KN-Q7 Accessories

Description: Accessories built so far include a linear power supply, a switch-mode power supply, a tuning aid, and a headset. An antenna tuner and SWR meter will be described later. To operate the new transceiver, a power supply was needed. Initially, a power supply with a linear regulator was built, followed by a modification of a laptop power supply. Details are described below. A tuning aid to assist in adjusting a manual antenna tuner is also detailed here on the website. Additional information about a new antenna tuner, complete with a simple SWR meter, will be added soon. Several power supplies are available, all with sufficient capacity to power the new KN-Q7 transceiver. The largest power supply is typically connected to the main 100W PEP SSB transceiver, capable of supplying 20A or more, although connecting other equipment to it is not straightforward. A smaller 8A power supply is used for other VHF and UHF transceivers. The design is straightforward and well-established, differing from the traditional approach by allowing the 2N3055 transistor to be mounted directly on the chassis or heatsink without the usual insulating washer. A low-cost 12V car battery charger was modified to create a suitable power supply, but it was found that the charger’s transformer could not supply the transceiver’s peak current load, despite being rated for 2.5A continuous operation. Additionally, the cheap charger transformer introduced low-level hum into the transceiver when placed on top of the supply. A salvaged transformer from an old stereo/CD audio system was found to be suitable, measuring 19VAC (no load) and dropping to about 16VAC under load. This transformer fit well into the original charger’s plastic enclosure. The regulator section of the power supply is a variation of the standard design for the LM7812 12V 1A regulator. To enhance the current capability, a high-power PNP transistor is used in conjunction with the 7812. By inverting the circuit and using a -12V regulator (LM7912), two advantages are gained: the use of a common NPN power transistor like the 2N3055 and the ability to bolt the transistor directly to a metal chassis without the need for insulating washers. A 10,000uF smoothing capacitor is utilized, exceeding the usual design rule of 2,500uF per amp. Although 4,700uF would suffice, a larger capacitor was available. The total cost of the power supply was approximately $2, primarily due to the need to purchase the LM7912. The audio system transformer features a copper band around the windings, effectively preventing the hum issue observed with the cheaper charger transformer. The LEDs from the original charger were reused, and the charger’s PCB, complete with LEDs and a matching front panel, was retained. The configuration is similar to that shown in the schematic, although relocating the red LED to the output of the power supply may provide additional benefits. Currently, the green LED functions as a current indicator, as the DC input to the regulator dips below the required voltage during current peaks.

The described power supply circuit operates effectively by utilizing a combination of components that enhance performance while minimizing costs. The linear regulator design, which incorporates the LM7812 and LM7912, is modified to increase current handling capabilities through the integration of a power transistor. This approach allows for direct mounting, simplifying the assembly and reducing the need for additional insulating materials. The selection of the 2N3055 as the power transistor is advantageous due to its robustness and availability.

The power supply employs a transformer that has been repurposed from a consumer audio product, demonstrating an effective recycling of components while ensuring adequate voltage and current ratings for the transceiver. The smoothing capacitor's capacity of 10,000uF is a strategic choice, as it provides a stable output voltage and minimizes ripple under varying load conditions. The design's simplicity is complemented by the use of readily available parts, making it an economical solution for powering amateur radio equipment.

The integration of LEDs for visual feedback enhances user experience, allowing for immediate observation of the power supply's operational status. The green LED serves as a current indicator, providing insight into the power supply's performance during peak demands. This design not only fulfills the operational requirements of the KN-Q7 transceiver but also aligns with best practices in amateur radio power supply design, ensuring reliability and efficiency in operation. Overall, the project exemplifies resourcefulness and technical proficiency in electronics engineering, particularly in the context of amateur radio applications.Accessories built so far include a linear power supply, a switchmode power supply, a tuning aid, and a headset. An antenna tuner and SWR meter will be described later. In order to operate the new transceiver, I needed a power supply. I began by building a power supply with a linear regulator, and later, I modified a laptop power supply.

The detail s are described below. A tuning aid to help adjusting a manual antenna tuner is also described in detail here on my website. I hope to add some details of my new antenna tuner, complete with it`s simple SWR meter, soon. As you might expect, I have several power supplies that have more than enough capacity to power my new KN-Q7 transceiver.

However, my largest power supply is normally connected to my main 100W PEP SSB transceiver. It is capable of 20A and more, but it`s not easy to connect other equipment to it. I also have a smaller 8A power supply, but I use this to power some other VHF and UHF transceivers. The design is simple and well-proven although it varies from the traditional approach to allow the 2N3055 to be directly mounted on the chassis or heatsink without the usual insulating washer I had a really cheap 12V car battery charger in the workshop which I thought could be easily modified to make a suitable power supply. I quickly discovered that the charger`s transformer was not quite able to supply the transceiver`s peak current load, even though the charger was rated at 2.

5A continuous operation! I also found that the cheap charger transformer induced some low level hum into the transceiver when I sat the transceiver on top of the supply. Fortunately, I had a transformer in my box of bits which I had salvaged a year or two back from an old stereo/CD audio system.

These consumer products seem to have a lifetime shorter than a mosquito! The transformer looked big enough, and I measured its secondary voltage at 19VAC (no load). A bit high, but under load, it dropped to about 16VAC. That would be OK. Another nice thing was that I could fit it quite easily into the original charger`s plastic box. The regulator section of the power supply is a slight variation on the standard regulator design shown in the datasheets for the LM7812 12V 1A regulator. To increase the current capability of the regulator, the datasheet shows a circuit using a high power PNP transistor wrapping around the 7812.

If the circuit is inverted, and a -12V regulator (LM7912) is used instead, you gain two advantages. Firstly, I could use a common cheap NPN power transistor such as the 2N3055 shown here. Secondly, the transistor can be bolted directly to a metal chassis without the need for insulating washers and other costly hardware normally required to keep the collector/case of the high power device isolated from the heatsink. I`ve used a 10, 000uF smoothing capacitor in this power supply. The usual design rule of thumb` is 2, 500uF per amp, so 4700uF would be OK. However, more is better, and besides, I had this larger capacitor on my shelf along with all of the other parts.

All told, this power supply probably cost me less than $US2! And that was because I didn`t have the LM7912 in my parts bin. The audio system transformer has a copper band around the outside of the windings, and that effectively prevents the induced hum problem noted with the cheap charger transformer. The LEDs were in the original charger, and the charger`s PCB, complete with LEDs and front panel which matched the LEDs, was reused.

It was arranged in a very similar manner to that shown in the schematic. I chose not to change this, although I think there is some benefit from relocating the red LED to the actual output of the power supply. As it stands, with my transformer, the green LED acts as a current indicator. Why Because, on current peaks, the DC input to the regulator falls below the voltage required to keep the combination of the 12V zener diode and 2V green LED fu