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Equipment for portable HF operations Portable accessories (IV) By accessories I mean all devices connected in a way or another to the transceiver, the power supply, the optional amplifier, fixing systems, including mobile antennas and microphone headset without to forget the CW key and the logger (not reviewed). If you are looking for smaller and lighter antenna models, if dipoles, small verticals and magnetic loops are still too big, I suggest you to check manufacturers of whips and other screwdrivers mobile antennas. These short antennas can be attached directly to the car frame or, if they are light enough, they can be mounted on a simple trunk lid mount like the Diamond K-400 mount displayed below. When their height exceeds 5 meters or so and their weight over 10 kg, the tripod is often too small and too light and become unable to support the antenna, excepted the largest models (e.g. ASG3 from UKW-Berichte). To ensure a maximum security, some manufacturers sell a cheap but resistant fork (e.g. MMF from UKW-Berichte) to place below an massive element (a ciment plate or a car tire).
At last, if you like to work free hands, you can buy a lighweight headset with a microphone cartridge, like the Heil Sound BM-10 equipped with the jack compatible with your RTX. Minus side, this headset is often expensive. If you are an handyman an alternative ten times cheaper is to build this set with accessories sold by Radio Shack. The power supply : battery and generator Once the location and the transceiver selected, the next problem concerns the power supply. This is trivial, but dame Nature is not connected to the main ! Thus you have to take it with you. This is your first constraint. You will maybe arg that you can use the car battery. Indeed, but as long as you have one... Admit that you have a car. In protecting your system with a 30 A fuse or so, having a good ground, and using a thick cabling system (4 mm tick for several meter long) you can connect your transceiver to your car battery. But usually you have only one, and even if it is in excellent state, if you want to use your dear barefoot emitter (100 W) hours long, there is a risk that you can no more start up your car once you have decided to go back home as you consumed most of its power. In fact, there are two safer and more professional solutions to power your transceiver and optional amplifier in the field : using either a powerful battery or an AC generator with a DC power supply providing about 100 Ah. The first solution is "light" and silent, the second noisy and more cumbersome but offer you a better security. With accessories both solutions will cost you the same price. Batteries As you will probably use high currents - say 50 Ah to be at ease for some hours - the most secure solution is to buy a 50-amps gel battery (or better an Absorbed glass mat battery) with its mandatory charger (manual or fully automatic). Forget the electrolytic model or the engine start battery that requests to be servicing and checked regularly. This way you keep your car battery under cover without risk to go home...barefoot, HI ! With the appropriate connectors and cable extensions, this battery can also be used to drive your antenna auto-tuner or a small rotator. However this car battery will be unsuited to draw the power requested by an amplifier. We will review this very special problem later. To read : Technical information about Gel batteries
If you need to feed an amplifier in the field, I suggest you to buy two gel batteries and to charge them separately. These accessories are sold in any Do-it-yourself shop, sometimes to your garage mechanist too. For your information a 12V at 85 Ah battery like the small one displayed below left and manufactured by Mastervolt in France is 33x17x23 cm in size; it looks light, but its weight is already about 33 kg. Its price is 360€ plus charger. Two of these fully charged batteries will last 2 hours at full power out. Knowing that you will be partly listening, you should be QRV for at least half a day up to 500 W. You can easily recharge them at home using a suited automatic recharger. If such batteries are heavy, they are not too cumbersome and offer the advantage to provide a silent solution, and without pollution. Two 12V at 85 Ah batteries plus a charger cost about 900€. This is also the price of a small generator with the advantage to be silent. The generator An alternative - the word is well choosen - is using in the field an AC/DC generator providing a power of 0.7-2 kW and 120 V AC/12 V DC (or 240 V AC/12 V DC). This type of generator is usually a 2-stroke engine. If we take the example of the small Arctic AC750GT ($570) and Honda EU200i ($1080) models displayed below, they count among the smallest generators available and suited to hams activities in the field. These engine are relatively noisy, producing up to 58-59 dB and their weight is about 21-23 kg, but it is lighter than the smallest gel battery delivering 85 Ah. Note that some competitors sell so-called "portable" models which weight is 85 kg, 90 cm wide, use a 4-stroke engine, and generating up to 75 dB at 7000 rpm ! Like APS, Tendaire Industries, Yamaha or Honda models, a generator requires gasoline and some oil. Due to its weight I suggest you to install it on a small trailer (~35 cm each side), often provided in option. If you have difficulties to find a dealer take also a look at nautical companies manufacturing generators for yachting. They usually provide power generators in the range 5-25 kW or higher but their smallest units might be suited to your activity.
Generator safety Honda that sells many models of generators reminds us that such equipments must be used with all required security. The respect of some basic rules are recommended to prevent any accident. If you need to power a home device, use a quality extension cord and surge protected power strip from the generator directly to the appliance that you want to power. Never operate an internal combustion engine inside your home, basement, garage or any other enclosed area. Even a hand held generator needs a minimum of 1m (3 to 4 feet) of spacing on all sides, including the top. A generator needs an unlimited supply of fresh air for proper cooling during operation. Since combustion engines create carbon monoxide, which can be lethal, good ventilation is critical. Keep the generator dry and always operate it on a level surface. Never add fuel to your generator when it is running and always store additional fuel in approved Gasoline containers. At last it is very important that you never feed power from your portable generator into a wall outlet. This is commonly called back feeding and causes several safety concerns. Depending on your vehicle, you can add a second alternator just for charging your RTX batteries, but a split charge alternator or a split charging system is an easier option if you select the second method. By way of conclusion, before installing your rig in your car, do consult a specialist used to work with RF fields and high power and a good advice, read the two next books (the second one is a PDF), dedicated to portable and mobile traffics. The third link is K2BJ website that provides among other things an image gallery of amateur mobile installations. Solar panels To be complete note that some manufacturers sell today flexible or rollable solar panels (e.g. Aspect Solar, Solar World, Solar Direct, VHF Technologies, etc). These flexible panels are still expensive and cost about $300 for a 20 or 32 W module. An alternative is to buy a portable power generator from Solar Direct using rigid solar panels. This solution is much cheaper than flexible solar panels ($450 for a 360W 12V kit including a 48 or 100 Ah battery). Compared to gel battery, solar panels are easy to use, they can be attached in succession to reach high power, and produce electricity even when the sky is overcast. But this energy is far to be free and is still reserved to the most fortunate of us. Finding a regulated power supply Now that you have the source of energy, remains to convert it to the input voltage of your devices.
There are several solutions, among them the simplest is to forget the external batteries and generators and to work directly with the car battery which power is well regulated. You can let your engine started while working on the air, but this is a source of pollution and noise, and you have to protect your circuit against RFI and other undesired currents that can get back to your RTX and mike. This solution works fine with any classic transceiver up to 100 W or for QRP activities. You can even work on the air engine off, the solution is safe due to the relative low power, and Alinco regulated PSU model DM-330MV (220€) is sold in that purpose (120/220V in, 5-15 VDC at 5-32A out).
Palstar PS-50 (250€) is another model of PSU delivering 13.8V at 40A out. It is well-known and even recommended by some amplifiers manufacturers who suggest to work with two units in parallel to get higher currents. You can also add a second battery delivering 90 Ah to connect to the PSU terminals; all this installation will allow you to run your installtion most of the day, the RTX, an optional small amplifier, and powered accessories (e.g. a magnetic loop antenna, an external SWR meter and an antenna rotor). Need of a portable amplifier too ? While working in the field with your 100 W barefoot transceiver, one or another day if you listen well all DX stations but if you note that you can't reach them easily, you will be perhaps interested in using a small HF amplifier. Why small ? Because moving a 1-kW linear is another affair. With its 40 kg, it is no question to move it in the car, maybe in a caravan. Then there is the problem of its power supply because such an amp draws about 100 Ah. We will have to find another solution. Unfortunatelly, there are not many linears suited for portable operations in the range 300-500 W PEP out. Most linears are kW amplifiers, they are heavy (30-50 kg) and cumbersome, using expensive tubes or transistors and requesting an external power supply connected to the power line and, last but not least they are amperes hungry. None of them can be used on portable or mobile. But by dint of searching on Internet I have found at least 4 models that might satisfy you ! My master choice is a performing amplifier made by a famous US company represented worldwide, using quality material : Ameritron ALS-500MX (X for export, also available at WSPLC). As most HF amplifiers fallling in this category, this is a solid-state model qualified as "mobile" working on 13.8V DC on all bands (with optional kit 10/12 m), offering a so-called instant bandswitching (there is a manual knob), requesting no warm up, no tuning, compact (23x9x38cm) and light (3.5 kg). In short, your ideal companion ! You can buy it between $450 (second-hand) and $850 (new), or 1440€ in Europe. Ameritron as some competitors, all designed with solid-stated power devices, but they are more expensive or bulkier. You will find hereunder the specifications of most interesting models :
But I have to stop you immediately ! Before buying one of these amps, be warned that such an amplifier draws 40-80 amps per hour and if you want to come back home by car, do not connect it directly to your battery or it will quickly gives up the ghost... (remember this simple formula, P = U.I : a 12 V battery at 100 Ah generates 1.2 kW during one hour). Then using high currents you need to protect your installation with a suited cabling system. Here are some advice. Electrical Security Using high currents and power in a portable installation requires to well understand and carefully plan RF and automotive systems. First of all do never use a switched-mode or analog regulated PSU with any amplifier because usually they are not designed to work with high RF fields. They might display instabilities, over-voltage and oscillations between the PSU and the amplifier. What you need is a regulated or not 11-14V DC 50 Ah or 100 Ah power supply. Yes, a so big installation ! This is mandatory once you work with 500 W amplifiers. Of course they are some low-cost solutions like batteries (lead-acid, gel) and small generators that we reviewed above. Usually the nominal current is 13.8V and most amplifiers will switch off automatically from 11V and will warn you over 14V (as well as if you try to work with high VSWR, over-power, etc). Select also the maximum current with care. If a 50 Ah supply is suited for SSB operations, you need 100 Ah to work in AM, FM or RTTY.
Then
you probably know that during transmissions high currents (over 20
A) flow in some parts of the antenna. Therefore your electrical
connexions must rigorously apply the theory of electricity. I mean
that if you try to force high currents in wire of small section
(below AWG#14 or Idem for your wire terminations. Working with high power use only UHF connectors like PL-259 plugs and avoid "push-on" solderness type connectors that quickly dismantle. If your feedline is shorter than 7m (25') you can use RG-58 coax but for longer distance do select a large coaxial like RG-213. At last, be also careful if you have a car with ECU unit (computer), and if you connect your system to the battery. Strange things may occur like fuel pump stopping, door lock, solenoids vibrating, blown fuses, noise through speaker systems... But personally I have never experimented such problems. Have fun ! For more information Selection of portable antennas (.xls 252 KB) Basics of Antennas (on this site) eHam reviews (Portable antennas section) Portable Wire Antennas, John Hill, Clear Springs Press, 2014/2015 Small Antennas for Small Spaces, ARRL, 2011 DX Zone : Antennas section, HF Vertical Antenna, HF Yagi Antenna (Search), Stealth, Portable ARRL Antenna Book, ARRL, specially chapter 16, 2011 (22d edition) The Mobile DXer, Davide Mangels, CQ Communications, 2001 Vertical Antenna Classics, ARRL, 1995/2001.
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1.65mm),
it will heat, probably melt and produce short-circuits if not a fire in your car ! So select always thick
wire, AWG#8 or #6 (about