On 2016-05-11 10:30, Mel Beckman wrote:
Read deeper into the thread and you'll find where I sourced inexpensive RF-based NTP servers using CDMA, GSM, and even WWV.
For shortwave, you would need to calculate propagation delay between transmitter and receiver. (does signal reach via line of sight, bounce against ionosphere ?). Since CDMA is dead outside the USA and drying in USA, I wouldn't rely on that. If GSM towers rely on a GPS receiver on the tower and those towers are near enough to your location (< 30km), then chances are that blocked GPS signals at your location would also jam the signals at the GSM antenna. And if you are setup to be totally autonomous in case of power failures, you need to know whether the GSM antenna you are relying on is also on permanent power backup or only has autonomy of a few hours.