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After performing calibration, it may be a good idea to check the calibration. Fundamentally, the open and short standards can be used. We should see a frequency independent short and open response when connecting the standards as done during calibration. Another possible check that works up to at least 150 MHz can be done by connecting two BNC 50 Ohm terminations to a BNC female-female-mal T-piece, as shown in the attached image. As the two 50 Ohm terminations are in a parallel connection (ignoring the effect of the T-junction which is OK for low frequencies) we get R = 25 Ohms and this results in VSWR = 2.0. If the instrument shows a VSWR value significantly lower or higher, then the calibration may be wrong. 73 Dieter, VK3FFB

Please post all matters related to antenna measurements with the FA-VA5 here.

I have assembled my FA-VA5 per provided instructions. On the initial power up I got an amber screen and nothing else. Per the instructions on page 7 of the English language instruction manual I rechecked all solder connections and reworked those that appeared to be inadequate. Under 10x magnification I did not detect any shorts or incorrect connections, This was verified with a VOM. I would appreciate any suggestions or workarounds for this problem. Thanks and 73, -- Joe KW4YW

Hi Recently, I have installed a HF vertical antenna fed via a remote tuner. The radiator is about 9.5m long and it sits on the center of a metal roof. The roof acts as a counterpoise and is about 5.4m by 5.5m large. A 2nd metal roof is nearby but at a higher level and with no connection to the lower roof. While the antenna radiator (telescopic aluminium tubes, starting with 25.4mm = 1 inch) is guyed at 6m height level with 4 guy ropes, it is held at the base with a vertical member via insulating clamps. I first used an aluminium extrusion for this, but I observed some antenna impedance changes, especially at frequencies where the feedpoint has substantial voltage (strong E-field). Therefore I changed to a cedarwood member which resolved the impedance issue. My design reference was a 3D model using the high-grade CST EM simulator. The graph below shows the simulated antenna impedance curves (Real, imaginary) and also a few measured points (dots) from FA-VA5 measurements for the frequency range from 7 MHz to 30 MHz. The agreement between the antenna model and the measurements is good below about 25 MHz. Some details are not included in the 3D model and this may be the reason why agreement is less good above 25 MHz. However, we can clearly conclude that given the good agreement between simulation and measurement, the accuracy of the FA-VA5 measurement is excellent. We can safely dispel any arguments related to any perceived fundamental difference between "theory and practice". No such thing in this day and age, provided that theory is used to a sufficient depth and with due attention to necessary detail. 73 Dieter, VK3FFB PS The curves below may seem unfamiliar to some members. The main features are the two peaks of the real part at halfwave resonance and at fullwave resonance. At both of these resonances the reactance of the antenna impedance changes abruptly from positive to negative with a zero-crossing at the resonance point. The quarterwave resonance at around 7 MHz (40m) is rather featureless and the only significant thing is the zero-crossing of the reactance (capacitive to inductive). It is this zero-crossing that identifies the quarterwave resonance. The 3/4-wave resonance occurs at approx. 21 MHz (15m) and is again identified by the zero-crossing of the reactance (red).