• Effective immediately we will be deleting, without notice, any negative threads or posts that deal with the use of encryption and streaming of scanner audio.

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Spectrum Sweeper - How it works

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NB0B

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Has anyone ever posted how Spectrum Sweeper actually works? I've picked up bits and pieces along the way through several threads. What I'm looking for is an authoritative, concise, semi-technical, "no kidding" description of how Spectrum Sweeper actually does what it does.

If you're not sure, speculation is not necessary.

Bob/NBØB
 

stevecubfan

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lest you think I'm speculating pages 48 and 49 in the manual . hint think frequency counter. good luck with that tude adjustment.
 

NB0B

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No "tude"

lest you think I'm speculating pages 48 and 49 in the manual . hint think frequency counter. good luck with that tude adjustment.
The manual certainly covers how to use it. That's not what I was asking. I was asking, "How does it do it?" And it's not a case of I'm too lazy to look for the information myself. I've read the manual, I've searched the forums here, and I've searched the Yahoo groups. The information available seems to be fractional at best. I'm looking for someone who can speak to the technical details.

And while "frequency counter" is a good analogy, it doesn't quite capture all that SS does.

Bob/NBØB
 

n4yek

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The manual certainly covers how to use it. That's not what I was asking. I was asking, "How does it do it?"

Bob/NBØB
What I'm looking for is an authoritative, concise, semi-technical, "no kidding" description of how Spectrum Sweeper actually does what it does.

If you're not sure, speculation is not necessary.

Bob/NBØB
Here you go, again 'think frequency counter': (Authoritative part)
(Here comes the concise part.)

1) deleted
2) Signal detected = radio tunes to that freq
3) Radio tunes to that freq = audio present
4) Audio present = voltage sent to squelch circuit (this is the semi-technical part)
5) Voltage at squelch circuit = open squelch
6) Open squelch = audio heard (this is the "no kidding" part)

Is this an authoritative, concise, semi-technical, "no kidding" description?
People on this forum board are nice and helpful people, please treat them as such.
 
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n4jri

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Nice link!

It's important to make that distinction, because unlike a frequency counter, Spectrum Sweeper's performance allows you to lock out frequencies, and you can really slow it down by doing so.

If I recall correctly, it quickly compares the levels of 1 MHz segments, and then breaks them down to the actual frequency. This is lightning fast, but any MHz where you've locked out more than a couple of frequencies will slow down to the point that you can identify them (the slowed-down 1 MHz segments) on the display. Make sure those lockouts don't pile up. Spectrum Sweeper's a great tool, but you have to keep it clean!

73/Allen (N4JRI)
 

stlouisx50

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I too like the tool but have found that it will not always pick up on certain frequencies. For example the national weather service comes in at a S5, but will not always pick up the signal during a search.
 

NB0B

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What constitutes a strong signal?

I too like the tool but have found that it will not always pick up on certain frequencies. For example the national weather service comes in at a S5, but will not always pick up the signal during a search.
Thanks! That's one of the reasons I asked in the first place. Unlike a regular LMIT search that stops on any active frequency, Spectrum Sweeper (according to the manual) "rapidly sweep a range of frequencies for strong signals from nearby transmitters." So the question is, how does it do that? It's obviously different from a normal scan. But how?

Bob/NBØB
 

stlouisx50

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I too am not a pro, but what I can tell you is I think it uses .500 step scanning. If a signal is strong enough to bleed over .500 khz away from the actual frequency It will zoom in on the proper channel. I believe this is how it works.

Example: Actual Police frequency of 155.4900 MHZ might be picked up by the signal sweep (if really close) by the scanner scanning 155.000, 155.500, 156.000 ect. If the signal is strong enough it will zoom in on it.

This is how I understand it..... However another odd thing is with the PSR500. If you watch the frequencies it scans when doing the sweep, it seems as if it skips some at certain bands. I don't have a clue why this is either.

Hope this helps.
 

mancow

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The entire thing is posted in the link above by UPMan.

It sweeps in 1 Meg chunks then narrows down if something is found within one of them.
 

WayneH

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It's important to make that distinction, because unlike a frequency counter, Spectrum Sweeper's performance allows you to lock out frequencies, and you can really slow it down by doing so.
If you toggle "spcl" on (indicated by "SPCL") and you have enough locked out freqs in that 1MHz block it will ignore it entirely. I don't recall how many need to be locked out.
 

Patch42

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Nice link to the patent. I just wish I could understand what they were saying. That's some of the least understandable text I've seen in ages. I can only assume it was translated somewhat verbatim from Japanese by someone who's not quite fluent in English. That's the only explanation for a sentence such as, "Therefore, when a firstly captured and received radio wave does not correspond to a target radio wave, the remaining frequency range is frequency-swept following its capturing to thereby capture the target radio wave." I have no clue what that means other than a whole lot of capturing is going on.

I did understand enough of it to verify that it works the way I thought I'd read elsewhere. Spectrum Sweeper combines a frequency counter with a limit search. It uses frequency counter techniques to find 1MHz segments with combined energy that exceeds some preset threshold, then does a limit search sweep of those segments. In theory this should allow you to pick up on many more active frequencies than a conventional frequency counter alone could do.

As to how a frequency counter does what it does, which I think was what the OP was asking, I haven't a clue.

I do wonder why the same technique isn't applied multiple times. When a 1MHz segment that exceeds the threshold energy level is found, subdivide that segment into 100kHz segments and apply the frequency counter again, rapidly narrowing the search down to 100kHz segments. At some point I assume there would be diminishing returns. Perhaps that point is 1MHz and that's why it stops there.
 

NB0B

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Lock-outs

Nice link!

It's important to make that distinction, because unlike a frequency counter, Spectrum Sweeper's performance allows you to lock out frequencies, and you can really slow it down by doing so.
It's also worth noting that all the search objects (LMIT, SRVC, SWPR) all share the same frequency lock-out table. So if you're going to do some serious sweeping, it may be worthwhile (either through your software or the GLOB menu) to clear out the FrLO table first.

Bob/NBØB
 

NB0B

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How many lock-outs

If you toggle "spcl" on (indicated by "SPCL") and you have enough locked out freqs in that 1MHz block it will ignore it entirely. I don't recall how many need to be locked out.
The default is 5. I haven't seen where to set it on the GLOB menu. But you can set it on the "Weather/Advanced Configuration" tab of PSREdit to some other value.

Bob/NBØB
 

stlouisx50

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The default is 5. I haven't seen where to set it on the GLOB menu. But you can set it on the "Weather/Advanced Configuration" tab of PSREdit to some other value.

Bob/NBØB

Thats why I thought 500 KHZ, my misunderstanding. I will email the gre team and see how to change it. Ill let you all know.
 

DonS

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I did understand enough of it to verify that it works the way I thought I'd read elsewhere. Spectrum Sweeper combines a frequency counter with a limit search. It uses frequency counter techniques to find 1MHz segments with combined energy that exceeds some preset threshold, then does a limit search sweep of those segments. In theory this should allow you to pick up on many more active frequencies than a conventional frequency counter alone could do.

As to how a frequency counter does what it does, which I think was what the OP was asking, I haven't a clue.
There is no frequency counter. The term "frequency counter" implies a wide-band receiver that is able to count "events" (e.g. zero-crossings, peaks above a threshold, etc.), comparing the count to an accurate timebase. The result (events per unit time) yields frequency.

The scanner tunes to the center of a 1MHz-wide segment and, via some dedicated hardware, checks for sufficient RF "field intensity" within that segment. If the field intensity meets a certain threshold, it then starts searching through that 1MHz segment to find the actual transmission. This second search, though, is still not the same as a "limit search".

I do wonder why the same technique isn't applied multiple times. When a 1MHz segment that exceeds the threshold energy level is found, subdivide that segment into 100kHz segments and apply the frequency counter again, rapidly narrowing the search down to 100kHz segments. At some point I assume there would be diminishing returns. Perhaps that point is 1MHz and that's why it stops there.
Subdividing into smaller segments would require more hardware for minimal gain.

The scanner's firmware does narrow the search somewhat. It doesn't necessarily have to search the entire 1MHz segment.
 

N7YUO

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Spectrum Sweeper Operation

I tried using the Spectrum Sweeper in my PSR500 at an event in Salt Lake City. Lots of security present as well as SLC Police. For over an hour there were no hits, even though I witnessed security using their radios.
I swept everything except aircraft bands. Finally, I looked at the display and it showed spcl. I changed it to SPCL and immediately there was reception on 461.1375.
When I got home, I read up on the SS function and the part about locked out search freqs.
I don't have any search freqs locked out, so the SS should have worked in either mode.
 

ScannerSK

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In some of the older scanners prior to Spectrum Sweeper there was a little trick some knew about. A person could use WFM during a limit search to rapidly search the spectrum for strong signals. Once the scanner stopped on a signal you could then switch over to NFM and search that MHz segment for the precise frequency.

Shawn
 
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