Construction Corner

How to Build Your Own Cost Effective Project 25 Scanner, By Ryan Martin KE8MSW

At the July 26, 2021 club meeting Ryan Martin, KE8MSW presented a fantastic program on building a Trunking Scanner by combining an SDR dongle (Software Defined Radio on a chip that plugs into a USB port on a computer), with a miniature Rasberry Pi computer, and some really magical free open source software.  He showed us how this combination could copy all of the police, fire, and public service channels in Lenawee County, plus a whole lot more interesting traffic.  Ryan has written up a summary of this project outlining what you need to know to do this project.  Furthermore, he has offered to help club members get it all up and working.  Read it over here.  It might make an interesting club project to do as a group on Monday nights if there is enough interest.  If interested in doing this project, drop an email to Ryan and Bob, K2IBM, and we will see what we can do if there is sufficient interest.

One Trim Dipole, by Paul Voorhees, W7PV

Submitted by Denny, WE8Z from an article that appeared in the TMRA newsletter by Paul Voorhees, W7PV, with the author's permission.
One Trim Dipole Simple wire dipoles are among the easiest and cheapest antennas to make, but getting the length and resonant frequency exactly right is often left to trial and error. It is well known that the formula for the length of a dipole Length = 468/Frequency, often provides the wrong result, due to various factors. However, there is a way, using an antenna analyzer, that you can get it down so you only trim the length once. First, use the standard formula. For a center frequency of say 14.2 Mhz, the length comes out to 32.96 feet, or about 16.5 feet per side of the half-wave dipole. Then add about 6 inches to that length on each side and put up the antenna where it will finally be. From your ham shack attach the antenna analyzer to the end of the coax and find the resonant frequency (lowest SWR). Now you solve for the REAL constant, by multiplying the total length you initially used (in our case 34 feet), times the resonant frequency you found on the antenna analyzer (Constant = Frequency X Length). In this case the analyzer shows resonance at 12.61 Mhz, so the real constant of this antenna is 34 X 12.61 or 428.7. Now, using the real constant, and the formula L = 428.7/14.2, you get 30.19 feet or about 15 feet 1 inch on each side. Since you used 17 feet per side to start with, just trim 23 inches off each end and voila! The antenna analyzer should now show a resonant frequency of 14.2 Mhz. 73, Paul Voorhees W7PV.


New Thinking on Magnetic Loop Antennas

By Cletus Brooks, K8TLT


"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.


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


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.

UBITX and QCX Transceiver Kits By Mark, NU8Z

With regard to last night’s program (11/26/18), have listed some UBITX and QCX links below.


If you were not at the meeting, if you review the below links you will learn more.

In a nut shell, the UBITX low dollar and high performance radio (for $129).  The board is assembled and needs to be wired into a case, firmware, software loaded etc. This is and open source project. The Ubitx can be hacked and improved via Firmware, software and the addition of simple hardware kits  (filters, agc, cw reading, Cat control, touch screen display and others. This little radio came out 1 year ago and over 6,000 have been sold. It is the fiddlers dream. Put a shine on that tennis shoe!

Check it out.

 I’m going to buy one!!!  Maybe others in club would join the fun??

We will talk again.

 The 10 Watt UBITX 5 Band CW/SSB Transceiver kit  

(assembled board open source radio project = hackable radio)

 Link to sellers website: (Great UBITX info site)

UBITX online help group    Be sure to check the WIKI section of this site.

Also,  just Google “UBITX Transceiver” and you will get lots of info, images, and videos about UBITX open source movement.

The 5 Watt QCX single band CW Transceiver kit  

Also,  just Google “QCX Transceiver” and you will get lots of info, images, and videos about QCX