straightforward linear addition of voltages. If both transmitters had same power and phase you will get + 6 dB on the receiver.

 

If you had two equally (in)efficient LF antennas on the same premises (ie. within a wavelength) and drove both equally, you'd need double TX power in total but achieve four times ERP. This is equivalent to a larger antenna with double efficiency.

 

The trick won't work that way at HF or VHF, where antennas are alraedy nearly 100% efficient, and mutual resistance will increase the required input power for one antenna when the other is activated. Then inducing directivity is the only way to increase gain.

 

Best 73,

Markus (DF6NM)

 

 

-----Ursprüngliche Mitteilung-----
Von: edgar <[email protected]>
An: 600m <[email protected]>; rsgb_lf_group <[email protected]>
Verschickt: Mi, 11 Sept 2013 7:05 am
Betreff: LF: Radio signals

Hi Group, 

  

 What is the mechanism for the way radio signals combine in the air? 

  

 For example 

  

 1.There are two transmitters each sending out the same fixed frequency  

 sine wave signal. 

  

 2. There are no other signals in space, and no background noise. 

  

 3. There are no propagation factors modifying the signals. 

  

 e.g. buildings, ionosphere layers. 

  

 4. Both transmitters are the same distance from the receiver. 

  

 5. Both signals have the same polarisation. 

  

 How have the signals combined when they reach a receiving antenna at a  

 reasonable distance from both transmitters? 

  

 It the process addition, multiplication or some other process? 

  

 Regards, Edgar 

 Moonah, Tasmania.