KFPA LO and IF chain calculation requirements

Modification Request #7 (C04 2009)



1. Introduction

In order for the observers, engineers and commissioners to effectively use the KFPA data, we must have an accurate description of the frequencies describing the observing configuration. This MR requests the same fine support for the KFPA frequency chain as is provided for the other GBT receivers.

2. Background

The KFPA LO chain has a frequency doubler in the amplifier chain and also use of the KFPA Rx requires setting both LO1 and LO2. Here we provide the LO equations and request that
  • The new KFPA LO equations be used to set up the GBT LO chain for a KFPA observation and
  • The LO chain information be added to the FITS files describing a GBT observation.

Also note that the KFPA design calls for unique use of the IF Rack for transmitting signals to the spectrometer and other backends in the GBT control room. Two beams or polarizations are carried on a single optical fiber. This must be properly accounted for when implementing the LO equations.

3. Requirements

The frequencies must be accurately described to the Astrid scripts used to configure the GBT and the frequencies must be accurately recorded in the GBT observing FITS files. Otherwise the GBT observing system should be changes as little as possible.

4. Design

The Config tool must be modified to include the KFPA LO equations. There are two LO equations that must be implemented for the KFPA and different polarization and beam combinations are routed through the same IF rack fibers. Below is the equation used with single pixel tests with the spectrometer. The KFPA observing sky frequency, using the spectrometer, is determined by 4 LO settings. These are the two LOs in the receiver room (LO1A and LO1B), the converter rack lo (LO2) and the input IF frequency of the backend. LO1A is the Doppler tracking LO. All the standard velocity reference frames must be supported (as is done for all other GBT Rxs) Note that the LO1A frequency is doubled before being supplied to the mixer. The Doppler tracking calculations must take this into account. Currently the KFPA design calls for LO1B to always have a fixed value, 8.9 GHz.

A confirmed spurious product, 2 x LO1A- 3 x LO1B, is present in the 1.8 GHz pass band (1.2-3.0 GHz) when LO1A is between 13.95 and 14.85 GHz (Fsky: 21.1 and 22.9 GHz. Also a spurious is produced from LO1A - LO1B that is introduced when the IDM outputs are multiplex on to the fiber. (ie 16 - 8.9 = 7.1). Thus LO1B should be set to 3/5 LO1A when LO1A is in the range 14.0 to 16.0. Potentially, others exist but have not been detected. The remedy as described in this document: IDM wiki page. The solution is to adjust LO1B to 3/5 LO1A over this range. The lower range requires the LO1B = 2/3 LO1A. The upper range requires LO1B = 1/2 LO1A.

Since the spurious are undetected for the upper and lower ranges, two modes should be implemented:
  • 1) LO1B is tuned in the middle range, but fixed to 8.9 GHz in the upper and lower ranges,
  • 2) LO1B is tuned over the full range as described in the "IDM1 Spur Avoidance Memo".

IDM-1-2 Page 2.jpg
IDM module schematics showing the LO chains for the 1.1 to 3.0 GHz IF in the IF-rack (top) and the 5.0 to 7.0 GHz IF in the IF-rack (bottom)

4.1 Two LO equations

KFPA IF

  • Nominally LO1A = (Fsky + 6.8)/2; Fsky can be tuned for each spectrometer sampler by changing LO2.
  • The KFPA design requires sending two IF signals down a single optical fiber.
  • One signal is on the fiber in frequency range 1.2 to 3.0 GHz (center 2.1 GHz)
  • The other frequency range is 5.9 to 7.7 GHz (center 6.8 GHz).

GBT Spectrometer IF

  • The Spectrometer has four different observing bandwidths, 800, 200, 50 and 12.5 MHz.
  • This correpsond to to Spectrometer IF center frequencies (SIF), 1.2, 0.9, 0.075, and 0.03125 GHz, respectively.

KFPA LO Equation TYPE I IDM

Fsky Forumula Spectrometer Bandwidth Fsky LO1A LO1B LO1B LO1B LO2
(GHz) (MHz) (GHz) (GHz) LO1A <14 14< LO1A >16 LO1A >16 (GHz)
(2 * LO1A)- LO1B - (10.5 - LO2) + SIF 800 24 15.4 2/3 LO1A 3/5 LO1A 1/2 LO1A 11.74
(2 * LO1A)- LO1B - (10.5 - LO2) + SIF 200 24 15.4 2/3 LO1A 3/5 LO1A 1/2 LO1A 12.04
(2 * LO1A)- LO1B - (10.5 - LO2) + (0.50-SIF) 50 24 15.4 2/3 LO1A 3/5 LO1A 1/2 LO1A 12.515
(2 * LO1A)- LO1B - (10.5 - LO2) + (0.50-SIF) 12.5 24 15.4 2/3 LO1A 3/5 LO1A 1/2 LO1A 12.47125

KFPA LO Equation TYPE II IDM

Fsky Forumula Spectrometer Bandwidth Fsky LO1A LO2
(GHz) (MHz) (GHz) (GHz) (GHz)
(2 * LO1A) + (10.5 - LO2) - SIF 800 24 15.4 16.1
(2 * LO1A) + (10.5 - LO2) - SIF 200 24 15.4 16.4
(2 * LO1A) + (10.5 - LO2) - (0.50-SIF) 50 24 15.4 16.875
(2 * LO1A) + (10.5 - LO2) - (0.50-SIF) 12.5 24 15.4 16.83125

Spectrometer IF Example: Sky Frequency is 23.8, the NH3 1-1 transition frequency.

Type 1 IF chain, from SKY frequency to Spectrometer IF frequency 1.2 GHz.

After LO Nominal LO Range Equation of IF Freq. Net IF Center IF Range
Mix LO Freq.   for Sky Freq. Side Frequency Frequency
  (GHz) (GHz)   Band (GHz) (GHz)
LO1A 14.75 12.8 to 16.2 (2 * LO1A) - SKY L 6.8 7.7 to 5.9
LO1B 8.9 8.9 LO1B + SKY - (2 * LO1A) U 2.1 1.2 to 3.0
LO2 11.4 10.5 to 12.3 LO2 + (2 * LO1A) - LO1B - SKY L 9.3 10.2 to 8.4
  10.5 10.5 10.5 + LO1B + SKY - LO2 - (2 * LO1A) U 1.2 0.8 to 1.6

Type 1 IF chain, from SKY frequency to Spectrometer IF frequency 0.9 GHz.

After LO Nominal LO Range Equation of IF Freq. Net IF Center IF Range
Mix LO Freq.   for Sky Freq. Side Frequency Frequency
  (GHz) (GHz)   Band (GHz) (GHz)
LO1A 14.75 12.8 to 16.2 (2 * LO1A) - SKY L 6.8 7.7 to 5.9
LO1B 8.9 8.9 LO1B + SKY - (2 * LO1A) U 2.1 1.2 to 3.0
LO2 11.1 10.5 to 12.3 LO2 + (2 * LO1A) - LO1B - SKY L 10.2 10.2 to 10.0
  10.5 10.5 10.5 + LO1B + SKY - LO2 - (2 * LO1B) U 0.9 0.8 to 1.0

Type 1 IF chain, from SKY frequency to Spectrometer IF frequency 0.075 GHz.

After LO Nominal LO Range Equation of IF Freq. Net IF Center IF Range
Mix LO Freq.   for Sky Freq. Side Frequency Frequency
  (GHz) (GHz)   Band (GHz) (GHz)
LO1A 14.75 12.8 to 16.2 (2 * LO1A) - SKY L 6.8 7.7 to 5.9
LO1B 8.9 8.9 LO1B + SKY - (2 * LO1A) U 2.1 1.2 to 3.0
LO2 11.1 10.5 to 12.3 LO2 + (2 * LO1A) - LO1B - SKY L 10.2 10.2 to 10.0
  10.5 10.5 10.5 + LO1B + SKY - LO2 - (2 * LO1A) U 0.425 0.8 to 1.0
  0.5 0.5 (2 * LO1A) + LO2 - 10.0 - LO1B - SKY L 0.075 0.05 to 0.10

Type 2 IF chain, from SKY frequency to Spectrometer IF frequency 1.2 GHz.

After LO Nominal LO Range Equation of IF Freq. Net IF Center IF Range
Mix LO Freq.   for Sky Freq. Side Frequency Frequency
  (GHz) (GHz)   U/D (GHz) (GHz)
LO1A 14.75 12.8 to 16.2 (2 * LO1A) - SKY L 6.8 7.7 to 5.9
LO2 16.1 15.2 to 17.0 LO2 + SKY - (2 * LO1A) U 9.3 8.4 to 10.2
  10.5 10.5 10.5 + (2 * LO1A) - LO2 - SKY U 1.2 0.8 to 1.6

5. Hardware IF path Spreadsheet

Because there are 7 different feeds in the KFPA, the IF path has many components. The configuration of the IF path for the two polarizations of each feed is described in a spreadsheet in the Spectrometer hardware section of the KFPA wiki. See page On the spectrometer modes Note the spreadsheet (Observing_Motes_6_9.xls) and printout of that document (Observing_Modes_6_19.pdf).

6. Deployment Checklist

Steps in the deployment checklist.

  • Use Astrid to configure the GBT for a single pixel PEAK observation with the center feed of the KFPA.
  • Use Astrid to configure the GBT for a dual pixel PEAK observation with two (observer selected) feeds of the KFPA.
  • Use Astrid to configure the GBT for a dual pixel FOCUS observation.
  • Use Astrid to configure the GBT for a dual pixel NOD observation (Observer selects two feeds).
  • Use Astrid to configure the GBT for a seven pixel TRACK observation
  • Use Astrid to configure the GBT for a four pixel, two frequency band Track observation (Observer selects four feeds).
  • Use Astrid to configure the GBT for a RaLongMapWithReference seven pixel observation
  • Use Astrid to configure the GBT for a RaLongMap seven pixel observation.

  • Demonstrate the use of the new Astrid scripts to the GB Staff
  • Newsletter article declaring the KFPA is available for observer use.

7. Test Plan

The test plan has several phases. The first phase will be to run the astrid scripts to configure the GBT, but without telescope control This can be done on a maintenance day. After all scripts have been checked out, we will ask for test time to run the simple peak and focus observations with a pair of KFPA pixels. (No full KFPA tests, except that we will be able to select which pair of pixels/feeds to use to perform the tests). Third phase of the testing will be spectral line observations, also with pairs of pixels/feeds. Fourth phase will be mapping tests with the full array.

After the internal tests and initial functional tests are complete, sponsor testing will be completed by astronomical observations (see below).

7.1 Internal Testing

The software group must fill out this section This section covers things like unit testing, simulator testing, and any other tests required to make sure this MR is ready for sponsor/integration/regression testing.

7.2 Sponsor Testing

The final phase of the test plan is sponsor testing. The sponsor testing will be done by making an series of astronomical observations of a reference radio source, using the KFPA. In the fall of 2009, we will observe the selected reference object with the current, 4 pixel, receiver. These observations will be reduced and documented in a GBT memo. In 2010, to complete the KFPA checkout, we will re-observe the reference source in the same manner.

The observing plan for the observation is described in the * KFPA pipeline document.

7.3 Integration/Regression Tests

What do the integration/regression testers need to do in order to test this MR. _Software Group will add this section_


Signatures

APPROVED: To the best of my knowledge, the request in this MR is complete. I have thought through this request, and believe it to be an important feature to implement or bug to fix.

ACCEPTED: I acknowledge that I have validated the completed code according to the acceptance tests.

Written ALERT! - Glen Langston - 2009 June 19
Checked ALERT! - name - date
Approved by Sponsor ALERT! - name - date
Approved by CCC ALERT! - name - date
Accepted/Delivered by Sponsor ALERT! - name - date

Symbols:
  • Use %X% if MR is not complete (will display ALERT!)
  • Use %Y% if MR is complete (will display DONE)


CCC Discussion Area-- GlenLangston - 2009-06-19

Topic attachments
I Attachment Action Size Date Who Comment
IDM-1-2_Page_2.jpgjpg IDM-1-2_Page_2.jpg manage 256 K 2009-06-24 - 14:31 GlenLangston  
Observing_Modes_6_19..pdfpdf Observing_Modes_6_19..pdf manage 22 K 2009-06-24 - 13:27 GlenLangston IF paths of the 7 beams to the converter rack and spectrometer
Observing_Modes_Spectrometer_6_19.pdfpdf Observing_Modes_Spectrometer_6_19.pdf manage 22 K 2009-06-24 - 13:26 GlenLangston KFPA spectrometer modes
kfpa7Use09May18.pdfpdf kfpa7Use09May18.pdf manage 415 K 2009-06-24 - 10:28 GlenLangston KFPA first test observation and Pipeline outline
Topic revision: r13 - 2016-06-08, PatrickMurphy
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