[CW] Charts of Radio Morse and American Wire Morse - wattmeter

[Danny Douglas via CW]

I have a Bird 43, and the plate on top says it is for 50 ohms.  Works 
quite well for anything I have ever needed.  Have several plugs for hf 
and vhf, including both 110 and 250 watt hf.  Never managed to find an 
affordable 1000 kc plug to replace the one I lost, somewhere around the 
world.  You are absolutely right about the prices.  A 1k plug costs more 
than just about any new SWR meter I have seen out there, and I have yet 
to see one on the 4 hamfests I regularly attend around here.

> Donald Chester via CW <mailto:cw at mailman.qth.net>
> Tuesday, November 04, 2014 2:50 AM
> The Bird 43 and its ilk are true average-reading meters only for modes 
> of emission with a steady carrier. They work fine for CW, FM and RTTY. 
> With AM they read the average carrier power, but will not the total 
> average power including modulation sideband power. Readings will be 
> erroneous for SSB and many digital type modes.
>
> The reason is that they are actually average-reading RF voltmeters, 
> not true RMS-reading RF voltmeters, with a scale calibrated to watts 
> into a 50-ohm nonreactive load. AVERAGE power is the product of RMS 
> volts X RMS amperes. Average a.c. volts X average a.c. amperes is a 
> meaningless quantity, a substantially erroneous variation from average 
> power.
>
> OTOH, a thermocouple RF ammeter is a true RMS-reading instrument. With 
> an AM signal 100% modulated with a sine-wave tone, the thermocouple 
> meter will show a 22.5% increase in rf current above the unmodulated 
> carrier reading. A diode rectifier type of RF voltmeter as used in 
> most "wattmeters" will theoretically show no increase with modulation. 
> This makes them useful for checking carrier shift with an AM transmitter.
>
> The APM-16 contains active circuitry to make the meter read true RMS 
> voltage. Like the Bird 42, the scale is then calibrated to indicate 
> watts into a 50-ohm non-reactive load. I seem to recall that Bird 
> wattmeters can be special-ordered for work at other load impedances, 
> like 72 ohms for example. No doubt ones built for odd-ball load 
> impedances would be very expensive.
>
> The APM-16 was specifically built for work with digital type 
> emissions, but they also work with SSB, AM and other analogue modes.
>
>
> Don k4kyv
>
>
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> =30=
>
> Richard Knoppow via CW <mailto:cw at mailman.qth.net>
> Monday, November 03, 2014 8:04 AM
>
> ----- Original Message ----- From: "Donald Chester via CW" 
> <cw at mailman.qth.net>
> To: <cw at mailman.qth.net>
> Sent: Sunday, November 02, 2014 12:55 AM
> Subject: Re: [CW] Charts of Radio Morse and American Wire Morse - 
> wattmeter
>
>
>   Try
> <http://www.birdrf.com/Products/Wattmeters_Line%20Sections/PortableWattmeters/APM-16_Average-Reading-Power-Meter.aspx> 
>
>
>
>
> -- 
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>
>
>
>
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>
> Donald Chester via CW <mailto:cw at mailman.qth.net>
> Sunday, November 02, 2014 3:55 AM
>> A true average-reading wattmeter is now commercially available, the Bird
> APM-16. See
> http://www.birdrf.com/Products/Wattmeters_Line%>20Sections/PortableWattmeter
> s
>> /APM-16_Average-Reading-Power-Meter.aspx
>
> For some reason the program added an erroneous line break to the URL, and if
> you click on the link it takes you to the wrong page on the Bird website.
>
> Here it is again, hopefully without the line break this time. Otherwise,
> manually copy and paste the URL into your address bar.
>
> http://www.birdrf.com/Products/Wattmeters_Line%20Sections/PortableWattmeters
> /APM-16_Average-Reading-Power-Meter.aspx
>
> Don k4kyv
>
>
>
>
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>

-- 
Danny Douglas


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