[Boatanchors] Using a SG-230 tuner on AM

[D C *Mac* Macdonald]

If you set up the spectrum analyzer with sufficient resolution,
you will see three separate "pips" representing the "carrier"
and each "sideband."  At 100% modulation, each sideband
should, IIRC, be 1/4 or 1/2 the size of the "carrier."  It's been
a long time (decades) since this was demonstrated in USAF
electronic tech school!
 
The explanation by Gary, K4FMX, is more complete and accurate
than that which I provided.  Thanks for completing my bit, Gary!
 

73 - Mac, K2GKK/5
(Since 30 Nov 53)
Oklahoma City, OK



* In my many years, I have come to the conclusion that one useless *
* man is a shame, two is a law firm and three or more is Congress. *

* -- John Adams (1735- 1826) *




From: km1h at jeremy.mv.com
To: garyschafer at comcast.net; k2gkk at hotmail.com; rbethman at comcast.net; boatanchors at mailman.qth.net
Subject: Re: [Boatanchors] Using a SG-230 tuner on AM
Date: Mon, 10 Aug 2009 12:09:04 -0400
 
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" 
To: "'D C *Mac* Macdonald'" ; "'KM1H Carl Huether'" 
; ; 
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