The user specifies the rest frequencies ("restfreq" keyword) and a range of radial velocities. The various IF filters are set to include the required range of frequencies in the local frame required by the radial velocity range. The configuration tool predicts the local frequency for each spectral window based on the rest frequencies and the radial velocity. This is not an exact calculation: the velocity definition ("vdef") is used, but not the reference frame ("vframe"). This approximation only affects the frequency spacing between the spectral windows. During observing the tracking LO will correctly track the velocity of spectral window #1. Because there is only one tracking L.O., the other spectral windows are set up with frequency offsets in the local frame with respect to window #1. Thus, for high velocities, the rest frequencies may not be centered in the bands of windows 2, 3, etc. Another consequence is that if one makes a large change in radial velocity (e.g. by >50000 km/sec), the spacing of windows in rest frequency will change significantly. Thus, when observing at a variety of high velocities, one should run the config tool for each change of velocity (i.e., do not rely on just changing the velocity in the LO1 manager), and one should set vlow=vhigh, or zlow=zhigh.
Finally note that the expert user may specify any of the IF conversion frequencies and total IF bandwidth, overriding the calculations done by the configuration tool. This option may be needed in some peculiar cases. Of course one needs a good knowledge of the LO/IF system to make use of this option.
Table 1: Summary of Configuration Keywords related to Frequency setups
Keyword | Description | Values |
---|---|---|
receiver | The frequency conversions and sidebands differ from one receiver to another. | The standard receiver designations are:
(prime focus) : Rcvr_342, Rcvr_450, Rcvr_600, Rcvr_800, Rcvr_1070 (gregorian) : Rcvr1_2, Rcvr2_3, Rcvr4_6, Rcvr8_10, Rcvr12_18, Rcvr18_22, Rcvr22_26, Rcvr26_40, Rcv40_52, Rcvr68_92. |
backend | Different input frequencies ("IF3") are required by different backends. | Backend designations are:
Spectrometer, SpectralProcessor, DCR, DCR_AF, BCPM, GASP, CGSR, VLBI, Radar, LLRADAR, RSR. |
nwin | Number of Spectral Windows | 1, 2, 4, 6, or 8.
{the maximum allowable depends on the receiver and backend} |
restfreq | Rest Frequencies of the desired spectral features. | A list of nwin frequencies, in MHz. |
deltafreq | Offsets to be added to the rest frequencies. They are added in the local frame. | A list of nwin frequencies in MHz. |
bandwidth | Bandwidth per window, in MHz. | Depends on the backend. |
swfreq | Switching offsets, if frequency switching. | A list of two frequencies, in MHz. |
vdef | Velocity definition. | Radio, Optical, Relativistic ("Rel"), or Redshift ("Red") |
vlow | Lower limit of radial velocity range. | Velocity in km/sec. |
vhigh | Upper limit of radial velocity range. | Velocity in km/sec. |
zlow | If vdef="Red", this is lower Z (and vlow is not used).
Note: only use "zlow" and "zhigh" if vdef="Red". | redshift parameter Z (= V/C) |
zhigh | If vdef="Red", this is upper Z (and vhigh is not used). | redshift parameter Z (= V/C) |
**for experts only: use the following keywords to override the calculated values. | ||
ifbandwidth | Total IF bandwidth, in MHz. | |
if0freq | Frequency (MHz) of center of window #1 after first mixer. | |
lo1bfreq | Frequency (MHz) of 2nd mixer (LO1B) for KA and W band receivers. | |
lo2freq | A list of nwin frequencies (MHz) for the G1-G8 synthesizers. | |
if3freq | A list of nwin frequencies (MHz): overrides the standard backend IF3 frequency. |
"LO1", as usual, is the frequency of the first mixer. In some cases this frequency is a multiple of the LO1 synthesizer frequency. The multiplication factor is "lo1mult".
A. Estimate frequencies in local frame.Use the following formulas for conversion to the local frame: Table 2: Doppler Formulae.
Now estimate the frequencies in the local frame for each window i = 1,2,.. nwin.
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B. Find the local center frequency and total IF bandwidth required.
If the standard BWtotal is being overridded by use of the keyword "ifbandwidth", use that value instead of the above calculation. Note also that BWtotal may be increased in a later step. Issue a warning if BWtotal exceeds the maximum bandwidth for the receiver. Check the next table for "Max Bandwidth". |
C. Settings of IF1NOM, sb, etc,etc, depend on the receiver. |
Table 3: Frequency Parameters and Formulae.
Receiver | Fcent | sb0 | sb1 | lo1mult | IF1NOM (MHz) | IF0 | IF1 | LO1B | MMCFilter | Max Bandwidth |
---|---|---|---|---|---|---|---|---|---|---|
PF1 (receivers 342-800) | -1 | +1 | 1 | 1080 | IF1NOM -(FLoc0-Fcent) | IF1=IF0 | 0 | none | 0.24 GHz | |
Rcvr_1070 (PF2) | -1 | +1 | 1 | 1500 | IF1NOM -(Floc0-Fcent)-900 | IF1=IF0+900 | 0 | none | 0.24 GHz | |
Rcvr1_2 (L) | -1 | +1 | 1 | 3000 | IF1NOM -(FLoc0-Fcent) | IF1=IF0 | 0 | none | 0.60 GHz | |
Rcvr2_3 (S) | -1 | +1 | 1 | 6000 | IF1NOM -(FLoc0-Fcent) | IF1=IF0 | 0 | none | 0.90 GHz | |
Rcvr4_6 (C) | -1 | +1 | 1 | 3000 | IF1NOM -(FLoc0-Fcent) | IF1=IF0 | 0 | none | 2.0 GHz | |
Rcvr8_10 (X) | -1 | +1 | 1 | 3000 | IF1NOM -(FLoc0-Fcent) | IF1=IF0 | 0 | none | 2.1 GHz | |
Rcvr12_18 (KU) | +1 | +1 | 1 | 3000 | IF1NOM +(FLoc0-Fcent) | IF1=IF0 | 0 | none | 3.4 GHz | |
Rcvr18_22 (K) | +1 | +1 | 1 | 6000 | IF1NOM +(FLoc0-Fcent) | IF1=IF0 | 0 | none | 4.0 GHz | |
Rcvr22_26 (K) | +1 | +1 | 1 | 6000 | IF1NOM +(FLoc0-Fcent) | IF1=IF0 | 0 | none | 4.0 GHz | |
Rcvr26_40 (KA) | 36.5-40.0 | -1 | +1 | 3 | 44000 -Fcent | 44000 -FLoc0 | IF1=IF0 | 0 | FL1 | 4.0 GHz |
Rcvr26_40 (KA) | 30.5-36.5 | -1 | -1 | 3 | 6000 | 44000 -FLoc0 | IF1NOM +(FLoc0-Fcent) | IF1 +44000-FLoc0 | FL2 | 4.0 GHz |
Rcvr26_40 (KA) | 26.0-30.5 | -1 | +1 | 3 | 6000 | 44000 -FLoc0 | IF1NOM -(FLoc0-Fcent) | 44000 -FLoc0-IF1 | FL3 | 4.0 GHz |
Rcvr40_52 (Q) | +1 | +1 | 4 | 6000 | IF1NOM +(FLoc0-Fcent) | IF1=IF0 | 0 | none | 4.0 GHz | |
Rcvr68_92 (W) | 68.0-73.5 | +1 | +1 | 4 | Fcent -66000 | FLoc0 -66000 | IF1=IF0 | 0 | FL1 | 4.0 GHz |
Rcvr68_92 (W) | 73.5-79.5 | +1 | -1 | 4 | 6000 | FLoc0 -66000 | IF1NOM -(FLoc0-Fcent) | FLoc0 -66000+IF1 | FL2 | 4.0 GHz |
Rcvr68_92 (W) | 79.5-85.5 | +1 | +1 | 4 | 6000 | FLoc0 -66000 | IF1NOM +(FLoc0-Fcent) | FLoc0 -66000-IF1 | FL3 | 4.0 GHz |
Rcvr68_92 (W) | 85.5-92.0 | +1 | +1 | 4 | 6000 | FLoc0 -66000 | IF1NOM +(FLoc0-Fcent) | FLoc0 -66000-IF1 | FL4 | 4.0 GHz |
Note:
For the KA- and W-band receivers, a warning should be issued if any of the
following conditions are exceeded, but configuration should proceed in
any case:
Table 4: Limits on KA- and W-band settings.
Rx/Filter | Sky Freq Range (GHz) | LO1B range (GHz) |
---|---|---|
KA/FL1 | Fmin>36 and Fmax<40 | N/A |
KA/FL2 | Fmin>30 and Fmax<37 | 14<LO1B<20 |
KA/FL3 | Fmin>26 and Fmax<31 | LO1B<13 |
W/FL1 | Fmin>68 and Fmax<74 | N/A |
W/FL2 | Fmin>73 and Fmax<80 | 14<LO1B<20 |
W/FL3 | Fmin>79 and Fmax<86 | LO1B<13 |
W/FL4 | Fmin>85 and Fmax<92 | LO1B<17 |
D. Setting of IF3 depends on the backend. | |||||||||||||||||||||||||||||||||||||||
"IF3" is the center of the IF band accepted by a backend. Table 5: IF3 requirements.
If the IF3 frequency is being set directly via the "if3freq" keyword, use "if3freq" instead of the above table. When using "if3freq" you must specify an array of size "nwin"; i.e., IF3 may differ for different windows. |
E. Set the "LO2" frequencies. |
For each spectral window, calculate the local frequency FLocal[i]:
This is the estimated frequency center for spectral window i. Note that the offset frequency dFreq has been added. The goal is to convert Flocal to IF3, so that the center of each spectral window appears at the back end device at the IF3 frequency needed by that back end. This is accomplished by two frequency conversions in the Converter Rack, the first is a mix with a fixed frequency of 10.5 GHz, the second by a mix with a frequency in the range 10.5 to 18.0 GHz. We refer to this "2nd" mixing frequency as "LO2", even though it is the 3rd or 4th mix that the signal from the sky has encountered. Using the "IF1", "sb0", "sb1" from Table 3, calculate: If the user has set the "lo2freq" keyword, use those values instead.
RoundingThe LO2 synthesizers have a resolution of 1 kHz, so we must check whether the LO2 frequencies need to be rounded off.
Let "LO2round" be the LO2 frequency rounded to the nearest kHz.
LO2 out of range?Next, check that the LO2 values are within the range 10600 - 17900 MHz.If the max(LO2round) is > 17900 AND the min(LO2round) < 10600, then issue an error message and abort the configuration. We just can't do it!
Adjust LO2s and IF centers.If either "roundfrac" or "lo2adjust" are non-zero, then we can adjust the LO2 frequencies, but we have to compensate by adjusting IF0 and IF1.
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F. Check the LO1 synthesizer. |
The LO1 synthesizer cannot tune above 20 GHz, so it is useful at this point
to estimate what frequency is required and to issue a warning if the
limit is exceeded.
"FLoc0" is the estimate of the frequency in the local frame that the LO1 manager will use, and "IF0new" is the value that will be set for the "ifCenterFreq" parameter in the LO1 manager. Thus the estimate of the LO1 frequency is: The synthesizer setting is thus:
If LO1synth exceeds 20 GHz, the config tool should suggest that the user may change IF0 (with the "if0freq" keyword) to produce a valid configuration. Suggest that IF0 may be set to:
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G. Check frequencies and adjust total IF bandwidth. | ||||||||||||||||||||
At this point, we calculate the conversion of each FLocal to the frequency
it would have at the input to the backend (the "IF3" frequency).
This is done to provide feedback to the user and to show if any of
the IF3s are not exactly as intended due to adjustments made to
IF0, IF1, and LO2. We also check if the total IF bandwidth needs to
be increased.
Determine the effective IF1 for each spectral window:
And the estimated IF3 for each window is: The user should be able to list a summary of the frequency data, and the list should include, for each i : To check if the total bandwidth needs to be increased, figure out: Table 7: Center of IF bandpass filter.
Then, as before, increase by backend bandwidth and switch frequency offsets: But if the user has specified "ifbandwidth", then use newBWtotal = ifbandwidth.
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H. Summary of M&C manager settings. |
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Finally, we have all the information needed to set the M&C manager parameters.
Table 8: M&C settings
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