The 'phasing method' of single sideband demodulation

On Tue, 21 Aug 2012 14:35:52 -0400, John Ferrell wrote:

> On Mon, 20 Aug 2012 12:19:53 -0500, Tim Wescott <tim@seemywebsite.com>
> wrote:
> 
>>On Mon, 13 Aug 2012 13:07:03 -0400, John Ferrell wrote:
>>
>>> On Sun, 12 Aug 2012 23:18:30 +0300, Tauno Voipio
>>> <tauno.voipio@notused.fi.invalid> wrote:
>>> 
>>>>On 12.8.12 11:00 , John Ferrell wrote:
>>>>>
>>>>>> 2. When comparing SSB or DSB performance to FM or AM, it is often
>>>>>> overlooked that the transmit power amplifier for SSB/DSB has to be
>>>>>> linear, whereas FM/AM amplifiers operate in efficient class C or D
>>>>>> or E mode. So, if performance is compared for the same power
>>>>>> consumption of the transmitter (and this is what matters), the
>>>>>> advantages of SSB/DSB are not so obvious if any at all.
>>>>>>
>>>>> This elderly, slow witted student is slowly beginning to understand
>>>>> the subject and then you say "FM/AM amplifiers operate in efficient
>>>>> class C or D or E mode". Tell me that was a simple miss speak and I
>>>>> can get back to the struggle!
>>>>>
>>>>> I am learning and enjoying the process but I doubt will ever be more
>>>>> than a student here. Thanks to all.
>>>>>
>>>>> John, de W8CCW
>>>>
>>>>It is possible to use a Class C (or higher) amplifier for conventional
>>>>AM, but the power of the amplifier has to be adjusted along with the
>>>>modulating waveform. There are two possibilites here:
>>>>
>>>>1. Adjust the excitation or operating point of the amplifier so that
>>>>    the output follows the desired envelope,
>>>>
>>>>2. Adjust the supply feed so that the output follows the desired
>>>>    envelope.
>>>>
>>>>The case 1 was known in the tube era as grid modulation. Both control
>>>>grid and screen grid modulation were used. Here the modulation comes
>>>>at the price that the efficiency of the amplifier is about the same as
>>>>the efficiency of a linear amplifier with the same PEP.
>>>>
>>>>The case 2 was known in the tube era as anode (or anode-screen)
>>>>modulation. Here the carrier efficiency at PEP is the classic Class C
>>>>level, but the price to be paid is the audio power needed from the
>>>>modulator, half of the RF stage input power. To have a fair
>>>>comparison, the modulator power must be calculated into the total
>>>>efficiency of the transmitter. Remember that the modulator must run in
>>>>Class B or AB, with the modest efficiency.
>>>>
>>>>Transistor power amplifiers often need an adjustment of excitation in
>>>>combination with the supply voltage modualtion, so pretty often two of
>>>>the last stages of the transmitter get modulated.
>>>>
>>>>---
>>>>
>>>>FM and PM (which are essentially the same thing) are different beasts,
>>>>as the output envelope is constant. These modulation methods are not
>>>>spectrally efficient, so their use is not a good idea on crowded
>>>>frequency bands.
>>> 
>>> Perhaps it is a matter of perspective. From my point of view you can
>>> modulate a Class C amplifier to produce an Amplitude Modulation Output
>>> in several ways. Further amplification of the AM output requires a
>>> linear amplifier.
>>> 
>>> I apologize if I am coming across as an Anal Troll, but you folks are
>>> normally very concise with your Math. If I am in error, please
>>> explain. I make many mistakes every day. I will not take offense from
>>> those who offer to teach me...
>>> John, W8CCW.
>>> John Ferrell W8CCW
>>
>>I'm still not sure where your misunderstanding arises, but I'll try.
>>
>>If you're going to make a purpose-built transmitter to operate on just
>>one modulation mode at a specific power level (or narrow range thereof),
>>and if it's a mode that'll support it, then you'll get better efficiency
>>in the RF final amplifier with class C (or E).  Adding a follow-on
>>linear amplifier isn't a consideration, because you're purpose-building
>>the thing (for instance, for an AM or FM radio station).
>>
>>You're probably used to current amateur practice where you want one
>>radio that does everything, so you get a Kenwood or Yaesu or whatever
>>that puts out 100W PEP, then if you want more punch you follow it with a
>>linear amplifier.  That makes sense in the amateur domain because (a)
>>the cost of the power that you use to operate costs a fraction of the
>>total station cost, and (b) the transciever + linear amp combination can
>>be used on any mode that the transciever is capable of, whereas a
>>station with a class-C final stage is much less flexible (you can't use
>>it on SSB, for instance).
>>
>>But if you only ever operate on CW, or AM, FM, or PSK, then you pay for
>>that linear amplifier in your monthly power bill, because it's not
>>operating with nearly the efficiency that a class C amplifier would.
> 
> Thank you,
> You spent quite a bit of time on me. I hope my dumb questions do not
> interfere with the discussions. I hope to better understand signal
> processing, especially in regard to software defined radio.
> 
> So, anything offered is appreciated but please just treat me like noise
> and filter me out when I become a nescience!
> 
> John, W8CCW
> John Ferrell W8CCW

That's OK.  I'm a radio amateur, even if my "operating" involves looking 
at my HF set and thinking "I might enjoy that if I took the time to 
string an antenna and re-learn Morse code".

-- 
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

On 8/21/12 2:46 PM, Tim Wescott wrote:
> On Tue, 21 Aug 2012 14:35:52 -0400, John Ferrell wrote:
>
...
>>
>> John, W8CCW
>> John Ferrell W8CCW
>
>   I'm a radio amateur, even if my "operating" involves looking
> at my HF set and thinking "I might enjoy that if I took the time to
> string an antenna and re-learn Morse code".
>


Morse code, Schmorse code.  nowadays everything is at 2-meters or 
higher, ain't it?

i used to be a ham operator too.  back in the late '60s and early '70s.

formerly WB0CCA.

-- 

r b-j                  rbj@audioimagination.com

"Imagination is more important than knowledge."

>
>That's OK.  I'm a radio amateur, even if my "operating" involves looking 
>at my HF set and thinking "I might enjoy that if I took the time to 
>string an antenna and re-learn Morse code".

Amateur Radio is expanding at the same or greater rate as the rest of
Technology. There are more hams now than ever.

If you are not familiar with PSK mode you should check it out. PSK-31
Was devised by (I think) AE4JY. While he was at it, he placed his work
in the public domain so there is a lot of development activity as well
as just contacts.  PSK-31 is Phase Shift Keying at 31 Baud. Some what
like RTTY but it takes only 31 HZ of spectrum for a contact. According
to what I have read 20 watts of   31 Hz is roughly equivalent to 2 KW
of speech. Whatever it is, I rarely run over 30 watts and I am working
the world.I have seen times when there were over 12 QSO's on a single
3000 Hz audio channel on 20 meters with minimal problems.

Best of all to me (Failing hearing) it can be done in silence with
"Waterfall" display. 

Code is not required for any US Amateur Radio License any more.
However, the CW bands are as active as ever. Radio Improvements have
not eliminated noise and crowding, but it has gone a long ways. 

Most of us believe Software Defined Radio is the way of the future.

Proficient CW operators are not pleased so far with the latency of the
system  but I expect better software/hardware will get there in time.

Thanks again for putting up with me, I am going to retreat to the
recliner for the evening. I downloaded a series of YouTube videos on
Fourier Analysis this morning. I(t is about time for me to try to read
Rick's book some more! 

John, de W8CCW

John Ferrell W8CCW