Sunday, April 10, 2016

Determining the radiant of a meteor using Graves radar (III): the details

In my previous post I explained what we did and what results we got. In this post I'll show you the technical details behind the experiment, with some hints and tips in the case you want to replicate it. As a guide, I'll solve a meteor step by step, from the wav file to the radiant, and then, the final orbit around the sun.

Friday, April 8, 2016

Determining the radiant of a meteor using Graves radar (II)

One year ago, I published my experiences about determining the radiant of a meteor using Graves radar. If you read it (I hope you really did it) a question arises immediately: What about three receivers? Fortunately David, amateur astronomer and ham radio operator also known as EA1FAQ joined the team so we could answer this question.

Figure 1: Transmitter and receivers location

We had some doubts. Could the same meteor head echo be received simultaneously by three different stations? some calculations and simulations were made with many interesting results.

Saturday, January 9, 2016

Wideband Quadrantids using Graves radar

Recently I realized one of the most limiting factors while measuring doppler head echoes is the limited bandwidth of SSB receivers. Sometimes you receive a really long head echo appearing at 3000 Hz and going down to 1000 Hz, the rest frequency when you tune 143.049 USB with Graves. And you wonder: how high the doppler can be? To answer that question I made an "special IF filter" for my FT-817. The filter is just a piece of coaxial, so I can receive the whole receive bandwidth. A dummy filter.

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