GBT Frequency setups for the RDBE

Here we try to document how to make frequency setups for the GBT for the new RDBE back end.

These notes indicate how to set frequencies in the "freq.dat" catalog of SCHED.

General principles

For receivers at C-band and higher frequencies, rf1 and rf2 will span exactly 1024 MHz; the center of the band should convert to 768 MHz at the inputs to the RDBE. For these receivers, sky frequencies rf1 and rf2 will be converted to 512 (1024) and 1024 (512) MHz at the inputs to the RDBE for upper (lower) sideband receivers.

The "freq.dat" file gives "lo1" in lower case.

The center of the band will convert to 768 MHz at the inputs to the RDBE.
Let:
  • Ksb = +1 for upper sideband receivers, and = -1 for lower sideband.
  • Fobs is desired observing frequency on the sky;
  • IFrdbe = frequency at input to the RDBE: range is 512 to 1024 MHz
  • lo1 = Fobs - (Ksb * IFrdbe)

The LO frequencies used at the GBT are designated LO1, LO2, LO3 (in upper case).
  • LO1 may be set in steps of 1 Hz
  • LO2 may be set in steps of 1 kHz
  • LO3 is fixed at 10.5 GHz.

Each GBT receiver has a "nominal IF1", i.e, the center of the IF band after the first mix with LO1. This varies with receiver, for example, IF1 for the X-band receiver is 3 GHz, for K-band it is 6.8GHz. See below for each receiver's IF1.

We have the following relations:
  • LO1 = Fobs - (Ksb * IF1)
  • LO2 = IF1 + LO3 - IFrdbe
  • lo1 = LO1 + Ksb*(LO2 - LO3)

The only thing that the VLBI user needs to specify is "lo1"; the GBT configuration software will set LO1 and LO2 in order to implement the specified lo1.


GBT Q-band : Rcvr40_52 (upper sideband receiver) :

Usable Frequency range: 40 - 48 GHz
freq.dat entries:
!------------------------------------------------------
!  7mm SiO lines at 42519.3, 42820.54, and 43122.03
!  VLBA standard band at 43135 MHz.
!  VLA band at 43289.90- 43339.90
!  These use the same sideband as the the VLBA so just
!  change the RF ranges.
!------------------------------------------------------
! GBT 7 mm receiver frequency range is 40.0-48.0 GHz.
!------------------------------------------------------
Name = gbt7mm_c7  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 42312, 42312    ifname = A,    C
  rf2 = 42824, 42824    fe  = '7mm', '7mm'
  pol =  RCP,  LCP    lo1 = 41800.0, 41800.0
  note = 'LO1=36.568, LO2=15.732, LO3=10.5 '
/
Name = gbt7mm_b8  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 42712, 42712    ifname = A,    C
  rf2 = 43224, 43224    fe  = '7mm', '7mm'
  pol =  RCP,  LCP    lo1 = 42200.0, 42200.0
  note = 'LO1=36.968, LO2=15.732, LO3=10.5 '
/
Name = gbt7mm_c8  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 42912, 42912    ifname = A,    C
  rf2 = 43424, 43424    fe  = '7mm', '7mm'
  pol =  RCP,  LCP    lo1 = 42400.0, 42400.0
  note = 'LO1=37.168, LO2=15.732, LO3=10.5 '
/ 

Explanation (Rcvr40_52):
  • rf1 will convert to 512 MHz at the input to the RDBE
  • rf2 will convert to 1024 MHz at the input to the RDBE

  • lo1 = 0.5*(rf1+rf2) - 768 MHz = rf1 - 512 MHz

Nominal IF1 for this receiver on the GBT is IF1=6000 MHz
  • LO1 = lo1 - (IF1-768) = lo1 - 5232
  • LO2 = IF1 + 10500 - 768 MHz = 15732 MHz
  • LO3 = 10500 MHz



GBT KU-band : Rcvr12_18 (upper sideband receiver) :

Range: 11.8-15.6 GHz (being rebuilt to increase range to 18GHz
freq.dat entries:
!---------------------------------------------------------
!  I have only included 2 setups at 2 cm, corresponding to
!  the main ones used on the VLBA and using the VLBA names
!  Many others could be added.
!  Both observatories use upper sideband so only the rf range
!  changes for the RDBE.
!---------------------------------------------------------
! Note: GBT 2 cm receiver range is 11.8-15.6 GHz
!---------------------------------------------------------
Name = gbt2cm_a2  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 11912, 11912    ifname = A,    C
  rf2 = 12424, 12424    fe  = '2cm', '2cm'
  pol =  RCP,  LCP    lo1 = 11400.0, 11400.0
  note = 'LO1=9.168, LO2=12.732, LO3=10.5 '
/
Name = gbt2cm_d2  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 14912, 14912    ifname = A,    C
  rf2 = 15424, 15424    fe  = '2cm', '2cm'
  pol =  RCP,  LCP    lo1 = 14400.0, 14400.0
  note = 'LO1=12.168, LO2=12.732, LO3=10.5 '
/ 
Explanation (Rcvr12_18):
  • rf1 will convert to 512 MHz at the input to the RDBE
  • rf2 will convert to 1024 MHz at the input to the RDBE

  • lo1 = 0.5*(rf1+rf2) - 768 MHz = rf1 - 512 MHz

Nominal IF1 for this receiver on the GBT is IF1=3000 MHz
  • LO1 = lo1 - (IF1-768) = lo1 - 2232
  • LO2 = IF1 + 10500 - 768 MHz = 12732 MHz
  • LO3 = 10500 MHz

Further Note: The KU-band receiver has been removed from the GBT indefinitely for refurbishment. Its upper limit will be increased to 18 GHz.


GBT K-band : RcvrArray18_26 (lower sideband receiver) :

Range: 18.0 to 27.5 GHz
freq.dat entries:
!-------------------------------------------------------------------------
!  For 1cm only give a few near the water line version
!  for now, matching VLBA sets.  Many more could be added.
!  This sideband is opposite the VLBA so frequency shifts
!  are needed.
!-------------------------------------------------------------------------
! GBT with new 7-beam 18-26 GHz receiver (KFPA)
!  for VLBI, we use just beam 1.   From email by Frank Ghigo Aug 15, 2011.
!-------------------------------------------------------------------------

Name = gbt1cm_a1  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 21312, 21312    ifname = B,    D
  rf2 = 21824, 21824    fe  = '1cm', '1cm'
  pol =  RCP,  LCP    lo1 = 22336.0, 22336.0
  note = 'LO1=28.368, LO2=16.532, LO3=10.5 '
/
Name = gbt1cm_a2  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 21512, 21512    ifname = B,    D
  rf2 = 22024, 22024    fe  = '1cm', '1cm'
  pol =  RCP,  LCP    lo1 = 22536.0, 22536.0
  note = 'LO1=28.568, LO2=16.532, LO3=10.5 '
/
Name = gbt1cm_a3  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 21812, 21812    ifname = B,    D
  rf2 = 22324, 22324    fe  = '1cm', '1cm'
  pol =  RCP,  LCP    lo1 = 22836.0, 22836.0
  note = 'LO1=28.868, LO2=16.532, LO3=10.5 '
/
Name = gbt1cm_b3  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 23512, 23512    ifname = B,    D
  rf2 = 24024, 24024    fe  = '1cm', '1cm'
  pol =  RCP,  LCP    lo1 = 24536.0, 24536.0
  note = 'LO1=30.568, LO2=16.532, LO3=10.5 '
/ 
Explanation (RcvrArray18_26):
  • rf1 will convert to 1024 MHz at the input to the RDBE
  • rf2 will convert to 512 MHz at the input to the RDBE

  • lo1 = 0.5*(rf1+rf2) + 768 MHz = rf1 + 1024 MHz

Nominal IF1 for this receiver on the GBT is IF1=6800 MHz
  • LO1 = lo1 + (IF1-768) = lo1 +6032
  • LO2 = IF1 + 10500 - 768 MHz = 16532 MHz
  • LO3 = 10500 MHz



GBT X-band : Rcvr8_10 (lower sideband receiver) :

Range: 7.9 to 11.6 GHz
freq.dat entries:
!   Frank:  I have made 3 X band setups because 800 MHz
!   is too wide for the 500 MHz VLBA backend IF.  I have
!   arbitrarily set the ranges to match the VLBA settings.
!   That simplifies matters for anyone trying to maximize
!   their instantaneous bandwidth.
!---------------------------------------------------------
! Note: X-band range is 7.9 - 11.6 GHz
!      more setups could be added
! The VLBA can match first LOs with the second 2, but prefers
! upper sideband low in the range.
!---------------------------------------------------------
Name = gbt4cma  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 7912, 7912    ifname = A,    C
  rf2 = 8424, 8424    fe  = '4cm', '4cm'
  pol =  RCP,  LCP    lo1 = 8936.0, 8936.0
  note = 'LO1=11.168, LO2=12.732, LO3=10.5 '
/
Name = gbt4cmb  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 8076, 8076    ifname = A,    C
  rf2 = 8588, 8588    fe  = '4cm', '4cm'
  pol =  RCP,  LCP    lo1 = 9100.0, 9100.0
  note = 'LO1=11.332, LO2=12.732, LO3=10.5 '
/
Name = gbt4cmc  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 8376, 8376    ifname = A,    C
  rf2 = 8888, 8888    fe  = '4cm', '4cm'
  pol =  RCP,  LCP    lo1 = 9400.0, 9400.0
  note = 'LO1=11.632, LO2=12.732, LO3=10.5 '
/ 
Explanation (Rcvr8_10):
  • rf1 will convert to 1024 MHz at the input to the RDBE
  • rf2 will convert to 512 MHz at the input to the RDBE

  • lo1 = 0.5*(rf1+rf2) + 768 MHz = rf1 + 1024 MHz

Nominal IF1 for this receiver on the GBT is IF1=3000 MHz
  • LO1 = lo1 + (IF1-768) = lo1 +2232
  • LO2 = IF1 + 10500 - 768 MHz = 12732 MHz
  • LO3 = 10500 MHz


GBT C-band : Rcvr4_6 (lower sideband receiver) :

freq.dat entries:
!---------------------------------------------------------
! C-band: range is 3.9-6.18 GHz
!       RF bandpass filters: 3.90-5.90 GHz, 3.95-4.65 GHz
!                            4.55-5.25 GHz, 5.15-5.85 GHz
!   Note: C-band extends from 3.9 to 6.18 GHz; more setups could be added.
!---------------------------------------------------------
! New versions provided on Jan 25 2008 by Frank Ghigo in email.
! I did not put in this file until Jan 6, 2009  RCW  Reconfirmed with
! Frank Ghigo at that time.
! Later they were adjusted for the RDBE.  For example, for the second
! To match the 512-1024 IF band when the VLBA LO is at 3900,
! the GBT will need to be at 4924+512=5436
Name = gbt6cma  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 3912, 3912    ifname = A,    C
  rf2 = 4424, 4424    fe  = '6cm', '6cm'
  pol =  RCP,  LCP    lo1 = 4936.0, 4936.0
  note = 'LO1=7.168, LO2=12.732, LO3=10.5 '
/
Name = gbt6cmb  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 4412, 4412    ifname = A,    C
  rf2 = 4924, 4924    fe  = '6cm', '6cm'
  pol =  RCP,  LCP    lo1 = 5436.0, 5436.0
  note = 'LO1=7.668, LO2=12.732, LO3=10.5 '
/
Name = gbt6cmc  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 4612, 4612    ifname = A,    C
  rf2 = 5124, 5124    fe  = '6cm', '6cm'
  pol =  RCP,  LCP    lo1 = 5636.0, 5636.0
  note = 'LO1=7.868, LO2=12.732, LO3=10.5 '
/ 
Note: Three other setups are in freq.dat, but not yet updated for the RDBE.

Explanation (Rcvr4_6):
  • rf1 will convert to 1024 MHz at the input to the RDBE
  • rf2 will convert to 512 MHz at the input to the RDBE

  • lo1 = 0.5*(rf1+rf2) + 768 MHz = rf1 + 1024 MHz

Nominal IF1 for this receiver on the GBT is IF1=3000 MHz
  • LO1 = lo1 + (IF1-768) = lo1 +2232
  • LO2 = IF1 + 10500 - 768 MHz = 12732 MHz
  • LO3 = 10500 MHz


GBT S-band : Rcvr2_3 (lower sideband receiver) :

freq.dat entries:
!----------------------------------------------------
! S-band: range is 1.68 - 2.65 GHz
!   RF bandpass filters: 1.68-2.65 GHz, 2.10-2.40 GHz.
!   Note: strong RFI from satellite at 2320-2345 MHz:
!   A notch filter has been installed which cuts out 2320-2345 MHz.
! VLBA and GBT can use the same LOs, so just adjust for 512-1024
!----------------------------------------------------
Name = gbt16cm  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 1680, 1680    ifname = A,    C         
  rf2 = 2088, 2088    fe  = '13cm', '13cm'     
  pol =  RCP,  LCP    lo1 = 2600.0, 2600.0
  note = 'LO1=7.832, LO2=15.732, LO3=10.5 '
/
Name = gbt13cm  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 1876, 1876    ifname = A,    C
  rf2 = 2388, 2388    fe  = '13cm', '13cm'
  pol =  RCP,  LCP    lo1 = 2900.0, 2900.0
  note = 'LO1=8.132, LO2=15.732, LO3=10.5 '
/
Name = g13cm_2  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 2076, 2076    ifname = A,    C
  rf2 = 2588, 2588    fe  = '13cm', '13cm'
  pol =  RCP,  LCP    lo1 = 3100.0, 3100.0
  note = 'LO1=8.332, LO2=15.732, LO3=10.5 '
/ 
Explanation (Rcvr2_3):
  • rf1 will convert to 920 MHz at the input to the RDBE for "gbt16cm"
  • rf1 converts to 1024 for the other setups.
  • rf2 will convert to 512 MHz at the input to the RDBE

  • lo1 = band center + 768 MHz
    • band center is 1832 for "gbt16cm"
    • band center is 2132 for "gbt13cm"
    • band center is 2332 for "g13cm_2"

Nominal IF1 for this receiver on the GBT is IF1=6000 MHz
  • LO1 = lo1 + (IF1-768) = lo1 +5232
  • LO2 = IF1 + 10500 - 768 MHz = 15732 MHz
  • LO3 = 10500 MHz



GBT L-band : Rcvr1_2 (lower sideband receiver) :

freq.dat entries:
!----------------------------------------------------
! L-band: Range is 1.10 - 1.75 GHz
! Ghigo email of 04/19/2011 indicates 1.1-1.8
! The entries below are both limited by this range.
! note there is an optional notch filter 1230-1340 MHz
!       to cut out a nearby radar
! RF bandpass filters: 1.10-1.80 GHz, 1.10-1.45 GHz,
!                      1.30-1.45 GHz, 1.60-1.75 GHz
! VLBA and GBT can use the same LOs, so just adjust for 512-1024
!----------------------------------------------------
Name = g20cm_1  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 1100, 1100    ifname = A,    C
  rf2 = 1588, 1588    fe  = '20cm', '20cm'
  pol =  RCP,  LCP    lo1 = 2100.0, 2100.0
  note = 'LO1=4.332, LO2=12.732, LO3=10.5 '
/
Name = g20cm_2  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 = 1376, 1376    ifname = A,    C
  rf2 = 1800, 1800    fe  = '20cm', '20cm'
  pol =  RCP,  LCP    lo1 = 2400.0, 2400.0
  note = 'LO1=4.632, LO2=12.732, LO3=10.5 '
/ 
Explanation (Rcvr1_2):
  • rf1 will convert to 1000 MHz at the input to the RDBE for "g20cm_1"
  • rf2 converts to 512 for "g20cm_1"
  • rf1 converts to 1024 for "g20cm_2"
  • rf2 converts to 600 for "g20cm_2"

  • lo1 = band center + 768 MHz
    • band center is 1832 for "g20cm_1"
    • band center is 2132 for "g20cm_2"

Nominal IF1 for this receiver on the GBT is IF1=3000 MHz
  • LO1 = lo1 + (IF1-768) = lo1 + 2232
  • LO2 = IF1 + 10500 - 768 MHz = 12732 MHz
  • LO3 = 10500 MHz



GBT prime focus : Rcvr_600 , 50cm (lower sideband) :

freq.dat entries:
!  I think setting the lo1 at 1536 will take care of having
!  512-1024 on the VLBA come out in 1024-512 in the GBT IF.
Name = gbt50cm  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 =  512,  512    ifname = A,    C
  rf2 =  690,  690    fe  = '50cm', '50cm'
  pol =  RCP,  LCP    lo1 = 1536.0, 1536.0
  note = 'LO1=1.848, LO2=10.812, LO3=10.5 '
/ 
Explanation (Rcvr_600):
  • rf1 will convert to 1024 MHz at the input to the RDBE
  • rf2 converts to 846 MHz

  • lo1 = band center + 768 MHz
    • band center is 768 MHz

Nominal IF1 for this receiver on the GBT is IF1=1080 MHz
  • LO1 = lo1 + (IF1-768) = lo1 + 312
  • LO2 = IF1 + 10500 - 768 MHz = 10812 MHz
  • LO3 = 10500 MHz


GBT prime focus : Rcvr_342, 90cm (lower sideband) :

freq.dat entries:
!  90cm will still have 500 MHz added on the VLBA, not 512.
!  So the full IF (mostly empty) corresponds to 12-524 MHz RF.
!  The GBT then needs to be at 524+512=1036 MHz to get the
!  same RF range.
Name = gbt90cm  Station = GBT_VLBA, GBT_COLD priority = 0
  rf1 =  290,  290    ifname = A,    C
  rf2 =  395,  395    fe  = '90cm', '90cm'
  pol =  RCP,  LCP    lo1 = 1036.0, 1036.0
  note = 'LO1=1.348, LO2=10.812, LO3=10.5 '
/ 
Explanation (Rcvr_342):
  • rf1 will convert to 746 MHz
  • rf2 converts to 641 MHz

  • lo1 = band center + 768 MHz
    • band "center" is 268

Nominal IF1 for this receiver on the GBT is IF1=1080 MHz
  • LO1 = lo1 + (IF1-768) = lo1 + 312
  • LO2 = IF1 + 10500 - 768 MHz = 10812 MHz
  • LO3 = 10500 MHz


-- FrankGhigo - 2011-10-13

This topic: VLBA > WebHome > GBTFrequencySetups
Topic revision: 2011-10-27, FrankGhigo
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