ANTENTOP- 01- 2016 # 020

Memorandum on the Beverage Wave Antenna

practically no effect on signals arriving in phase at A from B direction.  Therefore it is necessary to know the surge impedance of the two wires in parallel with respect to ground.

The transformer Tr reverses the phase and sends the signal which arrives from A direction back over the two-wire line

now acting only as a transmission line.  The primary coil is designated to match the surge impedance of the two-conductor antenna line in parallel with respect to ground and the secondary to match the same two-conductor antenna as a transmission line back to the station.

Circuit for Determining Surge Impedance Forward Reception

A signal is tuned in from A direction on the receiver. Frequencies of multiples of one-half wave length are preferred as the are more completely balanced out when the proper resistance value is used at Rb. The resistance Rb is adjusted for minimum signal in the phones and this value used as the antenna surge impedance. The surge impedance may also be determined by adjusting the resistance at the opposite end of the antenna.

In this case signals from B direction are tuned in to the receiver and balanced out by varying Ra.  This method will usually give a lower value of Ra than that recorded for Rb in the other case.  The difference is due to the R.F. resistance of the primary of the transformer and some residual inductive reactance, as unity coupling between turns is not possible.  If the recorded value of resistance is low it is an indication of high ground resistance. 

Values at Grand Island for two wires in parallel are approximately 300 ohms.

 Another and more simple method which has been employed is to make the resistance Ra, Rb variable in steps of 20 ohms from 230-440 ohms.  With an observer at the receiver, the readings are recorded as changed at the antenna terminal and as indicated on a meter in the second detector plate circuit of the receiver for each changed step of the resistance.  The observer at the receiver hears a click when the resistance is switched to the next step.  Its value is known according to a shifting plan as prearranged with the antenna terminal collaborator and the proper impedance value thus determined.

Circuit for Determining Surge Impedance Rear Reception

Figure 10

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