Palstar BT1500A Owner's manual - page 6
WARNING: Balanced antennas will produce high
RF voltages at the output post connectors. RF
burns may result if touched during transmission.
6 Installation
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Unpacking
Carefully remove the BT1500A from the shipping car-
ton and inspect it for signs of damage. If any damage is
apparent, notify the transportation carrier or dealer im-
mediately.
We recommend keeping the packing car-
ton for moving, storing or reshipping the tuner to
us for repair if required.
Location
Select a location for the BT1500A that allows the con-
nectors to be free from any possible contact with peo-
ple, pets or objects during operation, and with unre-
stricted air flow for cooling.
Installation Procedures
Connect a coax cable from your transmitter to the RF
INPUT connector on the rear panel. Keep the cable as
short as possible. If you use a linear amplifier, connect
your transmitter to the linear amplifier input and the lin-
ear amplifier output to the BT1500A.
Connect your balanced antenna feedline to the upper
white Nylon66
TM
BALANCED OUTPUT posts on the
back panel
.
Understanding Your Tuner 15
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two equal series portions, one in each leg of the network. The shunt capacitor has
the same value in both versions of the L-network.
Unlike the single-ended L-network, the legs of the balanced L-network are both
above ground potential. Hence, both the input and antenna sides of the network
are balanced. In order to accommodate the single-ended transmission line from
the transmitter, the tuner places a 1:1 choke (current) balun between the input
side of the network and the transmitter coax connector. The balun converts the
unbalanced input from the transmitter to a balanced condition for the network.
As well, it suppresses currents that might otherwise appear on the braid of the
transmitter cable.
Limitations:
Every antenna tuner, no matter what the type, has limits to the
range of impedances that it will match to the 50 Ohm input. The balanced L-
network is no exception. Understanding those limitations will help you to effect
a match on every band.
The impedance presented to the tuner antenna terminals is usually expressed as a
series combination of resistance and reactance, that is, R +/- jX Ohms. The L-
network that places its shunt capacitor on the antenna side is normally an up-
converter. The limiting lower end impedance is in the vicinity of 60 to 100 Ohms
resistive for a 50 Ohm input. The upper limit of impedance that the network will
match is a complex function of frequency, the component values, and the amount
of reactance that is part of the impedance at the tuner terminals. For most of the
HF Amateur bands, the upper impedance limit of the balanced L-network in the
Palstar BT1500A tuner is about 2500 +/- j2500 Ohms. This upper limit descends
slowly with rising frequency so that at 30 MHz the upper limit is about 400 +/-
j400 Ohms. The decrease in range results from the unavoidable minimum ca-
pacitance of the output variable capacitor.
The impedance presented to the antenna terminals may be any value of R and any
value of X. For a given R component, the tuner will require a certain setting of
the coil and also the capacitor. If there is reactance at the antenna terminals, then
the network requires a lower value of C if the reactance is capacitive, and a
higher value of C if the reactance is inductive. The network compensates for the
reactance by increasing or reducing the capacitive reactance required for a purely
resistive load with only small changes in the required inductance. The amount of
compensation available is a function of the maximum and minimum values of
shunt capacitance and the resulting reactance of this component. With finite
components, the range of reactance for which the network can compensate is
always limited.
As well, every matching network incurs losses within the network, mostly as a
function of the Q of the inductor and the ratio of the antenna terminal impedance
to the input impedance. For the balanced L-network with a shunt output capaci-
tor, the higher the impedance to be matched, the higher the losses. The losses
will be lower if the reactance at the antenna terminals is purely resistive and