John's Geekblog

If you've come here to find another (?) exciting, sexy weblog full of observations both witty and meaningful, you've come to the wrong place. I don't have any reason to believe that you'd find anything in my life very interesting.

This blog has one simple purpose: to be my on-line logbook for data from my experiments in ham radio and time/frequency measurement. If you want to know when I last adjusted the frequency of my Rubidium standard, then this is the place to be. Otherwise, forget it.
jra on 08.03.03 @ 10:11 AM EST [link]

Sunday, February 26th

28 Volt Battery System Details

I am using two 100AH AGM batteries in series. using an IOTA DLS 27-15/IQ4 15 amp charger. The IOTA is an intelligent charger with three modes:

LED steady on -- float charge at 2.266V/cell -- 27.192V total
LED slow blink -- absorption charge at 2.366V/cell -- 28.392V total
LED fast blink -- bulk charge at 2.466V/cell -- 29.592V total
jra on 02.26.12 @ 06:44 PM EST [link]

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:

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 voltage has been stable within +/-0.5 millivolt for 12 hours after initial power-on.

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

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]