HP 415E SWR Meter
© Brooke Clarke,
N6GCE 2003 - 2021
& Front of 2709A10766
Controls & Connectors
Back in the days of tube type equipment there was
an HP 415 SWR (Standing Wave Ratio) meter and there have been a
number of versions ending with the latest "E" model. This
instrument is a very narrow band 1 kHz attenuator and amplifier
and a precision rectifier. The relative amplitude of the 1
kHz signal can be read to scale ticks of 0.05 dB and interpolated
to 0.01 dB. There is also a scale for the original purpose
of reading SWR.
Note that if Full Scale is set on the "zero" range then when
reading down 10 dB on the 60 range you are reading a signal that's
down 70 dB.
The 415E is 6" high and 7 3/4" wide. This does not appear to
be a standard Rack Mount instrument
Controls & Connectors
The analog meter movement is a mirrored type where you look for
the reflection of your eye's pupil bisected by the needle and thus
eliminate parallax in the measurement. There is also a
mechanical meter zero pot. The correct way to use this is to
turn the pot in one direction so that the needle moves up scale
and and then comes back down scale and you stop turning when the
needle is over "2" on the expanded scale. If you over shoot,
do not turn the screw in the opposite direction, but rather,
continue turning and approach the zero position from up scale.
The POWER switch has positions for OFF, ON, (and for instruments
with the optional internal battery supply: Battery: ON, TEST and
The INPUT switch has positions for XTAL IMPED: HIGH, LOW or BIASED
(+1.3 VDC on the center contact with 12.6 mA of current
capability) and BOLOMETER: 4.5 mA or 8.7 mA. To match a wide
variety of input sources. The HIGH position is also used for
signal sources that are not from a detector or power sensor.
The INPUT is a BNC(f) connector with the shell 50 Ohms above
The FREQ adjust pot allows the center frequency of the 415 to be
set to match the frequency of the source generator.
The BANDWIDTH control adjusts the width of the passband and
therefore also controls the signal/noise ratio for faint input
signals. If the 415 is used with a sweeper this control
should be set fully CCW to increase the BW to allow for signal
variations as the sweep progresses. Also the amplifier
output should be used to drive a scope or chart recorder instead
of the recorder output since the latter has a low pass filter that
limits it's bandwidth.
The RANGE-DB control has an outer knob with positions for 0, 10,
20, 30, 40, 50, and 60 dB a very large dynamic range, and an inner
EXPAND knob with positions of: NORM, 0,
6 and 8 dB. By using the expanded
(red) scale positions you can read amplitude to 0.01 dB over the
full 60 dB range. On the 0-NORM range you can bring the
needle to full scale with an input signal between 0.120 VAC and
Comparing the 34401 DVM with the 415E shows that the noise
bandwidth of the 34401 limits its use:
|FS 10 range
|FS 20 range
|FS 30 range
|FS 40 range
|FS 50 range
|FS 60 range
|can not get signal this low
* 34401 is reading noise and 415E has a Full Scale reading.
The Gain & Vernier controls will bring the needle to Full
Scale with an input of more then 0.12 Volts up to more than 5
Note that the 415 reads 10*LOG(voltage ratio), this is called
"Square Law" and when the 415 is fed from a microwave detector
that has a low level signal at it's input the 415 will read the
same as a power meter becasue the detector has a "square law"
response. If you were trying to measure the dB difference in
two voltages you would normally use dB = 20 * LOG(voltage ratio),
but that's not what the 415 was designed to do.
On the rear panel there is a BNC(f) RECORDER output that has a 0
to 1 VDC signal to drive a chart recorder and a pair of banana
jacks on the standard 3/4" centers that has the amplified 1 kHz
signal. There is a covered hole that can be used to change
the input connector from the front panel tothe rear panel.
I used the 415E for making microwave Smith Chart
plots in conjunction with a slotted line and for making
attenuation and/or gain measurements using a crystal detector.
The 415E is very good for both of these measurements and
probably is the highest dynamic range scalar measuring instrument
around. It would also work fine for making optical
measurements with an optical to DC converter.
I'm considering using it to measure the output of magnetic field
sensors, where it's narrow noise bandwidth may greatly extend the
sensitivity of the sensor.
When a 5.04 k Ohm resistor is connected to the input and the range
set for Xtal Impedance High and both the gain and vernier knobs
are turned fully clockwise the meter reads 6.5 dB below full
scale. The manual addresses the theoretical KTBR noise of a
5 k Ohm resistor and how the 4 dB noise figure of the 415E will
show up in the measurement. This shows how sensitive the
Typical uses for the 15E are: SWR measurements using a slotted
line, Power measurements using a bolometer, Relative power
measurements using a crystal detector. In all cases the
source must have a 1 kHz square wave modulation.
Electronic ratio meter, Nicholas
L Pappas, HP
Inc, App: 1954-07-23, - by measuring relative to a reference
signal variations in the signal generator amplitude are
automatically cancelled. This probably was the HP 416 Ratio
TM 9-4931-321-34P Direct Support and General Support Maintenance
Repair Parts and Special Tools Lists Standing Wave Ratio Meter,
Hewlett-Packard model Y10-415E (NSN 6625-00-815-6273)
TB 9-4931-321-35 Calibration
Procedure for Standing Wave Ratio meter Hewlett-Packard model 415E
and PRD model 277D
00415-90009 SWR Meter 415E covers serial prefix 0990A- and with
Appendix II Manual changes covers 719-, 545- and 530-. The
Yellow Manual Changes sheets dated 3 February 1986 have changes
for: 1143A, 1709A, 1750A, 2031A, 2433A, 2507A, 2547A and 2509A.
But 2709A is too new for these changes.
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Page created 28 March 2003.