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.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|