December 2012 Archives

Cute Biquad Yagi

Flower Pot Antennas

The "Flower-Pot" Antenna is an antenna designed to look like the PVC support in a large flower pot holding up a plant. The designer's intent was to make an antenna that looked like a real plant; in that respect, the flowers are made of plastic as well.

The half-wave is a basic half-wave dipole (quarter-wave radiator over a quarter-wave groundplane) with a coax choke at the base. This compares to many commercial designs, including the Motorola TAD1002, 1960s vintage "trombone" antenna.

The 1964 manual for the TAD1000-series coaxial VHF antennas   donated by Skipp   Description, Installation, Assembly, Parts. 150 KB PDF file
Covers the models TAD1001x, TAD1002x, TAD1003x, TAD1004x, TAD6071x, TAD6072x, TAD6073x, TAD6074x (where "x" is an "A" or a "B").


Looking at the half-wave dipole, one can observe common elements.  Both antennae have a quarter-wave resonant radiating section, though the trombones use a folded dipole element for this purpose; the folded dipole provides a DC short for lightning, protects the receiver from high voltage static fields, provides structural support for the vertical element and changes the feedpoint impedance.  Both have RF chokes present, though it is not obvious from observation that the TAD1000 antenna does. This is because you have to see one up close and note that the lower section is a three-inch diameter brass sleeve mounted around a one-and-a-half inch diameter brass center support rod. In this manner, a coax choke/balun is built into the antenna.

This details how the quarter-wave coax balun and choke is implemented. Additional material on the subject is available in the ARRL and RSGB books; this object frequently appears in amateur radio microwave antenna designs.

The single 5/8-wave antenna uses a different approach to implement the antenna; a 0.2-wavelength stub is installed onto the coax in collinear fashion.

The dual 5/8-wave antenna uses a balun feed system similar to what MFJ used on an antenna they sell:

Dual-band half-wave:

This antenna uses external stub tuning, which is now some people have retuned Super StationMaster antennas for lower or higher frequencies.

Finally, the Dual-Band High-Gain Flower Pot:

My reading of this design, and the others causes me to make a critical point: drilling the PVC weakens it, and creates places where water can enter. Therefore, I suggest that if one builds any of these antennas for permanent external mounting on a tower, place a large diameter PVC or fiberglass pipe over the built antenna to provide additional structural support and weather resistance. 

Dell PS-2521-1D Power Supply

As I've discovered, and I'm sure someone knew, the Dell PS-2521-1D 550W power supply, used in the Dell PowerEdge 1850, is also an Astec DS-550. Astec has been purchased by EmersonNetworkPower, but they brought the product pages over. In addition to the mechanical drawings, there are pin-outs and a description of various signals present at the power connector.

The actual manual itself: 

Local/backup copy

I have not attempted to modify the power supply yet to see if I can get more than 12V out of it, nor have a made noise measurements to see what sort of conducted noise it generates.

Hawg Fence Antenna

I came across this the backwards way and found myself trying to locate what type of antenna this way without any information about the design. Turns out to be a simple parabolic like has, except it predates the design at that website. I found a one-sheet description by KD4SHH:

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