| Input Impedance : 50Ω, ac coupled |
| Divide by 16 Prescaler |
| <= 100 MHz to >= 1.3GHz |
| 100 MHz to 1 GHz : <= 20 mV |
| 1 GHz to 1.3 GHz : <= 30 mV |
|  |
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The Tektronix DP 501 Digital Prescaler is designed for use with all TM 500 - TM 5000 series counters.
The DP 501, however, can be used with any counter. The prescaler is connected between the signal
source and the counter input terminal. Maximum input frequency of the DP 501 is 1.3 GHz.
Two operating modes, prescale and direct, are available, In the prescale mode, the DP 501 divides the
input frequency by 16. In the direct mode, the input of the prescaler is connected directly to the
input of the counter. Selection of operating modes is accomplished by a front panel pushbutton or by
the PRESCALE commend sent via the IEEE 488 bus to the microprocessor in a programmable counter.
Communication from the IEEE 488 compatible counter to the DP 501 is accomplished by a one-wire
connection through the rear interface connector.
For certain counters with accessible clocks and time bases, the counters time base signal may be
routed to the DP 501, divided by 16, and returned to the counter. In these cases, the counter
displays the actual input frequency of the DP 501 (some display flicker is present when using the
DC 504A). Where these connections are not possible, the counter reading must be multiplied by 16
to obtain the correct DP 501 input frequency. In the prescale mode and automatic attenuation
circuit provides optimum immunity to input noise.
In the direct mode the input signal to the DP 501 is looped through the input and output terminals
to the counter in a 50 Ω environment.
An interface is provided for operation of the counter, spectrum analyzer, and tracking generator
(or other suitable device) for accurate readout of a selected frequency. This interface is
implemented through the rear interface connector and is useable only with counters having an
arming input.
ELECTRICAL CHARACTERISTICS
| Characteristics | Performance Requirements | Supplemental Information |
| Prescale mode |
| Input |
| Frequency Range | <= 100 MHz to >= 1.3 GHz | |
| Sensitivity |
| 100 MHz to 1 GHz | <= 20 mV rms (-21 dBm) |
| 1 GHz to 1.3 GHz | <= 30 mV rms (-17 dBm) |
| Impedance | | 50 Ω, ac coupled; Vswr <= 2.2 : 1 |
| Output | | From 50 Ω source |
| Amplitude |
| Into 50 Ω | >= 200 mV, peak-to-peak |
| Unterminated | | 2 X terminated value |
| Direct Mode | Input connected directly to output |
| Input |
| Frequency Range | | Dc to > 350 MHz |
| Impedance | Loop through characteristic impedance is 50 Ω;
nonterminated capacitance approximately 20 pF (no connection to output). |
Maximum Safe
Input Voltage | | <= 42 V, peak | ,/tr>
| Output | Less than 1 dB insertion loss up to 350 MHz (with power module) | Direct connection to INPUT. |
| Mode Switch and Mode Indicators | | Powers up in direct mode. Pressing
switch alternates between direct and prescaled output.
Prescale indicator is lit when in prescale mode.
Direct indicator is lit when in direct mode. |
| Overload Protection |
| Prescale | | Input disconnects when signal exceeds a continuous
overload (≈ 500 ms) condition greater than ≈ +20 dBm ± 5 dB. Overload indicator turns on and prescale indicator turns off, DP 501 sends PRESCALE OFF signal to counter.
After the overload is removed the instrument is reset by pressing the mode switch once or by sending a PRESCALE OFF command followed by a PRESCALE ON command.
| | Damage Level |
| Prescale | | Input may be damaged if signal level exceeds + 25 dBm. |
| Direct | | 42 V peak maximum. Maximum current is 250 mA. |
| Input Attenuation | | Automatic: up to 40 dB range. |
| Low Level Indicator | | Lights when input level is less than specified under Sensitivity yet at a level resulting in correct counting. |
| Tracking Generator Compatability | | Outputs will drive two standard TTL loads. Inputs represent two standard TTL loads. Requires arming input to associated counter. |
| Power Consumption | | 19 VA @ 120 V. |
above excerpts from DP 501 DIGITAL PRESCALER Instruction Manual
Connect the OUTPUT bnc connector to the input of the counter using a 50 Ω coaxial cable.
A 50 Ω termination may be used at the counter input. If a termination is used, the output of
the DP 501 will be terminated in both prescale and direct modes. Connect the signal source to the
input connector using a 50 Ω cable.
A FET probe such as the Tektronix P6201 can be used to input signals to the DP 501. The DP 501 may be
operated in either the prescale or direct mode using the FET probe. A 50 Ω environment for the
DP 501 output connections must be maintained in the direct mode to insure proper FET probe
termination.
When the input signal exceeds the maximum power level (approximately 20 dBm) the OVERLOAD light
illuminates and the input circuit opens. The overload disconnect capability does not operate in the
direct mode. The OVERLOAD light remains illuminated until the overload is removed (input signal
lowered to 100 mV, -7 dBm) and the RESET button is pressed or PRE ON command is sent over the GPIB
through a programmable counter. If the RESET button is pressed with the overload at the input,
the unit cycles to prescale and immediately to overload. If the DP 501 is turned on with the input
overloaded the DP 501 switches to the direct mode. If the button is pushed with the overload present
at the input the instrument goes into the overload mode. If the input frequency is high enough
(about 1 GHz) the DP 501 remains in the overload condition (whether the RESET button is pressed
or not) until the input overload is removed. Approximately 500 ms is required for the overload
circuitry to recover after the overload is removed.
above excerpt from DP 501 DIGITAL PRESCALER Instruction Manual
| Knobs |
| 1-1 | 366-1559-09 | Push Button:Ivory Gray,0.18 SQ x 0.43 H |
| Pots/Switches |
| S1121 | 260-1554-00 | Switch, Push:1 Button, 2 Pole, AC Coupling (Tektronix) |
| Microcircuits |
| U4151 | 155-0280-00 | Microcircuit,Digital:High Frequency Prescaler |
|
