Re: rf design

From: Active8 (reply2group_at_ndbbm.net)
Date: 11/20/04 

Date: Sat, 20 Nov 2004 05:28:13 -0500

On Sat, 20 Nov 2004 00:20:00 GMT, Rich Grise wrote:

> On Fri, 19 Nov 2004 06:41:11 -0500, Active8 wrote:
>
>> On Fri, 19 Nov 2004 01:25:10 GMT, Rich Grise wrote:
>>
>> <>
>>>
>>> If you look at each respective signal on a spectrum analyzer, then with
>>> AM, the carrier pip stays the same height, and the sidebands are a little
>>> audiophool equalizer display. When you look at an FM signal on a spectrum
>>> analyzer, the sidebands bear a very arcane relationship to the modulation,
>>> and the carrier bounces up and down. With AM, the modulation adds energy,
>>> with FM, it just moves it around.
>>
>> Three sentences. You win.
>>>
>>> Looking at the spectrum of a radar-style pulse is very interesting too,
>>> and until you've seen the output of a serrodyne-modulated TWAT,
>>
>> LOL. Please elaborate.
>>
>>> you
>>> wouldn't believe me if I told you what it looks like, and it almost
>>> can't be described in words anyway. )-; But it looks way neat!
>>>
>> Pictures!
>
> It's classified! Well, it was when I saw it in the USAF.
>
> OK, anyway. You've got this "jamming package," which is a spectrum
> display of noise through a fairly sharp, single-pole BPF - your
> normal bell-curve, but with the aspect ratio of a villus.
>
> When you apply the serrodyne modulation, (that's actually a variable-
> freq. sawtooth applied to one of the accelerator electrodes in a TWT)
> the package kind of "clones" itself. A copy appears right on top
> of the existing package, then starts slowly moving to one side, getting
> smaller like the e^(-t) curve, while the main one stays. This fools the
> hell out of doppler radar.

hmmm... TWT tom trickery.
>
> The outline of a pulse spectrum is just the harmonics in the pulse,
> which I was kinda surprised to see the outline looks like the path
> of that classical bouncing ball. As the pulse width decreases, the
> lobes get narrower and denser, and when it increases, the lobes get
> wider and sparser until at 50%, it's the harmonics of a square wave.

With the psuedo-random LFSR sequence, the longer the sequence (more
register stages,) the more Gaussian white noiselike it is. The
statistics are cool and give some insight into the reason for the
cool looking spectrum.

Out of half of the bits - rounded up or down (can't remember) - out
the end register, half of those will be stand alone ones (1-tuples)
and the other half zeros (also called 1-tuples.)

Those 1-tuples account for the spectral lines at the clock rate and
it's (what? odd?) multiples.

Of the remaining half sequence, half of those bits (rounded) half of
the 2-tuples will be ones and the other half zeros accounting for
spectral lines at 1/2 the clock freq and its (odd?) multiples.

And so on until you get a spectral line for the whole sequence which
could take years to repeat and thus be a very low frequency spectral
component.
>
> http://dependability.cs.virginia.edu/bibliography/Schleher526-ch04.pdf
> This guy's got some neat pix, but his serrodyne on p. 56 doesn't
> show the side lobe moving.

The PC MF spectrums are very PN like. 

-- 
Best Regards,
Mike

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