[AMRadio] FCC's AM power

w5jo at brightok.net w5jo at brightok.net
Tue Sep 27 15:27:06 EDT 2016

Bird made a "peak" reading meter   that used a slug for 2-30 megacycles, and 
other slugs were made for various large segments of the bands along with a 
variable switch that changed the power level of the meter.

I can't recall for sure but think the one I had was the 4311.  It was 
powered by AC and had a 9 volt battery for portable use.    I saw one of 
them before I saw the peak reading 43P kit to add to the 43.  The 
instruction book that accompanied the meter had a formula for calculating 
the true peak of the signal as the meter would not indicate it.

Another peak reading meter they made was the 4314 which was a variation of 
it.  Advertising for these meters said they would read the "Peak" power of 
an AM signal but I don't see how that is possible.  I sold my example of the 
4311 some years back and the manual went with it so I don't have specifics. 
Maybe someone has a manual  and can provide specifics.

I sold the meter for about $650 with the one slug.  It was a special slug to 
cover that much of the band, but was the classic Bird design with a diode in 
the slug.   If I recall correctly they claimed 5% at full scale for accuracy 
in a steady carrier but provided that formula for calculating the "true 
peak" .  I wonder if the documentation that accompanies the 43P has a 
formula or do they claim it to be accurate?

But as Gary said the Telepost unit does a better job for much less.


-----Original Message----- 

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 

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-----
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.


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