RF Spurious Emissions (aka Spurs) Example.

[marcspaz]

 

Hey folks... I have discussed receive and transmit quality with many of you in the past.  Especially focused around the quality of the transmit signal with regard to spurious emissions, commonly known as Spurs.  I wanted to share this info because with the introduction of the TinySA, some YouTubers are using these in their tech reviews, but really don't understand what they are looking at and end up giving out bad information.

Our friend NotARubicon recently reviewed the BTech GMRS 50V2 and did a great job of showing/explaining what is known as a harmonic spur.  Harmonics are a subset of Spurious signals found at integer multiples of the fundamental frequency of the signal.  If you haven't seen the review, I highly recommend it.  BTech GMRS 50V2 - Review & Power Test - Is BTech's New GMRS 50V2 Better Than The GMRS 50X1?

 

I got a couple of pictures I wanted to share, that relate directly to this.  These images may help understand the references when you see/hear reviewers discuss this topic.  I have a friend of mine who's repeater was not behaving well and upon testing with a tool called a Spectrum Analyzer, he found Spurs every 100 KHz above and below the carrier at 462.675 MHz.  In the GMRS world, that translates to the signal being transmitted over and over again, every 4th channel. 

Below are the images he sent from both prior to the repair, and after it was fixed.

Broken...

 

 

Fixed....

 

 

 

There are many, many types of spurs that can occur.  You are looking at the effects of noise generated by the exciter circuits (VCO for those familiar), known both as sideband spurs and Baseband Harmonic Images.

If this doesn't make sense, its okay.  Just know that if someone is doing a tech review and shows pictures or video like this, the radio is broken... not that it was designed poorly.

The next two pictures are of two of my radio's signals on a TinySA.  These images are great example of Phase Noise spurs.  The first picture, the issues seem pretty obvious to me.  The second picture shows one small spur.  It's not terrible, but it really shouldn't be there.

Warning... Geek Alert!

Phase Noise spurs are unwanted signals that occur due to the random fluctuations in the phase of the carrier signal. Phase noise spurs can degrade the quality of the transmitted signal.  Think audio and signal quality.  This is a symptom of poorly/cheaply designed radios and use of low-quality parts; not something that is malfunctioning. 

 

 

 

 

This was by no means meant to be technical.  It is just samples to help know whats broken vs. poorly designed, and a conversation starter. 

Let me know if there are any questions.  Either myself or one of the smart people in the room will answer them the best we can.

[WQWX838]

7 hours ago, marcspaz said:

 

This was by no means meant to be technical.  It is just samples to help know whats broken vs. poorly designed, and a conversation starter. 

Let me know if there are any questions.  Either myself or one of the smart people in the room will answer them the best we can.

Interesting yet missing important info... What was the equipment, coax, antenna, in use and what was the cause and cure?

[marcspaz]

55 minutes ago, WQWX838 said:

Interesting yet missing important info... What was the equipment, coax, antenna, in use and what was the cause and cure?

 

I didn't mention the radios because the images of spurs are not radio specific, they are symptom specific.  Meaning any radio can have those spur types.  Also, none of the test were conducted with coax or antennas connected.

For the one that was damaged, it was a QUANTAR repeater.  As mentioned in the original post, the VCO in the exciter had gone bad.  It was repaired with a card swap, placing a new exciter in the radio.  After 26 or 27 years in use... I'm sure some silicon-based part went Tango Uniform.

The other images, from the TinySA, are from my BaoFeng BF-F8HP handheld and my Yaesu FT3DR.

[Lscott]

The attached file, found on the Internet, is a test done on the often recommended UV-5R radio.

This is the FCC section dealing with emissions on the Ham bands.

https://www.law.cornell.edu/cfr/text/47/97.307

Section "e" is worth reading. Particularly about transmitters of 25 watts or less. That would include portable radios.

UV-5R VHF Harmonics Test.pdf

[marcspaz]

@Lscott Great find on the PDF!  and... Wow... that makes both my head and my heart hurt to look at.

[Lscott]

1 minute ago, marcspaz said:

@Lscott Great find on the PDF!  and... Wow... that makes both my head and my heart hurt to look at.

Yeah those Baofengs make great dual and triple band radios. You can transmit on several bands all at the same time!

[marcspaz]

LOL No doubt! 

 

For others who are not technically inclined, in the PDF, the smallest spur is -90 dBm.  To translate that to something easily understood... if you set a typical radio squelch to a 4, you only need less than half of that power to open the squelch and start hearing the signal.

[WQWX838]

Yeah, this plot is not very good... However, it was into a 50 Ohm load. A better measure in practice would be to do the same plot using the HT factory antenna, and measuring the same parameters using the off air antenna on the service monitor. A/B more complete characterization. Performance my be worse at 2nd or 3rd..., or could be better. Best I have ever heard is these radios are exactly what you pay for. They do have a giant upside though as people get in cheap with little downside $ risk. Oh, and was the one test sample random? How many were there? Just one won't do. Perhaps some are made that perform better?

[SteveShannon]

17 minutes ago, WQWX838 said:

Yeah, this plot is not very good... However, it was into a 50 Ohm load. A better measure in practice would be to do the same plot using the HT factory antenna, and measuring the same parameters using the off air antenna on the service monitor. A/B more complete characterization. Performance my be worse at 2nd or 3rd..., or could be better. Best I have ever heard is these radios are exactly what you pay for. They do have a giant upside though as people get in cheap with little downside $ risk. Oh, and was the one test sample random? How many were there? Just one won't do. Perhaps some are made that perform better?

The GT5R supposedly cleaned up spurious emissions:

 

[Lscott]

1 hour ago, WQWX838 said:

Yeah, this plot is not very good... However, it was into a 50 Ohm load. A better measure in practice would be to do the same plot using the HT factory antenna, and measuring the same parameters using the off air antenna on the service monitor. A/B more complete characterization. Performance my be worse at 2nd or 3rd..., or could be better. Best I have ever heard is these radios are exactly what you pay for. They do have a giant upside though as people get in cheap with little downside $ risk. Oh, and was the one test sample random? How many were there? Just one won't do. Perhaps some are made that perform better?

I have no idea how many were tested. I was doing my usual thing looking for documentation on the various radios I have. I found the test data during one of my search sessions. I keep a folder with all of my radio info in it. One of the hardest things to find is the service manual/schematic for the cheap radios. Usually the commercial types I had far better luck finding stuff.

I had zero luck finding the service manual anywhere on line for my Ham TH-D74A. I finally got a support tech from Kenwood sent me one complete with schematic. I passed that around to several people who wanted a copy. Also posted it on a user group too.

[axorlov]

Buyao-feng. (不要 - buyao - do not want)

[WQWX838]

6 hours ago, marcspaz said:

 

I didn't mention the radios because the images of spurs are not radio specific, they are symptom specific.  Meaning any radio can have those spur types.  Also, none of the test were conducted with coax or antennas connected.

For the one that was damaged, it was a QUANTAR repeater.  As mentioned in the original post, the VCO in the exciter had gone bad.  It was repaired with a card swap, placing a new exciter in the radio.  After 26 or 27 years in use... I'm sure some silicon-based part went Tango Uniform.

The other images, from the TinySA, are from my BaoFeng BF-F8HP handheld and my Yaesu FT3DR.

OK thanks for some context. Interesting display you have of your own radios also. It looks like digital artifacts from the main oscillator? DDS? Things like this can go away at higher sampling rates. I am not familiar with those two radio's you have and have never heard of them before. This kind of relates to another posting where I mentioned the issues with DSP hardware that have been known for two decades now. Radio manufacturers like DSP for some good reasons. Cost is one, and not less important is the fact that DSP circuits don't have the aging issues like the old hardware does. There are strengths and weaknesses for both schools. Sensitivity is not one, as there are plenty of old radios as sensitive as anything else you can buy today. DSP AGC issues are legendary but getting better, while many old school analog boxes have AGC's like butter. DSP IF's have made crystal and mechanical filters obsolete, yet some of the DSP noise reduction technology is kinda nasty also. Best advice though? Unless you are confident you can repair older hardware, stay clear of it.

[marcspaz]

1 hour ago, WQWX838 said:

....It looks like digital artifacts from the main oscillator? DDS? Things like this can go away at higher sampling rates.

 

I believe you are correct in that my phase noise comes from unwanted digital oscillations in the VCO circuit of the Exciter or between the VCO and neighboring circuits.  SA manufacturers have a feature to remove this from the results, referring to it as a "mirror spur".

 

I don't like suppressing them, because I want to know if there is a quality issue. I haven't built a transmitter in a long time, but knowing if my gear is any good is a plus.

[WQWX838]

15 hours ago, marcspaz said:

  SA manufacturers

What is this "SA"? I think this has appeared before? On another note, I was up early this morning and read through a number of other forum topics I had not seen. Some interesting things on here. Two things, I am in the process for obtaining a business license to get away from GMRS even with portable repeater use. The estimate is a wait time of 2-3 months for completion. The other is that while I have not worked in the Virginia/West Virginia area yet, I saw you mentioned you are a professional engineer. I would like to add you to my Linkedin profile, as I am always open to building my professional network to suit my needs. I have needs for various disciplines so do let me know. Perhaps we have the same alma mater? Thanks

[SteveShannon]

5 minutes ago, WQWX838 said:

What is this "SA"? I think this has appeared before? On another note, I was up early this morning and read through a number of other forum topics I had not seen. Some interesting things on here. Two things, I am in the process for obtaining a business license to get away from GMRS even with portable repeater use. The estimate is a wait time of 2-3 months for completion. The other is that while I have not worked in the Virginia/West Virginia area yet, I saw you mentioned you are a professional engineer. I would like to add you to my Linkedin profile, as I am always open to building my professional network to suit my needs. I have needs for various disciplines so do let me know. Perhaps we have the same alma mater? Thanks

SA is “spectrum analyzer”

[WQWX838]

Thanks Sshannon! Wow! I was thinking "South Asia"... Glad I asked as it seemed a super weird thing to say as the context was not clear on this. lol

[marcspaz]

55 minutes ago, WQWX838 said:

What is this "SA"? I think this has appeared before? On another note, I was up early this morning and read through a number of other forum topics I had not seen. Some interesting things on here. Two things, I am in the process for obtaining a business license to get away from GMRS even with portable repeater use. The estimate is a wait time of 2-3 months for completion. The other is that while I have not worked in the Virginia/West Virginia area yet, I saw you mentioned you are a professional engineer. I would like to add you to my Linkedin profile, as I am always open to building my professional network to suit my needs. I have needs for various disciplines so do let me know. Perhaps we have the same alma mater? Thanks

 

An SA is a spectrum analyzer, used to test electronic equipment of all types.  While folks like me typically use them for two-way radio work, they are also used in the automotive world, computer manufacturing and testing, and many others you may not even suspect, like robotics. 

As far as a business radio license goes, keep in mind that your privileges will be regional.  Meaning, you will only be legal to use the frequencies in specific areas.  This is to reduce interference around the country, due to the limited spectrum.

I am a Computer Systems Engineer and Systems Architect, with some background in Electronics Engineering.  However, I am not a P.E., which as a very different thing. The National Society of Professional Engineers and Professional Engineer Licensure College of Engineering have more or less hijacked the phrase 'professional engineer'.  They have sued people who have said they are professional engineers, taking the two words (used together) out of context and twisted statement to appear people were claiming to be College of Engineering accredited Professional Engineer (PE).  So, again, not a PE nor do I do what PE's do.

I don't have a LinkedIn profile, intentionally, for many reasons and won't be adding one anytime soon.  While I can do some volunteer work with some organizations not related to my career and help friends/acquaintances with small tasks, etc., I am on a very strict limitation with regard to providing any commercial services.

 

That said, notionally, I may be able to offer help/advise for things as they pop-up.  Just PM me here.

[WQWX838]

Hello and OK... Some things here. I too was unclear about the the license and I can operate nationally even with my repeater pairs no problem! I was not aware of this detail either until Gortex (many thanks!) told me and I talked with the coordinator via phone. I am no expert and don't want to pretend to be, but I did not understand the acronym "SA" was all. This is forum lingo and I am awash in this from so many places. I have a comfort level with the hardware and attached a photo of one of my work spaces for electronics.

I do in fact understand the protectionism engineering license boards are doing and it is necessary as there are issues. I was thinking mechanical, civil, chem, EE, or other when I saw engineer. Yes, Linkedin is kind of a cesspool and you have to be really careful! I use it for a contact network as phone and emails change at times.

[marcspaz]

20 minutes ago, WQWX838 said:

I too was unclear about the the license and I can operate nationally even with my repeater pairs no problem! I was not aware of this detail either until Gortex (many thanks!) told me and I talked with the coordinator via phone.

I'm sure it can be coordinated if there is an available national frequency.  It's not the norm, though.  Hopefully you will get something worked out.
 

9 minutes ago, WQWX838 said:

but I did not understand the acronym "SA" was all. This is forum lingo and I am awash in this from so many places.

SA is definitely not forum lingo.  I think, maybe, people like me have introduced it to this forum, though.  SA has been being used by every EE I personally know (grandfather, father and friends alike) for decades, to quickly describe System Analyzers, Spectrum Analyzers, Service Monitors, etc..

 

In fact, it's so prolific in the industry, that manufactures of the novice / entry level equipment are literally using the SA acronym as part of the device name. TinySA being the most well known.

 

23 minutes ago, WQWX838 said:

I have a comfort level with the hardware and attached a photo of one of my work spaces for electronics.

That's a nice collection of gear.  Signal generators, tone generator, O-scopes, service monitors, power supplies, etc.  I miss the days of having a work bench that looked like that.  I still spend good money on Weller equipment.  Especially the adjustable temp soldering stations.

 

33 minutes ago, WQWX838 said:

I was thinking mechanical, civil, chem, EE, or other when I saw engineer.

Yeah, when I saw your post, I figured that was the case.  That's why I clarified. 

I have to say, I understand the whole PE thing and it makes sence.  If you are not College of Engineering accredited Professional Engineer (PE), don't tell people you are.  No issue with that, whatsoever.  My problem is with many of the members, more so than the process. 

My opinion is, if you engineer stuff for a living, you are an engineer...  I have and continue to engineer RF and computer networking solutions for DOD, federal law enforcement, etc., with my professional title issued by those government agencies as either Engineer or Sr. Engineer.

However, I have had numerous PE's (that I am not acquainted with) tell me I am lying, there is no way I am an engineer.  They say I am nothing more than a talented technician working under a 'real engineer' (them implying a PE) and there is no way a government agency would hire an Independent Consultant to be a lead, senior or the only engineer on a contract if they are not a PE. 

Considering I spent 26 years of my near 39 year long career doing exactly what they say would never happen, I find the entire group snobbish, arrogant and ignorant, as they struggle to justify what they accomplish.  The sad part is, they don't have to justify anything.  From a skills and education prospective, PE's have accomplished amazing things in life.  They just need to stop tearing down other people who do the exact same work, but without the same certifications.

[SteveShannon]

31 minutes ago, marcspaz said:

However, I have had numerous PE's (that I am not acquainted with) tell me I am lying, there is no way I am an engineer.  They say I am nothing more than a talented technician working under a 'real engineer' (them implying a PE) and there is no way a government agency would hire an Independent Consultant to be a lead, senior or the only engineer on a contract if they are not a PE. 

One of the very best chief engineers I ever worked under had no college degree and no P.E.  He had been trained in communications by the US Navy, and he had the knack.

[WQWX838]

27 minutes ago, marcspaz said:

My opinion is, if you engineer stuff for a living, you are an engineer...  I have and continue to engineer RF and computer networking solutions for DOD, federal law enforcement, etc., with my professional title issued by those government agencies as either Engineer or Sr. Engineer.

 

Yeah, there is some truth in what you said... I agree on the task being accomplished vs. some type of title. Yet, where it no longer applies is in liability. If there is a question, investors, insurance underwriters, lenders, risk management, and all... When this "thing" was done, did the person doing it have all bases covered with the current knowledge  at the time? What did they know and not know? That is where the road can lead. It is indeed impressive that you have this title on the federal payroll. I have had some government jobs, and while I'm not an "engineer", they always fully vetted me beforehand. I expect it, and would not have it any other way. There is a large amount of fraud out there as usual also so that is part of the problem too. Ability, talent, formal training, can all be independent or unified.

On the other subject of national frequency coordination, according to the coordinator I'm working with (and what Gortex said), it is normal and common. The only caveat is that some locations we may hear each other, yet that likely will not be an issue. National coordination will really help! It will make things 100% legit and I can issue temp operation to anyone I need to... way overdue!

[WQWX838]

20 minutes ago, Sshannon said:

One of the very best chief engineers I ever worked under had no college degree and no P.E.  He had been trained in communications by the US Navy, and he had the knack.

I wonder are you talking about an engineer for TV or radio by chance? I expect you are 100% right, sometimes these guys are really on top of things!

[marcspaz]

8 minutes ago, WQWX838 said:

...they always fully vetted me beforehand. I expect it, and would not have it any other way.

No doubt.  100% agree.  What we do is way too important.

5 minutes ago, WQWX838 said:

On the other subject of national frequency coordination, according to the coordinator I'm working with (and what Gortex said), it is normal and common. The only caveat is that some locations we may hear each other, yet that likely will not be an issue. National coordination will really help! It will make things 100% legit and I can issue temp operation to anyone I need to... way overdue!

That's good to hear.  I stopped doing coordinations years ago.  Too much work for too little money.

Sounds like things have changed for the better.  Good luck and keep us up to date!

[SteveShannon]

17 minutes ago, WQWX838 said:

I wonder are you talking about an engineer for TV or radio by chance? I expect you are 100% right, sometimes these guys are really on top of things!

No, we were working for a startup company trying to come to market with an infrared laser surveying total station.  He could do the digital or analog design like few people I’ve seen before or since.

[WQWX838]

1 hour ago, Sshannon said:

No, we were working for a startup company trying to come to market with an infrared laser surveying total station.  He could do the digital or analog design like few people I’ve seen before or since.

Wow... Interesting! I am familiar with Trimble and Leica total stations. I do surveys, yet use several GIS technologies to do this. I do not do boundary survey projects though. What became of the startup?