The Doppler Effect on HD radio. More Junk Science?

[clouseau]

This post does not link to anything else. It asks the question....

The Doppler effect is caused by movement between a source and a receiver. This movement creates a frequency "Shift" which can cause problems in some radio transmissions, especially at high speeds.

Now the question is... How much shift can you expect. We have all heard how scientists can tell how fast a star is moving by the Doppler shift of a known color of light.

We've all heard a train go by and heard "The Doppler Effect" on the whistle or horn.

I'll take the scientist's word on the whole Light shift thing. And I sure as heck can hear it with sound. But how much shift could we expect from an AM signal?

As they say in "Gung Ho"... I don't know. Lets go find out...

I used 1700 KHz and 540 KHZ because they are on opposit ends of the dial.

Assuming you are in a car, travelling directly straight towards the tower at 60 MPH, it will change the length of the perceived wave and thus change the frequency. How much will it change you ask?

Assuming you're driving "TO" the tower, At 1700 it it would change the frequency to
1700.00049. Now it's true that the bottom of the dial gets worse. It goes all the way up to 540.0029. That's right, the shift is .49 HERTZ or .00049 KHz . At 540 the shift is all the way to 2.9 Hertz or .0029 KHz.

Both of these numbers are WAY below the normal drift of AM transmitters (Even new solid state ones. )

Can someone with a better background explain how, unless you're driving a SuperNova or the space shuttle, this could have any effect on reception? Or is this just another Bravo Sierra term thrown around by somenoe who knows nothing. It looks like junk to me.

Inquiring minds want to know...

Clouseau

 

[RadeoEngineer]

I'm not envisioning a scenario where Doppler has any effect on AM transmissions or reception. I saw where this was mentioned in a couple of other posts and kind of went "Huh?"

 

[Mike Walker]

Pretty f'ing silly, since radio waves move at the speed of light, and cars, well, don't. One would have to be going pretty darned fast for the "frequency shift" to be significant!

Silly. Desperate. And SAD!

 

[R.F. Burns]

Some of the comments coming from the anti side sound as if they are the result of the dopier effect.

 

[clouseau]

Some of the comments coming from the anti side sound as if they are the result of the dopier effect.

You owe me for some paper towels. I just spit soda all over my monitor.

Clouseau

 

[scanman1]

I have actually tried using my tabletop HD receivers in a moving vehicle (with an inverter and the ext. antenna jack connected to the car antenna) and have had pretty good results holding the HD signal im my tests going 85 MPH. So, I doubt the "Doppler Shift" will cause the frequency of the station to fluctuate enough to actually create problems. 8)

 

[clouseau]

"Re: In-dash HD Radio Catch-22 ?"

http://www.radio-info.com/smf/index.php/topic,71966.msg520590.html#msg520590

Why the new thread - these issues were already addressed in the above thread ? ???

Let me thank you for asking. I was willing to just pose the question and let it play out. However YOU have now called me out.

I posted a new thread, because your constant references to "The Dopplar effect" are garbage. I use the word "Garbage" because I think the phrase "Giant Steaming Pile of Mastedon Dung" might be a violation of the TOS. You brought this junk up. Don't cry to me when you are shown to be (Damn it... the TOS again)...less than accurate.

You post a link to an article (What a surprise) where you reference how you have covered this alledged "Dopplar Effect".

In it we get such gems as...

let's look at other emerging and proposed formats that may provide new competition for NPAD (non-program-associated data) delivery.

Yep. For those of you in Rio Linda, that's a reference to Non Program reception. Otherwise known as stuff that does not matter.

You are referencing an out and out lie. It does NOT say what you say it does.

I was referencing your posts here...

http://www.radio-info.com/smf/index.php/topic,72615.0.html,

http://www.radio-info.com/smf/index.php/topic,72574.0.html,

http://www.radio-info.com/smf/index.php/topic,71966.msg520590.html#msg520590,

and here...

http://www.radio-info.com/smf/index.php/topic,71708.msg522556.html#msg522556

where you spew garbage about the Dopplar effect. And it's effect on NPAD (That's YOUR article's description, NOT MINE.)

You have 3 choices.

1) Show us we're wrong and the dopplar effect has real merit on HD radio.

2) Tell us you don't know what the "Dopplar Effect" is... or

3) Crawl back in your hole like when everyone posted what their background was and you were vapor....

"THAT'S" why you have a new thread about the Doppler Effect.

Clouseau

 

[Tom Wells]

Not junk science, but probably not much of a problem, either.
The effect on tuning, as everyone before has noted, is minimal.
What is being referred to is more an issue with "slew rate", and whether the data, even as several slow-rate bitstreams,
will have sufficiently "sharp" corners to decode the zeroes and ones reliably.
The faster one travels, the less well defined are the "square waves".
As the shift makes an infinetesimal difference in AM wavelengths, I think the issue is more likely to be noticed on the FM,
where the 1 meter 100 mhz wave can be traversed quickly at car speeds.
I don't think this is likely to ever be an important limiting factor, but was noted as a theoretical limitation.
As scanman has noted, it seems to work in a car, even at extra-legal speeds.
Was this is in clear or multipath country?
Analog seemed to work fine when we went to the moon, even with a pretty darn large doppler shift, and the propogation delay.

 

[clouseau]

Not junk science, but probably not much of a problem, either.
The effect on tuning, as everyone before has noted, is minimal.
What is being referred to is more an issue with "slew rate", and whether the data, even as several slow-rate bitstreams,
will have sufficiently "sharp" corners to decode the zeroes and ones reliably.
The faster one travels, the less well defined are the "square waves".
As the shift makes an infinetesimal difference in AM wavelengths, I think the issue is more likely to be noticed on the FM,
where the 1 meter 100 mhz wave can be traversed quickly at car speeds.
I don't think this is likely to ever be an important limiting factor, but was noted as a theoretical limitation.
As scanman has noted, it seems to work in a car, even at extra-legal speeds.
Was this is in clear or multipath country?
Analog seemed to work fine when we went to the moon, even with a pretty darn large doppler shift, and the propogation delay.

I WAS inclined to beliee that "Short" wavelengths would be more affected than "Long" wavelengths. In fact, when I started the post, I thought that 1700 would be the "BAD" end of AM.

As I looked at it, the number of "Wavelengths" increased due to a fixed speed in Dopplar, The LOWER it got the worse it seemed to be - Deviation wise....

Anyone want to tell me I'm wrong? It seems it Could be possible the other way...

Clouseau

 

[dumber than a box of hair]

I WAS inclined to beliee that "Short" wavelengths would be more affected than "Long" wavelengths. In fact, when I started the post, I thought that 1700 would be the "BAD" end of AM.

As I looked at it, the number of "Wavelengths" increased due to a fixed speed in Dopplar, The LOWER it got the worse it seemed to be - Deviation wise....

Anyone want to tell me I'm wrong? It seems it Could be possible the other way...

Clouseau

In theory, short wavelengths would be affected more than long wavelengths, assuming the speed of the moving target remains constant. However, as has already been posted, to produce enough of a change to actually effect tuning, the target would have to be moving at nearly the speed of light, which is the speed at which radio waves propagate through space (and through our atmosphere, it's something like 99.995% of the speed of light in a vacuum). If this were a significant problem, we would have already experienced it with car reception of analog signals, and we don't. Cliff's Notes: Nothing to worry about.