in this frame
No fish depth, no size, no flag. Nothing.
Every previous sonde in this series sent a ready verdict: there is a fish at this depth, size two. This one sends nothing of the sort. It sends the raw cross section and there its role ends.
That is a difference in kind, not in degree. The fish icon, if it appears at all, is computed in the phone from the same image you have in front of you. You can turn it off and look at the echo. You can use a different app. With those other sondes you could not, because you simply never got the echo.
This is what a full cross section of 300 samples looks like
And a caveat straight away, because in the previous episodes I took manufacturers to task for confusing demo material with a measurement, so I have to hold myself to the same standard: the image below was built from the demo material shipped with this sonde’s app, not from my own trip on the water. These are real frames from a real device, with the full structure and correct checksums, but not from my water.
You can see the surface line, the bottom contour with a clear drop-off, the second bottom echo below it and fish arches in the water column. An arch, not an icon: a curved trace from which you judge for yourself whether it is a fish or a gas bubble.
A reminder of what the predecessors do in the same place: the PUPOPAN paints the bottom with a ready picture from memory, the Erchang on factory settings wipes the entire water column to a white background, and the Lucky FF918 drew the bottom from imagination.
What that means in centimetres, or why anyone needs 300 samples
This recording was made on the 27 metre range. Divided into 300 samples that gives 9 centimetres per slice of the image. The same range on 120 samples, which is the Erchang, is 23 centimetres.
| Range | Vexilar, 300 samples | Cheap balls, 120 samples |
|---|---|---|
| 6 m | 2 cm | 5 cm |
| 18 m | 6 cm | 15 cm |
| 27 m | 9 cm | 23 cm |
| 46 m | 15 cm | 38 cm |
To be fair: the number of samples alone does not make a fish finder. The pulse has its own length too and it is the pulse that sets what can physically be resolved. But at 200 kHz the pulse is shorter and the cone is narrower, so the two work with each other rather than against each other.
Three frequencies and three cones, switched from the phone
| Frequency | Cone | Circle of view at 10 m | What for |
|---|---|---|---|
| 80 kHz | 40 degrees | 7.3 m | searching, shallow water |
| 125 kHz | 30 degrees | 5.4 m | all-round use |
| 200 kHz | 20 degrees | 3.5 m | detail, bottom structure |
The choice of frequency travels in the frame from the phone, so you decide, not a counter inside the sonde. For comparison, the Erchang on its wide channel has a circle 8.3 metres across at 10 metres and jumps between channels by its own counter, while the PUPOPAN claims 105 degrees in its listing, a number that cannot be achieved at its frequency.
And now the compliments stop: password 12345678
Authorisation in this sonde consists of sending the string 12345678 as the master code. Exactly the same string as in the Erchang at a fraction of the price.
Whoever asks first becomes the master. The next client gets a “busy” reply. So the neighbour at a match will either take over your sonde or block you with his, with no effort at all. Nobody encrypts the data: depth, temperature and the whole echo cross section travel in clear text, exactly as in the cheapest ball from episode two.
Small details worth knowing
- The unit is in the frame. The sonde says whether it counts in metres or in feet. An app that hardcodes feet will show a depth more than three times too high.
- The range can be forced or left on automatic by writing zero.
- The frame from the phone goes out every 200 milliseconds and it is what keeps the sonde working. Stop sending and the sonde stops scanning.
- Supply voltage reported every 0.01 volt, so you see the real state of the battery, not four bars.
Verdict: four stars out of five
| What I rate | Rating | |
|---|---|---|
| What comes out of the water: 300 echo samples, five times per second | ★★★★★ | 5 / 5 |
| Honesty of the data: no verdict about a fish, a checksum on every frame | ★★★★★ | 5 / 5 |
| Image resolution: 9 cm per slice at 27 metres | ★★★★☆ | 4 / 5 |
| Choice of frequency: three real cones, controlled from the app | ★★★★☆ | 4 / 5 |
| Security: password 12345678, zero encryption | ★☆☆☆☆ | 1 / 5 |
| Is it worth buying as a fish finder | ★★★★☆ | 4 / 5 |
Check it yourself, on your own water
- Look at the water column with the fish icons turned off. Either the arches are there or they are not, and that is the whole answer to the question of whether the sonde shows a measurement.
- Switch 200 kHz to 80 kHz over the same spot. The arches will blur, the bottom will get thicker and the image will cover a wider piece of the bottom.
- Set the range manually to twice the depth. The image will lose half of its detail, because the same 300 samples will be spread over a section twice as long.
- Switch metres to feet and back. If the depth jumps by a factor other than 3.28, the app is reading the unit wrong.
Summary – what the Vexilar does differently from the cheap balls
- 300 echo samples in every frame, five times per second, instead of 120 or zero.
- Zero fish fields. The sonde does not guess for you, it hands over the raw cross section.
- The checksum covers the whole measurement and actually works.
- Three frequencies and three cones, switched from the phone, not by a counter inside the sonde.
- Unit and range stated explicitly, so the app does not have to assume anything.
- Password 12345678 shared by every unit.
- Zero encryption, the whole cross section travels in clear text.
- One master at a time, the next client is refused.
- The image still depends on the app, and the default one is, to put it gently, frugal.
This is the first sonde in the series about which I can write that it hands you a measurement, not a verdict. If you are looking for gear on which you can actually read the bottom, drop-offs and weed, this is exactly the difference you are paying for. Not for the brand and not for the housing, but for the number of measurements that come out of the water.
What I did not test and therefore do not write about: pulse length and the dead zone on the water, behaviour over silt, and a comparison with branded gear of the same class on the same water.
Sources and material worth checking
- NOAA – What is sonar? – how a fish finder works: a transmitted pulse, the echo return time, the conversion into distance
- FAO Fisheries Technical Paper 240: Fisheries Acoustics – beam angle, target strength and why the loudness of an echo says nothing about the length of a fish
- Episode 5: PUPOPAN – a set with its own screen, where the bottom is a picture from memory
- Episode 4: Erchang XF07C – 120 echo samples and a wiped water column
- Episode 3: the black ball XJ02B
In the last episode of the season: a sonde that sends the same frame byte for byte and the same 300 samples, only under a different brand and for a fraction of the price. There is one more detail there that gives this family away for good.
What equipment I use and on what basis I test this
Every device described in this series was bought with my own money and is my property. I examine them in order to know what really reaches the angler’s hands and what I can demand from the hardware I design myself. The analysis covers one specific unit and the firmware version I found in it; other batches, versions and variants of the model may behave differently.
Observing, studying and testing the functioning of a program in order to determine its principles is permitted for a person who lawfully acquired the device: article 75(2)(2) of the Polish Copyright Act, which implements article 5(3) of Directive 2009/24/EC. Reading the transmission concerned exclusively my own transmitter and my own receiver. I do not publish source code, memory dumps, keys or tools that would allow anyone to copy someone else’s software – only conclusions about what the hardware measures and what it does not.
Names and trademarks belong to their owners and are used solely to identify the hardware under test, within the scope of critical analysis and the right to information. Photographs from sales listings are used for the same purpose. If a manufacturer or a seller believes any conclusion is wrong, I will gladly repeat the measurements on a unit they provide and publish a correction.
That is how it works here: before anything goes into our boats, it passes across this bench. And if something does not pass, we say so out loud, even when nobody wants to hear it.
Asystent pomocy Extreme One