Timewave DM-1 User manual
DM-1 Deviation Meter
Operating Manual
August 1997
Timewave Technology Inc.
1025 Selby Ave.
St. Paul, MN 55104
http://www.timewave.com
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Reproduction, dissemination, or use of information contained in this manual for purposes
other than operation and/or maintenance of product is prohibited without written authorization
from Timewave Technology Inc.
© 1997 by Timewave Technology Inc. All rights reserved.
Copyright Notice
This document and all software or firmware designed by Timewave Technology Inc. is copy-
righted and may not be copied or altered in any way without prior written consent from
Timewave Technology Inc.
DM-1 Operating Manual / iii
Table of Contents
Introduction ...............................................................................................1
Features.................................................................................................................... 1
Specifications............................................................................................................ 2
Operation ...................................................................................................3
Battery Installation .................................................................................................... 3
To Turn On ............................................................................................................... 3
Selecting a Deviation Range .................................................................................... 3
Connections.............................................................................................................. 4
Measuring Deviation ................................................................................................. 4
Calibration .................................................................................................5
Circuit Description ....................................................................................6
Parts Pictorial ............................................................................................8
Schematic Diagram ...................................................................................9
If You Need to Call for Help.....................................................................10
Warranty...................................................................................................11
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DM-1 Operating Manual / 1
Introduction
Congratulations on your purchase of the DM-1 Deviation Meter. The DM-1 was designed to
permit easy measurement and adjustment of the deviation of FM transmitters operating in the
140, 220 or 440 MHz. amateur bands.
EventhoughtheDM-1’sfunctionsarestraightforwardandeasytouse,pleasereadthroughthis
manual.Thefollowingpagescontainsomeexcellentnotesandtipstohelpyougetthemostfrom
your Deviation Meter.
Features
• Fixed-tuned to ensure stability and to eliminate the need for tuning.
• Dual ranges allowing sufficient resolution for accurate measurement of
voice, data, DTMF and subaudible modulation.
• External digital or analog meter expandability for increased resolution.
• A low-level de-emphasized audio output for monitoring audio quality
through an external amplifier.
• Compact and battery-powered for convenient use anywhere.
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Specification
Frequencies: 147.9 MHz., 222.1 MHz., 444.1
MHz.
Deviation Ranges: ± 1 kHz.; ± 5 kHz. full scale
Readout: 10 segment LED bar and
provisions for external meter
Deviation resolution (LED): 50 Hz. on 1 kHz. range;
250 Hz. on 5 kHz. range
(Greater with external meter)
Accuracy: ± 5% of full scale
Audio Freq. Response: ± 2 dB. from 10 Hz. to 300 Hz.
(1 kHz. range); ± 3 dB. from
10 Hz. to 5000 Hz. (5 kHz. range)
Sensitivity (WHIP input): < 100 mV.
Operatingpower (through): 100 mW. - 100 Watts
SWR: <1.3
Audiode-emphasis: 750 us.
Battery: Standard 9 Volt alkaline
Battery current: 60 mA. typical
Battery life: 6-8 hours typical
Size: 61/8” W x 43/4”L x 13/8”H
Weight: 1 lb.
DM-1 Operating Manual / 3
Operation
Battery installation
TurntheDM-1Deviation Meteroffbefore installing abattery.Two screws(one
on each side of the DM-1) allow access to the battery compartment. Use one
standard 9-volt alkaline battery.
Replacethe screwsonthesidesoftheDeviationMeterandbatteryinstallationis
complete. Replace batteries following the same procedure.
NOTE:
When the battery voltage drops below approximately 5.5 Volts, the DM-1 is
automatically disabled to prevent erroneous readings.
To turn on
Press the ON/OFF button to turn the Deviation Meter on.
Selecting a deviation range
Select the deviation range. When making measurements on sub-audible tones,
use the ± 1 kHz. range. Otherwise, use the ± 5 kHz. range.
NOTE:
When the ± 1 kHz. range is selected, frequencies above 300 Hz. are rolled off to
avoid errors due to high frequency noise. Therefore, deviation readings with
modulating frequencies above 300 Hz. must not be made on this range.
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Connections
Connect your transmitter to the INPUT coaxial connector on the DM-1, and the antenna to the
OUTPUT connector, using adaptors if necessary. (If it is more convenient, you can swap the
input and output cables.) Insertion loss and SWR are low enough that the DM-1 may be left in
the line if desired.
Alternatively, a short piece of #12 AWG wire (or smaller wire soldered to a standard pin plug)
may be used as a pickup antenna by plugging it into the WHIP pin jack on the rear of the DM-
1. In most cases, this will provide enough signal from a nearby transmitter such as a handheld
transceiver in close proximity.
Measuring Deviation
Set the transmitter frequency to 147.9, 222.1 or 444.1 MHz. Key the transmitter, apply
modulation, and read the deviation from the LED bar using the scale corresponding to the
selected range.
If you wish, you can connect a voltmeter to the METER pin jacks on the rear panel to give an
analogreadoutwithbetterresolutionthantheLEDbarcanprovide.Afullscalereading(1 kHz.
or 5 kHz., depending on the selected range) produces 1 Volt at these jacks.
If you have a spare ammeter (200 uA. to 1 mA. full scale), you can use it instead with an
appropriateseries resistor. (Depending onthe meter,you mayneed toadjust R45.If youdo so,
you may want to mark the factory setting first.) Make sure the meter you use has a linear
response.
NOTES:
1) When two adjacent segments of the LED bar are lighted, the deviation is approximately
halfway between the values represented by those two bars.
2) Sometimesatransient,forexamplefromkeyingthetransmitter,may“peg”theLEDbaror
external meter. Make sure the DM-1 has had a couple of seconds to recover from the
transient before reading deviation.
3) Random indications of deviation may occur with no signal, or a signal of the wrong
frequency, applied. Turn the unit off to conserve the battery when not actually making a
measurement.
DM-1 Operating Manual / 5
Calibration
NOTE:
The DM-1 was calibrated at the factory. Recalibration should not be necessary unless repairs
are made.
1) Remove the cover.
2) Turn the DM-1 on.
3) Using a frequency counter and a 10:1 scope probe, measure the frequency at
test point TP. Adjust C28 with a non-metallic tool for a frequency of 74.000
MHz. Make sure the frequency is within +/- 1kHz. (73.999 - 74.001).
Thenextstepsrequirethe use ofacalibratedfrequency-modulated signal sourceofeither
100 kHz., 74.1 MHz., or one of the three frequencies printed on the front of the DM-1.
4) Connect the signal source to either the INPUT or OUTPUT connector on the
DM-1. Adjust the output of the signal source for at least 100 mV., and the
deviation for +/- 5 kHz. at a modulating frequency of either 400 Hz. or 1 kHz.
5) Preset trimpot R6 fully counter-clockwise. The LED bar should have segments
lighted near the center of the bar. Adjust trimpot R6 clockwise until the right
two segments are lighted. (They may be flickering slightly.) Adjust the trimpot
further clockwise until the right-most segment is lighted, and the segment next
to it just goes out and stays out (stops flickering).
6) Connect a digital voltmeter between the METER jacks on the back. Adjust R45
for a reading of 1.0 Volt.
7) Disconnect the test equipment and replace the cover.
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Circuit Description
Radio frequency enters the DM-1 either directly through the WHIP input J1 or the stripline
coupler between coaxial connectors J2 and J3. The stripline coupler provides 20 - 30 dB. of
attenuationto theinputsignal, dependingonfrequency. Thesignalis limitedbydiodes D1and
D2 to prevent damage to mosfet mixer Q1, with the remaining voltage getting dropped across
R30.
Q1mixestheinputsignalwith 74 MHz.fromcrystaloscillatorQ3 and bufferQ4,producingan
intermediate frequency (IF) of 100 kHz. L1 and C3 resonate at this frequency, and L2, R3 and
C4provideadditionalfilteringofanytheinputandlocaloscillatorsignalsappearingatthedrain
ofQ1. Q2 isbiased totranslate thelow level100 kHz.output ofQ1 toa TTL-compatiblesignal
to drive U1.
U1 is a retriggerable one-shot with Schmitt-trigger inputs and an output pulse width of
approximately5microseconds,asdeterminedbyR6,R7andC7.Sincethispulsewidthisfixed,
thedutycycleof U1’s outputisdetermined by theinstantaneous IF frequency.Sincethe output
levels of U1 are fixed TTL levels, U1 acts as a limiter to remove amplitude variations from the
IF.ChangesintheIFduetofrequencymodulationcausechangesinthedutycycleofthissquare
wave,sothatitsaveragevalueisalinearrepresentationofthemodulation.AdjustingR6changes
the quiescent duty cycle enough to allow calibration.
ActivelowpassfiltersU2AandU2BremovetheIF,leavingtheoriginalmodulation.U2isbiased
tohalfthebattery voltagebyR17, R20andC14. R9andC10 attenuatetheoutput of U1enough
to prevent it from overloading U2A at low battery voltages.
U4A is configured as a peak detector. The response of the display is determined by the time
constant of R58 and C35. D7 prevents transients from over-charging C35, which would result
in longer recovery times.
U4Bprovidesthegainrequiredforfull-scalereadings.Whenthe1kHz.rangeisselected,U4B’s
gain is increased by a factor of 5, and low-pass filter U2C cuts off at 300 Hz. to remove high
frequency noise, allowing accurate readings with sub-audible tones.
U2D provides audio for an external monitor amplifier. R28 and C22 provides 750 uS. de-
emphasis.
U5 is configured as a square-wave oscillator driving a charge pump to provide a negative
potential for U4.
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