The Nordholt antenna

This page is heavily under construction. Warranty is already void and the seal has been broken...

14 May 2010, Nordholt antenna uncovered

After functioning 30 years on the roof, the Active nordholt antennas used for the WebSDR receiver failed. One failed during repositioning of the supporting masts, and one did shortly after. If the large RADAR next to the antennas former place acted as lightning "rod" for all these years remains unknown. I opened up the antennas for closer inspection to find one damaged capacitor, looking like it suffered from severe over voltage (lightning?) and no visual defects on the other antenna.

However, this was not the most important finding! After some reverse engineering I found out that both antennas which worked fine for many years are NOT exactly what articles from Ernst Nordholt described. Interestingly enough, there are at least two more transistors, and only one rare FET instead of two!

The small Nordholt has been damaged by water ingress. When I opened the case, water was pooring out of it. The larger Nordholt is still closed and glued shut. It will take some time to carefully open and inspect it. Apart from the water damage, the small version also has an exploded tantulum. This might indicate lightning damage. However, the antenna would continue to work without this tantulum cap. Probably lightning is what has caused the reception problems, and the Nordholt finally had to give in to the force of mother nature after working fine for more than 30 years...

Last modification on: 23 Feb 2016. File: pa3weg/nordholt.php