[AMRadio] FCC's AM power


Gary Schafer garyschafer at largeriver.net
Tue Sep 27 16:10:51 EDT 2016


Hi Jim,

The manual for the 4311 is here:
http://www.birdrf.com/Resources/DiscontinuedProducts/BEC-UserManuals.aspx#.V
-rNifkrLcc

I think the calculation that you were referring to was to find the %
modulation of an AM signal by the power readings.

73
Gary  K4FMX

> -----Original Message-----
> From: AMRadio [mailto:amradio-bounces at mailman.qth.net] On Behalf Of
> w5jo at brightok.net
> Sent: Tuesday, September 27, 2016 2:27 PM
> To: amradio at mailman.qth.net
> Subject: Re: [AMRadio] FCC's AM power
> 
> 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.
> 
> Jim
> W5JO
> 
> -----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
> 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-----
> 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
> 
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