Building a Go-Kit

Building a Go-Kit
Original article by W5TI

What is a Go-Kit? A Go-Kit is a portable amateur radio station which the radio amateur can take when asked to go to an event which needs support with radio communication. What is consists of depends on the extent of the event, and the communication needs. Making a pre-planned kit helps the thought process as to what will be needed, and how it will be used. What I present here is the thought process which resulted in my current Go-Kit, which might inspire you to improve on it.

Recently, we had a triathlon in our town, with 600 entrants. The ham radio community was asked to help with communications, and many volunteers showed up to assist. Communications for the event were handled through two of our closest repeaters which were linked together for the event to provide nearly seamless communication throughout the community. Some of the volunteers showed up with a 2 meter HT, and nothing else in the way of communication equipment. Even with the best of repeater support, there were times when communications were spotty because of the low power hand-held transceivers, and the hilly terrain. I have seen this problem many times before, and it leads me to my first point. Sometimes it is necessary to go equipped with more than QRP (low power) equipment to achieve reliable communications. It is good practice to use no more transmitter power than required, but it is also necessary to have enough power available to complete the communications. This has led me to build a Go-Kit which is capable of more transmitter power than my HT. I do not have to use that power, but if I need it, it is there.

Sometimes also it is useful to have more than VHF/UHF capability. Depending on the event, it may or may not be possible to rely on repeaters to extend the range of hand-held, mobile, and portable stations. In major emergencies, it may not be possible to rely on the presence or operation of repeaters, and so longer range communications must be established some other way. This may be by well-situated stations, or stations with higher power and/or better antennas.

QSL card station
Front and rear view of Yaesu FT-817, with LDG Z-11 Auto Tuner and W4RT One Touch Tune

My first Go-Kit was based on a Yaesu FT-817 Ultra-Compact QRP radio. This is a particularly fine choice as it is very compact and portable, completely self-contained radio which covers most every ham band between 1.8 and 450 MHz, on FM, SSB, CW, and digital modes. I combined this with an LDG Z-11 tuner, and a W4RT Electronics One-Touch-Tune module. This served me well, with the exception that sometimes the five watts that the FT-817 produced was just not enough to reliably get through, due to terrain, propagation, and other issues.

In order to improve the transmitted power limitation, I added to my kit a Tokyo Hy-Power HL-50B linear amplifier. This boosted the five watts from the FT-817 to fifty watts, which boosted my signal by 10 dB. This was a very worthwhile improvement. There were two difficulties with the HL-50B. The first was that it is hard to buy, because of the current Part 97 regulations, and so I had to order it direct from Japan. The second difficulty was that I now had a considerably larger kit to tote around, as I could no longer just run from the internal battery pack on the FT-817. The HL-50B needed about 12 amps at 12 volts DC, and that meant that I had to also tote around either a power supply or a large battery. That having been said, it was a great amplifier, and very well built. The additional 10 dB often made the difference between failure and success in actually communicating in less than optimal conditions.

I sold my entire FT-817 kit in October of 2004, before my first cancer operation, to help pay for the hospital bills. While I missed it, it would be a couple of years before I would be considering portable operations again.

Building the New Go-Kit

During the summer of 2006, I decided to build a new Go-Kit, improved based on what I had learned from the last one I had. Several things had changed. First, it was obvious that, post-cancer treatment, I would not be backpacking equipment anywhere. My new Go-Kit would be portable, but meant to be carried about with assistance, requiring nothing fancier than a little red wagon. My new Go-Kit would dispense with the QRP radio with a separate amplifier, and instead substitute a 100 watt output radio, which could be throttled back in power as required. The new Go-Kit would include an AC power supply, but also be able to run on 12 volts DC. Additionally, I decided that I would include both a versatile all-band, all-mode radio, but supplement it with a dedicated 2 meter FM radio, since it seemed necessary under some circumstances to operate 2 meters simultaneously with whatever other bands or mode was currently required.

The Yaesu FT-857D was chosen as the basis for the new Go-Kit. It is extremely compact, operates virtually all modes and almost all bands from 1.8 MHz to 450 MHz, and outputs 100 watts on HF, 50 watts on 2 meters, and 20 watts on 450 MHz. I have a review of the FT-857 here. A Yaesu FT-2800 is the dedicated 2 meter FM radio. It is simple and rugged. I added an LDG Z-11 Pro antenna tuner, and an Astron SS-25M power supply. In order to have a better view into feedline and antenna conditions, I added a Daiwa CN-410M power meter/SWR bridge. The 12 volt power is distributed using a West Mountain RigRunner 4005 with five outputs, using the standard Anderson Powerpole connectors. Elecronically, this setup does exactly what I wanted it to do.

The Go-Kit is a completely self-contained radio kit, which can be moved as a unit, and set up with a minimum of fuss and bother. When it is not in portable use, it lives in a folding desk in our den, and provides a second operating position. The necessary accessories are carried in a separate compartmentalized foam-padded case. A battery, if required, is in a separate battery box, which protects its terminals, and provides a clean case with carrying handles. Using the Anderson Powerpole connectors, the Go-Kit can also be powered from an automotive battery or from a car or truck. It is very versatile.

I built a four-sided enclosure from high grade ¾ inch birch plywood. The radios are mounted to the enclosure using their mobile mounting brackets. The power supply was drilled with extra holes, and is screwed directly to the plywood base. The RigRunner is screwed down also. The other small accessories are attached with Velcro tape. The enclosure has a pair of heavy duty folding handles installed, one on each end, in order to provide a good hand hold to pick up and move the box.

The 12-volt power distribution system is based on a West Mountain RigRunner 4005, which routes the power from the source to all of the radios and accessories. The source would usually be the 25 amp switching supply shown, but is easily swapped out for whatever 12 volt source is available, whether a gel-cell, automotive power, or a solar generator. All of the 12-volt power outlets are fused, which reduces the chance of melting down the insulation on the wiring harness. It would look neater if it were not for the fact that each radio has its own unique power plug/jack assembly and fuse, in addition to the ones supplied in the RigRunner. Once the Anderson Powerpole connectors are added, it makes it much easier to swap equipment around, without having to always be looking for the peculiar molex connector required by each radio, or stripping wires and trying to hook everything to binding posts like we used to do.

There are a few new lessons learned while assembling and using this go kit. One is that the tiny new rigs require significant space around them, both for cooling and also for access to all of their controls and ports. The FT-857 has controls that extend around the front and right side of the removable faceplate, and has a headphone jack which requires access from the left side. The Go-Kit must be designed such that all of the controls and ports are accessible. Another lesson is that mounting brackets must be spaced to allow the radio mounting screws to be placed between them. The Yaesu mounting screws have a 7 mm hex head, which can be manipulated best with a 7 mm box or end wrench, once they are started. Starting them required significant patience, and having long, skinny fingers would really help also.

12-volt power distribution requires some thought and planning. Being neat, orderly, and consistent is a great help. Using the Anderson Powerpole connector system for 12 volt distribution helps also, but it is not a cure-all. Let’s look at some of the issues:

1. If the 12-volt power you are using does not come from that switching power supply, then it is necessary to interconnect with some other source, which may not have the same kind of connectors. I have a good friend who says that the problem with having standard connectors is that when you have to hook up to someone else’s power, you have to cut your connectors off to do that. That can be avoided, if you plan ahead. I have several stubs available with a Powerpole connector on one end, and stripped leads on the other, that I can always attach to non-standard sources or equipment. Go prepared with your own stubs, spare wire, and connectors to match yours, and this problem can be avoided.

2. Voltage drop becomes a real issue if you need to carry the 12-volt power very far. For wiring internal to the Go-Kit, I used the 12 AWG wire which came with the FT-857D. According to the wire table in the ARRL Handbook, it is safe to use 12 AWG wire with continuous duty currents of 23 amps, and so is safe for this application. Its resistance is 1.6 milliohms per foot, which may not seem like much, but which adds up in a hurry. The cable length back and forth, to supply the FT-857D totals nearly eight feet (round trip), and simple math shows that the resistance is thus (1.6 milliohms/foot) X (8 feet) = 0.0128 ohms. At a 20 amp draw (full power transmit) the voltage drop = (0.0128 ohms) X (20 amps) = 0.256 volts. So then, on transmit, if the power supply is supplying 13.8 volts, the amount reaching the radio is (13.80 volts) – (0.256 volts) = 13.544 volts. That much of a voltage drop is acceptable. However, let’s say that we choose to power the Go-Kit from a 12.6 volt gel cell battery, and the battery is 15 feet away, and we use that same 12 AWG wire. For a 15 foot cable, the round trip is twice that or 30 feet. So the resistance is (1.6 milliohms/foot) X (30 feet) = 0.048 ohms. The voltage drop on transmit will be (20 amps) X (0.048 ohms) = 0.96 volts. So the voltage from that 12.6 volt battery drops to (12.6 volts) – (0.96 volts) = 11.64 volts, which is too low to operate the FT-857D radio. The answer is to use larger wire, or shorter cable runs. This has to be considered before you take your kit into the field.

3. Just because the Anderson Powerpole connectors allow you to hook anything to anything, does not mean that you can do so without thinking about the results. It is always necessary to know what you are connecting, what is a source and what is a load, and which sources should not be attached to other sources. For the most part, power supplies and other sources (solar panels, for instance) should not be hooked in parallel. Doing so is a great way to risk burinig out one or both power supplies as they fight for control of the voltage. With some exceptions, batteries should not be hooked straight across a power supply. It is necessary to think before acting when working with any power distribution system. Just because you are working with “merely” 12 volts DC does not absolve you of the consequences of your actions. In the heat of an emergency, it is easy to just hook things up and ask questions later. I urge you not to do that. Stop and consider what the current flows can be, especially under fault conditions, before hooking up. And always fuse those big batteries at the battery terminals, so that if something does get hooked up wrong, that the fuse blows instead of burning up big wires and starting fires.

Conclusions

This Go-Kit works as I intended it to. The plywood was from scrap shelving, and so it cost very little to build, apart from the cost of the electronics. It is very sturdy, and provides significant mechanical protection for the electronics. Because it is used in daily operation, I have confidence that it will work when the next community service event occurs. All-in-all, I am pleased with the project.