[Elecraft] K2 S-meter output for antenna measurements?

[Charles Greene]

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