DRAKE MN2700 Manual de instrucciones - Página 7

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CHAPTER I

INTRODUCTION

4. Match an antenna to a transmitter having

The typical modern transmitter or high-power

amplifier has either a pi-network tank circuit or a

broadband transformer output and will work into

resistive loads of 50 to 75 ohms with Voltage

Standing Wave Ratios (VSWR) of 2:l or less. This

resistive load can only he achieved with a resonant

antenna; thus, for multiband operation, multiple

antennas are required. Space and cost considera-

tions render this solution impractical for most

amateurs. In addition, many singleband antennas

will not maintain less than 2:l VSWR across the en-

tire band. The MN-2700 impedancematching net-

work can:

1. Measure feedline VSWR, then reduce the

VSWR a t the transmitter output to 1:l.

2. Monitor transmitter power output in watts

directly and continuously.

3. Attenuate 2nd harmonic output from a trans-

mitter by 25 to 35 dB; thus i t may eliminate

the need for a low-pass TVI filter.

fixed loading.

5. Give optimum match with multiband

antennas.

6. Precisely match a transmitter to an antenna

across a complete amateur band.

Permit off the air transmitter tuning using a

dummy load.

8. Eliminate the necessity of

retuning the

transmitter when switching from "barefoot"

to linear amplifier operation since the

transmitter always "sees" 50 ohms resistive.

9. Help localize trouble by comparing trans-

mitter output into an antenna and into a dum-

my load.

10. Allow antenna comparisons with the use of

the internal antenna switch.

11. Permit the use of open-wire feedline antenna

systems, with the use of an accessory balun.

12. Permit the use of long-wires of various

impedances. The accessory balun can be used

to match the higher impedance ranges.