Antenna analyzer VK5JST

You would like an antenna analyzer and you do not have ten thousand to buy it? You have dexterous hands and a desire to make something useful on your own? At South Coast Amateur Radio Club Inc. www.scarc.org.au you will find a description of the VK5JST antenna analyzer. The connection is a combination of HF circuits and a single-chip microprocessor. SCARC offers those interested a complete kit containing a printed circuit board, components, display module, battery holder, box, buttons and front panel. The price including postage is 150 Australian dollars, which is about 2.300 crowns (76,34EUR).

The reproducibility of the wiring is confirmed by thousands of successfully manufactured analyzers around the world. You can also find compliments in the reviews at www.eham.net/reviews and the site of the well-known designer PA0FRI http://www.xs4all.nl/~pa0fri .

Appears on the display battery voltage, frequency, real impedance component, imaginary component of impedance and PSV in the range of approx. 1,3 up to 31MHz. It is also possible to find out the nature of the load with a small trick (inductive, capacitive). Additional source codes are available to allow capacitor measurement, inductances or impedance display in another form.

The antenna analyzer intrigued me so much, that I ordered and assembled one kit.
Nine days after the order was placed, the shipment arrived from Australia. In the envelope you will find precisely sorted and packaged components, printed circuit board, mechanical parts, display module, box and instructions. It pays to read it before the construction and mark important passages. This will greatly facilitate the construction, because there are many components and orientation on the printed circuit board is not easy.

Sort components by groups - especially resistors, especially capacitors, etc.. It is advantageous to pre-mark the holes on the panel according to the unmounted printed circuit board. It is advantageous to supply the jumpers first and then all the resistors. I recommend marking the mounted parts in the drawing with a typewriter. This is followed by capacitors and then transistors and IC sockets. Lastly, we install a range switch and a tuning capacitor. We are not connecting the display module yet, fine tuning and integrated circuits.

When I saw it, as the number of components increases comfortably, I doubted it, that such a complicated RF circuit can operate on first turn. Despite concerns about the connection of the supply voltage, the ammeter showed a consumption of about 70mA and the correct DC voltages at the measuring points. We disconnect the power supply and install operational amplifiers and a 50-ohm load (e.g.. consisting of two 100-ohm resistors). After reconnection, we can check the function of the measuring circuit and perform pre-calibration. This part of the construction took me about 6 hours of net work.

Antenna analyzer – printed circuit board
Now we drill all the holes for the controls, display and sockets. The opening on the display deserves the most attention, because it must be positioned correctly with respect to the printed circuit board. We will glue it into the box, whether we screw on the battery holders. The mechanical work took about 2 hours.

It remains to install the remaining integrated circuits and connect the printed circuit board to the display module. It takes patience and a certain hand. After the connection, we can connect the supply voltage and if everything is OK, the display first shows the voltage value and then the frequency, R, j a PSV. Fantasy, it works!

The kit is not only excellent electrically, but mechanically thought out and if we follow the recommended procedure, for more 2 the antenna analyzer will be ready.

Calibration is a matter of a few minutes and requires only a good 50-ohm load and an accurate one voltmeter. Most radio amateurs will want to connect a coaxial cable with a connector to the analyzer, it remains to produce a reduction from the analyzer terminals to the required connector. And we can measure!

Here are the measured results Diamond W-8010 in the SSB part of the 80m band:
3,60MHz 11ohm +/- j6ohm
3,62MHz 13ohm +/- j9ohm
3,64MHz 15ohm +/- j13ohm
3,66MHz 19ohm +/- j18ohm a 2,9PSV
3,68MHz 29ohm +/- j22ohm a 2,2PSV
3,70MHz 37ohm +/- j21ohm a 1,8PSV
3,72MHz 49ohm +/- j0ohm a 1,0PSV
3,74MHz 47ohm +/- j8ohm a 1,2PSV
3,76MHz 32ohm +/- j18ohm a 1,8PSV
3,78MHz 19ohm +/- j14ohm a 2,8PSV
3,80MHz 15ohm +/- j11ohm a 3,5PSV

I have already looked at the measurements on your website and also the experience of OM6IN, the antenna is actually quite narrowband in the 80m band due to its small length. However, the analyzer confirmed consistency between resonant frequency, which is 3.72MHz (zero imaginary component) and ideal impedance, which is an important prerequisite for efficient antenna radiation.

In addition to antennas, the antenna analyzer can be used to measure matching cells, tuning of amplifier input and output circuits, coaxial cable shortening factor detection.

Antenna analyzer is an excellent addition to amateur radio technology. For them, the kit is reasonably complex. Certainly, the analyzer should not be completed by a beginner or technician without reading the construction procedure.

The VK5JST antenna analyzer will bring fun during construction and use - I recommend it!