Freewave radio modem Frequency change
If 2 base stations are operating in close proximity to each other on the same frequency then it is possible for a mobile unit to receive differential corrections from either base station. The unit will only use corrections from one base station at a time, but will switch from one to the other if the connection to the base station is lost. This can potentially cause position jumps if the base stations aren't fully surveyed into an absolute position, which takes around 48 hours of data averaging.
This guide explains how to change the frequency of a Freewave radio modem to prevent the mobile unit from receiving data from multiple base stations.
The software required for this operation is:
- Freewave Tool Suite, available from https://www.freewave.com/products/software.aspx (requires user registration)
- To access the Freewave radio modem you will need to remove the top panel.
- Open Freewave Tool Suite and select Configuration:
- Delete any discovered devices and template devices (select Template Devices, highlighted red):
- Click Read Radio from the top menu:
- You will see this text box appear:
- Press the setup button on the radio modem , then click OK.
- Once the config has been read, click the Transmission Characteristics tab:e
- Click the drop-down menu for Hop Table Version, and select a frequency range:
- Ensure that there isn’t any overlap between base stations e.g. set one base station to 902-915 MHz and the other to 915-928 MHz.
- Click the All button:
- Press the setup button on the front of the radio modem again when prompted.
- To check that the config has applied correctly, follow steps 1 to 6 on this section and check that the frequency range (Hop Table Version) has updated when you reload the config.
- It is important that the mobile unit is set to the same frequency range as the base unit otherwise no radio link will be established.
How to check it's worked
- If possible, position the mobile unit within range of 2 base stations which have been reconfigured to transmit on unique frequency bands. The mobile unit should have been reconfigured to receive data on only one of the frequency bands of the base stations.
- Open a NAVdisplay template, check you are receiving differential corrections. Depending on the type of unit and base station, your position mode will be Differential, RTK Float or RTK Integer. In all cases, the Diff Age field, should usually remain below 2 s when receiving corrections.
- Power down the base station providing the corrections.
- The Diff Age field should begin to count up. RTK mode will remain for 60 s.
- After 60 s, if another base station is available, the unit will start to receive corrections again. The Diff Age reduces to <2 s and the position mode remains in RTK. This shows that there is another base station in the area outputting on the same frequency band.
- If the position modes changes to Differential, then this shows that the mobile unit is not in range of another base station, or the base stations are on different frequencies.
- Note that low accuracy units e.g. RT3100 will only achieve Differential position mode. This position mode is held for 5 minutes after differential corrections are lost.
- It is worth noting on the base station and mobile radio modems the new frequency bands.
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