FLDIGI Users Manual 4.0
The WWV mode is normally used to measure the offset of the sound card oscillator. (see WWV ppm measurement).
It can also be used to transmit time tick signals similar to the format that is used by WWV. The WWV modem sends a time tick which is a 200 msec wide pulse at a once per second rate when the T/R button is enabled. This pulse is shaped with a 4 msec raised cosine shape on the leading and trailing edges to reduce key clicks. The accuracy of the transmitted time tick is solely dependent on the accuracy with which the WWV ppm measurement was performed.
The purpose of the WWV time tick transmission is to allow other stations to calibrate their sound cards against your calibrated system. This can be used to align all systems in a VHF/UHF net for example. It is only necessary for one of the net members to be able to calibrate his or her sound card against WWV. The other's would then be calibrated by proxy use of the WWV time tick transmit mode. This can even be used in the case where no member has access to a HF transceiver. The "master" station would set the Rx and Tx ppm settings to zero. It would then transmit the time tick signal for the other stations to calibrate their sound cards against the master sound card. Having all of the stations calibrated in this way will insure that the modem decoders will give maximum performance. Here is an example of an advanced macro that will send a CW announcement, 2 minutes of time ticks and end with another CW announcement.
<MODEM:CW> <!GOFREQ:1000> <!WPM:24> QRZ QRZ de <MYCALL> <MYCALL> 2 minute time tick cal run follows <IDLE:2> <!MODEM:WWV><!IDLE:120> <!MODEM:CW><!IDLE:2> end of time tick run de <MYCALL> k <TX><RX>