This posting comes to us courtesy of Graham VE3GTC. He is a regular reader of the blog and you have seen him commenting on topics here for a long while now. In addition we both share the fondness for QRP, Portable Operating and Yaesu Radios…
Any comments about this posting should go directly to Graham via email….
The 2011 CQ Worldwide VHF Contest took place on July 16 starting at 1800Z and ended July 17 at 2100Z. What better way to enjoy Ham radio than by combining portable operations and contesting?
I am sure you can think of many other ways particularily if neither of the mention activities are of any interest. For myself however, they are a very good match. The more portable operating I do the more I look forward to the next time and any reason be it a contest or just a nice day just adds to the pleasure.
CQ has added a new category to their VHF contest referred to as the “Hilltopper QRP”. The idea being presumably to encourage activity just as it suggest – to operate portable out in the field from one or more hill tops.
There is not much in the way of hills around where I live. There are some relatively high hills to the north called the Gatineau hills which are a popular spot for some of the local hams to operate from. Members of the local Ottawa Valley QRP club and Polar Bear Club members frequently visit the hills to operate in some of the Polar Bear operating events or just to activate a summit in the SOTA program. There is also high ground further west near Almonte Ontario and further still at Foymont.
I choose however to go to my Super Secret Location #5. It’s at the public park located at the St. Lawrence Seaway locks in Iroquois, Ontario. The park overlooks the locks, there are lots of nice shade trees, public washrooms, a snack shack, and the diversion of ships of passing through from time to time. There is a also an osprey nest within easy view. The nest is currently occupied by a mating pair of birds which have two chicks. The birds are quite an attraction and draw quite a number of onlookers.
So there it was, the stage was set. My operating location was chosen and after monitoring sparodic E propagation the week before the contest I choose to operate my limited 6 hours of the Hilltopper category starting Sunday morning through to mid afternoon and to operate 6 meters only.
Now all I needed to do was to get off my behind and put together a suitable antenna. Trouble was what to build? Squalo? Halo? Moxon?
Something I had been toying with was the idea of a simple dipole. A simple dipole is normally about 75 ohm impedance, an inverted V dipole is usually considered to be closer to 50 ohm. But why do we mount dipoles in and inverted fashion? Simplicity I guess as in that configuration it needs only one support in the middle. A while ago I asked the question the propagation pattern of a dipole where the arms were extended upwards into a V rather than inverted. The general consesus was that the angle of radiation of pattern was more upward and more suitable to NVIS like operations.
Fair enough but what then happens if we keep the same 90 degree configuration but instead place the V horizontal? What then? A search of the internet found only a few references without much detail. In general however it was declared that an antenna in this configuration exhibitied gain of about 4 dBi over a simple dipole and some referred to this type of antenna as a single element beam. Seemed like the idea was worth exploring so I did.
After a few evenings work of bashing metal and plastic I had my horizontal Veetenna (for lack of any better name) and a suitable method of mounting.
Mounting is accomplished with a couple of hose clamps on the end of a 16 foot extensionable painters pole. A second pole across the roof of my van provides support for the primary pole as can be seen in the photo.
The antenna mount is simply a short length of two inch aluminum angle with mounts for the two arms. I made all the hardware myself save for the 3/8-24″ bolts from the local hardware store. It is possible to buy the antenna mounting studs off the shelf at any well appointed ham radio supplier. Time was not on my side so I made what I needed and save a few dollars in the process.
The antenna is fed with aproximately 30 feet of RG-8X of which about 7 feet is wound around a 4 inch diameter tube to fashion what is called an “ugly balun” and appears as the white thing in the pictures near the antenna feed.
The dipole arms themselves are made from collapsible fishing pole pieces each approximatley five feet in length with a loosely spiralled 16 gauge wire four feet 8 inches in length for the elements themselves. They have about 1 turn every 16 inches which I don’t belive is critical but 16 inches was just a convienient value and held in place with bits of heat shrink and tape.
Testing showed that the antenna as built was resonant at the lowe end of six meters and has a suitable bandwidth of 200+ khz. I don’t have a suitable SWR meter so this was judged using only the SWR/Power meter display capability of my FT-817. I plan to trim a quarter of inch off each arm next I set it up.
Gain? Directivity? Yes. In practice I can turn the antenna while monitoring a transmission and “peak” the signal. Not anywhere near what a 3 element beam would exhibit but there is a definite peak. How much gain? No idea.
All in all the antenna was a success even if the day’s operating success measured in number of contact was less than stellar. In six hours of operating I managed to scratch a grand total of six contacts. Two on SSB, the remainder CW. Actually, I heard more than four dozen stations but despite repeated calling only managed to make a enough noise to complete the six contacts. Operating QRP when conditions are marginal can be a real challenge but then that is half the fun.
More development work is planned on this antenna. I would like to try modeling it in something like eznec but so far have been unable to get the program to run on a LINUX machine. What is the radiation of the pattern of this antenna? Take off angle? Is it optimum to place the dipole arms parallel to the ground or up (or down) X degrees to optimize take off angle? What happens to the pattern if I where to put another element bisecting the V above the dipole arms at a 45 or 60 degree angle above horizontal (makes it looks like a tripod)? More directive? More Gain? Perhaps someone already knows and can point me to some references or can tell me how to get eznec of similar running on a LINUX box (Ubuntu).
As previously mentioned the above article was contributed by Graham VE3GTC (writeup and pictures) . I thank him for sharing this with us and remind you that any comments or questions should go directly to Graham via email. An email link is given to you above the start of his article.
Hope you enjoyed it…
Thanks again Graham