John's Geekblog

Wednesday, December 28th

Voltage Regulator for BVA


I'm using an "ALWSR" low noise voltage regulator to power the 8607 BVA. It is designed by Andrew Weekes and is based on Walt Jung's "Super-regulator". Andrew's web pages about the regulator start here: http://www.andrewweekes.talktalk.net/potentially_positive.htm.

The board has a pre-regulator stage but using this requires significant headroom above the output voltage -- abiout 4 - 4.5 volts. Since the oscillator wants 24 volts and the system is run off of 2 "12V" AGM cells in series connected to a float charger, this doesn't allow for much drop if the power goes off and the batteries start to run down. The main advantage of the pre-regulator is to improve the dynamic stability of the system (ie, reduce the output voltage change when there is a sudden change of input voltage). That's not a major issue for this application since the OCXO will draw nearly constant power once it's warmed up. So, I am bypassing the pre-regulator stage to reduce the headroom requirement.

With a 28.8V input, the output voltage is 24.023+ volts. Reducing the input voltage shows a very pronounced loss of regulation at about 24.5V, with about 0.1V reduction of the output over less than 0.1V change of the input. (The "+" signifies that the sixth digit on the HP 3456A voltmeter is cycling in the range of 3 to 7 after the regulator and power supply had been running for about 30 minutes; the DVM has been running for months, but is also a couple of years out of calibration.)

The circuit uses an LED which glows when the circuit is operating properly. The LED extinguishes at about the same point as regulation is lost, so it's a good reference point -- if the LED is fully lit, there's enough voltage to maintain regulation.

As a last bit of data, at 28.8V input, the regulator draws about 32ma with no load other than the DVM.


jra on 12.28.11 @ 03:03 PM EST [link]


Tuesday, December 27th

GPS Antenna Cable Delays


VNA measurements of the delay from each GPS antenna to the output of the splitters:

Antenna 1 -- Aeroantenna choke ring to HP 58517A 8-port splitter: 140 ns

Antenna 2 -- Motorola Timing2000 to HP 58535A 2-port splitter: 165 ns

Details at http://www.febo.com/pages/lab_documentation/gps_cable_delay/


jra on 12.27.11 @ 11:57 AM EST [link]


Saturday, December 24th

Z3801A self survey result


For comparison to the M12+ survey results, this is what Z3801A unit #1 came up with after doing its (shorter) self-survey:

33 52 43.214 N
84 02 29.041 W
325.20 M MSL


jra on 12.24.11 @ 02:37 PM EST [link]


GPS Coordinates


A 48 hour survey using a Motorola M12+ receiver shows the coordinates of the Aeroantenna GPS antenna to be:

Latitude: 33.8786812 N
Longitude: 84.0414157 W

Latitude: 33 52 43.252 N
Longitude: 84 2 29.097 W

Latitude: 33 52.7208720 N
Longitude: 84 2.4849420 W

Elevation 331.97 M MSL, 300.91 M GPS


jra on 12.24.11 @ 02:31 PM EST [link]


Restarting the Blog


After packing up the lab in Dayton, Ohio in late 2009, I'm finally getting things running in our new Atlanta-area basement.
jra on 12.24.11 @ 10:45 AM EST [link]