Determining the radiant of a meteor using Graves radar

Important
This article has been superseded by this one: http://ea4eoz.blogspot.com/2016/04/determining-radiant-of-meteor-using.html

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

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.

Looking inside a 144 - 432 - 1296 triplexer

It has recently come into my hands a 144 - 432 - 1296 MHz triplexer. A Comet CFX-4310. I was curious, so I opened it:

Sunspot region 2192 with a compact camera

These days a really large sunspot is visible on the sun. It's so big it is visible to the naked eye. I tried to take a photograph of it, just for fun:

Sunspot region 2192 on October 21, 2014

Revisiting DC blocking solutions for DC damaged IF filters

During these last years a new problem appeared in many commercial ham radio equipment, from many manufacturers. The receivers suddenly become deaf, hearing only really strong signals. The problem is the premature failure of IF filters, because DC is applied to them. Why?

Because applying DC to these piezoelectric devices causes electromigration, and therefore the filter destruction. Manufacturers warns about applying DC to the filters, but manufacturers have been ignoring this for decades.

A transceiver with this problem can be easily repaired by just replacing all the damaged filters, and to prevent this problem to appear again, a pair of DC blocking capacitors must be inserted at the filter input/output pins. In fact some manufacturers have modified their PCB in latest revisions to add these capacitors. But are these capacitors enough to keep DC out of the filters?

Simple phone battery test

Do you suspect from your phone battery? Testing today's mobile batteries is very easy: Lay it over a flat surface and make it to spin.

Installing BG7TBL noise source as poor's man tracking generator

After finishing the modification to the BG7TBL noise source, and put it in a shielded box, it was time to place it inside the spectrum analyzer, so I could use it as a poor's man tracking generator.