Spring 2023 Meetings: Antenna Tuning and Attenuator Building

KC9ON Fox Hunt Attenuator

At SPARC’s April, May, and June meetings, we continued working with the tape measure beam antennas we constructed in February. At the April meeting, we tuned the antennas to make sure they resonated at 146.565 MHz, the local t-hunting frequency. By adjusting the spacing of the steel elements, we made sure each antenna was ready to hear a hidden transmitter.

Checking the antenna on an analyzer
Testing the antenna in Eddie Park

At the May and June meetings, we constructed an attenuator kit to pair with the antennas. Stan, KR6CV arranged a group purchase of kits from KC9ON. The V7 kit provides 4 MHz of signal attenuation. KC9ON explains how that helps:

When you’re closing in on the fox [the hidden transmitter] you may find the signals to be strong enough you can no longer find a peak or null with your antenna. Sometimes the signal is so strong that the RF will leak straight into the radio, connections and other equipment making the antenna useless. The solution is to use an offset attenuator. The circuit consists of a small RF generator, in this case 4 MHz, which will mix with the incoming fox signal (such as 146.52 MHz) and produce new signals at plus and minus the fox signal (142.52 MHz and 150.52 MHz). A potentiometer on the board changes the injection level of the RF generator which in turn attenuates the incoming mixed signal to your radio to a level where tracking can continue.

KC9ON Fox Hunt Attenuator
Product image of the V7 attenuator from KC9ON
Building the V7 kit during the June 2023 meeting

Instructions for building the kit can be found here.

With our antennas and attenuators ready for action, we planned to hold a practice t-hunt at our August member meeting.

Constructing a 2 Meter Tape Measure Antenna

Inserting the tape measure segments

At our February 2023 membership meeting, the South Pasadena Amateur Radio Club organized a group building project. We constructed 2 meter tape measure antennas ideal for radio direction finding or “t-hunting.” The club provided a kit of necessary parts to all dues-paying members who wished to participate.

The project was led by Bob WB6YJJ, Rick KI6ZKM, and Stan KR6CV, who provided instruction and assistance as members assembled the antennas. The process involved measuring and cutting tape measure segments to the correct length, assembling a frame from PVC pipe sections, then soldering the components of the driven element (the part of the antenna that radiates).

There are various plans for similar tape measure beam antennas, or “cheap Yagis,” available on the Internet. Here is the schematic for the one we built, designed by Joe Leggio WB2HOL:


Visit Joe’s page linked above or this re-post for a full explanation of how the antenna works and instructions for building one.

Below are photos of all the steps in the building process, courtesy of Robert K6YZF, Stan KR6CV, and John KK6ZVQ.

Demonstrating the tape measure antenna
Bob Vanderwall, WB6YJJ demonstrates the 2 meter tape measure Yagi for the builders.
Template sticks for PVC and tape measure
“Story stick” templates for cutting the PVC pipe and tape measure segments.

PVC cutter
Once the PVC segments have been measured and marked, they are cut with a pair of ratcheting PVC cutters.
Cutting tape measure segments
The tape measure segments can be cut with a pair of tin snips or heavy duty scissors.

Sanded tape measure
The center pair of tape measure segments form the antenna’s driven element. In order to create an electrical connection, you must sand off some of the yellow paint on those segments.
Inserting the tape measure segments
Inserting the tape measure segments into the PVC frame.
Splitting the coax
Splitting the antenna’s coaxial cable is necessary to expose the pieces that get soldered to the central tape measure segments.
Coax error
Stripping coax is a delicate operation. Apply too much pressure, and you may end up with useless bits.

Soldering close-up
A close view of the soldering step.
K6XIX solders the central tape measure sections to form the driven element.
Soldering station
The two halves of the driven element are connected by a U-shaped wire.
Soldering the driven element’s components
Bob WB6YJJ solders the driven element’s components.
The wire choke
Five turns of the coax cable around the PVC frame form a common mode choke.
W9LBC and WB6YJJ discuss how to optimize the antenna’s performance.
Finished antennas
Three completed tape measure beams.
Once completed, the antennas were tested with an antenna analyzer or a NanoVNA, above, to measure their SWR.

This building activity was a welcome return to hands-on projects at our meetings, and we look forward to hosting more in the future.

Soldering Coax Connectors

Preparing the RG-8X

What good is a shiny J-pole antenna if you can’t connect it to your radio? It makes a nice sculpture — a “copper cactus” — but it won’t help much with reception. So for our latest SPARC build, the club met at the garage of Bob WB6YJJ to put our soldering skills to the test. Bob and Tim WA0PTC guided us through the process of soldering UHF connectors, also known as PL-259 connectors, to lengths of RG-8X coaxial cable. With some patience and steady hands, everyone went home with new, handmade cables to hook up and get on the air.

Checking the connector
Checking the connector

Soldering it all together
Soldering it all together

PL259 Diagram
How to connect PL-259 connectors to coax cable. Diagram via americanradiosupply.com

2 Meter Copper J-Pole Antenna

After two informative presentations from Allen Wolff  KC7O, first on soldering technique and then on constructing a 2m cooper j-pole antenna, SPARC members held a group build as our October meeting. Bob WB6YJJ generously hosted the eager builders in his garage workshop. The total cost of materials per antenna was only $20. And according to an antenna tuner, each j-pole had an impressive 1.2 : 1 SWR (standing wave ratio). Not bad! (I used my j-pole during our October 11 on-air net and received good signal reports. —ed.)

If you are interested in building your own 2m j-pole, Allen has graciously shared his presentation. Click here or on the image below to download it as a pdf.

If you have any questions about Allen’s design, feel free to reach out to us.

And here are a few pictures taken during the build.

A completed j-pole ready to go on-air.

Sending Data with Fldigi

Fldigi stands for Fast Light Digital modem application. It’s a free and open-source program that allows an ordinary computer’s sound card to be used as a simple data modem. (I’m paraphrasing Wikipedia here!) ARES Northeast has been spreading the word about Fldigi’s usefulness when other communication systems fail due to natural disaster or power outage. You can use it to transfer small files from your computer when the Internet is down.

SPARC’s own Oliver, K6OLI has created a guide to setting up Fldigi on a Windows PC. His step-by-step instructions, complete with screenshots, will get you up and running.

In addition, the following two videos come recommended by ARES NE director Gary Wong, W6GSW. If you are using Fldigi, consider dropping by an ARES activity day to compare notes with fellow SGV hams!

Fldigi: Learn How to Use It

Basic NBEMS Fldigi Setup

Winlink: Email Over Radio

At our January 4, 2017 meeting, SPARC president Bob Vanderwall WB6YJJ presented a video on the benefits of Winlink. Here is a simple definition of Winlink taken from its Wikipedia page:

Winlink is a worldwide radio messaging system that uses amateur-band radio frequencies to provide radio interconnection services that include email with attachments, position reporting, weather bulletins, emergency relief communications, and message relay.

The most common use of Winlink is sending email from an area where the Internet is unavailable. During an emergency that knocks out Internet access, Winlink can get a message to loved ones and other contacts. This powerful communication resource is an all-volunteer effort administered by a group called the Amateur Radio Safety Foundation Inc. Our Northeast section of ARES (Amateur Radio Emergency Service) uses Winlink as part of its preparedness plans.

With a relatively small investment in equipment (typically an external sound card and free software such as Winlink Express), amateur radio operators can get up and running. Over the course of 2017, SPARC will continue to discuss how to set up and use Winlink at our monthly meetings .

This video by Rick Frost K4REF is a great introduction to Winlink. Rick has posted a series of videos on various aspects of the system on his YouTube page.

Once you’re ready to give Winlink a try, here are recommended node frequencies for the San Gabriel Valley:
145.050 MHz, 1200 baud
W6GSW-10 (Alhambra)
KA6ECT-10 (Pasadena)
W6SGB-10 (San Gabriel)

431.125 MHz, 9600 baud: