[TowerTalk] Total Power

[jimlux]

On 9/26/16 9:11 AM, Robin Cross wrote:
> ​As an retired Broadcaster​, this is NOT the method of calculating
> total power.
>
> For a directional AM, the total power is measured at the Common
> Point.  The actual Transmitter output.  Towers can have negative
> impedence [power].  Instead of transmitting power, a tower can
> actually be adding power back into the antenna system.  It is due
> to 'mutual coupling'.  This is where a tower is receiving power from
> another tower because of proximity.
>

But if you had a multiple amplifier feeding multiple elements scenario, 
then there is no "common point" at which to measure.  This comes up all 
the time in microwave phased arrays, and negative power/impedance from 
mutual coupling also occurs (although older array designs tend to pick 
spacings that avoid it.)

In theory, the negative power flows back through the RF amplifier to the 
DC bus (depending on how your power device architecture looks.. if it 
were a 4 quadrant H bridge, then it can accept as well as supply power)




> Robin Cross
> w0fen
> RC Electronics LLC
> ret CE KCUR, WNIU/WNIJ
>
> ​-------------------------------
> So measure your output power at the system interface to the "antenna"..
> put 1500 watts (total) into your 4 antennas: sum the powers at each
> element (including if you have phased them so you have a negative
> element).  That's what commercial broadcasters do, isn't it?
>
> The regulations don't say "amplifier output", they say
> "PEP (peak envelope power). The average power supplied to the antenna
> transmission line by a transmitter during one RF cycle at the crest of
> the modulation envelope taken under normal operating conditions. "
> "(b) No station may transmit with a transmitter power exceeding 1.5 kW
> PEP. "
>
> If I define my "antenna transmission line" reference plane at the
> antenna feed points, I think that works.
> ​
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