I made N7DDC popular ATU-100 antenna tuner in the basic version (5×5) in 2019, and I added my experience with it on our website in the post CHA-250B antenna by SP5GNI.
Using the experience gained and left components, I decided to mount the extended version of the N7DDC (7×7) for the 1.8 -50 MHz range. After solving the problem of how to solder the SMD processor and making the coils, the assembly was easy. To program the processor on the board I used the PIC Kit2 programmer (too big time constant in the MCLR circuit – replacing the C20 capacitor with 10nF solved the problem). I have downloaded the latest version 3.0 available. During programming in accordance with the N7DDC instruction, it is possible to change some EEPROM memory cells. To adapt to my needs, I set the appropriate capacitance values, the appropriate I2C address of my display, automatic tuning activation, and the minimum power value (5W) and the maximum value (65W) required to activate the tuning. Board with OLED 128×32 display was placed directly on the programming pins. The hermetic Kradex ZP150 housing with a transparent cover was ideal for this construction.
Power to the system is supplied via the same cable as the RF signal to the UC connector. The voltage of 12-13.8V passes through the visible 220uH/2.5A toroidal coil and the 8.2uH series choke, and the RF signal through 5 x 10nF/3kV and silver plated wires to the tuner input.
To check the operation of the box, the tuner output (on the right) was connected to the long wire antenna, and the ground (on the left) was attached to the counterweight (in the form of 4 wires of random length) and to the ground (support made of a copper pipe). The wire, initially approx. 20 m long, was hung on tree branches at a height of approx. 5 m. For such an LW antenna, the tuner coped well with SWR <2 for the following bands: 3.5 – 10 – 14 – 18 – 21 – 24 MHz. It could not cope with 1.8 – 5.3 – 7 – 28 – 50 MHz. The case of 7 MHz with SWR = 4.5 can be explained, because 20m is the half of the wavelength, and according to the theory such an antenna has a very high impedance. After prolonging the antenna to approx. 40 m, the box could handle SWR <2 for the following bands: 1.8 – 5.3 – 7 – 10 – 14 – 18 – 21 – 24 – 28 MHz, and it could not handle for 3.5 and 50 MHz. The case of 3.5 MHz with SWR = 8.5 can be explained similarly to the above – 40m is a half wave.
Using FT991 I made about 80 QSOs on almost all bands, mainly FT8.
I had the opportunity to perform the next ATU-100 7×7 tests while working with the away QTH in Bieszczady mountains. I was there at the beginning of September 2020, taking advantage of the hospitality of Marek SP5MNF, who lends a house in Solina at the disposal of visiting hams (and not only). The tuner was attached to a section of a copper pipe driven into the ground. I supplied RF+DC power using the RG-58 cable, 10 m long. The ground output of the box was connected to 5 counterweights of different lengths. A copper wire, about 20 m long, hung on trees at a height of 3-4 m, as shown in the photos below, served as the antenna.
The ATU-100 tuned such an antenna very well in all HF bands – except for 7 MHz and 50 MHz. At 3.5 MHz the SWR (measured at the TRX FT-991 output) was 1.2, and at 14 MHz it was 1.1. Using the callsign of SP5GNI/8 I made 120 QSOs in the 3.5 MHz band. Reports from the SP were usually very good 59. There was also no problem with caling to European stations in the 14 MHz band.
Based on my experience, I can confirm that the ATU-100 is an excellent device.