CARMA

• 8 antennas are phased together in a set of beamformers and recorded on one Mk6 recorder. 
• a separate 'reference' antenna is connected to a standard BDC and R2DBE and is recorded on a separate Mk6 recorder.

f(LO1) = 3 * (7 * (9 * fsynth - 10 MHz) + 50 MHz)
       = 221099.999970 MHz (for fsynth = 1170.158730 MHz)

A diagram of the CARMA IF system is shown below.  The signals for the reference antenna are taken from wideband directional couplers in the fiber IF receiver boxes; these 1-9 GHz bands are sent to standard EHT block downconvertes and R2DBEs.  The signals for the beamformers are taken from the outputs of the CARMA analog downconverters.

The beamformers are channelized as shown below (same as 2013):

The sky frequencies corresponding to these channels are shown in the diagram below ("caseD") ;

Test tone: injected 215.2 GHz tone into receiver on one antenna, derived from a separate synthesizer (8662).  Tone appeared at 650 MHz on output of CARMA downconverter.  Mixed this down to 10 MHz, examined with scope, triggering off 10 MHz (derived directly from maser).  Here is a video of the tone - we change the scope averaging from 1 to 2 to 8 to 64 during the course of the recording.  There is a small amplitude glitch about every 1 sec - not clear what this is due to, but should not have big impact on vlbi.

TestTone.mp4