The Real Reason Your Radio is DIRTY

Рет қаралды 6,879

Күн бұрын

How does a seemingly clean radio, with no spurious emissions still produce harmonics when transmitting into an antenna? What about two transmitters in close proximity - Let's find out what happens and why.
Why Your Receiver Doesn't Work 👉 • This Will KILL Your Ra...
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⏱️Chapters⏱️
0:00 Testing Radios for Harmonics
1:12 Clean As A Whistle
3:06 The test environment
4:48 Huh?
6:40 Even worse!
9:03 What's going on?
11:01 SUM and the Difference
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Пікірлер: 59

@HamRadioDX 26 күн бұрын

📋Equipment I use in this video (Amazon Affiliate) TinySA Ultra 👉 www.amazon.com/dp/B0BMPSSFTK?tag=hamradiodx-20 RF Adapter Kit 👉 www.amazon.com/dp/B079K65LHK?tag=hamradiodx-20 Attenuator 👉 www.amazon.com/dp/B07MZLVY9T?tag=hamradiodx-20

@Bond2025 26 күн бұрын

Why buy faulty test equipment?

@HamRadioDX 26 күн бұрын

@@Bond2025 Where is the faulty test equipment?

@HamRadioCrashCourse 26 күн бұрын

That was fun. Nice job on the explanation!

@HamRadioDX 26 күн бұрын

Thanks Josh 👍

@simongordon8182 23 күн бұрын

Totally agree, all sorts of causes especially with all that other kit, you may find if you did the same outside you would see far less

@TheSmokinApe 24 күн бұрын

Very nice test Hayden. You are correct about the FCC rules. I suspect you are seeing mixing artifacts internal to the SA as a result of proximity between the transmission and the receiver. The external gain setting isn’t valid because you don’t have an attenuation device but you can adjust the internal attenuator which would help identify a mixing issue being the cause. Maybe test with those adjustment or an inline attenuation device and see what happens. Great job 👍

@robwoodwe5495 25 күн бұрын

Way back when I was in radio tech school (USAF), what you showed in your video was one the things they taught us would/could happen - all the more reason to have the best connections possible when doing direct tests on equipment - to eliminate as much outside interference as possible. (also recommend getting a bigger attenuater so as to have less connections between devices) . Always enjoy watching !!

@mikesradiorepair 26 күн бұрын

I did basically the same test several years ago with similar results. I would agree it is IMD. I went a step further a couple years later. I made a homemade anechoic RF test chamber and when I repeated the test the spurs disappeared. It confirmed the spurs were coming from the DUT (device under test) signal mixing other signals.

@101blog 26 күн бұрын

Probably getting most of those mixing products were in that SA ...it was definately overloaded Good point you made there !!

@donnakano3697 3 күн бұрын

Much of what you discussed is pretty well known in the testing community, but I had never thought about mixing occurring due to rectification in nearby lighting fixtures, etc. Thanks! Since a dummy load with a -40dB attenuator is cheap enough, it makes sense to spend a little more to make a better measurement. It also allows us to test unknown transmitters without putting them on the air.

@theknivjocke 16 күн бұрын

You're probably right. Something that came to mind was also the intermediate frequency stages in the radios, could they perhaps be subject to interference which is then carried along through the output stages? Depends on what filtering is used in the later stages of course.

@FEPLabsRadio 26 күн бұрын

Great video, Hayden. This really shows what intermod is, and how the signals can interact in a non-positive way. It makes me wonder, if I repeat this with a dirty radio (I have a collection!) how much more bad it would be. Or with some more separation between the TSA and the source signals. Something to tinker with... In any case, crackin' good job!

@HamRadioDX 26 күн бұрын

Thanks Jim! Yeah it was an interesting test, good to learn how mixing occurs

@WECB640 26 күн бұрын

Excellent demonstration Hayden. Many decades ago when my broadcast station did a remote from a site where other broadcasters might be using wireless mics, cameras or any thing that transmits RF, we all had to submit our frequencies to the FCC coordinator far in advance so that we would not HARMONICALLY interfere with each other under the same roof or close proximity. I have also seen many cases where a broadcast transmitter (perhaps one on MW) had a signal leak in from another station within a few miles down the road, or perhaps one further away but in a highly directional pattern. That 2nd signal got in and mixed with the first one and both were amplified and spit out to the antenna system. It would show up when the station did an annual proof of performance as shown on a spectrum analyzer connected to the transmitter. Keep up the great work. 73 OM

@kenenglish124 26 күн бұрын

We have the exact same thing here in Salt Lake City . With several high-powered stations at the north end of the valley, they are being mixed within the 700 KHz transmitter. There are quite a few spurs, but no second harmonic is radiated, since the transmitter filters it out (as it should). There are plenty of beats between stations, but only intermittently. Maybe wind or weather?

@johnwest7993 26 күн бұрын

You're not wrong. I just shook my head when I saw that other video you mention. KZfaqrs who talk about technical subjects really need to understand their subject or they will sound foolish. Unfortunately, along with good channels like yours, (and some truly expert channels,) there are those who talk about subjects they don't know much about. You can use a separate radio on the frequency of that spur and actually hear the AM station or other HT or whatever source you're mixing with and verify what is going on. Strong signals are just being mixed together outside the radio, not inside it.

@K2DXK 26 күн бұрын

Another great video Hayden. You’re definitely over driving the SA and the intermods are happening within the SAs receiver which most likely has very poor filtering. K2DXK

@HamRadioDX 25 күн бұрын

Thanks mate!

@chrisjohnson8741 26 күн бұрын

I can think of a couple of things that may mess up this kind of test: First, as you pointed out, you are likely overloading the SA when using it with an antenna at close range. Second, it is worth noting that the receiving antenna has a frequency response, and may be more nearly resonant at a harmonic than at the fundamental-- at the very least, you can't expect it to be flat. If you want to use an antenna input for this, you want a really short antenna: just a half inch or so of wire stuck in the input SMA. This will assure a more or less flat frequency response and less likelihood of overloading. But in the end, you are so close to the SA that the signal may bypass the input entirely, since the TinySA is pretty much unshielded. It may not be the best tool for the job. Doing this kind of measurement with a lab SA is tricky enough, introduce all the unknowns of the Tiny and measurement results are better than guesswork but not much. An interesting demo of intermod though.

@victorcharlie7491 22 күн бұрын

The real reason my radio is dirty is cause i haven't dusted it of in a while, tnx Man!

@Ressy66 24 күн бұрын

great points you made, its why you can't just move a repeater to another site without approval, that site owner and ACMA (like when getting a new freq for a site) run the frequency through software that checks for all those goodies and nasties at each site, and if at a known tx location, for all nearby sites (ever wondered why you can temp move a repeater to a location within X distance of the assigned location, thats why, they deem it shouldnt be a problem within that distance)

@KS0JD 25 күн бұрын

Other case of mixing can be what is called re-radiation. This is the transmitted signal being picked up by another transceiver and it is re-radiated by the second transceiver. This is usually very much caused by antenna proximity between the two transceiver antennas. We find this a lot on aircraft installations. Particularly when the antennas from both transceivers antennas are mounted on a similar location on the aircraft, ie both on the top or booth on the bottom of the aircraft. Once design change to over come it was to have a transmitter interlock between the two transceivers. This function turns the receiver off of the unit that is not transmitting when the other one is transmitting. Antenna separation can also somewhat alleviate the problem depending upon the transmitter power. You are right to assume the FCC rules apply to the signal out of the unit. Any outside actor causing a problem does not men the unit has failed the FCC specification. 73

@moozoowizard 26 күн бұрын

Well when I did this I put a 40db attenuator between the tinysa and the whip because I was worried I'd damage the tinysa.

@Hank_W6IR 26 күн бұрын

Thanks Hayden for picking up where Jim left off. I made the comment about the "at the transmission line" being the rule to him.

@3henry214 26 күн бұрын

That was very interesting to this newbie! Thank you!

@oldfartonabmx2122 25 күн бұрын

I’ve heard of a guy with rusty bolts in his tower causing interference to a nearby airport, when another ham nearby was also transmitting.

@HamRadioDX 25 күн бұрын

Yep! Intermod at it's best happening!

@TheHandyHam73 26 күн бұрын

Great Content, Thanks!

@acestudioscouk-Ace-G0ACE 25 күн бұрын

You make some good points, nicely done! Thanks.

@bob505470 26 күн бұрын

What you're seeing on the tiny sa is almost certainly input compression from the front end being over driven which is why you see harmonics appearing with just the single transmitter. With both going, the IMD products you are seeing are most likely being created inside the tinySA's itself. For this sort of test to be accurate, you need to take care not to exceed your ip3 or p1db compression point specified by the spectrum analyzer manufacture to ensure the spurs you are seeing are indeed real.

@bitemykrank1970 25 күн бұрын

If radio's were actually clean, how would the bad guy, bent on world domination be able to transmit his manifesto on every TV and radio station simultaneously globally ?? It always works in the movies....

@ianwalker1182 24 күн бұрын

I would suspect the telescopic antenna, the sliding parts and swivel constitute dissimilar metals in contact, these will act like tiny diodes and create harmonics. You could eliminate this by trying a single wire on an SMA plug. You could eliminate your environment by repeating the experiment in an open field, metalwork in your shack could also cause harmonics (the "rusty nail effect"). Passive intermodulation (PIM) is real problem where a cell site has multiple, mulrichanel transmitters.

@johnwest7993 26 күн бұрын

While it's possible for a bad impedance match to cause a spurious oscillation in the final, all those spurs seen are most likely intermod. There's a reason we look for harmonics with our source signal shielded and fed directly to the SA.

@garryhammond3117 24 күн бұрын

RF could also be getting directly into the circuitry of the TinySA - Do we know how well the internals of this unit are shielded? - Cheers!

@keithbroughton4476 15 күн бұрын

An excellent demonstration of IM artifacts. Can you begin to imagine what it's like when you have 20 or 30 wireless microphone transmitters working in a corporate or performance stage environment? Welcome to my world (LOL)

@HamRadioDX 14 күн бұрын

I just recently did a Shure Wireless training! It would be a nightmare!

@ronboe6325 26 күн бұрын

Thanks for pointing out that the FCC defines the signal quality as supplied to the antenna. Since the antenna is such a wild card that would be about the only fair test for every transmitter. The downside to that; when we're out there using our radio's receivers are hearing what the radio and antenna system is transmitting (not the same as the ideal lab setting)- which begs the question: will a poor quality antenna stress the circuit to the point of a dirty signal? Another very good point; you need to know the test conditions in your "lab" when doing an over the air test and in Jim's situation we don't know. You can repeat the tests for all the transmitters in the same conditions and if a clean transmitter is still clean when transmitting over the air vs a closed test system then that tells you something too. If you have one or more of the Chinese radios (especially a known dirty one) to retest as in the video. That Tiny SA is just too cool, may have to grab one of those!

@BrianFields 26 күн бұрын

Absolutely - at one time I'd actually found the test lab conditions used and it was specifically a direct connection from the device under test to the SA. I've been trying to find it again since I saw Jim's video, but I can't seem to locate it.

@ronboe6325 26 күн бұрын

@@BrianFields This reminds me of this nice fellow that does projects for the RV world. He had decided to test a bunch of antenna's (to boost cell phone coverage, so on top of the rigs). He placed a small forest of antenna's on the same mounting plate - at the same time. Several of us pointed out that this was very problematic (I do understand why he wanted to conduct the test that way, the top of his RV was high), but in the end he didn't think it would be a problem and went ahead as planned. A shame as he can do really good work when he stays in his lane.

@matsbengtsson3756 26 күн бұрын

Radio -> 4odB attenuator -> SA is a good way to measure to avoid mixing products. Thanks.

@frequencywatchers 25 күн бұрын

Video You Mentioned I Commented On.. Hey Mom, Im Learning!!!

@temporarilyoffline 26 күн бұрын

Thanks!

@HamRadioDX 26 күн бұрын

You bet!

@normanalbrecht2103 26 күн бұрын

You still need attenuation with the antenna. Overdriving front end of sa

@GH0ST369 25 күн бұрын

Question: So to isolate the noise floor signals you can use the antenna on the SA and turn off equipment to see where the spikes disappear right?

@HamRadioDX 24 күн бұрын

You could narrow some/find some noise sources that way

@Maker_Mikey 26 күн бұрын

Would monitoring the on the TinySA be more accurate with an antenna tuned to the frequencies and harmonics you intend to measure? Was the telescoping antenna tuned prior to the measurements? I would love to see another video where this calibration is performed as part of the video to have baseline expectations of the TinySA readings.

@lisocampos8080 26 күн бұрын

Real cowboys wear spurs

@Qietman 26 күн бұрын

As long as the receiving antenna is within a few inches...

@DonzLockz 26 күн бұрын

It's very interesting, but I have no idea.

@rheynaldyrama9978 26 күн бұрын

Review ham dmr

@yungsmile7546 26 күн бұрын

😂hmmm😮

@VK2AAK 25 күн бұрын

If you want to see examples of amateurs causing interference without knowing it, just tune to one of the popular nets on 40m and watch the 10 KHz wide signals from people who overdrive their amplifiers and have their mic gain and compression turned up far too high. It’s just embarrassing to look at the waterfall and see horrible signals from long-term amateurs who really should know better.

@kkendall99 25 күн бұрын

All radios are not the same, the normalized FCC test data shows that quality radios have cleaner output. Granted the "cleaner" radios vs cheap radios are not really an issue these days, but a clean signal will always propagate better.