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Basically the antenna coupler is an impedance
transformer, transforming the impedance of the
transmitter to the impedance of the transmission
line and antenna system. Referring to Figure
24, coil L1 should match the impedance of the
coaxial cable as closely as possible at the fre-
=
quency of operation. The circuit consisting of
L2, Cl and C2 must tune tothe transmitter fre-
quency. If it is desired to series tune the an-
tenna, the shorting bar between 3 and 4 is opened
and the transmission line connected at these points. For parallel tuning, 3 is shorted to 4 and
the transmission line connected to 1 and 2. Taps are provided on the coil L2 to facilitate match-
ing the transmission line.
Figure 24
Such a unit can be built up from this or other suggested circuits or may be purchased commer-
cially as a completedunit. In any case, feeding folded dipoles, end-fed "Zepps" and similar an-
tenna types will require an antenna coupler or balun coils since the normal output of the DX-100
ig designed for single-ended, unbalanced operation.
LOW PASS FILTERS: The harmonic rejection of the pi netowrk output circuit of the DX-100 is
excellent and will attenuate harmonics considerably when the transmitter is properly grounded
and carefully tuned. However, additional harmonic attenvation may be had with the use of a low-
pass filter between the output of thetransmitter and the feed line or antenna. Such a filter should
be designed to handle the maximum power output of the transmitter and must be operated intoite
nominal impedance.
Needless to say, no attempt has been made here to cover the theory of antennas, as such, since
much has been written on this subject. The possibilities in different antenna types and different
feed systems are many and thefactors mentioned herein only scratch the surface of the subject.
Each operator will need to do bis own investigation into the advantages and disadvantages of the
various systems to determine just which one will best suit his needs. Basic data is available
through the Radio Amateur Handbooks and other technical publications.
Some formulas that should prove helpful are Listed as follows;
1 wave length in space = 300,000 meters
Fre
468
Center fed dipole one-half wave long (length in feet) = =~
me
Folded dipole one-half wave long (length in feet) = 462
Fine
Zepp antenna one-half wave long (length in feet) = 492
"me
REPLACEMENTS
Material supplied with Heathkits has been carefully selected to meet design requirements and
ordinarily will fulfill its function without difficulty. Occasionally improper instrument opera-
tion can be traced to a faulty tube or component. Should inspection reveal the necessity for re-
placement, write to the Heath Company and supply all of the following information:
'A.
Thoroughly identify the part in question by using the part number and description found in
the mamual parts list.
B. Identify the type and model number of kit in which it is used.
C. Mention the order number and date of purchase.
D.
Describe the nature of defect or reason for requesting replacement.
Page 61
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