John Monro wrote: ...>> A synchronous signal will demodulate it. Ordinary modulators won't >> change phase when the modulating signal changes polarity. >> >> Jerry > > Depends on what you call 'ordinary.' A double balanced modulator is an > off-the-shelf component and it changes phase.You're right again. I was back in the days of plate modulation. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
"Beat frequency" phenomenon, but with 3 sine waves?
Started by ●December 6, 2007
Reply by ●December 7, 20072007-12-07
Reply by ●December 7, 20072007-12-07
John Monro wrote: ...>>> Unfortunately I did not see Maxie's picture as the page would not open. >> >> http://en.wikipedia.org/wiki/Beat_frequency opened for me. Maybe you'd >> like to try again. > I just did, successfully, and it supports what I have been saying about > the envelope. The expression is for the instantaneous value of the > waveform. It shows that while the 'sum' frequency signal is varying > rapidly it is being slowly medulated by the 'difference' frequency > signal. The instantaneous amplitude of the difference signal is exactly > equal in magnitude to both the top edge of the envelope and the bottom > edge. In other words, the envelope is given by: > Magnitude(2*cos(2*pi*((f1 - f2)/2))*t) > Now, the magnitude of a sinusoidal wave is definitely not a sinusoidal > wave.I think now you know what I mean. When the envelope gets to zero, the sum signal inverts, so what were positive peaks become its negative peaks and vice versa. Of the two envelope curves, one is tangent always near zero phase, the other always near 180. You don't have to buy that, but I think I made clear what I mean. If we really understand each other it's time to stop. I'm not proselytizing for a conversion! ...> To go a little off-topic, for the special case where the con rod is > equal to the crank throw it appears to be three possible actions. > 1. The piston can stay in the line of the crankshaft for an indefinte time.Yes. I neglected that case.> 2. The piston can do a positive excursion. > 3. The piston can do a negative excursion. > > At each 'decision time,' (when the con rod is horizontal) there does not > appear to be any way to predict which of these things will happen, so I > suppose you could describe the mechanism as 'chaotic.'Not really. When the piston approaches the stable position from an excursion, it is moving at maximum velocity. It must either stop abruptly or continue onto the other side. Your list works statically, but dynamics nearly forces a combination of 2. and 3. There is a mechanism called a trammel that forces the motion statically as well. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●December 8, 20072007-12-08
Jerry Avins wrote:> John Monro wrote:>>> A synchronous signal will demodulate it. Ordinary modulators won't >>> change phase when the modulating signal changes polarity.>> Depends on what you call 'ordinary.' A double balanced modulator is >> an off-the-shelf component and it changes phase.> You're right again. I was back in the days of plate modulation.So what do that actually build AM radio transmitters out of now? -- glen
Reply by ●December 8, 20072007-12-08
glen herrmannsfeldt wrote:> Jerry Avins wrote: >> John Monro wrote: > >>>> A synchronous signal will demodulate it. Ordinary modulators won't >>>> change phase when the modulating signal changes polarity. > >>> Depends on what you call 'ordinary.' A double balanced modulator is >>> an off-the-shelf component and it changes phase. > >> You're right again. I was back in the days of plate modulation. > > So what do that actually build AM radio transmitters out of now?I don't know, but there are few if any 50 KW transistors. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●December 9, 20072007-12-09
On Dec 8, 9:51 am, Jerry Avins <j...@ieee.org> wrote:> glen herrmannsfeldt wrote: > > Jerry Avins wrote: > >> John Monro wrote: > > >>>> A synchronous signal will demodulate it. Ordinary modulators won't > >>>> change phase when the modulating signal changes polarity. > > >>> Depends on what you call 'ordinary.' A double balanced modulator is > >>> an off-the-shelf component and it changes phase. > > >> You're right again. I was back in the days of plate modulation. > > > So what do that actually build AM radio transmitters out of now? > > I don't know, but there are few if any 50 KW transistors. > > Jerry > -- > Engineering is the art of making what you want from things you can get. > �����������������������������������������������������������������������see http://hawkins.pair.com/wabcnow.shtml and enjoy Mark
Reply by ●December 9, 20072007-12-09
Mark wrote:> On Dec 8, 9:51 am, Jerry Avins <j...@ieee.org> wrote: >> glen herrmannsfeldt wrote: >>> Jerry Avins wrote: >>>> John Monro wrote: >>>>>> A synchronous signal will demodulate it. Ordinary modulators won't >>>>>> change phase when the modulating signal changes polarity. >>>>> Depends on what you call 'ordinary.' A double balanced modulator is >>>>> an off-the-shelf component and it changes phase. >>>> You're right again. I was back in the days of plate modulation. >>> So what do that actually build AM radio transmitters out of now? >> I don't know, but there are few if any 50 KW transistors. >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can get. >> ����������������������������������������������������������������������� > > see > http://hawkins.pair.com/wabcnow.shtml > > and enjoyI did; thank you. To the transmitter actually uses banks of up to 1 KW in parallel. My suspicion about the scarcity of 50 KW is not necessarily disproved thereby. I worked nearly in the shadow of that transmitter at Mathe Chemical Company in the early 50s. It was WJZ then. I built a crystal receiver with a foot-diameter loop as resonant antenna and got enough signal to drive a loudspeaker. The volume control was a turntable to orient the loop. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●December 9, 20072007-12-09
Jerry Avins wrote: (snip, I wrote)>> So what do that actually build AM radio transmitters out of now?> I don't know, but there are few if any 50 KW transistors.Just after I submitted the follow up, I thought about direct digital generation of the modulated AM signal from a digital source. That shouldn't be hard for AM, a little harder for FM. -- glen
Reply by ●December 10, 20072007-12-10
glen herrmannsfeldt wrote:> Jerry Avins wrote: > (snip, I wrote) > >>> So what do that actually build AM radio transmitters out of now? > >> I don't know, but there are few if any 50 KW transistors. > > Just after I submitted the follow up, I thought about direct > digital generation of the modulated AM signal from a digital > source. That shouldn't be hard for AM, a little harder for FM.Accorting to the page at the link that Mark gave us above, that's done now. It seems that the tank circuit and antenna coupler serve as a reconstruction filter. There may be some duty-cycle juggling going on, but I missed it if it says so. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●December 12, 20072007-12-12
Jerry Avins wrote: (snip)> I worked nearly in the shadow of that transmitter at Mathe Chemical > Company in the early 50s. It was WJZ then. I built a crystal receiver > with a foot-diameter loop as resonant antenna and got enough signal to > drive a loudspeaker. The volume control was a turntable to orient the loop.Somehow this reminds me of discussions about people living near large power lines on building loops big enough to extract a measurable amount of power. Though it is probably easier at RF for those living close to radio transmitters. -- glen
Reply by ●December 12, 20072007-12-12
On Sat, 8 Dec 2007 20:31:35 -0800 (PST), Mark <makolber@yahoo.com> wrote:>On Dec 8, 9:51 am, Jerry Avins <j...@ieee.org> wrote: >> glen herrmannsfeldt wrote: >> > Jerry Avins wrote: >> >> John Monro wrote: >> >> >>>> A synchronous signal will demodulate it. Ordinary modulators won't >> >>>> change phase when the modulating signal changes polarity. >> >> >>> Depends on what you call 'ordinary.' A double balanced modulator is >> >>> an off-the-shelf component and it changes phase. >> >> >> You're right again. I was back in the days of plate modulation. >> >> > So what do that actually build AM radio transmitters out of now? >> >> I don't know, but there are few if any 50 KW transistors. >> >> Jerry >> -- > >see >http://hawkins.pair.com/wabcnow.shtml > >and enjoy > >MarkHi Mark, thanks for that URL. That was neat! I worked in an AM radio station, in Ohio, many years ago to help pay my way through college. So looking at the modern RF (and audio) equipment on that website was very interesting for me. [-Rick-]