Detailed Tuning Instructions for Receiver W

Version 4, 14 December 2008 (updated from 3 August 2004)

These are rather complete instructions but they still assume you know where the different parts of the receiver system are - see the detailed description of the receiver. A short check-list instruction set will follow when the tuning process has been finalised.

The B band and D band tuning processes are very similar so the instructions are combined below. In many places you have to be sure to adjust the right unit. For example, there are four SIS bias supplies - one for each mixer. When tuning at B band you need to check the current on the supplies used for the B band. In order to keep the instructions below readable this is not explicitly mentioned in every place. Make sure you are looking at or tuning the unit for the right band if there are units for both bands! The same applies for the channels - make sure you are looking at, say, the A channel IF power when you adjust the A channel IF attenuation.

Note: these instructions are under construction. They will be updated and things will change!

Detailed Tuning Instructions

Before starting for the evening: Check that the lamp in the receiver cabin is ON as early as possible to allow the tuner to warm up and stabilize for as long as possible before observing.

In the control room:

• Tune RxA3i to 221.3 GHz LSB (0 km/s topo) to avoid an interference spike due to its X40 synthesizer in RxW spectra. For more details (or other possible frequencies) see the bottom of this page. One can also tune RxA3i later to this frequency, but then do not repeat the RxW tune command.

• Before running up the mwttel window, type into a console on palila:

  • xhost +mwttel

• After running up ICL and running the RX_FOR_ACSIS command type:

  • RXW_SCREEN palila

    This will start the RXW display screen. It gives you a bunch of useful information that it is good to watch during RxW D observations including mixer currents, LO modulator settings, sideband, frequency etc.
    

• Send the RxW MSB to the OCS. This should load the receiver and prepare the system for tuning. On ICL by the way: Try to note any messages about motors being stalled. If that happens the micro will anchor them and they have to be unanchored again from the W micro pushbutton controls. You will see an “E” for ERROR come up on the left hand side of the status display when this occurs. If this happens, see instructions for how to get the motors out of this error, if needed.

• When the screen stops with the instruction "set to local - push remote or type ^C to continue" then

• Wait for the tuning screen to appear and select the appopriate option:
  

  • Tuning Complete - your are done! The observation can go ahead
  • To Zenith + Tune - new frequency you need to tune
  • To Zenith - already tuned but you need to lock the Gunn and/or check/optimize the tuning.
  • Abort Obs

• Go to the cabin...

In the cabin:

• Set the two LO injection grids to the correct band (i.e. B or D).

• Check the intensity button on the spectrum analyser under RxA and make sure it is connected to the right band (B or D). It should be at 450MHz for D band.

• On the micro tuning panel press the backshort button for the required Gunn. The backshort tuning is on the opposite side to the Gunn output both on the Gunn itself and on the tuning panel.

• Tune the appropriate Gunn backshort to the value indicated. The B band Gunn is to the right and the D band Gunn to the left on the receiver frame. Each turn on the tuner is 25 divisions so 0.025 on the display would be one turn out from zero. So, e.g. 0.077 would be three turns and 2 divisions out from zero. See the bottom of this page for more information about the micrometers.

• On the micro press the frequency tuner button for the required Gunn.

• Set the appropriate Gunn frequency tuner to the value. The tuner is on the side of the Gunn.

• Look at the phase lock unit (at bottom of receiver). The B band section is at the top of the unit and the D band is at the bottom. Make sure that the Gunn is on as indicated by the lights and lock the Gunn by adjusting the frequency tuner. The Gunn tuning tables are good so if you have to turn far something has been set incorrectly. The "level" light will come on when you are in range, followed by the "lock" light when you very close. There may be more than one nearby tuner settings where you can get a lock; choose the one which is not touchy. On a few D-band frequencies, especially if the Gunn is a little cold, you may get "lock" without the "level" light. This is ok, so long as in the next part of your tuning, you get enough mixer power. You may need to adjust things a little later on when the Gunn warms up.

  In particular the D-band Gunn is very touchy and can drift out of lock within a few minutes. You will need to check the lock during the tuning and before leaving the cabin. The D-band Gunn may drift during the observing, and this will be indicated by a message about the "PLL" (phaselock loop) on the screen downstairs; this is your cue to go to the cabin and adjust the Gunn tuner.

• Check the lock on the spectrum analyzer under RxA. There should be one clean line, possibly with two small lines on both sides but many db lower. To obtain a clean(er) lock one can adjust the backshort to slightly lower values, but ensure that the output level does not drop off. If the Gunn output levels drops off it will be indicated by a digital readout on the PLL unit, and also reduced drive to the multipliers will result in reduced LO illumination of the mixers, which will show up as lower mixer current.

• For D-band: next press the buttons for the multiplier settings and set the four tuners on the used multiplier. The same buttons are used for the B- and D-band multipliers. Each turn on the tuners is 50 divisions! So 0.88 on the display is one turn and 38 divisions out from zero. Note the difference from the Gunn nomenclature - for the Gunn 0.050 means 50 divisions out. For the multiplier 0.050 means 5 divisions! Several of the tuners do not go down to zero - do not try to force them. Each turn is marked on the barrel, by tick marks alternately up and down. 0 at the top, 50 (one turn) on the bottom, 100 at the top (two turns) and so on. Note that some of the tuners are upside down as seen by the numbers. The tuning tables are always recorded by turning the micrometers outwards. (Skip this section for B-band as it does not have multipliers to adjust).
  

• Turn the LO modulator switch to 'manual' and ramp up the pot until you start to see mixer current. You may do this either by watching the mixer current values, or turning on the SWEEP and I/V curve at the bottom of the micro and watching the curve ramp up. The SIS bias supplies should now show some mixer current. If you adjust the mixer currents manually don't forget that you will have to put the LO control back to computer control at the end.

  You can check if there is mixer current due to LO power by blocking the LO signal between the turret used for equalizing the mixer currents and the LO injection grid.

• Gently peak up each multiplier once you have current. If there is no current check the Gunn tuning and the multiplier settings. It is easy to interchange the Gunn backshort and tuner or get a multiplier setting wrong. If it all look OK try to get some current by gently move the multiplier tuners one by one. Usually tuner 2 and 4 are the most sensitive (they are the output tuners on the doubler and tripler respectively) but also tuner 3 can have large effect. It should be easy to get current except for perhaps close to the end of the tuning range.

  • As the LO power increases while adjusting the multipliers, it will probably be necessary to readjust to modulator so that the mixer is not saturated, otherwise small improvements in the multiplier setting cannot be discerned. There is often interaction between the multiplier and the gunn, so after the multiplier is peaked up, the PLL centering meter should be checked and gunn adjusted if necessary.

• Assuming you have current, set it to ~0.028mA for D-band using the LO power modulator in manual mode and rotating the tuner turret to even out the power between the two mixers. Note the longer tuning pin should always be on the outside. Make sure you set the LO power modulator back to computer control.

• Now press the remote button on the micro once. That should set the correct IF levels. You can check the IF levels on the Trx module with the switch on the IF control module in the Total Power position (left position) and manually set the level by selecting manual mode (don't do this unless you are desparate). If you do that make sure the B/D band selector on the same module is in the right position - up for B band and down fro D band. There are LEDs to warn you if the levels are out of bounds.

• Checking junction characteristics If this is the first tuning for the night now is the right time to check the Josephson current. Make sure the SIS bias control is on computer mode. Turn on the sweep on the selector module to the left of the scope. Select Pwr-V on the other switch and choose a mixer with the selector switch. Look at the mixer response curve on the scope (it may be necessary to turn up the scope intensity).

  The D-band is more likely to have severe Josephson current problem. This can be seen by huge fuzzy humps or regions in the IF power curve. If you have large fuzzy regions and humps increase the magnet current to maximum and then decrease it again. This might clear up some of problems. While decreasing the current note that there is more than one value of the current that minimizes the fuzzy regions and humps. But they are not all the same. We use a current of 60 - 120 mA. Lower current does not give a good suppression and a higher one gives bad Trx and makes the designer nervous. A high current can cause nasty effects if the receiver suddenly warms up. Also be aware that the rate the current can be changed is limited internally. If you wind the knob quickly you will get ahead and the current will continue to change even after you stopped turning the knob. After checking the Josephson current turn off the sweep. It is not good to observe with the sweep on.

• Next optimize the interferometer. Select TRx (right) position for the meter on the Trx monitor module. THIS IS VERY IMPORTANT - you will not get a good tuning with the switch in the Total Power position. But it will be normal at least to start with. It is easy to mess up.

  Set the sky and load chopper to local mode. The sky chopper should be in the IN position and the load chopper in phase lock (PLK) position. The load chopper in the receiver should start spinning. After about 10 seconds you should see the meters on the Trx Monitor increase. After 10 more seconds the readings should be stable. These values are an indication of the S/N. After the tuning the readings should be ~0.4 for a decent D band tuning, higher preferably.

• Press the button for the LO diplexer Martin-Puplett (same button for both B and D band). Tune for maximum on the Trx meter - make sure you look at the right meter. Top is for the A channel with the B channel meter below. It is not usually necessary to adjust the Martin-Puplett SSB filter. Be sure if you try not to take it too far from its nominal value or you may be tuning it DSB. During the tuning the mixer current might change. If it drops below .010 mA or rises above .03 mA it should be adjusted with the LO power modulator.

• Now balance the mixer current between the channels and repeat the optimization for the B channel. All the B channel buttons are below the A channel buttons on the micro.

• Lastly, while watching the Trx meters, tweak the LO power modulator again for maximum S/N.

• When finished make sure the mixer currents are set correctly then return the LO power and IF attenuator modules to remote control. Now pressing Remote on the micro should set the LO power and IF attenuation correctly and leave the receiver in remote control. Note that this does take some time. Even if this does not work, leave the LO power modulator in remote control. The way to check if the command to set to remote has worked is to look at the IF power meters. The meters need to be out of Trx mode to do this.

• Check that the LO lock meter is still centered and adjust if necessary, check that the sweep is turned off, and turn down the intensity on the scope, before you leave.

Back in the control room:

• If everything is happy the tuning screen should now give you a green “LOCKED” indicator light. Click “Tuning Complete” in the manual observing window and observing will start.

The Micrometers

Micrometer	Fully clockwise position	reading	turn
D Band Gunn Tune	zero	0	25 per turn
D Band Gunn Backshort	0.5 above zero	0.5	25 per turn
D Band Multiplier 1	12 below zero = -12	38	50 per turn
D Band Multiplier 2	2 below zero = -2	48	50 per turn
D Band Multiplier 3	1 below zero = -1	49	50 per turn
D Band Multiplier 4	1 below zero = -1	49	50 per turn

Please, if you do turn a micrometer fully clockwise to find it's starting position, do so very gently. You don't really need to do this, and to reduce wear on the micrometers I recommend that you avoid it. You can figure out the setting by looking at the hash marks.

Making a positive identification of the position before you start adjusting will help avoid confusion when setting the micrometers.

The Gunn TUNE and BACKSHORT micrometers are 25 units per turn. These units are actually thousandths, so there are 25 thousandths (0.025) per turn. They have three lengths of hash marks. The longest are at 0, 100, 200, 300 thousandths. The shortest are at 25, 75, 125, 175, 225, 275 thousandths. The medium length hash marks are at 50, 150, 250 thousandths.

The Multiplier tuning micrometers are 50 units per turn. These units are actually thousandths or 0.050. These micrometers have two lengths of hash marks which are on opposite sides of the line. The longer lines on the clockwise side of the line are at 0, 100, 200, etc. The shorter lines on the opposite (anticlockwise) side of the line are at 50, 150, 250, etc.

The digital readout that tells you where the set the micometers has it's decimal point in a strange position. For the multipliers when the digital readout is at 01.377, the micrometer should be set to 138 thousandths. With the Gunn micrometers when the digital readout says 00.045 the micrometer needs to be set to 45 thousandths.

There are a lot of web sites showing how to read micrometers. A good one is here .

RxA3i interference in RxW spectra.

The part of RxA3i that interferes with RxW is the X40 synthesizer. This synthesizer produces a signal 40 X the frequency coming out of the PTS synthesizer. It operates from 5.000 GHz to 5.3xxx GHz. It only produces an interference spike on RxW when it is operating at the lower end of its range. So in order to prevent the interference to RxW we "park" RxA3i on any frequency that results in the X40 synthesizer being up at the high end of its range. There are actually several frequencies you could set RxA3i to, that will accomplish this, because the 5.0 - 5.3xxx GHz range of the X40 synthesizer is repeated as the harmonic mixer in the PLL uses different muliplication factors at different frequency ranges.

RxA3i Frequencies that set the X40 synthesizer to the high end of it's range:

fSky LSB	fSky USB	fLO	fGunn	fX40 synth	fPTS synth	Harm N value
221.3	229.3	225.3	75.1	5.357143	133.9285714	14
236.3	244.3	240.3	80.1	5.333333	133.3333333	15
251.3	259.3	255.3	85.1	5.312500	132.8125000	16
266.3	274.3	270.3	90.1	5.294118	132.3529412	17

All of the above frequencies are in GHz, except for the PTS synthesizer frequencies which are in MHz. I suppose that the first frequency on the list may be best, since it gets the X40 synthesizer set at the highest frequency. Any of these frequencies should keep the interference spike out of RxW.