Monthly Archives: November 2015

The ground plane antenna temporarily mounted on the SSC's winch for real-world testing.

A ground plane antenna for the VHF aeronautical band

Last month I built my first antenna. It was a ground plane antenna constructed out of a UHF female jack panel mount connector (sometimes referred to as a SO-239, like this one) and approximately 10-gauge clothes hanger wire.

A ground plane antenna made from a panel mount UHF connector and 5 segments of clothes hanger wire.

A ground plane antenna made from a panel mount UHF connector and 5 segments of clothes hanger wire.

I also used a male UHF to female BNC adapter and built my own 10 ft coaxial cable with BNC connectors. I used RG-58 and these BNC connectors because they don’t require an expensive crimp tool.

The reason I built this antenna is that for years the Saskatoon Soaring Club has struggled establishing reliable radio communications between their winch and their gliders. It’s important to mention that at Cudworth (CJD2), we use 123.2 MHz for communications. What was happening is that while the glider is on the ground, the winch can “hear” the glider, but the glider can’t “hear” the winch. A hand held radio is used in the winch and a more powerful radio permanently mounted radio is used in the glider. Testing revealed that it was likely that the radiation pattern of the antenna on the winch poorly suited for the needs of the club (more details below). The solution was to build this ground plane antenna, since they have the radiation pattern required by the club.

The old quarter wave antenna on the winch relied on using the metal roof of the cab as the “ground plane”. So long as the ground plane is sufficiently large (at least 1/4 wavelength in radius around the feed point of the antenna) the radiation pattern will be toroidal (donut shaped) and able to cover low elevation angles.Screenshot of spectrum analyzer At 123.2 MHz, a quarter-wavelength is approximately 60.9 cm (24 inches). Unfortunately, the amount of metal on the roof of the cab was insufficient (only about 20 cm). Theoretically this means that the resulting radiation pattern will be conically-tapered in elevation resulting in very little radiation being emitted at low elevation angles (low to the ground).  This document describes the problem in greater detail and shows that for real-world situations the radiation pattern is in fact more complicated than the naive description just given. In contrast, the ground plane antenna is built to include it’s own ground plane (see the 4 radials in the picture above). While searching for antenna solutions, I also stumbled upon the inverted L antenna, very cool.

Cutting the vertical wireAfter building the antenna, I needed to tune it. Thankfully, I was allowed to use a network spectrum analyzer at work to do this. The antenna started at a resonant frequency of 98.995 MHz (with the vertical wire at a length of about 30 inches). Of course, tuning the antenna to a higher frequency required me to shorten the vertical wire and the radials. It was interesting to shorten the antenna wire by 2 inches at a time and observe the resulting change to the resonant frequency measured by the spectrum analyzer. By carefully trimming the wires of the antenna, I was able to tune it to a resonate frequency of 123.7 MHz with a bandwidth of approximately 20 MHz or so.

Finally, the antenna was tested in by mounting it to the winch. This was accomplished using U-bolts, tape, and 5 feet of PVC pipe.

The ground plane antenna temporarily mounted on the SSC's winch for real-world testing.

The ground plane antenna temporarily mounted on the SSC’s winch for real-world testing.

Testing was performed by first attempting to communicate with a grounded glider using the old antenna on the winch and then mounting the new antenna and attempting communication. As before, using the old antenna, 2-way communication could not be established, but when using the new antenna the problem was resolved!

The antenna works well and club members are very happy to be able to now communicate more easily with the winch. This has made the winch launching operation safer too.

The SSC's L-23 coming in for a landing.

Gliding with the Saskatoon Soaring Club

The SSC's L-23 coming in for a landing.

The SSC’s L-23 coming in for a landing.

This March I joined the Saskatoon Soaring Club (SSC) and started attending the glider ground school. Hearing gliding stories from John Toles who led the instruction only bolstered the excitement I felt about the prospect of learning to fly a glider (one of my favourites is how he was “beat by a bladder”). Little did I know the excitement I felt was only the beginning. My first flight was on May 9th at the Cudworth Aerodrome. It was a cool Saturday morning with clear skies and a light breeze. Fernando Garza was the Pilot in Command and we were flying in SSC’s Super Blanik L-23 (a beautiful glider with a wise and confident appearance). We launched via aerotow and on my first ever flight Fernando taught me how to do co-ordinated turns. On my third training flight I learned how to thermal as Fernando and I reached over 6000ft AGL!

A view from the cockpit of the SSC's Schweizer SGS 1-26. This plane was built from a kit in 1956 and still flies like a champion.

A view from the cockpit of the SSC’s Schweizer SGS 1-26. This plane was built from a kit in 1956 and still flies like a champion.

Since then I have managed a 52 minute solo flight from a release altitude of 1300ft AGL (and soared with Fernando who was in another glider) and I only need 3 more solo flights to get my glider pilot license. I have had the opportunity to fly solo in each of the club’s three gliders, the L-23, a Blanik L-33, and a Schweizer 1-26 (acquired this summer). It has been a fantastic summer!

As a final hurrah of this gliding season, some of us flew up to Birch Hills (CJD3) on a cross-country aerotow with the L-23. We visited with the Prince Albert Soaring Club and were able to fly winch launches in their K-7.

Gliding is an exhilarating and freeing experience. The raw mechanical feel of the glider enables the plane to somehow become an extension of yourself; as if you were the one with wings. Each flight provides the opportunity to learn and a chance to hone your skills. Gliding can also be a relaxing escape into the vertical

Fernando (in a Super Blanik L-23) and I (in a Schweizer 1-26, you can see my wing) soaring together 2500ft above Cudworth, SK.

Fernando (in a Super Blanik L-23) and I (in a Schweizer 1-26, you can see my wing) soaring together 2500ft above Cudworth, SK.

dimension, where far below one leaves the everyday things to be replaced with eagles and hawks (they show you where the thermals are!) and stunning views of the clouds and the prairie below. Perhaps more importantly, gliding is a social sport. It is about teamwork and camaraderie; we take pride in each other’s accomplishments. It’s a bit like joining a second family. Even though this gliding season is ending, the Club is making plans to keep active over the winter season. This is only the beginning of my gliding adventures!

Below you can see more pictures of the SSC gliders. If you are interested, I have an album on Flickr with even more photos.

The Schweizer SGS 1-26 purchased this summer by the SSC.

The Schweizer SGS 1-26 purchased this summer by the SSC.

The L-33 Blanik Solo glider owned by the SSC.

The L-33 Blanik Solo glider owned by the SSC.

A cross-country aerotow from the low position. Heading to CJD3!

A cross-country aerotow from the low position. Heading to CJD3!

Members of the Prince Albert Soaring Club and the SSC with the Prince Albert Soaring Club's K7.

Members of the Prince Albert Soaring Club and the SSC with the Prince Albert Soaring Club’s K7.