[Boatanchors] Using a SG-230 tuner on AM
rbethman
rbethman at comcast.net
Mon Aug 10 13:03:51 EDT 2009
Carl,
Isn't 6dB actually a power increase 10 times the original?
My understanding that 3dB is a doubling.
This is why I made the comment about the instruments of/for measurement.
I'm with you that running a BC-610, that there is NO way to get 4X the
carrier whether it is by scope, voltage and current measurements, OR
peak reading wattmeters.
This is one of those topics that get haggled to death when it comes up.
The last place for a "firestorm" or "firefight" was the AM List.
Bob - N0DGN
Carl wrote:
> 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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>>
>>
>
>
--
+------------------------------------------------------------------+
| AM Amateur Radio Operator NØDGN |
+------------------------------------------------------------------+
| Bob Bethman \\\|/// " The absence of a danger |
| \\ ~ ~ // signal does *NOT* mean |
| rbethman at comcast.net (/ @ @ /) that everything is OK " |
+-------------------------oOOo-(_)-oOOo----------------------------+
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