Construction Corner

"In today’s world the hams satisfaction comes from building a part of their own station. In the early days it usually started with building the transmitter or receiver and connecting it to a wire and seeing how far away you could contact another station.  Today the normal transceiver has at least 10 amateur bands with at least 4 modes of communication and is in a box the size of large book.  Not something most hams want to tackle."  Quote from Cletus, K8TLT

The above is a quote from Cletus' article below on Magnetic Antennas.  I (webmaster) liked it so much that I thought we should have a webpage devoted to construction.  Thus was born, in Cletus' words, "Construction Corner".   Members are invited to share their construction articles or projects with club members and hams around the world.

New Thinking on Magnetic Loop Antennas

By Cletus Brooks, K8TLT

 

 Ok let’s look at the wire antenna.  This is not something that can be stuffed into a small box and still work. Or will it.  The intriguing size and performance of the magnetic loop is still a mystery to many hams.  The standard design and cost may prevent some of us from attempting this project.  Most commercial units for the HF bands that can be used for transmitting are in the $500.00 range.  With the standard design a very expensive high voltage capacitor and a difficult to manage matching network may make us think this project is not worth the effort.

So let’s redesign it!!  When we are constrained by someone else’s thinking we have a tendency to lose the battle. Scrap the designs and start over.  First we start with a 10’ piece of ½”soft copper pipe cut it in two, place 2 copper T’s on the ends and form a loop with the T’s pointing at each other.  Then we cut 2 pieces of hard copper pipe and solder them in the inside of the loop leaving about a ½” gap between them.  At this junction point solder a capacitor with the appropriate value for the band you want to work.  1000pf for 75 meters. Since this point of tuning has a much lower voltage an inexpensive variable capacitor may be used.  Next we connect the shield of the coax to the bottom of the loop and the center conductor around the loop at a point where the match is 1 to 1

The observed usable bandwidth on 75 is 28 kc. The matching network is very easy to tune with an antenna analyzer.  You will notice a big reduction in the noise level.  Here a few readings compared with a dipole at 50’

Magnetic antenna      dipole                                                                                                        

Noise level

S6                                +20 dB

Signal zolevel

S7                                +30 dB

Lightning crashes

Nil                                +20dB

 

Get the DC wiring right on your mobile...

Check out this DC wiring chart courtesy of Denny, WE8Z

The BIG STICK ,VHF ANTENNA by KB5WMY Carl

Justin Brown, KC8WKJ,  has contributed an article about a small sized J-Pole antenna that can be setup for Hams on a budget/limited space/apartment or moving around a lot.  The plans were provided by his good friend Carl McNair ( KB5WMY ).  Check it out!

Build a 9db 70cm Collinear Antenna from Coax by N1HFC

Here is a nifty way to get considerable gain on 440 Mhz. (Found by Cletus K8TLT)

The DBJ-1: A VHF-UHF Dual-Band J-Pole Ed Fong WB6IQN

Ed Fong seems to have solved the problem of poor match (SWR) and poor radiation in a dual band J-Pole (2M & 440).  If you don't feel like building it, it is available on Ebay for $40 Shipped.  You need to buy a PCV pipe from Lowe's but that's it.  Check out the details here.