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TADD-1 Assembly and Operation Manual
Six Channel RF Distribution Amplifier
Revised: 5 April 2014
©2005-14 Tucson Amateur Packet Radio Corporation
NOTE: This is an update to the 2007 version of the manual that collects and hopefully corrects some
additional information (including the change from the MAX477 to the AD8055 amplifier chip), and
also provides some new performance information.
The TADD-1 is a six channel RF distribution amplifier. Its primary purpose is to allow one frequency source
(typically a frequency standard) to drive several loads (typically the "external reference" input of frequency
counters or other test equipment) with high isolation. The input frequency can range from 500 kHz to 30
MHz.
While the signal from a frequency standard is normally in the range of 0 to +13 dBm, an adjustable gain
control allows the TADD-1 to be used with a wide range of input signal levels. The maximum output signal
is approximately +12.7 dBm into 50 ohms (2.75 volts peak-to-peak, or 0.97 volt RMS). Maximum output
voltage into a high impedance load is slightly higher. A jumper allows the input signal to be terminated in 50
ohms, or to operate at high impedance (approximately 47 kohms).
Each RF input and output on the TADD-1 is transformer coupled to minimize the possibility of ground loops.
In addition, the connectors are capacitively coupled to ground to further improve isolation (and allow
operation with signals riding on DC bias).
The TADD-1 includes a fused and reverse-polarity protected 9 volt regulator. The supply voltage can range
from 11.5 to 24 volts. Current drain will depend on the output loads, but is typically in the range of 60 to 150
milliamps.
See the "Performance" section for further details.
Introduction
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Table of Contents
Summary of Contents for Tucson TADD-1
- Page 1 While the signal from a frequency standard is normally in the range of 0 to +13 dBm, an adjustable gain control allows the TADD-1 to be used with a wide range of input signal levels. The maximum output signal is approximately +12.7 dBm into 50 ohms (2.75 volts peak-to-peak, or 0.97 volt RMS). Maximum output voltage into a high impedance load is slightly higher.
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Page 2: Circuit Description
Trimmer R13 adjusts the gain of IC1. The gain of a non-inverting op amp is equal to 1+Rb/Ra. In the TADD-1, Ra is R10 (220) plus R13 (0 to 2.5 kohm) and Rb is R11 (2.7 kohm). Therefore, the gain ranges from about 2 (when R13 is set to 2.5 kohm) to about 13 (when R13 is set to 0 ohms). - Page 3 to break into parasitic oscillations. R9 provides a low impedance load at the beginning of the "serpentine" and helps to stabilize IC1. It also provides a load for the bandpass filter if that is used. C12 prevents the DC bias from being grounded through the resistor. The 100 ohm resistors at the input to each of IC2 through IC7 decouple the amplifier from the long traces and are primarily responsible for stabilizing the system.
- Page 4 OPTIONAL BANDPASS FILTER NOTE: We do not recommend using the filter unless it is required by the application. Any tuned circuit will produce phase shifts that vary with temperature, and this creates an additional source of instability. Also note that the earlier version of this document had some erroneous information about component values and toroid winding.
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Page 5: Typical Performance
TYPICAL PERFORMANCE... -
Page 6: Phase Noise
PHASE NOISE This plot shows the residual phase noise of TADD-1 units. The blue trace is of a unit built with the MAX477 chips, and the magenta trace is a unit built with the AD8055. REVERSE ISOLATION Isolation from an output channel to the input, and from output-to-output is typically greater than 80dB at 5... - Page 7 PHASE DELAY ACROSS CHANNELS This plot overlays the phase delay at 5 and 10 MHz of each of the six channels in a unit built without the bandpass filter. Channels 1 through 3 form a tight group with almost identical phase through the amplifier. Channels 4 through 6 show slightly higher delay (about 0.75 degrees at 5 MHz;...
- Page 8 Maximum output level into high impedance: 5.12V peak-peak Harmonics* Source (+6.7dBm) Minimum Gain Maximum Gain Second Harmonic Third Harmonic Fourth Harmonic * This table is suspect because the gradually increasing gain curve of the TADD-1 through 40MHz will amplify the source harmonics more than the fundamental.
- Page 9 All components are mounted on the top of the PC board. If you plan to mount the TADD-1 using the four corner holes, now is a good time to use the PC board as a template for marking the mounting holes in your enclosure.
- Page 10 Parts Inventory Value Part 0.001uF C5, C6, C7, C8, C18, C19, C33, C34 0.01uF C11, C13, C14, C25, C26, C37, C38 C1, C2, C3, C4, C9, C10, C12, C15, C16, C17, C20, C21, 0.1uF C22, C29, C30, C35, C36, C41 0.33uF C42, C43, C44 10uF...
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Page 11: Resistor Installation
Resistor Installation Procedure Install a 1 ohm resistor at R27. Solder and clip 2 leads. Install a 51 ohm resistor at R5, R7, R18, R19, R21, R25, R26 Solder and clip 14 leads. R12 provides a termination for the RF input. You have three configuration options: (a) Do not install the terminator (which will require using an external termination on the RF input cable);... -
Page 12: Diode Installation
Diode Installation Diodes are polarity sensitive devices. The cathode end of the diode is banded and corresponds to the banded silk-screen legend on the PC board. If you have never worked with these devices, take a look at the photograph showing the banded ends. Procedure Install a SA15A TVS diode at D1. -
Page 13: Capacitor Installation
Capacitor Installation Procedure Install a 0.001 uF (102) capacitor at C5, C6, C7, C8, C18, C19, C33, C34 Solder and clip 16 leads. Install a 0.01 uF (103) capacitor at C11, C13, C14, C25, C26, C37, C38 Solder and clip 14 leads. Install a 0.1 uF (102) capacitor at C1, C2, C3, C4, C9, C10, C12, C15, C16, C17, C20, C21, C22, C29, C30, C35, C36, C41 Solder and clip 36 leads. -
Page 14: Transformer Installation
Transformer Installation The small dot, or the notch in the transformer body, is on the end with pins 1 and 6. Make sure the notch or dot on the component matches the notch on the silkscreen! Procedure Install a T1-1X65 transformer at T1, T2, T3, T4, T5, T6, T7. Solder and clip 42 leads. - Page 15 Initial Test -- 1 Preliminaries Errors take two forms, the kind that damage components and the kind that don't. Neither is desirable, but the type that damages components will require you to find a replacement part. Before connecting the board for the first time, check the following: Procedure Polarity of the electrolytic capacitor.
- Page 16 Initial Test -- 2 Procedure Place the ground lead of your voltmeter on the anode (opposite the banded end) of D1. This is ground reference for all measurements. Apply 13.8V power to JP5. Measure the voltage on the 9V bus by connecting the other lead of the meter to the cathode of D1.
- Page 17 Optional Bandpass Filter Installation Mounting points are provided on the circuit board for a bandpass filter that can be used to improve the waveform of the input signal. This may be useful, for example, if your frequency standard has a square wave output and you would like to distribute sine wave signals.
- Page 18 Board Check This completes assembly of the TADD-1. At this point, components, their location, and proper orientation should be double-checked. Soldering must be carefully inspected, preferably with a lit magnifier. If there are any suspicious solder connections, reflow the solder and check the result. Do this until you are satisfied that the board is OK.
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