Query on over-range for LC meter
I’ve just built an LC Meter kit (SILICON CHIP, May 2008) and have successfully calibrated it for capacitance. However, there’s a problem with the inductance mode.
When S1 is set to the inductance position, the meter immediately pro-
duces an “Over Range” message. Placing the shorting bar across the test terminals and pressing S2 does zero the reading (initially 0.00µH, straying upward to 0.02µH) but the “Over Range” message immediately reappears when the shorting bar is removed.
Can you please suggest what might be the problem? (P. R., Maroochydore, Qld).
• The LC Meter does give an “Over Range” indication in the Inductance measuring mode when there is nothing connected to the test terminals. That’s because the meter sees a very high impedance across the terminals, which it assumes to be a very high inductive reactance. However, as soon as you connect a physical inductor across the terminals, you’ll find that the meter will indicate its inductance value, as it should.
This is not a fault. It’s just a result of the way the meter works. In capacitance mode, it interprets a very high impedance across the open terminals as a very small capacitance but in inductance mode it interprets the very high impedance as a very large inductance – hence the “Over Range” indication until you connect a smaller physical inductance.
A Corner Reflector Antenna For UHF TV
I built the Corner Reflector Antenna for UHF (SILICON CHIP, June 1991) some six years ago. Not being happy about having to paint it and the way the coax cable had to be connected by soldering it to the PC board, the antenna was put in to the too-hard basket and forgotten.
Now necessity has finished the project. I soldered a PCB-mount F connector to the PCB and this made it possible to connect aluminium RG6 twin-shielded coax cable to the antenna with ease.
The antenna system is now working very well with one set-top box, an 81cm CRT TV and a new 66cm Sanyo flat screen HD TV. Both pictures are perfect, with no pixellation evident in dry or wet weather.
The antenna is supposedly one kilometre out of adequate coverage according to the ABC frequency information on the internet. But signal strength as indicated on the Sony TV is two bars down on all but two channels which are three bars down on signal strength.
What I would like to know is how much trust can be put on the indication of the TV signal strength indicator? Or an after-market signal strength meter? How can one know that the signal is in the “digital window”? Also can you please explain bit error ratio and modulation error ratio and how they fit in to signal strength and with what and how they are measured? (G. M., via email).
• We simply don’t know how accurate the signal strength indication is on an STB or after-market signal strength meter. However, the fact that the signal strength reading from a TV or STB is comparative rather than in microvolts means that it is indicative only.
In any case, you already know that your signals are within the “digital window” since your reception is free of pixellation and presumably has no sound drop-outs, particularly in wet weather.
We suggest that you read our articles on digital TV in the March & April 2008 issues and in March 2010.
zero set-up error
Thank you for your Milliohm Adaptor for DMMs (SILICON CHIP, February 2010); another contribution in your seemingly endless arsenal of useful measurement projects. I built the adaptor as described and calibration was straightforward with gain resistance, in this circuit 680Ω + VR4, very close to the calculated resistance, as per the AD623 data sheet, for a gain of 100.