RF Spectrum Analyzer

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AnabolicHippo
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RF Spectrum Analyzer

Post by AnabolicHippo » Sun Dec 17, 2017 7:50 am

Our station has been asked to do the following scan:
Please provide us with the following information as late as the day after the tests.

- Carrier level…………….?
- Frequency? …………………….Not more than + - 1KHz
- Modulation? …………………..not more than + - 75 KHz
- Level of the 2nd harmony……………………………?

- Scanning the aeronautical band (From 108 MHZ to 138 MHz) and if you have detected spots, please tell us their levels relative to the level of the carrier.
Now, we would normally have a contractor do this, as we don't have a spectrum analyzer, but they aren't going to be available for the next month or so. I was wondering if this would be appropriate to do the testing?

https://www.ebay.com/itm/USB-RF-Spectru ... 2961285853

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RGORJANCE
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Re: RF Spectrum Analyzer

Post by RGORJANCE » Sun Dec 17, 2017 8:36 am

Who, or what agency has "ASKED" you to do this. And just what is "second harmony"??

Fossil

AnabolicHippo
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Re: RF Spectrum Analyzer

Post by AnabolicHippo » Sun Dec 17, 2017 9:26 am

RGORJANCE wrote:
Sun Dec 17, 2017 8:36 am
Who, or what agency has "ASKED" you to do this. And just what is "second harmony"??

Fossil
It is a regulatory agency within Canada, they are responsible for "Spectrum Management"; because of proximity to an airport, they are asking for more detailed scans. I'm thinking that the "2nd harmony" is referring to the second harmonic.

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Re: RF Spectrum Analyzer

Post by RodeoJack » Sun Dec 17, 2017 10:25 am

I know next to nothing about Canadian communication rules, but looking at the analyzer you're asking about, a couple of things come to mind:

First of all... does your regulatory agency require some kind of calibration reference? If so, there doesn't seem to be anything on the Ebay page that says the analyzer has a calibration and what you'd have to do to get it renewed and certified. Without that, do your results mean anything?

As regards the harmonic and spurious emission request: The trace pictures on the Ebay page barely get down to -80dB, and that's only when the input is attenuated by 10 to 20 dB. The one trace that's shown to go to 0dB full-scale doesn't get below about -70 before everything drops into what looks like the noise floor. If all that's correct, then based on carrier level, the analyzer may not have enough range to do the job you need it to.

You've acknowledged you'd normally use a contractor. Are you confident your "do-it-yourself" measurements would pass regulatory scrutiny? If some kind of "statement of qualification" normally goes along with a project like this, it might be difficult to state that this was the first time you'd ever attempted the work... especially if your results weren't at least verified by someone with experience and a more-common analyzer.

All of this may mean nothing. Like I said... I'm not completely sure I know what I'm talking about... but your direction seems to say that you're considering taking on an official submission for the first time, generating numbers you might not be able to verify, and using equipment who's calibration may not be known and may not be sensitive enough to do the job in the first place.

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RGORJANCE
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Re: Who, or what agency has "ASKED" you to do this. And just what is "second harmony"??

Post by RGORJANCE » Sun Dec 17, 2017 10:49 am

Ok, that clears up my foggy mind. I thought you were in the US, and I am easily confused.

As for a spectrum analyzer suggestion, I only am familiar with the $2K plus units.

Fossil

AnabolicHippo
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Re: RF Spectrum Analyzer

Post by AnabolicHippo » Sun Dec 17, 2017 11:07 am

RodeoJack wrote:
Sun Dec 17, 2017 10:25 am
I know next to nothing about Canadian communication rules, but looking at the analyzer you're asking about, a couple of things come to mind:

First of all... does your regulatory agency require some kind of calibration reference? If so, there doesn't seem to be anything on the Ebay page that says the analyzer has a calibration and what you'd have to do to get it renewed and certified. Without that, do your results mean anything?

As regards the harmonic and spurious emission request: The trace pictures on the Ebay page barely get down to -80dB, and that's only when the input is attenuated by 10 to 20 dB. The one trace that's shown to go to 0dB full-scale doesn't get below about -70 before everything drops into what looks like the noise floor. If all that's correct, then based on carrier level, the analyzer may not have enough range to do the job you need it to.

You've acknowledged you'd normally use a contractor. Are you confident your "do-it-yourself" measurements would pass regulatory scrutiny? If some kind of "statement of qualification" normally goes along with a project like this, it might be difficult to state that this was the first time you'd ever attempted the work... especially if your results weren't at least verified by someone with experience and a more-common analyzer.

All of this may mean nothing. Like I said... I'm not completely sure I know what I'm talking about... but your direction seems to say that you're considering taking on an official submission for the first time, generating numbers you might not be able to verify, and using equipment who's calibration may not be known and may not be sensitive enough to do the job in the first place.
I appreciate the input, granted, I have very little experience doing something like this, so I'm trying to test the waters to see how viable a 'do-it-yourself' approach is going to be. Speaking to the qualifications of the contractor, I'm fairly certain that he does not have any, so I don't think it is a requirement; though he is a knowledgeable technician and came recommended even by the individual requesting the submission.
RGORJANCE wrote:
Sun Dec 17, 2017 10:49 am
Ok, that clears up my foggy mind. I thought you were in the US, and I am easily confused.

As for a spectrum analyzer suggestion, I only am familiar with the $2K plus units.

Fossil
Would you be willing to make a recommendation for a unit? We have recently expanded our network and, at the price point, it would be justifiable to make an investment in that kind of equipment; we are quite remote and travel fees on contractors are high and, if we can do this in-house, would be better spent elsewhere.

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Deep Thought
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Re: RF Spectrum Analyzer

Post by Deep Thought » Sun Dec 17, 2017 12:15 pm

Check out the Rigol units. I have this one and for US$1300 it does everything one that cost ten times that did from 20 years ago:
https://www.rigolna.com/products/spectr ... dsa815-tg/.

The only real downside is the phase noise isn't as good as on the "lab grade" units, but then again it is certainly good enough for field work and won't set you back $20K.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

TPT
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Re: RF Spectrum Analyzer

Post by TPT » Sun Dec 17, 2017 5:34 pm

Apparently some pilot thought he heard your station in their aircraft radio, and complained. Regulatory folks want measurements showing your station meets Canadian emission limits.

You are dealing with bureaucrats. They deal with their pals--or at least their acquaintances. You are not in that crowd. Hire the contractor to take the measurements. Then, assuming everything is OK, the bureaucrats can go back to whoever complained and say :

"See, John Smith did the measurements. We know John Smith. There is no problem. Go away. I'm late for an important mid-morning meeting at Tim Hortons."

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Re: RF Spectrum Analyzer

Post by BigRed » Sun Dec 17, 2017 10:37 pm

Asked by whom? And why? Is there a specific interference problem that can be pointed to or is the interested party just on a fishing expedition? (And what part of the "Great White North" do you hail from?)

And as to spectrum analyzers, I believe that it was Bill Machrone of PC Magazine that once said that the computer you want will always cost $5,000. And so it is with spectrum analyzers. High featured, low cost ones like the Rigol look pretty but fall short when you need to actually makes serious measurements. There's always some issue like limited dynamic range, high noise floor (at the sweep and bandwidth settings that you need to use), poor phase noise, poor TOI (which creates internal spurs that can be hard to pin down, among other issues), or a combination of those issues. [I know of a radio group chief that bought a number of the Rigol analyzers, complete with tracking generators, with the justification being to do the NRSC measurements on his AM's. They can't do it, don't have a prayer. (Rigol does have a few models that can do that work, but they're north of $8,000.)]

It does sound to me like you actually need someone to do the measurements on your behalf though if you're asking about the suitability of those cheapo units on eBay, or even the Rigol. (My "serious" measurements analyzer is an Agilent E4404B as it just covers the necessary UHF TV measurements, a Tek 2712 with tracking generator is my "Simpson 260" for RF.) But if you do want to brave it you can always rent an analyzer for a couple of weeks or a month. Heck, I've even been known to feign interest in buying a unit just to get my hands on a "demo" unit for a while.

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Deep Thought
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Re: RF Spectrum Analyzer

Post by Deep Thought » Mon Dec 18, 2017 12:07 am

"High featured, low cost ones like the Rigol look pretty but fall short when you need to actually makes serious measurements"

You evidently haven't used one.
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BigRed
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Re: RF Spectrum Analyzer

Post by BigRed » Mon Dec 18, 2017 8:41 pm

Deep Thought wrote:
Mon Dec 18, 2017 12:07 am
"High featured, low cost ones like the Rigol look pretty but fall short when you need to actually makes serious measurements"

You evidently haven't used one.
Of course I have, or tried to use a Rigol DAS815 on several occasions. It just didn't prove to be useful. The one I had (a borrowed unit fresh out of the box) coughed up blood each time. Once was trying to track down an interference source at a transmitter site with very high RF levels from a variety of transmitters. Connecting and disconnecting the directional antenna that I was using made little difference to the display. My Agilent didn't have a problem (other than its weight).

And then there was the attempt to do NRSC measurements on an AM station. It's crummy phase noise performance shot it down for that. But don't take my word for it. Have a look at this independent field test write-up: https://www.thebdr.net/articles/ops/sho ... ostout.pdf

All those published performance numbers for test gear actually do affect the unit's performance: things like inherient noise, linearity as a function of both frequency and input amplitude, phase noise, third order intermodulation (and what is that for the Rigol? Can't find it in the specs for some reason.) . . . There's a decent tome that you might be interested in titled The Fundamentals of Spectrum Analysis by Christoph Rauscher that gives a pretty decent explanation if you're interested (your local R&S rep might even be able to send you a copy, and if you're really brave ask for a copy of the Fundamentals of Vector Network Analysis too).

As to the Rigol, for the price it's an OK unit for day-to-day work, like a toolbox DVM, only for RF, just like my Tek 2712. But for serious measurements, measurements where repeatability and traceability are important, I'll stick with something from Agilent/Keysight like my E4404B, or something from Anritsu or R&S.

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RFWarrior
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Re: RF Spectrum Analyzer

Post by RFWarrior » Wed Dec 20, 2017 8:38 am

AnabolicHippo wrote:
Sun Dec 17, 2017 9:26 am
It is a regulatory agency within Canada, they are responsible for "Spectrum Management"; because of proximity to an airport, they are asking for more detailed scans. I'm thinking that the "2nd harmony" is referring to the second harmonic.
I'd question this - Industry Canada has vans very well equipped with measuring equipment and field engineers very well versed in how to use it - I got to meet two of them the day we were ready to end the test phase of our community's 1kW FM and they were quite insistent that they wouldn't accept any scans from us (coincidentally, I do have access to that sort of equipment), I suspect due to the possibility of us not being versed in how to use the measuring gear the correct way (having an analyzer is one thing, knowing how to use it to take a proper measurement is a very different, much more complex, thing).

I also question that they'd use "harmony" in place of "harmonic" unless that was a transcription error. Did the email come from NavCanada? That would also be strange, as they almost always go straight to Industry Canada with any pilot complaints. I guess what I'm trying to say is to verify that the request is legitimate - having worked with both NavCanada and Industry Canada extensively over several decades, what you're presenting seems quite out of the ordinary. Did the request come from somebody with a navcanada.ca or ic.gc.ca email address? Is this a new station, or have you been on air for awhile? What frequency are you on (it's also very rare for them to ask for any special measurements in the aircraft band unless you're at 107+ MHz)?

In short, the Rigol won't do what you need, not accurately - and an inaccurate measurement is more dangerous than not responding. Best bet, if it's assured that the request is legitimate, would be to book the date with your consulting engineer (or ask them for a referral if there's somebody else they know in the area who they think could do a good job more quickly), then go back to the originator of the email, tell them you've booked the consultant and the measurements are scheduled to be taken on x date. If they didn't send you a "shut it off, now" message, then it's unlikely that there have been any firm complaints, or somebody reported a problem and somebody else is just fishing around trying to find the possible cause.

Two disclaimers - I'm neither a lawyer nor a professional engineer, so this is an opinion only, but that's how I'd proceed if my station got a similar request.
Jeff Welton, CBRE
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COMMENG
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Re: RF Spectrum Analyzer

Post by COMMENG » Thu Dec 21, 2017 12:25 pm

AnabolicHippo wrote:
Sun Dec 17, 2017 9:26 am
RGORJANCE wrote:
Sun Dec 17, 2017 8:36 am
Who, or what agency has "ASKED" you to do this. And just what is "second harmony"??

Fossil
It is a regulatory agency within Canada, they are responsible for "Spectrum Management"; because of proximity to an airport, they are asking for more detailed scans. I'm thinking that the "2nd harmony" is referring to the second harmonic.
Agreed, specifically, what is the name of the Regulatory Agency listed in the correspondence or on the letterhead? The more I read this the more I question the legitimacy of the request.

And, what RFWarrior said is good advice.


Commeng

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KPJL FM
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Re: RF Spectrum Analyzer

Post by KPJL FM » Fri Dec 22, 2017 8:07 am

My first harmony and I have been married for over 40 years.
She doesn't know about my second harmony :lol:
Trim to fit, paint to match, tune for minimum smoke.

Ray
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Re: RF Spectrum Analyzer

Post by Ray » Fri Dec 22, 2017 9:40 am

I know one engineer that has not been so fortunate in marriage. He has been married about five times now. Being a real engineer , he says he is currently married to wife 3.2 (third wife, revision two). I suppose we got off-topic on this one. I hope everyone has a great Christmas and maybe Santa will bring all of us new spectrum analyzers. Ray

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