Improving the Versatility of a Portable JPC 12 Antenna
Improving the Versatility of a Portable JPC 12 Antenna
Video
Introduction
When it comes to portable amateur radio antennas, there are always challenges to overcome. In this blog, we will discuss a portable antenna with a 10 mm thread that poses some issues for users. However, with a simple modification, this antenna can become much more versatile and allow you to do things you couldn't do before. We will explore how to overcome this problem and make the most of your portable antenna. Let's dive in!
The Issue with the Portable Antenna
The portable antenna we are discussing today is the JPC 12. While it is an efficient antenna, one of the most obvious problems is its 10 mm thread. This poses a challenge for users who are accustomed to the standard 3/8 in thread used in amateur radio circles, especially in America. The slight difference in thread size means that 3/8 in attachments cannot be easily used with this antenna. However, with a simple modification, you can make this antenna much more user-friendly and expand its capabilities.
Modifying the Portable Antenna
To overcome the issue with the 10 mm thread, you will need a few materials. Start by acquiring a short length of alloy angle from a DIY store. Once you have the angle, drill two holes in it – one with a 10 mm diameter and the other with a 3/8 in diameter. Next, obtain 10 mm bolts and nuts, which can be found at most hardware stores. While the bolts may be too long, you can easily shorten them by adding a nut near the bolt head and cutting off the excess. As you unscrew the nut, it will smooth out any rough edges left by the cut, resulting in a bolt that is the perfect length for your needs. Additionally, drill a couple of holes on the other edge of the angle to accommodate thinner bolts and wing nuts. These additional holes will make it easier to attach radials or other accessories to the antenna.
Benefits of the Modification
By making these simple modifications, you can make the portable antenna much more versatile. The addition of the 3/8 in thread adapter allows you to connect various 3/8 in attachments to the antenna without any compatibility issues. This opens up a world of possibilities for using the antenna in different scenarios. For example, you can now mount the antenna on a vehicle using a magnetic mount, creating an ideal setup for mobile operation. Additionally, by mounting the coil on top of one of the base sections, you can create a highly effective mobile antenna system for when you are parked. These modifications greatly enhance the antenna's usability and expand its range of applications.
Testing the Modified Antenna
Now that we have discussed the modification process, let's see how the antenna performs in real-world scenarios. To test the antenna, we used an ICOM IC-705 and a zoom antenna analyser. The antenna analyser makes it quick and easy to tune the antenna for optimal performance. Additionally, having a portable CW key and microphone on hand allows for different operating modes. When operating QRP, or low power, CW is often preferred.
Installation
For a simple installation, mount the antenna on your vehicle using a 3-inch bolt into a mag mount. This will provide a sturdy base for the angle bracket. On the opposite side, attach the 10 mm nut to one of the base units of the antenna. With this setup, you have now created a magnetically mounted antenna, perfect for mobile operation. You can also mount the coil on top of the base section to create a highly effective mobile antenna system, but keep in mind that this setup is not suitable for use while on the move.
Performance and Resonance
With the antenna set up, it's time to test its performance. Using an antenna analyser verify the VSWR (Voltage Standing Wave Ratio) and resonance of the antenna. Installing a ferrite choke on the coax near the antenna helps reduce RF issues. By optimizing the antenna's length and adjusting the coil, you can achieve excellent VSWR readings and resonance. The antenna performs well on multiple bands, including 17 M, 10 M, 6 M, and 4 M. On 20 M, it is almost full size, while on 40 M, it functions as a half-size vertical. Although a vertical antenna may not be the best option for certain scenarios that require higher angle radiation, it still performs admirably.
Portable Operation
Operating the antenna in a portable setup provides unique challenges. However, this modified antenna proves to be quite effective in such situations. While rain and extensive exposure to the elements are not recommended, occasional use in less-than-ideal weather conditions is acceptable. Simply wipe the antenna dry before storing it to prevent corrosion. The antenna's low profile and slim whip make it resilient against wind, if it is not exposed to extreme gusts. It is important to note that when running QRP power levels (5-10 watts), the risk of electromagnetic field (EMF) exposure is minimal. However, operating at higher power levels (100 watts) is not advisable.
Additional Mounting Options
Aside from mobile and portable setups, there are other creative ways to mount the antenna. For example, if you have a garden table with a hole in the middle, you can easily poke the antenna through it and create a convenient operating station. However, finding a table with a hole in the middle is not always easy. It's a unique solution worth considering if you happen to come across such a table.
Adding Radials
To enhance the antenna's performance, the addition of radials is recommended. The modified antenna allows for easy attachment of radials using the screw terminals on the bracket. While radials may not provide significant benefits when mounted on a vehicle, they are highly effective when the antenna is mounted on a different system. By adding radials, you can improve the antenna's ground plane and overall efficiency. Remember to keep the length of the radials around 3 m and avoid tangling them to ensure optimal performance.
Installation and Fine-Tuning
To install the radials, use tent pegs at the ends of the wires to stretch them out and secure them to the ground. This ensures that the radials are fully extended and allows for maximized performance. Additionally, the use of ferrite clips on the coax helps reduce common-mode currents and prevents unwanted RF issues. Fine-tuning the antenna can be done by adjusting the telescopic length and the coil's position. Experiment with different configurations to achieve the best resonance and VSWR readings for your operating preferences.
Conclusion
In conclusion, the JPC 12 portable antenna is a great option for amateur radio enthusiasts on the go. While it presents a compatibility issue with its 10 mm thread, a simple modification can greatly improve its versatility. By adding a 3/8 in thread adapter and utilizing an alloy angle bracket, you can overcome this challenge and expand the antenna's capabilities.