[Boatanchors] Using a SG-230 tuner on AM
Carl
km1h at jeremy.mv.com
Mon Aug 10 12:09:04 EDT 2009
OK, I'll have to set up a different test.
However a SA set to peak hold with a steady tone should be able to read true
PEP....correct? I only see about 2X with a 1000 Hz sine wave.
So if I set up a calibrated FS meter I should then see a 6dB increase when
100% modulated with a steady tone
What I dont understand and hasnt been answered is the modulator power. Is a
modulator output measured in peak, RMS or average power? IOW, a modulator
rated at 100W is doing what? Since a 100W modulator xfmr is self limiting
(core saturation) with 100W tube capability so it cant provide more than
rated power. OTOH my PP 304TL's using a 5KW BCB TX xfmr knows no limits (-;
I remain confused!
Carl
KM1H
----- Original Message -----
From: "Gary Schafer" <garyschafer at comcast.net>
To: "'D C *Mac* Macdonald'" <k2gkk at hotmail.com>; "'KM1H Carl Huether'"
<km1h at jeremy.mv.com>; <rbethman at comcast.net>; <boatanchors at mailman.qth.net>
Sent: Sunday, August 09, 2009 11:44 PM
Subject: RE: [Boatanchors] Using a SG-230 tuner on AM
> 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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