Jean-Francois, Signal tracing can be quite effective - I applaud your goals.
Signal tracing of a transmitter path can usually be done with only an RF probe since the signal levels are usually large enough to measure easily, although a 'scope is more informative because you can see the relative frequencies involved. For the K2, just follow the steps detailed in the Transmit Signal Tracing section of Appendix E in the manual. Receive Signal Tracing is a bit more 'iffy' - although the method in Appendix E of the K2 manual works well, one must use a relatively strong signal source (such as the oscillator shown in the manual) to have a large enough signal in the receiver to measure (very small readings are likely just noise picked up by the probe). One must remember that in the RF and IF stages, a signal that can be observed on a 'scope or RF probe is much greater than the normal signal levels handled by the receiver - none-the-less, the procedure can be informative in identifying a failing stage, but it cannot be used to evaluate distortion levels since the stages are being overdriven by the generator with this elementary test. If one uses a normal receiver input level signal, there are devices to effectively measure those small signal levels (Spectrum Analyzer for instance), but the signal path must usually be broken and the signal level transformed to 50 ohms to do proper measurements. A more effective method of troubleshooting a receiver is to use a signal generator to do 'signal injection' at each stage of the receiver - for the sudio stages, that requires a generator that will produce audio frequencies, and for the IF stages it requires a signal generator that can produce a frequency equal to the IF frequency. The RF stages require a signal generator at the receiver tuning frequency. This generator should have a controllable output level so the levels can also be evaluated. Normally one would start at the audio stages and move toward the antenna one stage at a time, injecting the level and frequency that each stage should respond to. Using that procedure, it is sufficient to measure the ouput of the receiver either with an AC Voltmeter or just the ears listening to the speaker. There ued to be 'signal injectors' available that produced an audio square waveform that was very rich in harmonics that could be used as a relative indicator of functioning receiver stages - if you can hear a good response when moving from the audio stages toward the antenna, it can quickly identify a failing stage. Bottom line - receiver signal tracing begins at the antenna and works toward the receiver audio stages, signal injection works the other way around. Both methods verify the operation of each stage in turn until the failure point is found. The generator that you referred to is a Function Generator which is great for evaluating audio and low frequency IF stages, but if you are using a K2 for this 'education', the IF is at 4915 KHz and that generator will not go above 3000 kHz. As I indicated, if you are just trying to isolate a failing stage, the large signal injected at the antenna (tune the receiver to the signal generator frequency) will usually suffice, but if the problem is more subtle than just a failing stage (distortion for example), the controlled level signal injection at each stage is required - along with a good knowledge of 'what is normal'. 73, Don W3FPR > -----Original Message----- > > I would like to learn and explore more «signal tracing» procedure and > technique. I actually have a Fluke 196C. But I don't have a signal > generator. > > A friend of mine have his signal generator for sale. The model is an > Instek GFG-8216A. I would like to know if the device will be good for > signal tracing or the specification of this device is not enough for > this purpose??? I know that I could build the one in the K2 building > manual or at least use the technique «Cheap'n Dirty» from N0SS... but > that's not my point.... ;-) > > The specification can be viewed at > http://www.instek.com/pdf/Generator/GFG-8216A8215A.pdf > > Thanks for all your advice. > > Best 73 > > J-F VA2VYZ > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
