Assembling a Portable Station
Over last few days I have received numerous questions relating to how the equipment, shown in my Winter Field Day Project, is connected to make a functional portable station.
The following “Block Diagram” shows how all the components are connected and how they interact. While this may appear slightly daunting at first sight, in reality, it can be divided into five (5) sections:
- Power Sources
- RF Generation
- Signal Routing
- Antenna Options
- Computer Control
These sections are all inter-dependant and crucial to successfully assembling a functioning portable station. Section one (1) is however the critical area with the capacity to make or break the operational efficiency of the portable station if it is not well developed.
The “Block Diagram” is not a wiring diagram; but instead, it is intended to show the relationship of all of the portable station components required to establish a successful station in the field. In a practical sense each or the interconnection in the system are labelled and rely heavily on the fact that different plug and socket combinations are used to simplify the whole process of inter-connect, thereby overcoming delays in assembling the station quickly.
The entire Portable Station revolves around the Radio Console that houses the RF generation of the portable station. However, as outlined above, without the power system / sources, this portable station would not function.
It is therefore prudent to begin the explanation of the “Block Diagram” starting with the power system which has as its centre piece two (2) 150ah AGM Batteries.
The AGM Batteries were selected for two reasons:
The robust construction and lack of soluble acids in the manufacture of AGM batteries.
The “charge – discharge” cycle of AGM batteries is preferable to many of the “deep cycle” batteries used in many portable situations today.
While these statements tend to prompt debate in some circles, from my experience working in engineering projects, with both types of batteries in a variety of situation in this country and else where, has shown that the AGM batteries are the clear winners for portable operation.
While it is important to select the correct battery for the task, it is equally important to set up a system of charging that will provide many years of good service from the batteries being used. It has been my experience that without appropriate care and attention (this also entails the charging process), even the best battery will fail. Charging a battery involves more than just placing any old charger across its terminals and hoping for the best! Charging of today’s modern batteries is about obeying the rules of the battery manufacturer and this extends to the use of a multi-stage charger. These chargers ensure maximum charge is applied to the battery in a form and time frame to produce long and efficient service. To achieve this I have included the CTEK 25000 charger in my portable configuration. The advantages of this type of charger have been well document in Trade Magazines, Caravan and Motor Home Magazines and on the internet by a variety of sources and therefore the need for further discussion in this forum is unnecessary.
During daylight hours I use 160watts of solar panel to trickle charge the batteries thereby prolonging the time between charges. In the evening I use a 240 volt AC 2kVA Honda Sine Wave Alternator as the charging source.
The “Block Diagram” also shows that, when running the Honda Alternator, two additional power supplies are used, one to supply the ICOM IC7000 Transceiver and the other to charge the Laptop internalBattery. The Laptop Computer usually has an operational time from its internal battery of approximately 7 hours. While this is a relatively lengthy time for a laptop battery to last, it hardly sufficient for long duration Field Days. To assist in this regard a portable power supply was selected that provided dual input that allows the laptop to be charged from the Honda alternator 240 AC output as well from the 12 DC battery supply.
For a portable power supply system to be successful there is a need to consider how and where the supply is routed and how the power source is protected. This system is no different; with all cables being terminated in a common plugging system that checks the polarity of the source and also provides overload protection. To this is added a metering system that displays the DC supply Voltage and Current drawn by the total system.
It should be noted that in this system there are no unterminated cables in the DC line, so the potential for reverse polarity or short circuits have virtually been eliminated.
RF Generation is the next area of focus in the “Block Diagram”. The system uses five (5) transceivers to ensure total flexibility of the portable station. With this combination of transceivers the frequency coverage achieved is from 80m to 3cm; however in reality most portable operation centres around eight (8) bands from 6m to 3cm with the HF section dedicated to specific Field Days. While the most common mode used in this portable station is SSB, CW is available across all the bands, with FM capability being available from 6m to 23cm independently of the SSB Transceivers/Transverters. The YAESU dual band FT-8800R offers further flexibility by functioning as a repeater.
When operating in the Microwave region of the frequency spectrum, frequency accuracy becomes an issue. To ensure that all the transverters are as close to frequemcy as possible, each transverter is locked by a GPSDO (GPS Disciplined Oscillator). This ensures a Maximum frequency discrepancy of +/-50Hz across the frequency range. This unit is described else where in this blog.
Signal routing from the central console is the next area to be considered in the “Block Diagram“. This process can make or break a portable station. In many cases the number of feed lines that are connected to the antenna farm can be a “nightmare waiting to happen” when trying to setup a portable station quickly or for that matter working out whether all the transceivers are connected to the correct antenna.
In this portable system every feed-line is labelled at each end of the cable. In addition where there are antennas that work on multiple frequencies, all the combiners (diplexers / triplexers) are positioned at the centre console thus limiting the number of coax runs.
In the case of the transverters, instead of running separate IF feed to each transverter, a relay switching tree has been developed that is located on the mast near to the transveters. This relay tree has its remote head positioned in the centre of the radio console. A simple turn of the central knob routes the signal to and from the required transverter. The only change over switch that is separate from the radio console switches the HF Vertical antenna to the HF Tri-band beam. This switch is mounted in a separate switch box.
In the case of the GPSDO, a common feed is routed to the mast and then a passive splitter is used to direct the signal to the transverters.
The Antenna System used by this system is self explanatory except for the “squid pole” vertical. Many people use this style of system for HF, however what was of concern in the assembly of this portable system was the method used to ensure that the “squid pole” remained vertical and that the setup time was minimal. What was needed was some form of screw in base that didn’t require driving large stakes into the ground. The solution turned out to be quite simple. A visit to the local hardware store uncovered a tube assembly with a tapered lower section that had a course external thread. This device also had a number of concentric bushes that acted as reducers in the top that turned out to be just ideal for the “squid pole”. As if this was not enough there was “more”; it came with a piece of reinforcing rod that provided a way to screw the whole assembly into and out of the ground. What was this device indented for? Assurances were received from the salesman that this device was a “Beach Umbrella stand”!
The last area of the “Block Diagram” relates to the Computer control of the transceivers. This achieved by building three interfaces that connect to the laptop computers USB ports. These interfaces allow complete control of the YAESU FT-817ND’s and the ICOM IC-7000 and add a great deal of flexibility to the total operation.
Thank you for the emails asking how the portable station equipment was interconnected. I hope this article has addressed most if not all of your questions.