VK4ZXI

Cavity resonators; size does matter and preview of my HP 8591A spectrum analyzer The Q or quality of a cavity resonator or filter is critical. The simplest way of increasing Q is to increase the diameter. The club has been lent what seemed a pretty ordinary 2 m cavity resonator; even has UHF rather than N connectors and is light. I wasn't expecting too much. But it is 150 mm diameter compared to the 100 mm ex-government cavity filters the club has. The two cavity filters. Note that the filters are not tuned to the same frequency; but they are not too far apart to make a difference to Q. However, what a difference size makes! The Q is visibly much better. Note, none of the instruments were calibrated for this exercise, it is just to show the qualitative difference. First, the quick and dirty antenna analyzer and a 50 Ohm terminator. Then with the club's Rigol spectrum analyzer. Then with my recently acquired HP 8591A spectrum analyzer; 1990s

HP 437B power meter: new toy; traps for beginners Introduction and traps for beginners I have recently turned 60 and decided to get some new toys, in the form of stand-alone test equipment. For some odd reason, mainly curiosity, I decided a power meter would be useful, so I bought a 20 year old HP 437B power meter, with sensor and attenuators. Modern power meters of similar capability are about $10K or more! As well as being expensive, the meters are not particularly intuitive to use, primarily because they use a range of power sensors that have very different features, discussed in this post, as it is a trap for beginners. In my case, the sensor was too sensitive for the unit's calibration signal; requiring attenuators just to get the device working. Power measurement is not a simple task, other than for a unmodulated carrier; much less, a 7 MHz wide digital TV signal, especially DVB-T with 8000 carriers across its bandwidth.  Power measurement is not covered well in the l