Start with the work, not with the spec sheet
When someone asks us which receiver to buy, the first thing we want to know is what they do for a living. A cadastral survey of a village with an open horizon, staking out axes in a construction pit, checking an embankment along a road, a control network measured in static mode. Each of these jobs loads a different part of the instrument. The A90 and the A66 MAX look similar on paper, and in the field they feel different.
Our advice is to write down the three jobs you do most often and one that happens rarely but costs you a lot of nerves. Then read the catalogue through that list rather than through the channel count.
An example: a firm that mostly does cadastral surveys in villages and holiday zones will spend half its time under fruit trees and along fences. For them, how the receiver behaves under a partly blocked sky matters more than anything else in the table. A firm staking out on a motorway job looks at other things: radio range, a battery that lasts the day, and how quickly the receiver fixes again after passing under an overpass.
RTK or static
Most surveyors in Bulgaria work almost entirely in RTK. The receiver gets corrections from a base or from a network over the internet and gives you a coordinate within seconds, at centimetre level. That is the mode for stakeout, for detail points, for the daily grind on site. Static is the other one: the receiver sits on a point for a long time, logs raw data, and you process it in the office. You use it for control points, for long baselines and for places where there is no RTK link at all.
If you will do both, make sure the receiver logs static data and has memory for it. The A66 MAX, for example, lists a separate static accuracy alongside its RTK accuracy, and a separate battery time for static mode. The A90 has 8GB of internal memory plus a card. Small details, until you are on a hilltop with four hours of static ahead of you.
Pole tilt and the IMU
IMU tilt compensation is the feature that changed daily work the most in recent years. You no longer centre the bubble on every point. You lean the pole against the kerb edge, the base of a post, the corner between two walls, and the receiver works out where the tip is. Both receivers in our range support tilt survey up to 60°.
There are conditions. The IMU needs to initialise, usually with a bit of movement, and you have to keep an eye on the setting in the software. At steep angles the accuracy drops, which is physics rather than marketing. For control points, or for anything someone else will check later, we still recommend a vertical pole. For detail points and stakeout on a site, tilt saves real time, especially for someone working alone. The classic case is surveying a pipe in an open trench: the pipe is at the bottom, you are on the edge, you lean the pole down to it and take the point without climbing in.
Base link and network link
Corrections come either by radio from your own base or over the internet from a network. Radio works where there is no coverage, but its range depends on terrain and antenna. Internet is convenient in town and along roads, and then in the gully behind the hill the mobile signal drops exactly when you need it. A receiver that can do both is a safer buy. The A66 MAX has built-in 4G and a 1W radio, the A90 has internal and external radio plus WiFi and Bluetooth. Check how you will manage it too. Both have a WebUI over WiFi, so you can open the settings from your phone without a special cable and without hunting for the laptop in the car.
Where GNSS will not save you
Under tree canopy in summer, in a narrow street between five-storey buildings, next to a steel tank, or in a deep pit with vertical walls. There the number of visible satellites drops, signals bounce off the walls, and the receiver either does not fix or fixes wrongly. More channels help, and the A90 and A66 MAX track all the main systems, but they do not perform miracles. In such places it is more honest to bring a total station, or at least to measure the point twice at different times of day when the constellation has moved.
Then there are the plain things: rain, cold, mud. Both receivers are IP68 rated with an operating temperature down to -30°C, which is enough for a Bulgarian winter. Batteries lose capacity in the cold though, so always carry a spare, in a pocket close to your body.
A90 or A66 MAX
If your work is mostly survey and stakeout in open terrain and you want a compact receiver with good satellite tracking, an IMU and Android software, the FOIF A90 covers the daily work. If you often need points you cannot stand on, such as a roof edge, a fence base behind a ditch or a part of a structure, the laser positioning on the FOIF A66 MAX solves exactly that. The dual camera for visual stakeout also helps a new team member find the point without counting steps along an arrow on the screen.
The practical advice is simple. Take your list of jobs and compare it with the models in the GNSS receivers category. If something is unclear, ask. At Geonextech we would rather spend half an hour talking before the purchase than look at a returned instrument a month later.
