User's Manual

Suggestions for Improving the Connection

Optimum performance between two WHM900 modules will vary depending on the

proximity of the two modules and the type of antenna used. Try adjusting the antenna for

best reception. Start by positioning the antenna straight up and adjust as necessary.

Pointing the antenna towards the other module will not improve the reception. Do not

place the antenna next to large pieces of metal because it will cause additional

interference. The distance between the two modules will effect the modules connect

speed and data throughput. Operating two modules too close to each will cause

saturation of the receiver. Allow at least three feet separation between the two modules.

The WHM900 data rate (AT%Mn) and transmit level (AT%An) commands can be used

to help optimize the modules performance. Setting the data rate lower (AT%Mn) and

increasing the transmit level (AT%An) will increase the distance but lower the data

throughput. If interference from other digital devices is suspected, try changing the

frequency that the modules are operating on. See the AT%Fn command. The module

frequency hopping option may be useful to counter interference. See the ATBn

command.

Changing from Data Mode To Command Mode

The WHM900 has the capability of exiting the On Line Data Mode to either change or

check specific module settings then return to the On Line Data Mode or to end the RF

data link and return to the Off Line Command Mode.

1) The On Line Command Mode can be entered if the host transmits three consecutive

“ +” s. The “ +++” must be protected by a one second delay before and after it is sent.

When the module detects this sequence, the OK result code will be displayed and the

module will be in the On Line Command Mode. You are now able to enter specific

commands to change or check module parameters. An example would be to change

the modules transmit level with the AT%An command. After changing or checking

the settings, you must enter the ATO command to return to the On Line Data Mode.

To end the data link and return to the Off Line Command Mode, enter the ATZ or

ATH command. The ATZ command will end the data link and also reset the module

to its stored configuration. The ATH command will end the data link without

resetting the module. If frequency hopping is enabled only the “ ATH” and “ ATZ”

command are valid. Once the module is in the Off Line Command Mode the “ ATD”

and “ ATA” commands must be entered to return to the On Line Data Mode.

2) Setting the Inactivity Timeout with the AT\Tn command can be used to exit the On

Line Data Mode. If no data is transmitted or received in the time specified by the

AT\Tn setting, the module will disconnect and return to the Off Line Command Mode.

3) Resetting the modules power or toggling the Reset Line (Pin #16) will end the RF

Data Link and return the module to the Off Line Command Mode.