in the tube days you directly modulate the finals with actual audio power.
For example you have a 100 watt TXer. you would need 50 watts of audio to
modulate the 100 watt carrier to 100% modulation. Thus you will be adding
power to the carrier. This is called high level modulation.
Low level modulation is done in the driver or exciter. This will produce
AM but not the same power out. For instance most SSB rigs that have AM,
actually produce AM by removing the SSB filters (now you have Double
Sideband) and unbalancing the ring modulator (I.E. inserting or allowing
a carrier to be sent thru). This will produce a carier of 1/4 rater output
power, and will actually sound the same as high level, IF you have a 6 KC
filter on the TX.You can not have AM on a SSB filter < 3 Khz, you need
Double Side band 3 KHz + 3 KHz = 6 KHz Minimum. You can get by with 5 KHz
but it will have some lost audio response.
Think of AM as 2 SSB signals transmitted at the same time on the same freq.
LSB and USB, both of them will have a common center freq. Lets use 14.300
MHz. A 1 Khz tone in the mic will produce a carrier and a tone with a freq
1 KHz higher and 1 KHz lower. So now you will be looking at 3 freqs:
14.300 carrier
14.301 USB
14.299 LSB
On a AM receiver it will sound like a single 1 KHz tone.
-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of David Willmore
Sent: Wednesday, July 31, 2002 11:57 PM
To: [email protected]
Subject: Re: LF: Re: Re: Droitwich carrier
let's see this one get there, too. :)
Let's see if this gets to the list !
100 percent modulated AM transmitter
will show 22 percent power output increase
during a sustained 100 percent modulation
condition !
This is different from what I would expect to happen.
To start with, one takes a carrier or some power, then
one modulates its amplitude. This process spreads some
of the energy into the symetrical side bands--taking
power out of the carrier, thus causing 'downward
modulation' of the carrier, right? I believe the
Yaesu FT-817 uses this scheme for its AM transmit. I
think it was described as 'early modulation' of the
signal. Does that mean anything to you?
How would one modulate a carrier and add power? I
must be very lost.
Cheers,
David N0YMV
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