about the group delay

Today , I test the DUT by the network of agilent 8347ET
,but the delay is the negative,
who can explain this for me?Thanks
The DUT consist of LNA +downmixer +Uppermxier,the frequency of both the mixer
is equate.

The delay is calculated by these types of test equipment by measuring the phase at two close frequencies and doing a d(theta)/d(frequency) calculation. You need to make sure that the delta frequency step is small so that you do not exceed 360 degrees of DUT phase shift between them. There should be a setting on the instrument to change the delta frequency step.

Hmmmm. This is important. Save that design! Build around 10 amplifiers stages in series with that design, pass an rf feed of the stock market ticker thru it, and when you see a stock go up, buy 1000 shares right away!

The group delay is calculated (not observed directly).
GD = Δφ/ΔFreq.

What happen if you perform an "inverted band" conversion? (Like down-LSB conversion). The Δφ change sing and VNA show a negative value.

I i well understand your particular case, you peform 2 conversion to reach, at the OUT, the same freq at the IN. But does the conversions are SSB or DSB? And more, if are DSB are you sure that LSB vs USB are exactly level balanced ?

hi, the mixers are both SSB。I think the phase of the two lO not equate.So the delay may be negative.

Hi guys .. I'm quite new to this topic.. but I'm really curious ..can anyone give me the definition (or "pdf" stuff) about GROUP DELAY adn its measurements?

Thanks in advance.. I really need it.

Lupin

There are two delays, group and phase.

Group is the speed that a modulated waveform moves through a system or transmission line or space.

Phase is the speed that a constant phase point moves through the above.

Phase can be faster or slower than the speed of light because it is an artificial thing.

Group has to be equal to or slower than light because it is a physical thing (transmission of information.)

One way to think about this is a pair of scissors. When the two blades approach each other, the point that partitions space between the blades not touching and the blades touching move much faster than the blades approaching each other.

Another example is a spot on a wall made by a laser pointer. If your wrist is fast enough, the spot can go faster than the speed of light, but the photons going to the wall still go at the speed of light.

if the delay line delay too fast what could I do, if i want to let the time down?

There is a good explaination in the DN0004.pdf

**broken link removed**

Dear Flatulent,

I don't agree with "Group has to be equal to or slower than light because it is a physical thing (transmission of information.)"

In fact, in general that is not true. I copied the page 333 and 334 from Stratton, Electromagnetic Theory, McGraw-Hill, to explain it.

Regards.


If the dispersion of the medium is normal and moderate, a pulse or wave packet may travel a great distance without appreciable diffusion; since the energy is presumed to be localized in the region occupied by the field, it is obvious that the velocity of energy propagation must equal at least approximately the group velocity. In a normally dispersive medium an increase of wave length results in an increase of phase velocity and hence the group velocity under these circumstances is always less than the phase velocity. If on the contrary the dispersion is anomalous - as in the case in conducting media - the derivative d v/d lambda
is negative and the group velocity is greater than the phase velocity. There is in fact no lack of examples to show that the group velocity may exceed the light velocity, c.
Since at one time it was generally believed that the group velocity was necessarily equivalent to the velocity of energy propagation, examples of this sort were proposed in the first years following Einstein's publication of the special theory of relativity as definite contradictions to the postulate that a signal can never be transmitted with a velocity greater than c. The objection was answered and the entire problem clarified in 1914 by a beautiful investigation conducted by Sommerfeld and Brillouin, which may still be read with profit.

Sommerfeld, Ann. Physik, 44, 177-202, 1914.
Brillouin, ibid, 203-240.

flatulent said:

There are two delays, group and phase.

Group is the speed that a modulated waveform moves through a system or transmission line or space.

Phase is the speed that a constant phase point moves through the above.

Phase can be faster or slower than the speed of light because it is an artificial thing.

Group has to be equal to or slower than light because it is a physical thing (transmission of information.)

One way to think about this is a pair of scissors. When the two blades approach each other, the point that partitions space between the blades not touching and the blades touching move much faster than the blades approaching each other.

Another example is a spot on a wall made by a laser pointer. If your wrist is fast enough, the spot can go faster than the speed of light, but the photons going to the wall still go at the speed of light.

Click to expand...

Dear friends,

just a question: the group delay concept can be considered equal to the signal transit time, can't it be? If no, what's the difference?

Regards,
Lupin

Im sorry, I got dazed in the math, isnt group delay the delay of the signal components of the signals frequencey spectrum. some have no delay others are dragged and lag behind a signal through the system?


In a mathamatical sense, can you achieve greater speed through the system
then entered, I think this may be possible, if an inductor leads by 90deg.

But in a physical sense is this possible?

Lupin said:

Dear friends,

just a question: the group delay concept can be considered equal to the signal transit time, can't it be? If no, what's the difference?

Regards,
Lupin

Click to expand...

If you consider the signal transit time as the energy transit time (associated with the signal) the group delay concept can't be considered equal to the signal transit time. Very often the group delay and the signal transit time have the same value (not in the case of anomalous dispersion) but in any case the concepts are different. You can refer to the previous reply.

Regards