My latest piece of test equipment is a HP Z3801A GPS Time and Frequency Standard. This fantastic piece of equipment has hit the surplus market. For a time it was as inexpensive as $249.00 with an antenna and power supply. The HP Z3801A's frequency accuracy is better then 1 X 10 -9 (better then 1 hz in 10 GHz) and has been measured to 1 X 10 -11 (you do the math). It is comparable to a Rubidium frequency standard ! The standards were originally utilized in CDMA sites for synchronization of the various cell site towers and transmitters as well as in E911 dispatch sites. They make a great laboratory standard and their frequency and timing accuracy can be traced to NIST. The standard has a handy 10 MHz BNC output on the rear.
The best web site available with understandable information for the amateur radio operator and others interested in the HP Z3801A is Bill Jones's, K8CU Real Ham Radio Site. Bill authored an article published in QEX regarding the utilization of the Z3801A for weak signal VHF work... an idea which has also caught on with owners of high end HF rigs like the Ten-Tec Orion.
A great amount of information on this standard is available via links from the above page. Also available from the page are links to Z3801A and other receivers online... that display graphs of their status. Great control and monitoring software named GPSCon is also available for purchase there.... check my GPS receiver status on line as logged by GPSCon.
W9WIS's HP Z3801A Current Status Page