Thank you all for your help with the Amplifier Class questions. I have
found schematics and confirmed CBs use Class B in the final, the driver
and sometimes earlier transistor circuits which ultimately feed a tank
circuit before output to the antenna; It is clear the modulation happens
way before it becomes 27MHz which makes good sense.
By the way this all came about because I was trying to make a point to
the CB crowd about their radios being constructed with the barest
minimum components to get the job done. The CB finals I found handle 6
watt average max (heat sinked of course) which I hope will dissuade
folks from trying to tweak tens of watts continuous out of these poor
radios.
As a bonus I learned more about how the various Elecraft products do
their thing and for that I thank you all.
We can consider this thread closed.
Onward to a K2...
John Huggins wrote:
Yes the handbooks are the place to go and I will sit with one tonight
to "reboot." A splendid suggestion thanks.
The information on what modern Ham Transceivers (like the K2 and K3)
do is also very handy. Thanks for that too.
John
Gazdzinski, Brett J (Brett) wrote:
On AM, most CB sets, if not all, use class c in the final,
(single device), and collector modulate it with a push pull
class b modulator.
Look up plate modulation, same thing but with tubes.
You use class C on FM, and class ab1, ab2, or class b
on ssb.
Most modern ham rigs if not all use low level modulation
on AM, like ssb but with both sidebands and a carrier, and
amplify it like ssb, but with a much higher duty cycle.
Class C can only be used with CW, FM or plate/collector modulation
AM.
SSB amplifiers (and AM amps) can be class B, AB1, or AB2, or A.
Class A is VERY inefficient!
All this stuff and more is in the handbooks.
Brett
N2DTS
Ladies and Gentlemen,
I frequently contribute technical knowhow to a CB trucker's forum
(before you press delete please read on). The question came up
concerning my assertion the single final transistor amplifier,
typical in CB transmitter output circuits, operates as a Class A
amplifier since the modulation required is AM and sometimes SSB, both
being amplitude style modulations, and both desiring of good
linearity in the amplification (at least I think so).
I know for sure CB output circuits are not push pull since they have
only one power amplifying transistor.
Some are suggesting the less than 180° Class C amplification method
is what CBs use. I understand this requires a good tank circuit to
complete the sine waves, but is supposedly inappropriate for
amplitude style modulations like AM, DSB and SSB. Various resources
suggest Class C is fine for CW and FM.
I am sure by now you are saying "That's interesting John, really, but
what does this have to do with Elecraft?"
Well, I suddenly remembered some advertisement for an HF Ham
Transceiver that offered Class A mode in its output circuit for some
improvement in some parameter. Funny thing is I guess I thought Ham
Transceivers always used either Class A with a single device or,
perhaps, Class AB or B in a push-pull arrangement.
What I need to know from Elecraft and/or any of you is:
- What is the final amplifier class (A, AB, B or C) used in, say, the
KX1, K2 or K3?
- Is it actually possible to use Class C with an amplitude modulation
scheme like AM, DSB and/or SSB?
- Is the final amplifer in the KPA100 Class A?
- Do most Ham Transmitters utilize pairs of power devices in a Class
AB or B in a push-pull arrangement?
Hopefully this will fine tune my EE knowledge of circuits and make
sure I have not missed something I should know so I can continue to
represent the ham community well when offering advice to the other
radio groups.
Thanks for your help.
John
KX4O
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