# Base options

This topic describes any field that may appear in the Base options screen. The Base options screen becomes available when you set the Broadcast format in the Rover options screen to CMR, CMR+, CMRx, or RTCM RTK for the RTK survey type.

The fields available in the Base options screen are similar for any survey type selected in the Survey type field, but the fields available will change depending on the GNSS receiver selected from the Type field in the Antenna settings group box.

The Base options screen is not available with the Trimble DA2 receiver.

Survey type

Select the type of survey you want to use. The rest of the fields in the screen update to reflect the survey type selected.

Generally, when a GNSS surveying system setup consists of one base and one rover receiver, make sure that the survey type selected in the Rover options field and the Base options field is the same. However, when there are multiple rovers, you can have various configurations but make sure that if the rover is logging raw data your base station is also logging raw data.

Antenna settings

If the software is not connected to a GNSS receiver, select the antenna from the list of antennas in the Type field. The Part number field automatically displays the part number.

Select the correct measurement method for the equipment and type of survey. To set the default antenna height, enter a value in the Antenna height field. The Part number field automatically displays the part number.

Enter the serial number.

Elevation mask

You must define an elevation mask below which satellites are not considered. For kinematic applications, the default of 10° is ideal for both the base and rover.

For differential surveys where the base and rover are separated by more than 100 kilometers, Trimble recommends that the base elevation mask be lower than the rover setting by 1° per 100 kilometers of separation between the base and rover. Generally, the base elevation mask should be no lower than 10°.

Real-time survey settings
Broadcast format

The broadcast message format generated by the base depends on the selected survey type.

- For real‑time kinematic surveys, the format of the broadcast message can be CMR, CMR+, CMRx, or RTCM RTK.

  The default is CMRx. It is a compressed data format designed to handle the extra load of additional GNSS signals from modernized GPS, GLONASS, Galileo, QZSS, and BeiDou. Only use CMRx if all receivers have the CMRx option installed. To check if this option is installed in the receiver, select Instrument / Receiver settings on the controller that is connected to the receiver, see Operating several base stations on one radio frequency.

  To operate several base stations on one frequency, use CMR+ or CMRx.

  Some receiver firmware produced after 2018 obsoleted the use of RTCM RTK v2.X messages. If you attempt to use such firmware in the rover receiver, then the RTK survey will not start in Trimble Access because the receiver cannot decode incoming RTCM v2.x RTK messages. For more information, refer to the release notes for your receiver firmware.

Station index

You can set the Station index for the base receiver to a number between 0 and 31, and you can set the Use station index for the rover receiver to Any or to the same number that the base is transmitting.

The base station index number is automatically generated according to the controller serial number. To limit the chance of multiple base receivers transmitting the same station index, different controllers default to different numbers, which means there is less chance that you accidentally receive corrections from the wrong base.

Postprocessed survey settings
Logging device

With survey types that involve postprocessing, set the Logging device to the receiver or the controller.

Logging interval

To define the logging interval, enter a value in the Logging interval field. The base and rover logging intervals must correspond to (or be multiples of) each other.

When using an RTK and Infill survey type, the Logging interval is for the infill session only.

When using an RTK and data logging survey type, the Logging interval should be the same for each receiver – typically 1 second. The RTK interval remains at 1 second, regardless of the interval selected in the Logging interval field.

When using Trimble receivers , Trimble recommends using a logging interval of 1s. There are many benefits in using this interval: more measurements enable faster convergence, better Ionoguard™ performance, increased redundancy for validation and more robust outlier detection (including cycle slip detection). This is especially important in challenging environments. Even with base data logging at a slower rate, rover data at a faster divisor of that base interval is beneficial.

GNSS signal tracking

To use observations from a GNSS constellation in a real-time or postprocessed survey, you must enable tracking for each signal type you want to use in both the Rover options and the Base options screens. See GNSS signal tracking options.