I have used in AM band and in SW bands too.

And the 'best' part of it is -- you can 'cover' the MF, HF, and, likely, most of the VHF band with a single oscillator! Golly! Golly!!!

The issue here is user error (errors), not the conceptual soundness of this design.

Connected and working as intended, there will be output (in 'half-power' decrements) every other 1 MHz on up the bands! -- If that now qualifies as 'sound design' that's truly sad!

As to "square wave", you should put your scope on the output and you may be surprised at how "unsquare" wave they are.

Sufficient instrument bandwidth and properly terminated probes will help that! --- Even 100 MHz SXOs beat their transition time specs!

I don't understand why people are coming to the defense of this appalling circuit?! -- Operated at, say, 100kHz, and promoted as a 'signal injector', it would represent a passable beginner project --- But describing a modulated noise source as a communications device is sending the wrong message to both the nubes and their nearby neighbors alike!

With genuine respect
HP

 

This is the original form of amplitude modulation, used before the vacuum tube was invented

Yebut -- As I understand it, even spark-gap transmitters were followed by a BPF (Specifically a 'tank')?

Best regards
HP

 

I think this is what @Aleph(0) had in mind.

HP, you know I respect greatly your opinions. Anyone who thinks 100 kV is a nice starting point gets my attention. But I have to disagree with you on this one.

I know what a Pierce oscillator is. I was questioning the appropriateness of it as a response to this OP. I think burying a new-new-newbie under the complexities of RF oscillator design and construction is a sure-fire way of killing every particle of enthusiasm. Also, the original circuit has everything needed to demonstrate the effects of carrier purity, modulation depth, frequency response, and antenna design on signal range and distortion.

That this guy might radiate a milliwatt of RF hash is not a problem. The problem is that there aren't three more just like him on his street trying this and other things. I have no idea who or how old the OP is, but electronically he (she) is very young. Let children be children. Let them play. Let them get dirty and eat mud pies. They'll learn, and grow up, soon enough.

ak

 

I don't understand why people are coming to the defense of this appalling circuit?!

Because those people understand what this circuit intends to do and focus themselves on that.

Every circuit, however well designed, has "appalling" shortcomings. Great circuits are great because of those very "appalling" shortcomings. The goal for a great engineer is NOT to design a circuit without any shortcomings - that is the goal of a terrible engineer. But instead, to design a circuit that gets the job done in spite of those great shortcomings or sometimes because of those shortcomings.

 

Sufficient instrument bandwidth and properly terminated probes will help that! --- Even 100 MHz SXOs beat their transition time specs!

You didn't understand the simple point I was trying to make: many of today's oscillators generate non-square waves - clipped sine waves are fairly common for example. That's my encouraging you to put a scope on the output pin.

That's particularly true at high frequencies. Granted, older and low frequency oscillators (certainly 4Mhz and lower) tend to be more squarely. But with a short wire as the antenna, there is very little energy radiated out, particularly on the harmonics.

 

HP, you know I respect greatly your opinions. Anyone who thinks 100 kV is a nice starting point gets my attention. But I have to disagree with you on this one.

I know what a Pierce oscillator is. I was questioning the appropriateness of it as a response to this OP. I think burying a new-new-newbie under the complexities of RF oscillator design and construction is a sure-fire way of killing every particle of enthusiasm. Also, the original circuit has everything needed to demonstrate the effects of carrier purity, modulation depth, frequency response, and antenna design on signal range and distortion.

That this guy might radiate a milliwatt of RF hash is not a problem. The problem is that there aren't three more just like him on his street trying this and other things.

ak

Very good points!

As I've said -- I'm no instructor (as my recent efforts on the homework forum aptly demonstrate) -- I concur with your observation that prospective engineering students are too few and far between to risk 'scaring off' --- So, granting that @Aleph(0) 's (quite understandable) suggestion of multiple stages (such that 'pure AM' might be achieved) is likely asking too much of the beginner - I point to the fact that following the SXO with an acceptable low-pass filter need add only two passive components (and, perhaps, some shielding) -- Via monitoring the odd-harmonic frequencies with an HF receiver the experimenter could observe the effects of filtered vs. unfiltered output -- not only would said activity serve as a practical lesson in applied electronics but it may likewise assist intuitive understanding of math concepts...

As always - maintaining an open mind!

Best regards
HP

 

You didn't understand the simple point I was trying to make: many of today's oscillators generate non-square waves - clipped sine waves are fairly common for example. That's my encouraging you to put a scope on the output pin.

That's particularly true at high frequencies. Granted, older and low frequency oscillators (certainly 4Mhz and lower) tend to be more squarely. But with a short wire as the antenna, there is very little energy radiated out, particularly on the harmonics.

Again, I attempt to maintain an open mind - If you can direct me to a datasheet indicative of such 'soft' transition times - I'll happily concede the point -- In my experience even the VHF (e.g. 100 Mhz) oscillators are better than their (rather stringent) specifications... --- In any event my concern is less with RFI than with teaching 'sloppy' habits - a stance that my discussion with @AnalogKid (above) is causing me to reconsider...

The goal for a great engineer is NOT to design a circuit without any shortcomings - that is the goal of a terrible engineer.

Agreed! - Striving for 'the impossible' is a waste of resources -- Not the least of which is time!

Great circuits are great because of those very "appalling" shortcomings.

On this point it seems we're too far apart for fruitful debate

But instead, to design a circuit that gets the job done in spite of those great shortcomings

Agreed - So long as acceptance of said 'shortcommings' is compensated by 'eased' attainment of other design goals (e.g. cost, reliability, etc...)

...or sometimes because of those shortcomings.

But then they're not really 'shortcomings' -- but, rather, 'characteristics' put to advantage?

To 'cut to the chase' -- I grant that educational projects must be held to a unique standard - one that I'm largely unfamiliar with --- still - that 'project' is hard to look at!

Very best regards
HP

 

If you can direct me to a datasheet indicative of such 'soft' transition times - I'll happily concede the point

Better yet - get a scope.

Otherwise, just pick a few random crystal oscillators and check out their datasheets.

The RF issues created by sharp transistors have been long understood by everyone in the industry and there have been available countless (clipped) sine oscillators on the market, since my childhood days.

 

Better yet - get a scope.

IWHT that possession and use of appropriate instrumentation went without saying!

Otherwise, just pick a few random crystal oscillators and check out their datasheets.

Over the years I have profiled many oscillator chips operating in the 10 MHz through 120 MHz range (via TDO and/or SA [i.e. FDO]) -- and always with the same result - To wit: transition characteristics that a Schmitt trigger would be proud of! Here's a sampling of manufacturer's IDs apparent upon cursory inspection of a random 'handful' pulled from my lab stock (all of which were profiled/checked against Spec prior to initial placement therein) -- Ecliptex, Saronix, MF electronix, Motorola, NEL, FOX --- Note that said stock is represented by devices featuring both 'TTL' and 'CMOS' output topologies...

The RF issues created by sharp transistors have been long understood by everyone in the industry

I take it you mean 'sharp transitions'? -- RFI is mitigated via shielding, 'trapping' and 'considered layout' -- Not by 'low-level' crippling of hardware! -- It seems there's a major misunderstanding 'at work'? - or, perhaps, you're having me on? -- Well hey! -- Despite my apparent 'intensity' I'm generally a 'good sport' -- That said, April 1 is yet 84 days hence --- If you are indeed serious - please direct me to a datasheet applicable to such a device --- Following my (painful) discovery of externally supported CRTs -- I'll believe almost anything!

Genuinely intrigued!

Best regards
HP

OBTW -- Here's my 'representative handful'

Mod edit: reduced image filesize

 

I point to the fact that following the SXO with an acceptable low-pass filter need add only two passive components (and, perhaps, some shielding) -- Via monitoring the odd-harmonic frequencies with an HF receiver the experimenter could observe the effects of filtered vs. unfiltered output -- not only would said activity serve as a practical lesson in applied electronics but it may likewise assist intuitive understanding of math concepts.

All true, completely possible, and very instructional and informative - AFTER the lesser performing circuit is up and running in almost zero time. Struggling with something miles over your head for a week or two doesn't teach anything about those issues, but it does teach something you do not want taught at that stage. Besides, there's a guy named Colin on another forum that's made that his life mission. ("Come back in 20 years and maybe you'll understand." - honest-to-god direct quote.) Something that is quick and dirty, has a bit of instant gratification, and is able to be improved incrementally as the student progresses cements the concepts in ways a complete and legal transmitter just is not capable of doing. So, step 1 - this circuit. Step 2 - *everything* else.

Now that every moron on the street has world-wide real time audio and video comms in his pocket, radio has lost some of its experimenter allure. Still, while the ARRL probably doesn't have the membership it once had, the APGL (American Power Generation League), ASSTL (American Servo Systems Theory League), and ADPL (American Device Physics League) have zero membership because they don't exist. Of all of the various and wonderful things in the universe of electricalityism, *nothing* has the draw, the snap, the appeal, the hook of radio.

Invisible airwaves crackle with life
Bright antenna bristle with the energy
Emotional feedback on timeless wavelength
Bearing a gift beyond price, almost free

Neal Peart, "The Spirit of Radio"

ak

 

Once again - Point well taken! --- It seems my mental 'scotoma' as regards science/math instruction owes to my personal high degree of motivation from an early age -- I can see where nurturing the interest of an (initially) dispassionate student requires a bit of 'TLC' --- And yes! There is something about electromagnetic communication!

Invisible airwaves crackle with life...

Ah Ha! --- That makes more sense! -- All these years I thought the lyric was "Invisible railways crackle with light -- Spice and ginger, whistle with the energy..."

Very Best regards
HP

 

Besides, there's a guy named Colin on another forum that's made that his life mission. ("Come back in 20 years and maybe you'll understand." - honest-to-god direct quote.)

You sure he's not on this forum too? I've seen some of that around here lately (not referring to this thread, but several others in the last week or two.)

 

You sure he's not on this forum too? I've seen some of that around here lately (not referring to this thread, but several others in the last week or two.)

He dips in occasionally, but not nearly as often as elsewhere.

Unfortunately, the tactic of building oneself up by knocking down others is not as rare as it should be, especially on a help forum.

ak

 

Unfortunately, the tactic of building oneself up by knocking down others is not as rare as it should be, especially on a help forum.

Sad, but true.

When I first started pursuing my interest in electronics, I learned a lot from the Adafruit tutorials, but it didn't take long before I had questions and needed help. I was amazed by how many forums seem to be dominated by people with that sort of bad attitude.

I was greatly relieved when I found this forum. Here, even when there is heavy criticism or disagreement, it's usually handled in a constructive way, not in a mean way. I really appreciate that. I don't know if it's just a self-perpetuating culture or if there's active work to keep this place positive. Either way, I'd like to take this opportunity to thank the mods and active members who make this forum so helpful and positive. You all are great!

 

Struggling with something miles over your head for a week or two doesn't teach anything about those issues, but it does teach something you do not want taught at that stage.

I can see where nurturing the interest of an (initially) dispassionate student requires a bit of 'TLC'

I'm not sure about that! I was building balanced modulators and product detectors at 6 yoa and _designing_ BEM and MTCM systems by 10 and nobody was less motivated than me! You can ask HP! If I had been given a dumb project like circuit in the op I would probably turned to collecting Barbies and become just another silly knuckle dragging conformist lackey! So I'm saying newbies aren't dumb and publishers shouldn't be treating them like that!

 

nobody was less motivated than me! You can ask HP

And I assert that you were highly motivated! -- for the subjects' 'malleability' - for their 'approach' to physical realization of the abstract - and, perhaps, most of all, to your (admirable) insistence upon maintenance of said parallels where the discipline specific 'narratives' erred on the side of 'dumbed-down obfuscation' -- Yes indeed! I well remember, for instance, your (justifiable) annoyance with the common description of SSB communication -- and your demonstration of the fact that said technique is, in essence, nothing more (or less) than 'conversion' of the AF signal via heterodyning of same with an 'RF tone' -- Point being, without wishing to over-dramatize, you tend to be a bit of a 'crusader' - which being a very good thing -- I'm merely pointing up the fact that such 'qualifies' as motivation - strong motivation!

If I had been given a dumb project like circuit in the op I would probably turned to collecting Barbies and become just another silly knuckle dragging conformist lackey

Not a chance! -- You would have conceived and assembled a proper circuit! --- And isn't that the whole point?

So I'm saying newbies aren't dumb and publishers shouldn't be treating them like that!

No arguments there (on the face of it) -- though I'm bound to say that education is a 'tricky' area -- sometimes a tacit insult of the student's intelligence provides that 'game changing nudge' in the direction of initiative!!! --- 'Tho I'll grant it's a 'tough call'...

Very best regards
HP