Frequency Analyzers measurements

Discussion in 'General Electronics Discussion' started by danny davis, May 18, 2012.

1. danny davis

306
0
May 9, 2012

On the spectrum analyzer I set the center freq. to 418MHZ, at a span of 100K hz

The problem I don't understand is that the receiver sends four pulse signals at 410MHZ

What I don't get is that when you view it on the frequency analyzer each pulse is at a different DB lever because its sweep a span of frequency's

So it makes the receiver circuit look like the pulses are WEAK, but really they can't weak its because the frequency analyzer is sweeping a span of frequency

If the receiver is sending out 4 pulses at 418MHZ, how can i see/view it on the Frequency analyzer so each pulse has the same DB level?

I don't want it to be sweeping the frequency, I just want to make it FIXED at 418MHZ

2. davennModerator

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Sep 5, 2009
so did you see the 418 MHz signal as well ?
the signal at 410 MHz may be a spurii or a sideband of the main signal
I'm assuming if the 418 MHz signal was there then this 410 MHz signal would hopefully be at a lower strength level ?

If it was the only signal visible ... ie. there was no 418MHz signal as there should have been, then the oscillator is off frequency by 8 MHz and needs to be tuned

Dave

3. danny davis

306
0
May 9, 2012
There is 4 pulses

If one of the pulses hits the 418 frequency it will have a large strength but the other pulses with be weak Looking, but technically the other 3 pulses are strong strength its just because the frequency analyzer is sweeping below and above 418, so it makes the pulses look weak even tho they aren't

I'm trying to set the Frequency Analyzer so it doesn't Sweep at all and it FIXED at 418

Do u know how to do this?

4. danny davis

306
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May 9, 2012
Only if one of the 4 pulses is in sync with the sweep time that passes 418MHZ, if not all 4 pulses will Look WEAK because they aren't in sync with the 418MHZ

The SPAN will span frequency below and above 418MHZ

**""The 4 pulses look WEAK when the spectrum analyzer is below or above 418MHZ""

How do i set up the Frequency Analyzer So all 4 pulses Look like they have good strength?

Cause only at 418MHZ will the pulse have max strength

5. davennModerator

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Sep 5, 2009
OK Im not going to spend much more time on this, you have techs there ask them OK

Firstly, before we go any further, what is the source of these pulses ?
and are the 4 pulses supposed to be on the same frequency ?

Also .... post a photo of the screen of the analyser showing the signal(s)

Dave

Last edited: Jun 28, 2012
6. danny davis

306
0
May 9, 2012
It's a transmitter sending out a 418MHZ signal

YES, that's why the signals look WEAK is because the Frequency analyzer keeps sweeping below and above 418MHZ, so the 4 pulses at 418MHZ look weak

I don't know how to set up the frequency analyzer so i can see all 4 pulses at 418MHZ

The frequency analyzer center frequency is set at 418MHZ
Since the frequency analyzer is sweep below and above 418MHZ
the 4 pulses at 418MHZ all look weak

7. gorgon

603
24
Jun 6, 2011
@Davenn

I really admire you, the giant mountain of patience

TOK

8. davennModerator

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Sep 5, 2009
lol thanks gorgon

Ok Danny
With the analyser scanning over a given bandwidth , that is NOT going to cause anything to look weak. The analyser is just going to show any signals present within the range its scanning and its going to show the relative strengths of those signals
IF all the signals are NOT on 418 MHz then there's a problem with the transmitter or the initial signal generation.

Again I ask for a photo of the spec analyser display for these signals and a wider pic showing the settings of the analyser.
A pic of the transmitting equip would also help
till you provide those I wont respond again

Dave

9. (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010

Especially the bit after "READ CAREFULLY WHAT FOLLOWS", and especially the bit before "till you provide those I won't post again".

I'm going to start moderating you to prevent more time wasting Danny.

10. danny davis

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May 9, 2012
How do u upload a word Document file? i have the pictures in a doc file.

11. (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
I don't believe we allow uploads of doc files.

Find an external hosting site and provide a link.

Even better, just size the images appropriately and upload them here.

12. danny davis

306
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May 9, 2012
Well my work did the pictures in a word doc file and i have it and it tells alot about this problem

does this site have an email address i can send it to the admin or moderators sites email address

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Jan 21, 2010

306
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May 9, 2012
15. danny davis

306
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May 9, 2012
Did you guys look at it and get it?

16. davennModerator

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Sep 5, 2009
it was too difficult to read the info on the analyser screen

D

17. (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
And I believe Dave also asked that you show the configuration of the device (this may be difficult).

Perhaps start with a single *sharp* image, and tell us (well Dave -- because I'm not going to be able to help) exactly what you're measuring, the current settings of the analyser, possibly how it's connected to your equipment under test, what the equipment under test is (or is supposed to be) doing, etc.