ASTI Total Power setup

See the memo TA#0017.MEM by Bregman.

1. Get the correct telescopes in the tied array, the right observation setup and start a test observation, Setup the IF/Pol box correctly. This will normally be 285MHz on the synthesizer and LCP to IF1 and RCP to IF2. Check that ASTI box connectors at back are terminated (20dB attenuators Connect spectrum analyzer to IF1 monitor output to cover 92.5 to 192.5MHz range at 2dB/division
2. Set all fine level attenuators to 3.0dB. Switch 3+6+12dB in Y channels of each DCB band
3. Get all X and Y ASTI total power meters reading just more than 1.0V . For small numbers of telescopes ( fewer than 5) this will not be possible, so adjust the values to 0.5V. With only 2 telescopes adjust values to 0.4V.
   • use 1.5 and 0.75dB from ASTI X to get levels equal at spectrum analyzer
   • use up to 0.3dB in fine X attenuators
4. Setup the video converters for the coming VLBI (with the correct settings)
5. Using the IF attenuators get about 0.5-1V total power in the upper sidebands if all video converters. Normally this corresponds to 49-52dB of attenuation in the IF distributor.
6. Find the mapping of DCB bands to VCs. See See section Default settings for tied-array VLBI
7. For each DCB band
   • Chose a VC that comes from that DCB band
   • Make ASTI Y setting equal to ASTI X setting +18dB
   • Measure the total power at the VC with X only. Note it down
   • Take out 18dB from Y and put extra 18dB in X.
   • Using the fine attenuators get the same total power in the VC as c)
   • Take out the extra 18dB from X.
   • If needed readjust all the total power levels in each IF as in step 5)

Now the differences between bands in the ASTI settings reflect the bandpass shape. The X-Y differences in fine attenuator settings reflect the gain path in the signal path from the adder through ASTI, IF/POl select, rail injector and IF1 input. From MOSYS output we must derive the difference in system temperature between the X and Y channels. This is most likely the same for all bands. The channel with the lowest system temp the needs some additional attenuation to compensate for its relatively larger on-source step, to make the two source contributions equal for proper LCP and RCP.

        Table to fill in for ASTI  total power setup (per setup)

Comment:

DCB band#          0        1       2       3       4       5       6       7

3a
TP in X                 |       |       |       |       |       |       |
TP in Y                 |       |       |       |       |       |       |

3b 
Attn in X               |       |       |       |       |       |       |
Attn in Y               |       |       |       |       |       |       |

5
IFD settings

7a
VC# chosen              |       |       |       |       |       |       |

7c (18dB extra in Y)
TP in VC                |       |       |       |       |       |       |

7e (18dB extra in X, 12dB removed from Y)
Attn in Y               |       |       |       |       |       |       |

8
IFD settings

Final comments:

Final Attn settings
X                       |       |       |       |       |       |       |
Y                       |       |       |       |       |       |       |

When the table is completed, save it for checking purposes later.