On Dec 3, 2010, at 12:19 PM, Corboy - Poteet wrote: > So my question is: if someone puts a spectrum analyzer on the CW output of a > K3, are key clicks detectable? On make, on break? Close in, far out, in > between?
If you have one of these new fangled digital 'scope that takes a USB memory stick, you can record the time sequence and do your own FFT to get a good approximation of the spectrum. There is no need for a spectrum analyzer. Take the data from one complete pulse, and prefill and post fill with zeros (so you can take a long FFT for good frequency resolution), and you get the envelope of the keyclick spectrum. Take the leading edge half of the pulse only, but postfill the data with an identical high voltage of the on state of the pulse, and you get the contribution from only the "make" part of the keying waveform. If you prefill the data with the same high voltage right up to where the key starts breaking, you get the contribution from the trailing edge. FFT lengths and sampling periods will determine how much and how far away you can see. For many applications such as this, you can even do without a scope. Just connect a sound card to a second receiver that is tapped off a directional couple in line from the test transmitter to a dummy load. But you will need to use a Softrock or LP-PAN if you want to see what the keyclicks look like 20 kHz away. Or, just transmit at 8215 kHz and connect the LP-PAN to the directional coupler tap and you won't need a second receiver :-). 73 Chen, W7AY ______________________________________________________________ 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
