Equipment information:

Johnson Viking Matchbox Antenna Coupler
Model: Viking Matchbox
Category: Radio, Communication
Group: Antenna Coupler
                                    The Johnson Matchbox is an antenna coupler designed for
matching antenna and transmission line impedances to a 52
ohm impedance within the amateur bands from 3.5 to 30
megacycles. The Matchbox also provides band switching and
transfer of the coupler from transmitter to receiver and in
addition mutes the receiver and grounds the receiver antenna
terminals during transmission.

The Matchbox is capable of matching the 52 ohm coaxial
output of a transmitter into loads ranging from
approximately 50 ohms to 1200 ohms for balanced lines, and
50 to 2000 ohms for unbalanced lines. Large amounts of
reactance can be compensated for by the coupler, the amount
depending upon the frequency, line or antenna resistance.
The Matchbox, or any coupler, installed at the transmitter
end of the transmission line cannot correct the standing
wave on the transmission line. This standing wave is a
matter of impedance match between the antenna and the
transmission line and may be eliminated in various ways
described in antenna and transmission line literature.

The coupler circuit consists of a parallel resonant network
utilizing an inductor with a coaxial wound coupling link, a
dual tuning capacitor, and a dual differential matching
capacitor as shown in Figure 1. Impedance matching for
either balanced or unbalanced transmission lines and
antennas is accomplished by the front panel controls of the
two dual capacitors without resorting to the customary coil
taps or link adjustments. Adjustment of the Matchbox must be
accomplished by the use of a directional coupler, such as
Johnson no. 250-37,

The Matchbox tuned circuit provides additional harmonic
attenuation of the transmitter output by at least 15 db. The
52 ohm coaxial line between the transmitter and coupler
provides for the insertion of a low pass (TV1) filter such
as the Johnson 250-20 for improved harmonic attenuation. A
terminal is provided on the terminal board for the
installation of an R. F. probe for use with an oscilloscope,
modulation indicator

The Kilowatt Matchboxes (part nos. 250-30 and 250-30-3) have
a switching relay system designed for ,ffast make-slow
break" operation allowing the final amplifier plate voltage
to be cut off before the transmitter load is removed. The
time of delay is fixed between . 15 and .25 of a second
which is ample to allow the relay contacts to break without
any arcing,

These manuals are available for the above equipment:

Johnson -- Viking Matchbox -- User Manual
File name: Johnson-5496-Manual-Page-1-Picture
Manual Type: User Manual
Pages: 11
Size: 604.67 Kbytes (619177 Bytes)
Language: english
Manual-ID/Number: 2-0250-023
Quality: Scanned document, all readable.
Upload date:
MD5: 6e0506d16f60b0bc8e6d43dddcbc81c4
ed2kID: 9f49ae9433269e6b49db867d3a0434bb
Downloads: 176 since 01 March 2014
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