+++++++++++++++++ Date: Tue, 03 Dec 2002 07:02:26 -0500 To: "Parker Buckley" From: Charles Greene Subject: Re: [Elecraft] K2 S-meter output for antenna measurements? Cc: Parker, I have recently used both Spectrogram and a PSK31 program, MixW to measure relative receive strength on two different antennas. Spectrogram enables you to read the audio input to +/- 1 dB. In MixW, its spectrum display has 10 dB horzontal lines. You can sue the same connection between the receiver and computer that you did when you used Spectrogam for setting the filters. You need to set the AF gain control about 3/4 way up on the K2. turn the AGC off and control noise floor gain with the RF gain control. You need to find a place on the receiver RF input that is linear. You may need to use the attenuator in conjunction with the RF gain control to do this. I used a precision signal generator to assist, but you can vary your input to the antenna under test to do the same thing. Pick a time of day and frequency where there are no signals, set your transceiver to SSB, start with a bandwidth of 2 kHz but narrow it if there are any signals. Set Spectrogram to measure the bandwidth 300 to 2khz and use the 90 dB amplitude range, line spectrum. The K2 bandpass has ripples in it, but as long as you are using a fixed frequency and don't vary the receiver frequency, it doesn't matter, as you are taking readings that are relative to each other. The setup I used enabled me to measure relative signals over about a 55 dB range, from a noise floor of 3 dB on spectrogram, to a signal level of about 55 dB. I verified the linearity using the calibrated attenuator on the precision signal generator as a check on linearity, but not part of the measurement. Don't forget, any strong signal in the receiver bandpass is going to affect the ground floor, hence the reading. You can use the receiver filters to help, but a strong signal inside the roofing filter bandpass will affect readings too by decreasing receiver sensitivity. Above level of 60 dB, the noise floor started to decrease, indicating I had exceeded the range of linear gain. I possibly could have been a bit higher if I had played around with RF gain, but this level exceeded my range of measurement as it probably will yours too. Of course, for your application, you need one transmitter or signal generator driving the Quad as you rotate it, and another to make the measurements. If you have any questions, contact me by private post. At 07:50 PM 12/2/2002 -0500, Parker Buckley wrote: >Now that my K2 is on the air, filters aligned with >Spectrogram, etc., my thoughts return to tuning my 5 band >quad. I have in mind picking off a voltage somewhere in the >K2 that is proportional to signal strength, feeding that to >some sort of A to D converter for my PC, then using the PC >to plot single strength around a 360 degree azimuth. >Simliar ideas have been documented in the ARRL antenna books >using VU meters and X-Y plotters, but I can't help but think >someone has done this more recently with a PC. Can anyone >point me to such a scheme, or provide hints for wading into >this? Thanks in advance. > >Parker WD8JOL 73, Chas, W1CG K2 #462 +++++++++++++++