rf - Free and Open Source Software

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5/9+ reports to the Eastern half of the
U. S. A., 5/8 reports to Germany etc. Conelusion:
The results shown ab ove are not
precise, nor can they be expected to be
precise. There are too many unknown factors
entering the electrical picture, such as
those which required a shortening of the
feed line. in this example, to somewhat less
than a half wave length. But the bridge
showed us the overall picture and suggested
what was required to be done. The on-the-air
results show that it was giving us a good
picture and a result that was very satisfactory
for my friend's needs.
Why not construct an rf bridge and check
you own antenna system? I suggest it will
payoff and be very informative to you,
showing you what your antenna system
looks like electrically and what to do to
bring your whole system to the resonant
frequency you wish to obtain. . .. VE3CEA
Short Cut to Matching
In building an inexpensive, short space,
two element beam for twenty meters, considerable
difficulty was met in obtaining an
acceptable match from the feed line ( RG-58)
to the center coil of the driven element (link
coupling met ho d...ref. Radio Amateur Handbook,
three element beam for twenty meters).
The initial set-up is shown in Fig. l.
ItG~8
fEED
I §3
LINK COUPLE
OIttvEIt
43 TUItNS
DIRECTOR
4 2 TURNS
F ig. 1. L ink c o upli ng as in the original set up.
After initial tweaking, the best VSWR obtained
was a disappointing 3: I. Varying factors
such as changing the number of turns,
spacing of turns and antenna height resulted
only in increasing the VSWR.
Further thought and many aggravating
trips up and down the ladder resulted in a decision
to use an old approach to the problem
by going to the " Gamma Match" method in
Fig. 2.
The Gamma match was accomplished by:
I. Tying the shield of the RG-58 coax to the
center turn 1/2 1 o f the 43 turn center coil of
the driven element and,
2. Connect ing the coax center conductor to
the 31 st turn on the coil. This gave a starting
point of 5:1 VSWR.
With a little hint from the handbook, a
ItG 58 coax
Fig. 3 .
""
140uu r
'--I." I
I GA"' '''A "'ATCHI
Hg. 2 . Using the ever popular " G a m m a
Match:'
140 picofarad capacitor was dug out of the
"junk box" and inserted in the coax center
conductor line...going to the tap on the coil
as in Fig. 3.
4 3 TUR N
CENTEIt COil
DR I"'E N
ElE"'ENT
OI RECTOIt
itEr ONLY
Adding capacitor for best match.
The capacitor was set at several different
positions and minimum of 3:I was obtained
at a max capacity setting. This appeared to
be little headway for all the trouble, but past
experience pointed to the possibility that the
antenna height was a remaining variable not
yet changed. A little experimentation with
antenna height (more trips to roof) showed
best results with it raised just five feet.
A check of the VSWR bridge showed a
rewarding 1.5: I for all our efforts to obtain
a match.
Bernard Oliver, K6CZJ
DX QUIZ
OK, you D'X'ers, how are you on
fixes? Score five points for each correct
fix . \Ve are in Africa this trip.
Congo
Republic of
Republic
Guinea
Republic of th e Uganda
Congo
Rwanda
Mali
Niger
Central African Tanzania
Republic
Gabon
Senegal
Spanish
Cabindi
Guinea
Fernando
Mauritania
Poo
Lesotho
Zanzibar
Mozambique
Chad
Botswana
pre­
pre-
You'll find the answers on page 50 No
fair peeking until you've committed yourself
to good guesses.
38 73 MAGAZINE