Morris Instruments Inc. Morris Instruments Inc.1382 McMahon Ave., Ottawa, Ont., Canada K1T 1C3
tel: (613) 523-7448
e-mail: morris-instruments@rogers.com
ROM version 971201 to 080301.
This package includes this manual,the Sweeper unit, and the battery charger.
The polycarbonate screen is highly resistant to impact, however care must be taken not to scratch it.
This unit is designed for use in tuning properly shielded magnetic resonance probes and filters, it is not intended to be used as a signal source for intentional radiation.
Note: This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in accordance with the instruction manual, may cause harmful interference to radio communications. Operation of this equipment in a residential area is likely to cause harmful interference in which case the user will be required to correct the interference at his own expense.
Caution to user: Changes or modifications to this equipment not expressly approved by Morris Instruments Inc. for compliance could void the userŐs authority to operate the equipment.
This equipment must not be left running with an unterminated cable attached to either BNC connector. All cables and connectors used with this product must have 100% shield coverage and be in good condition. All devices to be tuned using this equipment must be 100% shielded (This would include operation of this equipment within a 100% shielded room as is commonly used to house MRI magnets.)
This equipment has been designed to operate within the fringe field of large bore superconducting magnets. The use of magnetic materials in the manufacture of this equipment has been minimized, however a few components are unavoidably magnetic. The case is aluminum which although not magnetic does support eddy currents which can make manipulation of the unit difficult at very high field strengths. For these reasons care should be taken when handling the unit close to the bore of a magnet. For safety, do not bring the unit within six feet of a magnet which contains a human subject. Avoid using the unit in locations where physical forces on the unit due to eddy currents or ferromagnetic effects exceed one lb. Never bring the charger into the fringe field of a magnet.
This product has been developed specifically for tuning NMR probes, although it may also find application in other areas of RF design, in particular scalar analysis of one and two port devices. Important features include:
A simplified block diagram of the sweeper is shown in fig. 1.
fig.1 Block Diagram
The CPU section contains the microprocessor, RAM, ROM, and the analog to digital converter (ADC). The microprocessor receives commands from the keypad, drives the display panel, and loads the RF synthesizer.
The synthesizer consists of a phase locked loop section which generates frequencies from 165-405, 205-505, 250-610, 300-710, 350-810 MHz, depending on the model, in 50kHz steps (100kHz steps for ROM versions 980101 and earlier), and a divider section which can divide the output of the PLL section by successive powers of two up to 128. Thus the total frequency range is 1.3 to 405 MHz for the 405NV+ and 1.6 to 505, 2.0 to 610, 2.4 to 710, or 2.7 to 810 MHz for the 505NV+, 610NV+, 710NV+, and 810NV+. The step size is finer in the lower ranges due to the division. (See specifications.)
The synthesizer output level is controlled by an automatic levelling circuit (ALC) which may be set by the manual level adjustment on the side of the unit or by a digital control from the CPU. (The two control voltages are multiplied together and the result used to control the ALC.) The switch between the two BNC connectors allows the synthesizer output to be sent directly to the RF OUTPUT port, or to be applied to the integral tuning bridge. With the switch set to the tuning bridge position, a device to be matched to 50 ohms may be connected to the TUNING BRIDGE port for adjustment. When the switch is set to the RF OUTPUT position then the other port becomes a 50 ohms RF detector. This allows tuning of two port devices such as filters.
The rechargeable battery is of the sealed lead acid type, chosen for its non-magnetic properties and its standby characteristics. The battery should never be deep discharged, therefore it is important to recharge the unit as soon as the battery indicator flashes on the screen (see fig. 2 below), or within 60 days, whichever comes first.
fig. 2
As of ROM revision 20061001 the battery level indicator shows the approximate amount of charge remaining in the battery during discharge. It should always indicate full while charging. Earlier versions simply indicated the battery to be OK or flashed a LOW warning. In either case the indicator flashes when the battery needs recharging.
To recharge, simply plug the charger into the jack on the side of the unit and then plug the charger into the AC. The charging rate is much faster if the unit is switched off than if it is on, although the unit may be operated indefinitely while connected to the charger. An overnight charge will completely recharge the battery. When charging is complete, unplug the charger from the AC and then unplug the charger from the sweeper. The charging circuit has been set for cyclic as opposed to standby use, so that for optimum battery life, the charger should be turned off and disconnected once a full charge has been reached. Operating time on a full charge is at least 3 hours.
If the low battery indication is showing on the screen or if the battery is so low that the unit will not come on at all, then switch it off, and charge the battery as stated above, after 5-10min you may turn the unit on while charging although this will increase the time required to reach full charge.
The charger itself may contain magnetic components and must NEVER be brought into the fringe field of NMR magnets!
Upon startup, the model and ROM version numbers are displayed for three seconds, then the unit automatically calibrates the ADC offset (zero or match line) and resumes operation using the parameters last in effect before it was turned off. (fig. 3.) If the screen remains blank the battery is most likely low. In this case the unit should be switched off and recharged. (See section 3. Battery Charging)
There is an autorepeat function on all of the keypad buttons which activates when a button is pressed and held.
To adjust the screen contrast, press the MENU button to pull up a menu of choices for the "soft" buttons on the right column of the keyboard. Use the UP and DOWN arrow keys to select LCD Contrast and press ENTER. Adjust the contrast using the UP and DOWN arrow keys then press ENTER.
If the frequency of interest lies in a lower band press the left BAND button (decreasing arrow) successively until the desired band is reached. The right BAND button reverses this action. The frequency bands overlap but generally one should select the lowest band which contains the range of frequencies of interest in order to minimize the harmonic content of the signal and to gain the finest possible resolution. The SWEEP WIDTH buttons allow the sweep width to be adjusted. For zero span or CW see cursor operation below. The FREQUENCY buttons allow the center frequency to be changed in increments of half the displayed sweep width (limited by the ends of the frequency band). In CW mode the frequency buttons operate in the finest steps available and the frequency band will automatically switch as the frequency crosses the top of each band. For fine control of the center frequency use the cursor to select the desired center frequency and press the ZOOM button to initiate a narrow sweep centered on the selected frequency.
fig.3 (model 505NV+ shown)
The digitized detector signal is displayed as a function of frequency. Pressing the ADC button increases the vertical gain by successive powers of two up to 8 times. Pressing this button one more time brings the ADC scale back to x1.
The manual R.F. LEVEL control on the side of the instrument allows analog adjustment of the R.F. power. In addition, the power can be controlled digitally via the RF Output Level menu selection. This digital power setting is not saved with the other sweep parameters, and reverts to the default (maximum level) value when the sweeper is turned OFF and back ON. The analog and digital R.F. power settings are multiplied together to yield the actual power control setting.
The LAST SWEEP key displays the last sweep that was either saved or recalled (see Store and Recall functions in the Soft Key section), indicating this condition with "MEM" displayed in the upper left corner. Pressing any key will return the unit to real time operation - but using the instrument parameters in use before pressing LAST SWEEP. This key is useful when comparing a stored trace against the current real time display.
Begin by setting the output switch (located between the BNC connectors on the side of the unit) to the position nearest the TUNING BRIDGE / DETECTOR port. Connect the device to be tuned to this port. Adjust the display as discussed above so that the frequency range of interest is displayed. It is not necessary to place the desired frequency exactly at the center of the display as the cursor (see below) may be placed anywhere on the screen to act as a marker. Place the cursor at the desired frequency using the CURSOR buttons. Adjust the ADC SCALE and RF level so that the full vertical range of the screen is used. Now adjust your device under test (NMR probe) so that the trace meets the match line exactly at the cursor frequency. (see fig. 4) In some cases near the bottom edge of each frequency band the trace will not quite reach the match line due to a small amount of harmonic content in the signal. In such a case simply adjust your device (probe) to bring the trace as close to the MATCH line as possible, or switch to the next lower band if the frequency of interest can still be reached.
fig. 4 Tuning a 282.4 MHz NMR probe.
For this mode of operation set the output switch (located between the BNC connectors on the side of the unit) to the position nearest the RF OUTPUT port. The maximum output level is nominally 0dBm ±3dB. You should insert an appropriate attenuator between the RF OUTPUT port and the input of your device if the maximum safe input level of your device is less than this amount. The TUNING BRIDGE / DETECTOR port will now be operating as a 50 ohms RF detector. It has a maximum safe input level of +10dBm. If your device has gain, be sure to attenuate its output appropriately before connecting to the DETECTOR. In this mode the display will be proportional to the detector output voltage as a function of frequency. (see fig. 5)
fig. 5 Tuning a 20 MHz bandpass filter.
The cursor left and right buttons allow the cursor line to be moved across the screen. To move the cursor quickly; simply press and hold the appropriate cursor button and release it when it is at the desired location. The cursor position is indicated in MHz. Pressing the CW button causes the unit to switch to CW mode at the cursor frequency (zero span). Pressing the CW button again returns you to the sweep mode at the minimum sweep width centered on the cursor frequency. Pressing the ZOOM button will center the sweep on the cursor position at the minimum sweep width (equivalent to pressing the CW button twice).
To sweep about an arbitrary frequency, select the appropriate BAND then move the cursor near to the desired center frequency. Press the CW button and then use the FREQUENCY buttons if required to fine tune the frequency. Press the CW button again to go back to swept mode. Use the WIDTH and ADC buttons to adjust the span of the sweep and vertical sensitivity if required.
The rightmost column of gray keys are used for various functions including adjusting the screen contrast, the R.F. level (may also be adjusted using the manual potentiometer on the side of the unit), storing and recalling sweep setups and screen traces, inverting the sweep, switching between DOT and CURVE type displays, and finally to Clear the non-volatile RAM which will erase all the stored data and revert the instrument to the default parameters.
LCD Backlight - ROM versions 020901 and later (for earlier versions see below) - If your sweeper has the LCD backlight installed, and ROM version 020901 or later, the backlight may be toggled on and off by simply pressing the ENTER key when you are not in menu mode. To conserve battery power the backlight will turn itself off after 3 minutes if there has been no keyboard activity.
To access the menu mode, press the MENU key. To immediately exit from the menu mode back to the normal operation mode simply press any of the black or red (orange) keys.
LCD Contrast - When the sweeper is powered up it sets the LCD contrast to the value last used before power down, or to a default setting if the last used value falls out of pre-set bounds. (ROM versions earlier than 990101 do not save the last used contrast setting but always power up using the default.) To adjust the screen contrast press the MENU button, use the UP and DOWN arrow keys to highlight LCD CONTRAST and press the ENTER key. At this point you can adjust the contrast using the UP and DOWN arrow keys. When the desired contrast is reached, press the ENTER key.
RF Output Level - The final control voltage to the automatic gain control circuit is the product of the setting of the manual potentiometer on the side of the unit and a digital value set by the RF Output Level menu choice. The digital control allows the user to preset a maximum R.F. setting. To set this value press the MENU button and then use the up and down arrow keys to select RF Output Level and press ENTER. Use the up and down arrow keys to set the desired RF level. When correct press ENTER to save this value.
These functions allow for the storage of four instrument setups (windows) and four sweeps (static displays) with their associated setups. (Alternatively one can view this as eight instrument setups with four of these also having an associated sweep trace.) The memory is non-volatile and remains valid even when the unit is turned off. Memory may be lost if the unit is left switched on until the main battery is completely exhausted. To avoid this occurrence always recharge the unit if the low battery indication is showing.
Store Setup - from the main menu selecting Store Setup and pressing ENTER brings up the storage location selection display. To store just the current sweep parameters choose one of the four Store Window locations and press ENTER. To store the current parameters and also a picture of the current trace choose one of the four Store Sweep locations and press ENTER. If a location already contains stored data then the associated cursor frequency will appear in the list on the right hand side of the Store Setup display. To abort a store operation without affecting any of the storage locations simply press any one of the black or red (orange) keys.
Recall Setup - from the main menu selecting Recall Setup and pressing ENTER brings up a choice of stored windows and sweeps with their associated cursor frequencies listed. Use the up and down arrow keys to select the desired data to recall and press ENTER. If the item recalled was a window then the unit will immediately start sweeping using these parameters. If the item recalled is a sweep then the unit will display that sweep with a caption MEM indicating that the display is showing a stored trace instead of a real time sweep display. Pressing any key starts the unit sweeping using the parameters associated with the recalled sweep. To abort a recall operation simply press any one of the black or red (orange) keys.
Inverted Sweep - Select this option and press ENTER to invert the display so that the zero or MATCH line may be placed at either the top or bottom of the screen at the users discretion.
Dot/Curve Display - The Dot/Curve Display menu selection toggles the display between the DOT type display with discrete dots and the CURVE type in which the digitized points are joined for improved visibility. In a sense the DOT type display is more accurate since only the true digitized points are shown, however the line type display is more visible. The sweep rate is slightly slower in the CURVE display mode and depends on the number of pixels to be filled in. In DOT mode the sweep rate is constant. A comparison between the two types of display is shown in figure 6.
fig. 6 DOT vs. CURVE display
LCD Backlight - ROM versions 990601 and earlier (for later versions see above) - If your sweeper has ROM version 990601 or earlier with the optional LCD backlight installed then this menu choice allows the backlight to be turned on and off. To conserve battery power the backlight will turn itself off after 3 minutes if there has been no keyboard activity.
Note: As of ROM version 020901 the operation of the backlight was changed to enable the ENTER key to act as a single button toggle switch (see previous page). This was done so that the backlight could be easily turned on even if the room was too dark to read the unlit screen at all. If you have an earlier ROM version and would like to update your backlighted sweeper to the latest firmware version please contact Morris Instruments Inc.
Clear NVRAM - clear all the non-volatile RAM. This will usually not be used but may be useful to return the instrument to the default state. This option requires ENTER to be pressed to confirm. Pressing any other key will abort the command.
Generally very little is required in the way of maintenance for your sweeper. The battery should be fully charged before storing the unit for an extended period of time, and it should be recharged at least every 90 days. The recommended temperature range for operation or storage is 10C to 25C. The connectors should be kept clean, especially the TUNING BRIDGE / DETECTOR port as a poor connection here will affect the readings and may cause radio frequency emissions. Avoid leaving the unit in direct sunlight as this will degrade the performance and life of the LCD screen.
The following is a list of common problems and solutions. Please consult Morris Instruments Inc. (ph. 613-523-7448, fax 613-523-4112) in the case of more serious difficulties. We will be glad to help you. Our e-mail address is: morris-instruments@rogers.com
Band 405NV+ 505NV+ 610NV+ 710NV+ 810NV+ Resolution (kHz) 1 165.00 - 405.0 205.00 - 505.0 250.00 - 610.00 300.00 - 710.00 350.00 - 810.00 50.0 2 82.50 - 202.5 102.50 - 252.5 125.00 - 305.00 150.00 - 355.00 175.00 - 405.00 25.0 3 41.25 - 101.25 51.25 - 126.25 62.50 - 152.50 75.00 - 177.50 87.50 - 202.50 12.5 4 20.625 - 50.625 25.625 - 63.125 31.250 - 76.250 37.500 - 88.750 43.75 - 101.25 6.25 5 10.313 - 25.313 12.813 - 31.563 15.625 - 38.125 18.750 - 44.375 21.875 - 50.625 3.125 6 5.156 - 12.656 6.406 - 15.781 7.813 - 19.063 9.375 - 22.188 10.938 - 25.313 1.5625 7 2.5781 - 6.3281 3.2031 - 7.8906 3.9063 - 9.5313 4.688 - 11.094 5.469 - 12.656 0.78125 8 1.2891 - 3.1641 1.6016 - 3.9453 1.9531 - 4.7656 2.3438 - 5.5469 2.7344 - 6.3281 0.390625 (Note: Table applies to ROM versions 990601 and later. Earlier versions min. resolution double listed value.)
All units are covered for one full year against defects in manufacture, or failure under normal use.
Paul Morris 2010-01-31
morris-instruments@rogers.com