Amateur radio, programming, electronics and other musings

Archive for Aug, 2017

A number of people have had trouble sourcing the Netduino boards and asked me for help. I have now added support for the GHI FEZ Lemur board which is a perfect replacement for the Netduino devices. They seem to be in stock from places like Mouser which is also handy.

In theory, we should be able to get this working on any pin similar board such as the GHI Panda III or Cobra III etc. If you have a board you need support for, let me know and I’ll roll out a new project. I have simplified the projects to use shared files and ifdefs so it is quite quick.


For the PCB see

I’ve had an MFJ-269B for many years.  It is a useful tool to have when building and testing antennas prior to putting them into service.  It runs from 12v and allows you to fill it with 10AA batteries.  I filled it with 3000mAh batteries.  The problem I found was it always seemed like the analyser was out of charge.  The analyser contains a charge circuit and if the jumper is in the “charge” position the batteries are charged when plugged into an external 12v source.

Looking at the schematic it shows that the charge circuit is only capable of providing 69mA at best.  I’ve heard others indicated it could be as low as 20mA.   This means the charge time could be anywhere from 2-7 days!  Not useful at all.

I decided to pull out the batteries and replace with a LiPo battery.  I took some measurements of the available space and went hunting for a suitable battery from HobbyKing.  Once the battery arrived I took some photos of the mods to share here.

The process was as simple as this….

  1. Remove the rear casing (8 screws)
  2. Remove the battery holder (2 screws)
  3. Snip the wire off of the battery holder and terminate it with either a JST or PowerPole.  I use PowerPoles on EVERYTHING.
  4. Cut some cardboard to provide some insulation between the battery and the PCB.  It will also ensure that anything sharp won’t pierce the battery.
  5. Ensure that the “charge” jumper is not enabled.
  6. Ensure the battery is fully charged.
  7. Mate the two power connectors
  8. Place the battery into the analyser
  9. Replace the back cover
  10. Check the analyser is still working.

I may install a panel mount PowerPole and balance cable so that I don’t have to remove the back cover to charge the battery.  The LiPo lasts far longer than the batteries and can be charged extremely quickly when it does go flat.

You may find your Trimble Thunderbolt Monitor is showing the incorrect date at the moment.  It could be showing the year as 1997.  This is due to the date in the Thunderbolt being reported incorrectly.

GPS Time is a continuous counting time scale beginning at the January 5, 1980 to January 6, 1980 midnight. It is split into two parts: a time of week measured in seconds from midnight Sat/Sun and a week number. The time of week is transmitted in an unambiguous manner by the satellites, but only the bottom 10 bits of the week number are transmitted. This means that a receiver will see a week number count that goes up steadily until it reaches 1023 after which it will “roll over” back to zero, before steadily going up again. Such a week rollover will occur approx. every 20 years. The last week rollover occurred in 1999 and the next one will be in 2019.

The Thunderbolt manual states…

The ThunderBolt adjusts for this week rollover by adding 1024 to any week number reported by GPS which is less than week number 936 which began on December 14, 1997. With this technique, the ThunderBolt will provide an accurate translation of GPS week number and TOW to time and date until July 30, 2017.

The Thunderbolt can now not be trusted to give the accurate date and time and the responsibility of the time correction has now been forced onto the hardware/software which is reading data from the Thunderbolt.  I have written a fix and released v1.0.4 which attempts to correct the time.  Please visit and download the latest version.  Give it a try and report back any issues.

It is very likely I will have to patch again when the GPS system rolls its week over on April 6th 2019.