[ARC5] T-19 Real World Antenna Matching Problem

[Christopher Bowne]

Rather than using the tuner, can you resonate the antenna so it presents a 
nominal 50 ohm load at its feed point?  


I match my T-19 to the antenna using a command set transmitter variable cap in 
series with the coax feed center conductor.  On the DM-33 where the inverted vee 
antenna presents a near 1:1 SWR on the wattmeter (which is of course in the feed 
line downstream of the series variable cap), I typically will see 40 to 50 watts 
output on CW, best location of the roller inductor seems to be at about 30-40 
percent over from the left end.  At frequencies away from the antenna resonant 
frequency, I wll see slightly higher power indications due to reflected power 
adding back into the measurement.  Generally no significant difference is tuning 
to a dummy load or the antenna.

Walt Hutchens in ER once discussed using a matching network consisting of a 
parallel resonant circuit that was tapped about three turns from the grounded 
end for the feed from the transmitter, and at about 6 turns from the ground end 
for the antenna connection.  There was also a nominal 150 to 200 pf cap in 
series with the feed from the transmitter to the coil lower tap point.  The  
variable cap connected to the top of the coil, but nothing else was connected to 
that point.  It basically acts as an auto-transformer to provide better matching 
of the relatively high 50 ohm impedance of a typical coax fed antenna to the 
command set, the link coupling of which was designed to work into very low 
impedance short aircraft antennas with lots of capacitive reactance.  I built 
one using an old Eico 720 pi net coil and a command set variable and it worked 
quite well.  It also provides harmonic reduction.  Another idea I tried that 
worked fairly well was using a 4 to 1 balun as an impedance matching 
transformer, with the antenna on the high side and the T19 on the low side, I 
think I also kept the 200 pf in series with the T-19 feed in that setup.


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