Note
73, Nov 1977. (Tufts Radio Catalog ad, unnumbered pages)
The Swan MMBX "Matchbox" is a compact R.F. impedance matching device (commonly referred to as an antenna tuner or coupler). It is designed for both fixed and mobile amateur and commercial radio systems. Its primary purpose is to match the antenna's impedance to the output impedance of a transmitter, ensuring efficient power transfer and a low Voltage Standing Wave Ratio (VSWR). The unit is bi-directional, meaning it can be used to "step up" or "step down" impedance depending on how the transmitter and antenna are connected to its ports.
Features
– Toroidal Transformer Design: Utilizes a toroidally wound transformer for efficient impedance transformation.
– Seven-Position Selector: Features a rotary switch that allows users to select between different transformer taps to find the best impedance match.
– Bi-Directional Matching:
Standard Mode (Step-Down): Connects the transmitter to the "XMIT" port to match antennas with lower impedance than the transmitter.
Reverse Mode (Step-Up): Connects the transmitter to the "ANT" port to match antennas with higher impedance than the transmitter.
– Rugged Construction: Housed in a durable metal box with integrated mounting flanges for easy installation in vehicles or stations.
– Wide Frequency Range: Capable of operating across a broad spectrum of the HF (High Frequency) bands.
Specifications
– Frequency Range: 2 MHz to 80 MHz
– Power Rating: Up to 500 Watts R.F. power
– Connectors… Two (2) SO-239 UHF co-axial connectors (XMIT and ANT)
– Matching Ratios: Selectable via 7-position switch (1:1 up to 1:6.3)
| Dimensions | 3" L x 2-1/2" W x 2-1/8" H |
– Circuit Type: Tapped toroidal transformer
– Impedance Ratios (at 50 Ohms Reference)
Step-Down Ratios (XMIT to ANT):
50Ω (1:1)
38Ω (1.3:1)
28Ω (1.8:1)
19Ω (2.6:1)
12Ω (4.2:1)
10Ω (5:1)
8Ω (6.3:1)
Step-Up Ratios (ANT to XMIT): These are the inverse of the above, used when reversing the unit to match high-impedance antennas (e.g., 50Ω to 300Ω).
Operating Note
CRITICAL: Do not move the rotary switch while the transmitter is keyed. This can cause arcing across the switch contacts and permanently damage the unit. Always adjust the switch during receive.
