- 03 Nov 2008
Testing the KFPA receiver in the lab
Cold KFPA 1 pixel receiver with 300k waveguide load on feed window
connected to test converter unit, then feeding lab spectrometer.
LO1=14650 at +6dbm
LO2=8900 at +4.2dbm
LO3=8800 at 0dbm
Rx out set to ~-20dbm, input to lab spec set to -16dbm
After the initial test receiver testing from 05sep08, we decided to do
take a detailed look at the system. The sept 5 data showed baseline
instabilities, but we didn't have time to try and insolate where the
problem stemmed from.
The KFPA receiver was installed on 9/9/08, and removed on 9/18.
During this time, we used the spectrometer test box to inject a
signal directly into the lab spec. We concentrated on samplers 2 and 4.
Given proper connections, power levels, and good room thermal stability,
we were able to get good consistent flat baselines.
Beginning this date, 29 sept, the rx is back in the lab and we are
setup for more testing. Once again, the plots looked bad. Since the
baselines looked very good from Glen's observations on the GBT, and the
lab spec looks good by itself, we are going to concentrate on the test
I'll talk to Galen and have him check the test converters. Typical scans:
Testing with lab spectrometer in conjunction with the KFPA receiver
From the sep 29 notes, we have concluded that baselines from the
rx by itself look OK, and that the lab spec by itself looks OK.
The receiver was installed for a second time on the GBT on 9/30
and was removed on 10/14.
Galen took this time to look at the test converters. In the top unit,
#1, he found a chip capacitor cracked in one of the input amp stages.
Also, a wire on the +5v terminal strip was loose. This could/would cause
an instability in both units.
We used the HP noise source s/n 2330A03018, thru milliwave amp S94-5680,
then milliwave amp S93-2908, attenuator, then a weinschel pwr divider
model 1515, and into test converters 1 and 2. The attenuator was adjusted
to give -20 at the test converter input. Pwr to lab spec was set for
-16dBm. We were careful to keep cable lengths shorts and well thermally
Ran scans over night. Things looked very good once the room temps
and equipment stabilized.
Next, we will connect the receiver up. Typical scans:
Testing the KFPA receiver in lab.
We now have good stability from the lab spec and the test converters,
Rx is cold
300K load on feed input
Fsky=22500, LOa=14650, LOb=8900
Pwr at test converter input ~-20dbm
Pwr at lab spec input ~-15dbm
Looks good, typical scans: