[600MRG] transmitting power

[Rudy Severns]

Just a heads up on transmitter output power measurements.

 

Like many of us with experimental licenses I’ve had to dial back transmit
power, 6 dB in my case.  To estimate my radiated power I’ve been using a
measurement of transmitter output power and the efficiency of my  antenna.
I derive my radiation efficiency using the ideal antenna Rr from NEC divided
by the measured input resistance from the antenna.  This gives a reasonable
estimate of efficiency.  My amplifier has a power output meter which I was
using but recently I was able to acquire a Bird 4410 directional wattmeter
with the 200-535 kHz slug (4410-1).  I discovered my transmit power was
about 20% lower than what the Bird was reading!  

 

In the past I’ve seen the Bird 200-535 kHz slugs for Bird wattmeters but
they are marked “10 kW”, which is a tad high for me so I gave them a pass.
That rating is what you might get in a Bird model 43 which many of us have
but the 4410 has a dial-in divider which will take the power level down to
10W!  If you are a ham flea market habitué keep your eyes open and grab one
if you see it.  Later if you have a chance to beg,  borrow or steal a 4410
you’ll have a very good estimate of output power. 

 

This is of course not the only way to estimate output power but it’s really
handy if you get the chance.

 

73, Rudy N6LF