Amateur Radio Field Days have the ability to conjure up many and varied images depending on the experiences of those involved while portable. For many they are a fantastic experience to allow those participating the opportunity to test their operating skills, equipment reliability and their ability to establish a fully operational station in some remote location. On the other hand for others, field days / portable events are or have been nothing short of a full blown disaster, resulting in the operator vowing never to undertake the experience again!
From my point of view, field days are a challenge and though I can say I have had the odd bad experience for the most part the experience has been extremely rewarding. My experience spans the last 50 plus years beginning the late 1950’s on frequencies from 160m to 3cm with equipment that has been predominately “home brew”. In the early days every thing was Xtal locked Transmitters and a variety of second world war radio equipment with AM reigning supreme, then Phasing and Filter SSB and FM (transmitters, receivers and transceivers both valve and solid state) all of which provided substantial rewards with a few disasters thrown in for good measure.
The 2011 Winter VHF / UHF Field Day has come and gone and for the most part all who participated had a good time proving once again, that these events can be fun provided suitable planning is adopted to ensure, as far as possible, all the variable are under control
The following is an account of my efforts to participate in the 2011 Winter VHF / UHF field day activities using an entirely new configuration from previous years. The catalyst for this new configuration was defined by a major portable disaster that was inflicted on me earlier in the year. The disaster occurred due to a freak wind gust that virtually saw all of my microwave equipment and its respective antennas blown over and slammed into the adjacent roadway. Determined that this was never going to happen again, I set about designing a solution that would allow my field day / portable operation to occur at any location that a 4×4 and trailer could drive to!
With this in mind I settled on a design that relied heavily on the use of a standard box trailer. I was however, determined to produce a system for mounting antennas that was easy to set up for field days / portable operation, but flexible enough to allow the trailer to be used as a trailer at other times.
From past experience the design for such an antenna system also had to accommodate the ability for any mast to slowly rotate while supporting antennas for at least eight bands VHF / UHF and Microwave (6m, 2m, 70cm, 23cm, 13cm, 9cm, 6cm and 3cm). Because I also wanted to operate portable on the HF bands the design needed to allow for a HF Mosley TA33jr tri-band Yagi to be installed in the place of the VHF / UHF and Microwave antenna.
The design had to allow for all of the antenna and mast components to fit into the box trailer. The thought of having antenna components draped all over my vehicle was not an option even for transporting pipe sections and antennas.
For those of you familiar with going “off the beaten track” the last thing you need is to have low lying branches getting tangled up with your carefully designed and crafted VHF / UHF antennas. The antennas will always come off second best resulting in a disaster and spoiling what could have been a great portable experience.
With these thoughts clearly in focus, the build requirements began to take shape.
If the design was to be robust and reliable a number of major factors had to be addressed.
Firstly the mast needed to have a solid base with a means of rotating but be devoid of any support “guy” wires. In addition, with so many antennas (which includes a number of off-set and prime focused dishes) on the mast, the design must incorporate an easy solution to raising and lowering the mast in windy conditions.
In addition to those items identified there was a need to ensure that the total system could be assembled and raised & lowered by one person!
The following images show the system on its maiden field day outing during the Winter VHF / UHF and Microwave Field Day 2011. The systems performed flawlessly with a set-up / dismantle time of about 45minutes.
The base for the system is manufactured from 50mm angle iron that was formed into a frame that sits in the base of the trailer. To this is added cross braces, made from the same material and positioned in the centre of the frame to hold the base solidly in the trailer while providing an anchor point for the tilt over pivot. The base frame has a vertical mast section attached that is supported by 25mm angle iron diagonal struts. This mast section acts as a “gin” pole for raising the main antenna mast. A standard boat winch is fitted to the back stay with the cable passing through an enclosed pulley at the top and then connecting to the mast section. The winch is stabilised by a diagonal strut that prevents the winch from twisting. The base pivot is a 200mm stub of 40mm galvanised water pipe on which is mounted a Yaesu G-800DXA variable speed Rotator. This rotator is pinned through the stub to ensure it always has a fixed location.
The mast section is 50mm x 3m aluminium scaffold tubing which is further reinforced with an additional 45mm aluminium pipe in the centre that then protrudes 300mm out of the top of the main mast to facilitate a support for a further 40mm x 2m aluminium mast to accommodate the VHF / UHF Antenna.
Note: This upper section can be replaced by a 50mm x 3m aluminium mast section on which the Mosley TA33jr is mounted for HF operation.
The top section for the mast, when used for VHF / UHF, supports “Loop” antennas for 6meters and 2meters, a GPSDO (GPS Disciplined Oscillator for locking the Microwave Transverters) antenna and an 14 element Yagi for 70cm. The 2 meter “Loop” can be replaced by an 8 element Yagi if greater gain and directivity is required. In addition there is a tri-band Vertical for 2m, 70cm and 23cm located at the top of the mast.
On the 50mm section of the mast there are two cross arms. The top cross arm supports the 23cm Yagi plus Transverter, the 13cm (Square Patch) Antenna plus transverter and the 3cm – 300mm Prime Focus Dish plus transverter.
On the lower cross arm there are two stub masts to support the 9cm and 6cm off-set dishes. These stub masts are pinned to the cross arm so as ensure they are angled forward by 22degrees to the vertical. In addition this cross arm is pinned to the centre mounting plate to ensure that this angle is always maintained.
Note: With off-set Dish Antenna the plane of the dish needs to be set at 68 degrees with respect to the horizontal to ensure that the focal point of the dish points to the horizon. Since every off-set dish is slightly different the exact angle needs to be derived experimentally. The mounting plate for these types of dishes has an adjustment protractor so it is a simple matter to change the actual position within a few degrees.
The bottom section of the 50mm mast has a bearing fitted with a suitable plate that attaches to an angle plate on the centre tripod to ensure the entire assembly is stable and aligned for rotation when vertical.
To ensure total stability of the box trailer 50mm stabilising legs were added that are adjustable to cater for undulating ground. The wheels of the trailer were also “chocked” using caravan wheel wedges to complete the stabilisation process.
The cable assemblies for all the antennas, DC feeds for the transverters and IF & PTT cables are bundled into three looms that are supported by attachment tabs that bolt to the mast to ensure no load is placed on the equipment and antennas. Short sections of PVC tubing are affixed to the cross arms to route the cables to the respective transverters again removing loading on the connectors.
The 12volt DC feeds to the transverters are terminated in a distribution box that is attached to the base tripod with a single feed going directly to the main DC distribution centre that monitors voltage and current to the transverters. This distribution centre also provides polarity and overload protection for all the devices connected which includes the GPSDO.
Note: The 12 volt DC feed to each transverter uses standardised polarised plug to ensure compatibility of all of the transverters. This also applies to the IF / PTT cables that are all terminated in BNC connectors.
Every cable (Antenna feed-lines, DC supply cables and IF/PTT cables) has identifying labels at each end that have clear heat shrink tubing over them to protect the label from damage. This ensures that there are no “slip-up’s” when assembling the system.
Each transverter has its own metering system that monitors Voltage, PA Drive and Power Output. These meters are easily visible from the operating position and ensure that the systems are working effectively.
As shown in the following image all of the equipment is carried in the SUV in a dedicated frame made specifically to ensure that all of the equipment travels safely. Aluminium carry cases are used to house many of the items to ensure nothing is forgotten and provide protection for individual components.
There are five major cases that house essential equipment required for successful Field Day operation.
• The first of these is a battery box with built-in protection that contains the 150 ah AGM Battery and 600 watt Sine Wave DC to AC inverter to provide 240v AC for the YAESU Rotator and any other AC system that may be required. (A second 150 ah AGM Battery is also carried to support the main Battery)
• The second is a “roady 19” rack case” that has been setup to hold all the Transceivers required for the VHF / UHF & Microwave operation. These include ICOM IC7000, ICOM AT180 Tuner, ICOM IC1200 FM, YAESU FT-817ND Tuneable IF, and a YAESU FT-8800R.
A second version of this case has been developed for HF that houses a ICOM IC-7000, ICOM AH-4 Tuner and IC 208H dual band FM transceiver.
• The third case is the Stanley “FATmax” Toolbox that is central to all the portable operation. This unit has three large draws that allows storage of all the cables, the YAESU Rotator control head & rotator cable and DC control Centre. The three draws open out to form a natural console for operating with the “roady” case placed on top of the toolbox with the lid acting as a table top. To achieve a flat surface an insert of 3ply was shaped to fit into the lid. The lid needed to be supported as the hinges would not be able to hold the weight of a laptop and so a support was produced using two pieces of aluminium tube. One as a cross brace and the other as a strut from the axle of the toolbox.
• The forth case houses the laptop computer, and transceiver interfaces that allow interconnect with the ICOM and YAESU transceivers. The Laptop provides for logging of contacts by reading the Frequency and Mode directly from the transceivers. There is also an added advantage in making this interconnection with the transceiver because the Laptop also displays the Frequency in large figures that are easy to read in direct sunlight. This fact alone overcomes the deficiency of many transceivers being impossible to read their LCD displays in sunlight.
• The last case houses the 160watt Solar Panels that provide a trickle charge for the AGM Battery throughout the daylight hours without having to resort to use fuel based charging systems.
When operating HF portable the system is supported by a 2 KVA four stroke Honda Generator that produces little noise and allows prolonged operation during the evenings.
Lastly my thanks go to all those operators who provided the contacts with me throughout the 2011 VHF / UHF & Microwave Winter Field Day. I was fortunate to make numerous contacts on all of the 8 bands that this portable system supports. The contribution made by all of the operators has contributed, in a very positive way, to the success of the project that yielded a very rewarding and satisfying experience for me!