Saturday, November 28, 2015

Simple WGS 84 - ECEF conversion functions.

One of the most unexpectedly complicated things I have found during my research into determining the orbit of a meteor using Doppler measurements is the conversion between geographical coordinates and rectangular, or Cartesian coordinates, also called ECEF (Earth Centered Earth Fixed) coordinates:

At first sight it seems easy: The earth is a sphere, so it only need a few sines and cosines. But later, when you need more precision, you discover earth is not a sphere, it is an ellipsoid, so things start to become problematic.

Tuesday, September 1, 2015

V2000 teardown

Over the years I have receive a lot of questions about the inners of the V2000 50-144-432 MHz antenna. I guess it is because of this. The most common question was about the capacitor values: many hams have burn them out and want to repair the antenna.

Thursday, August 27, 2015

A simple PPS pulse shortener

¿How long is the pulse in a PPS signal? If you test some GPS units, you will find very different values. Some GPS produce a 100ms long pulse, but other ones produce pulses in the millisecond or microsecond area.

Usually, this is not a problem. A PPS signal works on the rising edge, so the circuit where the signal is used senses only the positive edge. In this way no matter how long the pulse is. It will work.

Monday, May 18, 2015

Determining the radiant of a meteor using Graves radar

This article has been superseded by this one:

During the last months of 2014, Iban EB3FRN and me were recording meteor head echoes using Graves. But to make things interesting, we synchronized the recordings using a PPS GPS signal. The idea was to analyze the Doppler from the head echoes and and see if something useful can be extracted from them.

Typical Graves' head echo followed by a large tail echo

Thursday, March 5, 2015

A 50 MHz trap

These days I have been thinking in a new antenna experiment. If works as expected, I could install it on my roof and add one or two new bands in my shack. But for the experiment I need a trap tuned to 50 MHz.

I do not have any experience working with traps in HF frequencies, but it was obvious the main problem will be the capacitor. A trap is a parallel connected LC at the top of an antenna radiating some power, so it was obvious the capacitor would need to withstand very high voltages. How high? I don't know. Maybe 5 kV or maybe 20 kV. A very high value in any case.