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 950404 to 950420 and SPC405.
This package includes this manual,the Sweeper unit, and the battery charger. The rubber bumpers on the sweeper are permanently fixed to the unit and are designed to serve as feet and to protect the unit. 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 user's 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, it is highly magnetic.
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:
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 165 to 405 MHz (205 to 505MHz) in 100kHz steps, and a divider section which can divide the output of the PLL section by successive powers of two up to 64. Thus the total frequency range is 2.6 to 405MHz (3.2 to 505MHz). 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 which may be set by the manual level adjustment on the side of the unit. 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. Unlike nickel-cadmium batteries, the sealed lead acid battery should never be totally drained as this will shorten the life, therefore it is important to recharge the battery as soon as the low battery indication flashes on the screen. (see fig. 2 below)
fig. 2
To recharge the battery simply plug the charger into the jack on the side of the unit and then plug in the AC line to the charger. 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 AC line to the charger and then unplug the charger from the sweeper. The charging circuit has been set up 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 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 contains a transformer and so it is highly magnetic 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 no picture is seen or if the display is completely blue at startup, adjust the contrast to obtain a clear picture. If the display remains off then the unit should be switched off and recharged. (See section 3. Battery Charging) If the frequency of interest lies in a lower band, then press the BAND DOWN button successively until the desired band is reached. The BAND UP button reverses this action. (Note that for all UP/DOWN button pairs the left hand button decreases and the right hand button increases frequency or width.) The 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 highest possible frequency resolution. The 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. There is an autorepeat function on all of the keypad buttons which activates after the button has been held down for more than 1 second.
fig.3 (model 505NV shown)
The digitized RF level is displayed as a function of frequency. Pressing the ADC SCALE 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 level adjustment on the side of the instrument allows continuous variation so that the full dynamic range of the screen may always be used. The DOT/LINE button toggles the display between the DOT type display and the LINE type in which the digitized points are joined vertically. 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 LINE display mode and depends to some extent 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 4. Finally the DISPLAY INVERT button allows the display to be inverted so that the zero or MATCH line may be placed at either the top or bottom of the screen at the users discretion.
fig. 4 DOT vs. LINE 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 R.F. 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. 5) 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. 5 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 ohm 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. 6)
fig. 6 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. Thus to sweep about an arbitrary frequency, select the appropriate frequency band then move the cursor to the desired center frequency. Press the CW button twice and then use the Sweep Width buttons to adjust the width of the sweep about your desired center frequency.
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 in operation 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.
The bottom row of four keys control these functions. For each key there are two functions. The primary function is shown above the key and the secondary function below. The secondary function provides for the selection of either a window or sweep, and is activated after the primary function has been selected.
ERASE 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 MEM1 (the secondary function of the same key) to be pressed to confirm. Pressing any other key will abort the command.
STORE - brings up the storage location selection display. The user may wish to store the current window or sweep. After pressing STORE the user will press the desired memory number key (MEM1 - 4). Pressing this key once, causes the box around the selection (WINx) to flash three times; then the parameters are saved and the unit returns to real time operation. Any other key pressed while the box is flashing aborts the command. To save the sweep the user must press the same MEM1 -MEM4 key a second time while the WINx selection box is flashing, which will cause the sweep selection box (SWPx) to flash three times after which the sweep data and instrument parameters are saved and the unit returns to real time operation. Again, if any other key is pressed while the box is flashing the command is aborted.
RECALL - brings up the recall selection display. The user may wish to recall a saved window or static sweep (with its associated window parameters). If there is no data saved at the selected location then a message indicating this is displayed. In the same fashion as for STORE the user selects a window (WINx) or a static sweep (SWPx) for recall. If a window is recalled then the unit returns to real time operation and starts sweeping using the recalled instrument setup parameters. If a sweep is recalled then the instrument statically displays that sweep and indicates this condition by displaying MEM in the upper left corner. When the user is finished viewing that sweep then pressing any key will return the sweeper to real time operation using the recalled parameters.
LAST SWEEP - displays the last sweep that was either saved or recalled, 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.
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 10 to 25 C. 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. at (613) 523-7448 in the case of more serious difficulties. We will be glad to help you. Our e-mail address is: morris-instruments@rogers.com
Band Model 405NV Model 505NV Resolution (kHz) 1 165.0-405.0 205.0-505.0 100.0 2 82.5-202.5 102.5-252.5 50.0 3 41.25-101.25 51.25-126.25 25.0 4 20.625-50.625 25.625-63.125 12.5 5 10.313-25.313 12.813-31.563 6.25 6 5.156-12.656 6.406-15.781 3.125 7 2.578-6.328 3.203-7.891 1.5625
All units are covered for one full year against defects in manufacture, or failure under normal use.
Paul Morris 2010-02-02
morris-instruments@rogers.com