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Someone suggested getting the handbook for the Boonton 260 Q-Meter. Since Boonton did this already perhaps you can get some inspiration from it. Of course its tubes but nonetheless one can use the same principles for SS. Also look at the type 190, the VHF version of the Q-Meter. Essentially both use a constant current source to drive the test circuit. Also, download the set of Boonton newsletters, which are available at the -hp- archive where the handbook is. Boonton more or less invented the Q meter and wrote a lot about its theory of operation.
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?? A note: The meter scale is matched to the amplifier. Usually, the amplifier has an extremely long life but both go together. For this reason the solid state replacement for the tube will probably not match the meter scale. ?? If you obtain a Q-Meter also find some standard coils to check its calibration. They are quite accurate. Note that Boonton supplied both "standard" and "working" coils. The "working" coils are very convenient to have but one can make them. The Boonton coils are very high Q. The "standard" coils are calibrated for Q, and resonant capacitance. ??? I found on the Q-Meters I have dealt with that the oscillators are quite well calibrated. I think there is really only one setting that gets all ranges on frequency. Be careful of the adustment for the capacitor. It should really be set with a standard coil that resonates near the minimum capacitance. These things have become somewhat of orphans because they are "old fashioned" but in fact they are extremely useful. ??? I will put in a good word for the Boonton RX meter also. A one piece impedance bridge with oscillator, bridge and detector in one box. Unfortunately mine came a cropper by falling off a table. Too bad. As with the Q-Meter the internal oscillator is usually very well calibrated and, again, Boonton published a very good handbook and lots of application notes. On 8/4/2022 8:41 AM, Oz-in-DFW wrote:
On 8/4/2022 3:19 AM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:Can anyone think of a way of turning a signal generator to have an output impedance of 1 milli ohm?Like most engineering decisions, it depends.? In this case my first though would be negative feedback around an amp.? You can get /almost/ arbitrary reduction of output impedance as a tradeoff for other parameters.? This is much more practical at much higher frequencies than years past. --
Richard Knoppow dickburk@... WB6KBL |
