the isolation for the IF2 port1a monitor port was increased. After
the increase it was still possible to affect the correlator bandpass by
changing the cables on the monitor port. On 04sep03 the isolation was increased
for IF2 monitor port 1a. The configuration for the ports were:
|port 1A before change||10dbPad-24dbamp(30dbRevIsol)-3db pad||19db|
|port 1A after sep03 change||10dbPad-24dbAmp(30dbRevIsol)-15dbPad-11dbAmp(16dbRevIsol)||36db|
To test the new isolation two experiments were done.
The first did a 900 second on/off with the correlator. The correlator was set to 25 Mhz bandwidth (over 1024 channels). After acquisition the data was smoothed by 9 channels to increase the signal to noise. The On was with a cable going from the monitor port to a 5 Mhz filter. The off was with nothing connected to the monitor port. This emulates someone connecting/disconnecting something on the monitor port during a normal observation. This was done to the modified monitor port (1A) and to an unmodified monitor port (2A). Without sufficient isolation, reflections from the 5 Mhz filter would cause ripples in the bandpass.
The second test injected a sine wave into the monitor port and measured how much of it ended up in the correlator bandpass. This test used a 390 Khz correlator bandwidth with 1024 channels. The data was then hanning smoothed. This resulted in a resolution of 760 Hz.
The test results are shown in the plots:
The loss equation is (let T be the noise power in 1 channel,A be the
amplitude of sinewave,L be the loss from the components above, X be the
loss through the splitters back to the correlator, R be the measured ratio
of sinePeak to T)
(A1*L1*X + T)/T=R1=.25db=1.07 Then L1*X=T*(R1-1)/A1
(A2*L2*X + T)/T=R2=14.8db=30.2 Then L2*X=T*(R2-1)/A2
L2/L1=A1/A2 * (R2-1)/(R1-1)=100*(30.2-1)/(1.07-1)= -46db the expected difference was -55db so we're off by 10db somewhere...