Final Amplifier Class
Locked
 
|
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 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
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 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
In reply to this post by John Huggins
In a message dated 9/1/07 8:07:53 PM Eastern Daylight Time,
[hidden email] writes: > 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. It depends. Modes like DSB and SSB are usually generated at a low level at a fixed frequency, then heterodyned and amplified to the operating frequency. All stages in such a transmitter must be linear, which means Class A, AB, or B. Class C is right out because it's not linear. AM is different. Some AM rigs generate the signal in a manner similar to DSB or SSB, and in such cases the stages must be linear. But AM can also be generated by modulating the final stage of the transmitter. In such "high level" modulation schemes, the final stage does not have to be linear, and is almost always Class C. Look at amateur AM transmitters such as the EFJohnson and Heathkit for examples of how this was done. 73 de Jim, N2EY ************************************** Get a sneak peek of the all-new AOL at http://discover.aol.com/memed/aolcom30tour _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
In reply to this post by Brett gazdzinski-2
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 >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >You must be a subscriber to post to the list. >Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > >Help: http://mailman.qth.net/subscribers.htm >Elecraft web page: http://www.elecraft.com > >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >You must be a subscriber to post to the list. >Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > >Help: http://mailman.qth.net/subscribers.htm >Elecraft web page: http://www.elecraft.com > > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
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 >> _______________________________________________ >> Elecraft mailing list >> Post to: [hidden email] >> You must be a subscriber to post to the list. >> Subscriber Info (Addr. Change, sub, unsub etc.): >> http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/subscribers.htm >> Elecraft web page: http://www.elecraft.com >> >> _______________________________________________ >> Elecraft mailing list >> Post to: [hidden email] >> You must be a subscriber to post to the list. >> Subscriber Info (Addr. Change, sub, unsub etc.): >> http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/subscribers.htm >> Elecraft web page: http://www.elecraft.com >> >> >> > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |