[Boatanchors] Using a SG-230 tuner on AM

Sun Aug 9 23:44:36 EDT 2009

Actually the doubled current (and voltage) comes from the modulator during
modulation. If the modulator has its own high voltage supply all the extra
power comes from it. If the modulator shares the same supply then of course
it all comes from the same supply.

Spectrum analyzers are really power meters. They measure the voltage across
50 ohms and are calibrated in power levels.

Peak envelope power is not visible on a spectrum analyzer because all the
power is not on the same frequency. A spectrum analyzer displays the power
levels in each frequency component.

An average reading wattmeter will read the composite of the carrier and side
bands together. A 100% modulated transmitter will show 1.5 times the average
carrier power when modulated by a steady tone.

When using a peak reading wattmeter on SSB it will read the true peak
envelope power of the transmitter due to the time constant of the metering
circuit. 

A PEP wattmeter such as the Bird will read ok on SSB but will not give a
true PEP reading with an AM signal. The reason being that the carrier causes
a bias on the detector so that it can not detect the full peak voltages
present.

Some of the digital wattmeters are able to give true PEP readings on AM
signals. The other way to read true PEP is with a scope.

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of D C *Mac* Macdonald
> Sent: Sunday, August 09, 2009 9:56 PM
> To: KM1H Carl Huether; rbethman at comcast.net; boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Using a SG-230 tuner on AM
> 
> 
> The doubled current IS supplied by the power supply,
> but NOT just the transformer but the filter capacitors
> on a VERY short term basis AND the "spikes" supplied
> by the modulator and ITS power supply.
> 
> 73 - Mac, K2GKK/5
> (Since 30 Nov 53)
> OKlahoma City, OK
> 
> 
> p.s.  Spectrum analyzers with which I'm familiar
> shows ONLY voltage level.  I believe that an
> average-reading Wattmeter would show 1.5 times
> the carrier reading with 100% modulation by a
> single tone.  It HAS been a while since I have
> made that test on a spectrum analyzer, but I
> service FAA's VHF and UHF transmitters which
> are set for 10W carrier power.  Set up for 90%
> modulation with 1 kHz tone, the Marconi (and other)
> service monitors show approximately 14W.  They
> will show 15W at 100% modulation.
> 
> p.p.s.  I am not familiar with using a peak-reading
> wattmeter, depending on the decay time-delay of the
> particular wattmeter, I can see where you would never
> see the actual peak ENVELOPE power.
> 
> 
> 
> ----------------------------------------
> > From: km1h at jeremy.mv.com
> > To: k2gkk at hotmail.com; rbethman at comcast.net; boatanchors at mailman.qth.net
> > Subject: Re: [Boatanchors] Using a SG-230 tuner on AM
> > Date: Sun, 9 Aug 2009 19:36:30 -0400
> >
> > Where is this doubled current coming from? There is only one voltage
> source
> > feeding the final and that certainly isnt pulling 2X key down.
> >
> > I dont see 4X power on a peak reading wattmeter or spectrum analyzer.
> >
> > Carl
> > KM1H
> >
> > ----- Original Message -----
> > From: "D C *Mac* Macdonald"
> > To: ;
> > Sent: Sunday, August 09, 2009 4:15 PM
> > Subject: Re: [Boatanchors] Using a SG-230 tuner on AM
> >
> >
> >>
> >> I'm certainly not looking to start a "firefight."
> >>
> >> HOWEVER, if you will display an unmodulated "carrier" on an
> >> o'scope, then modulate it 100%, the VOLTAGE when amplified
> >> will double. Since ohms law states that if you double the
> >> voltage you will also double the current.
> >>
> >> Since P = I x E, 2I x 2E will give you 4P.
> >>
> >> It's basic Electronics 101.
> >>
> >>
> >> 73 - Mac, K2GKK/5
> >> Oklahoma City, OK
> >>
> >>
> >>
> >> ----------------------------------------
> >>> Date: Sun, 9 Aug 2009 16:11:02 -0400
> >>> From: rbethman at comcast.net
> >>> To: boatanchors at mailman.qth.net
> >>> Subject: Re: [Boatanchors] Using a SG-230 tuner on AM
> >>>
> >>> This always starts "some" sort of a firefight.
> >>>
> >>> I can argue either side. The basic reasoning gets down to WHAT
> >>> measurement INSTRUMENTS are being used.
> >>>
> >>> The current 1500W limit is to be measured in PEP. Darn few folks do
> >>> so. They are still using equipment that doesn't get the job done
> >>> correctly.
> >>>
> >>> The only thing I could remotely suggest is to TRY the tuner on a
> single
> >>> antenna with a radio of the desired output. Brief duration as I know
> >>> Carl WOULD do.
> >>>
> >>> Then go from there.
> >>>
> >>> I'm going to leave the firefight. Been in to many real ones.
> >>>
> >>> Bob - N0DGN
> >>>
> >>> D C *Mac* Macdonald wrote:
> >>>> At 100% modulation peak, the instantaneous voltage
> >>>> AND current are both double the static values.
> >>>>
> >>>> V^2 times I^2 gives you four times the static power.
> >>>>
> >>>> Current FCC rules allow for 1.5 kW output power.
> >>>> That is why the old kilowatt rigs such as Collins
> >>>> KW-1 and Johnson Desk Kilowatt can now only be run
> >>>> at 375 Watts carrier power.
> >>>>
> >>>> 73 - Mac, K2GKK/5
> >>>> Oklahoma City, OK
> >>>>
> >>>
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