James, What do you propose to measure a 50 uV signal with? If you have equipment that will measure levels that low, then well and good, but if you are expecting to see it on an oscilloscope or RF Probe, you may as well forget it. Recall that 50 uV is an S-9 level, and is -73 dBm which is a very low level to measure.
There are power measurement devices that will detect levels that low, but most of the commercial ones are priced out of the range of amateurs. One that can be homebrewed and will measure levels down to -80 dBm is the W7ZOI design using the AD8307 Logarithmic Amplifier as the front end (see Experimental Methods in RF Design, Measurements chapter or the QST article from June 2001 p38ff). To calibrate it, one must have a known level source of RF at two different levels. Those with a calibrated HP8640 signal generator (or similar) will be able to calibrate that meter with no problem. For anyone considering building such an instrument, understand that it must be well shielded. Stray coupling into the meter will produce erroneous results. Mine is in a shielded enclosure with an internal battery, and even that is not enough, the front end circuits are shielded from the rest of the assembly. Yes, it can even measure the total signal level coming in from an antenna, so it is a good performer if properly calibrated and is a very sensitive detector. With the 40 dB Power Tap, it can accurately measure power levels up to +50 dBm (100 watts), and will work up to 500 MHz with careful construction. If you want accurate power measurements, consider building one, but you need access to a calibrated power source to calibrate it - calibrate at 10 MHz, 50 MHz, 144 MHz and 450 MHz so you have a good idea of the variation with frequency - there will be some variation. 73, Don W3FPR James Sarte wrote: > Hmm... just out of curiosity, couldn't I measure the IF output using the XG2 > signal generator set to 50uV? How strong does the signal have to be? > > I'll go ahead and check the junction voltage at R9 as you suggested. > > Mni tnx! > James K2QI > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
