Table of contents
EHT observations at 230 GHz are carried out in the 5-9 bands.
At 345 GHz 4-8 GHz IFs are being used which requires the following changes:
Filter change
The 4 filters connected to the IF inputs of the DBBC3 need to be manually exchanged:
| Freq | Filter |
|---|---|
| 230 GHz | 5-9 GHz |
| 345 GHz | 4-8 GHz |
Downconversion setup
The LO frequency of the DBBC3 has to be changed to match the hardware filters.
The LO-frequencies for the four bands are defined in /etc/backend.conf:
dbbc3.all: {layout: dbbc3, hostname: dbbc3, port: 4000, mode: "OCT_D", sw_major: 120, sw_minor: 220831,
boardA: {bitfile: "dbbc3_oct_D_2hv2_221122.bit", filter1: "2000-4000_64taps.flt", filter2: "0-2000_64taps.flt", synth_freq: 9048},
boardB: {bitfile: "dbbc3_oct_D_2hv2_221122.bit", filter1: "2000-4000_64taps.flt", filter2: "0-2000_64taps.flt", synth_freq: 9048},
boardC: {bitfile: "dbbc3_oct_D_2hv2_221122.bit", filter1: "2000-4000_64taps.flt", filter2: "0-2000_64taps.flt", synth_freq: 9048},
boardD: {bitfile: "dbbc3_oct_D_2hv2_221122.bit", filter1: "2000-4000_64taps.flt", filter2: "0-2000_64taps.flt", synth_freq: 9048},
...
The correct setting is depending on the observing frequency:
| Freq | DBBC3 LO setting |
|---|---|
| 230 GHz | 9048 |
| 345 GHz | 8048 |
- Edit /etc/backend.conf
- execute (on VLBI control computer ccpico)
backendctl dbbc3 dbbc3 configure
Remember to revert the changes when going back to 230 GHz!
Comments