> Decode the WWVL long wave broadcasts. ^ Make that "WWVB" ^ http://www.boulder.nist.gov/timefreq/stations/wwvb.htm > placement and orientation of automatic clocks makes a big difference. I > have two automatic clocks, and they only seem to pick up the signal at > night, sometimes. Signal propagation at these frequencies is primarily via "ground wave" - with little propagation via 'sky wave' as one is accustomed to experiencing at night on the AM broadcast band ... More likely your clock sets itself at this time (night) versus continuously running the VLF receiver (and thereby draining the battery) OR there is less interference from man-made devices at this time (TV sets, standard video display monitors, etc). The over-earth path loss at 60 KHz is around 120 dB. Given WWVB's approximate 50 KW transmit power (and assuming through antenna efficiency values for simplicity at 50%) the resultant received values are [1]: Field strength at receiving site 1.56 micro-volts per metre 50-ohm matched receiver input 981.52 micro-volts Receiver S-meter reading S9 + 26 decibels Real-world receive power-value figures will be much lower due the ferrite rod antenna normally used to receive the 60 KHz WWVB signal. RF Jim [1] Program name: GRNDWAV3.exe Author: R.J.Edwards G4FGQ (C) 4th July 2001 ----- Original Message ----- From: "Olin Lathrop" To: Sent: Tuesday, December 17, 2002 11:36 AM Subject: Re: [PIC]: How to obtain the official US time clock? > > I really need to design a product that knows the official U.S. time, > aside > > from other features. Can someone tell me what is required for the > hardware > > and software to acquire the official time? And what kind of connections > are > > required? > > There are several ways to do this, but you need to first decide what > accuracy you require. If the gizmo already has an internet connection, > then the contacting a NNTP server requires no additional hardware. There > are other options: > > 1 - Have the user set it occasionally and use a real time clock in > between. > > 2 - Decode the WWVL long wave broadcasts. These are designed for this > purpose, but your hardware is susceptable to antenna orientation and > distance from Boulder. Here in MA we are 2000 miles from Boulder and > placement and orientation of automatic clocks makes a big difference. I > have two automatic clocks, and they only seem to pick up the signal at > night, sometimes. > > 3 - Decode WWV broadcast. These are at several shortwave frequencies. > I know 10MHz is one of them, and I think there are also broadcasts at > 2.5MHz, 5MHz, and 15MHz, but I'm not sure. These may be more difficult to > decode, but the coverage should be wider. I'm not totally sure they even > have encoded data on them. > > 4 - Canada also broadcasts a time standard. The radio station is called > CHU if I remember right. I don't know whether it contains coded > information that a micro can use. > > > ***************************************************************** > Embed Inc, embedded system specialists in Littleton Massachusetts > (978) 742-9014, http://www.embedinc.com > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu