HP 415E SWR Meter
© Brooke Clarke,
Front of 2709A10766
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 size.
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
when the needle is over "2" on the expanded scale. If you over
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 CHARGE).
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 ground.
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
415 is used with a sweeper this control should be set fully CCW to
the BW to allow for signal variations as the sweep progresses.
the amplifier output should be used to drive a scope or chart recorder
instead of the recorder output since the latter has a
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, 2, 4, 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 readng noise and 415E has a Full Scale reading.
The Gain & Vernier controls will bring the needle to Full Scale
an input of more then 0.12 Volts up to more than 5 Volts.
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
I used the 415E for making microwave Smith Chart plots
with a slotted line and for making attenuation and/or gain measurements
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 Imped 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 meter is.
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.
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
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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