[AMRadio] FCC's AM power


Robert Bethman oldrotorheadsarge at outlook.com
Tue Sep 27 13:42:01 EDT 2016


I happen to use the Bird 43P.  It does read peaks.  As with any other "Peak" reading device, it does NOT keep up with the peaks!  The only way to obtain peaks with these devices, is to use CW as the mode to read the Peak Power Level.

I have been threatening to place an internal thermocouple ammeter in line with the output.
I do in fact have at least one or two around.  They came out of the BC-939 Antenna Coupler.  It is mis-labelled as an antenna tuner!

Regards, Bob - N0DGN

-----Original Message-----
From: AMRadio [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Gary Schafer
Sent: Tuesday, September 27, 2016 1:11 PM
To: 'Donald Chester' <k4kyv at charter.net>; amradio at mailman.qth.net
Subject: Re: [AMRadio] FCC's AM power

The Bird APM-16 is about 3 times the price of the Telepost unit and you still have to buy slugs at close to $300.00 apiece for the Bird unit.

Measuring power with a directional coupler is common practice. Even the Bird
43 uses a directional coupler and it measures forward current and voltage as well as reflected current and voltage.
It uses a diode as a peak detector, calibrated in average power. The line impedance does not have to be exactly 50 ohms in order to have accurate measurements same as other watt meters using a directional coupler.

73
Gary K4FMX 
> A better choice for that kind of money, according to Bird, the 
> self-proclaimed "RF Experts", would be the APM-16, Average Reading 
> Power Meter, which "is designed to keep pace with the ever growing 
> complexity of digitally-based communication systems. Bird's model 43 
> and most other wattmeters available today were designed to measure 
> power of CONSTANT AMPLITUDE, SINUSOIDAL WAVEFORMS.
> 
> "Modern wireless communication systems can use a variety of digital 
> techniques to combine many voice data channels into a complex, 
> composite RF signal. Measurement of such signals with a conventional 
> wattmeter may yield unacceptable errors. The APM-16 employs active 
> circuitry to deliver accuracy of ± 5% for multiple-access technologies 
> such as CDMA, TDMA, FDMA and other digitally-encoded communication 
> systems.
> 
> "Designed especially for RF power measurement in PCS, cellular, ESMR, 
> paging and similar communication systems, EQUALLY EFFECTIVE for 
> measuring RF power in CONVENTIONAL ANALOGUE SYSTEMS, uses APM-series 
> plug-in elements to cover a wide range of frequency and power levels. 
> Simple Thruline® style operation for instant forward or reflected 
> power readings."
> 
> http://www.birdrf.com/Products/Wattmeters_Line%20Sections/PortableWatt
> me
> ters
> /APM-16_Average-Reading-Power-Meter.aspx
> 
> 
> A true direct-reading RF power meter would have four terminals, one 
> pair in series with the load and another pair bridged across the load, 
> to sample RF current and RF voltage.  It would still be accurate only 
> when working into a purely resistive, non-reactive load, unless it 
> contained built-in circuitry to correct for power factor.  Such 
> instruments exist for 60~ a.c., but I'm not sure about RF.
> 
> Don k4kyv
> 
> 

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