In the recent WAPC SSB 2023 competition, I participated in the single-operator, full-band, low-power category. Although I used antennas and cables from other stations during the contest, I still considered it a comprehensive test of my equipment over the past year.
As you know, I live in the central area of Shanghai. The significant background noise from the city and the inability to install antennas on rooftops are just a few of the problems that make using an outdoor antenna my only option for operating my own radio station. Furthermore, due to the difficulties associated with using vehicles, I am forced to use public transportation to reach parks in the suburbs where I can set up my radio station. In this context, I have identified the following key requirements:
- It must be able to fit in my backpack, and any items that don't fit should be easily carried by hand.
- It must be possible to take the subway.
> According to Shanghai Metro regulations, lead-acid batteries are not allowed on the subway, but lithium batteries are exempt from this restriction.
- It must be sufficiently safe, and obviously, a battery is required. There have been numerous incidents involving electric vehicles charging that have resulted in fires, so it is essential to ensure the safety of the batteries.
> If I can't guarantee a safe charging environment… then I'll just have to charge it outdoors on a sunny day.
- Under suitable conditions, it can support a power of 100 watts;
> Of course, you don't necessarily need 100W. After all, solar activity is currently high, and QRP can also achieve good results.
- It can support digital modes;
> Translating this into everyday language means that this equipment likely needs a computer.
Antenna
Material
A telescoping antenna provides a good option for adjusting the length of an antenna. It is much easier to adjust than other types of antennas, but telescoping antennas can also have strength issues, and long telescoping antennas can be difficult to safely pack into a backpack. Another option is to use a "Gypsy" antenna, which is a "V-shaped" dipole (DP) antenna that can be adjusted in length by winding it around.
When setting up a tower outdoors, the antenna's bandwidth is also something to consider. A wide enough bandwidth antenna can be sufficient for chasing DX (long-distance contacts) and reduce the need to adjust the antenna length frequently. The antenna's bandwidth is related to the diameter of the conductor. Considering weight, DP antennas made from wire typically use 18 AWG conductors, but telescoping antennas have a conductor diameter of almost 1 cm in their thickest part, which is much larger than typical conductors. This feature allows telescoping antennas to naturally save on adjustments.
Types
When setting up an antenna in the field, securing the antenna is also a key consideration. The method used to secure the antenna directly determines which type of antenna can be used.
When setting up a tripod in the wild, the attachments are often very basic. If there are sufficiently tall trees near the tripod location, using tree-mounted tripods is a good option. However, not all locations have suitable trees. In some cases, the vegetation may be so dense that it makes tripod setup difficult.
In flat areas, a triangular tripod is a worthwhile option to consider. You can easily purchase 2.8-meter tripods online. However, they are difficult to carry in a backpack due to their weight (around 2 kg), but they can still be held by hand. It's not easy to use a 2.8-meter tripod to raise the antenna (especially the feed point) to an acceptable height. If there are small buildings or slopes nearby, fixing the tripod and antenna on the top of the building or slope can mitigate the problem of the tripod being too short. When using a tripod, you also need to prepare some nylon rope to securely fix the tripod – after all, it's a lightweight but heavy object.
If you're operating in a coastal area, a GP antenna is an excellent choice. Wet ground is generally more suitable for GP antennas than dry ground – GP antennas rely on the "reflection" of the ground to function effectively, and wet ground can provide lower noise levels and better standing wave ratios. I once used a GP antenna with its base embedded in wet soil after a rainstorm; it produced one of the most beautiful standing wave curves I've ever seen. Most GP antennas don't require additional mounting hardware, and they are often able to withstand moderate winds. If you're concerned about strong winds – especially overnight – you can consider positioning the antenna so that its top passes through the branches of a relatively thick tree.
Equipment
Many people believe that a portable antenna and a transceiver (or a transceiver with built-in SWR meter) are essential. The SWR meter allows the transceiver to operate safely at high power levels, even when using a less-than-ideal antenna, and also saves time on antenna trimming when operating from a portable location. However, it's important to note that in many transceivers, especially QRP transceivers, the SWR meter takes up a significant amount of space, and its components, such as the ferrite core, can add considerable weight. If you are using a GP antenna with a pull-out handle, then the SWR meter is almost unnecessary; you can simply use the transceiver's SWR meter to find the resonant frequency of the antenna and begin transmitting.
A spectrum analyzer is a useful tool, especially for less experienced operators. It allows you to quickly identify active frequencies and gain a better understanding of interference situations, including the type and characteristics of the interference, as well as the propagation and noise levels of the current frequency. Of course, in an outdoor setting, a spectrum analyzer can also be seen as a cool and interesting gadget if someone happens to see it.
Some people prefer radios with a lower standby current, and this is certainly an important consideration. However, I don't believe that a radio with a 2A standby current is unsuitable for use in remote areas. Considering that a radio transmitting at 100W can draw up to 15A, the impact of a 2A standby current on battery life is relatively small – especially when only using the radio for half a day. Therefore, improving your communication skills, reducing transmission time, or carefully selecting the location where you set up your radio, and lowering the transmission power are more effective ways to extend its use than focusing solely on achieving a lower standby current.
Of course, if the goal is to achieve extremely low standby current, using a QRP radio with an amplifier is a good option. However, it's important to note that a QRP radio and amplifier combination will generally have slightly lower receive and transmit performance compared to a comparable 100-watt radio. For example, radios like the IC-705 and IC-7300 will typically have several decibels of difference in their specifications compared to the IC-7300. Therefore, it's important to make your choice based on your specific needs and circumstances.
Power supplies are essential equipment that require careful consideration, as they can be the most dangerous of all. Regarding power supplies, I only recommend lithium iron phosphate (LiFePO4) batteries. LiFePO4 batteries have both clear advantages and disadvantages. Their main advantages are safety and affordability, while their main disadvantages are weight and capacity. LiFePO4 batteries are arguably the safest type of lithium battery, and if you need to keep the battery indoors, this is a factor that must be considered. A 14.6V, 25A LiFePO4 battery pack weighs approximately 2.5 kg. When using it in FT8 mode for general communication, it can provide almost an entire afternoon of use.
The choice of a computer is subjective, and if you are already using a "lightweight laptop," you generally don't need to purchase a new one. However, if you only have a desktop or gaming laptop, a lightweight laptop weighing around 1 kilogram and with a thickness of around 1 centimeter can significantly improve your experience. It can support at least several hours of use. If you limit the data mode to only a few modes such as FT8, then software on a smartphone or tablet might be sufficient, but if you also want to conveniently record communication logs or use other niche data modes, considering user experience and the software ecosystem, a lightweight laptop might be a better choice.
Venue
If there's one thing that absolutely needs to be considered when setting up a temporary tower in the wilderness, it's likely the location.
When setting up a base station outdoors, people may be completely exposed to high-frequency electromagnetic fields due to the lack of buildings or other shielding. While there is currently no evidence to suggest that prolonged exposure (to excessive electromagnetic radiation) leads to long-term (or chronic) health problems, it is always better to minimize the amount of exposure. Generally, using SSB or CW communication modes poses minimal RF exposure risks because the duty cycle is relatively low and the antennas are typically close together. However, if data modes with higher duty cycles are used, RF safety must be considered.
According to calculations, operating at 50% duty cycle with 100W in the 6-meter band (which is also the most stringent frequency band for RF safety among amateur radio bands) results in a relatively safe distance of approximately 5 meters from the antenna. For other shortwave bands, this distance would be shorter, but I still recommend maintaining at least 5 meters of distance from the antenna whenever possible.
Furthermore, it is important to note that pedestrians may be attracted to the antenna, potentially lingering nearby or even touching it. If you don't want to have to hang warning signs like "DANGER" on the antenna, positioning it away from the sidewalk to avoid contact with other pedestrians is a good option.
Finally, before heading out into the field, be sure to check the current solar and geomagnetic activity for two minutes, and verify the real-time propagation situation on websites such as Reverse Beacon and PSK Report. Also, confirm that you have all your equipment and that it is functioning properly, to avoid wasting time and effort carrying a heavy load of approximately 10 kilograms.
Recommended equipment
The following list summarizes the devices I (and a friend) use for personal purposes, and is not affiliated with any particular brand or manufacturer.
- Radio: IC-705 (compatible with amplifier) or IC-7300
- Antenna: PAC-12 (GP antenna), also using a 5.8m pull-out rod, with 12 ground wire lines and a 10m -3 soft feed line.
- Battery: 14.6V 25Ah lithium iron phosphate battery
- Computer: ThinkPad X1 Carbon
Thank you to BH1OFJ and BH1UZJ for their suggestions.
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