Part 15.219(b) rule

[SUPERCASTER]

R. Fry said:

However the discussions in this thread have concerned either the horizontal part of a tee antenna, or buried ground radials -- not a counterpoise.

No.
Your original claim was that a center fed conductor, such as in a ground radial system, counterpoise (or vertical monopole?) does not radiate because equal, in phase currents traveling in opposite directions toward the ends of the conductor cancel and do not produce an RF field. This is false.

You then threw in the diagram of the Tee antenna (with no ground system) as a misdirection (red herring) saying it won't radiate.

Neil E. said:

The equivalence between the top hat wires and the radial wires was only to illustrate that the fields from each cancel by the same mechanism,

Clearly false. Center fed conductors do radiate. (See above).

and:

the currents are travelling in opposite physical directions in the opposed radials and this is what makes the fields 180 degrees out of phase and the fields add to zero.

RF currents traveling in opposite directions to the ends of a center fed conductor (such as in a counterpoise, ground radial system or even a vertical monopole antenna) are not "180 degrees out of phase and the fields add to zero", as you claim. They are in phase and additive.
RF energy whether end fed or center fed to a single conductor will still radiate.

 

[rfry]

Your original claim was that a center fed conductor...does not radiate. No. ... This is false.

The far-field radiation envelope of a tee antenna in the link posted earlier shows that there is no radiation from the horizontal wire. And this envelope is very nearly identical to that of a vertical monopole using 120 buried radials each 1/4-wave long, which shows that the radials do not radiate, either. These are facts of physics that really aren't open to debate.

Maybe if you downloaded the demo (free) version of EZNEC, and constructed/analyzed a simple model of a center-fed wire it would help you see the reality of this. I'd be glad to work with you on this if you wish. You can contact me through my website http:rfry.org.

Otherwise both Neil E and I have tried our best to explain this, and if we've had no success, then probably there is no point in pursuing it further with you. Hopefully the information has been useful to others.

//

 

[Timewarp]

100 mw on AM with 10 feet of antenna is kind of like playing with my old electric train. Fun
for about 10 minutes. Then, time to pull the plug and put the toy away.
If you guys are for real about wanting to own a station, your last chance may be right now.
You don't have to spend thousands on lawyers and engineers. Study and do it yoyurself.
File with the FCC for free.

 

[Ur-A-Dawg]

Timewarp give it up! Only dreamers dare to win and only winners dare to dream. None of
those on this thread. These guys don't want an FCC license or more power.
They are happy with one tenth watt on AM. Let em be!

 

[Neil E.]

100 mw on AM with 10 feet of antenna is kind of like playing with my old electric train. Fun
for about 10 minutes. Then, time to pull the plug and put the toy away.
If you guys are for real about wanting to own a station, your last chance may be right now.
You don't have to spend thousands on lawyers and engineers. Study and do it yoyurself.
File with the FCC for free.

Not everyone, despite the title of this board category, is interested in part 15 radio to "serve the community". Some are, and that is fine, but some aren't. Your input about obtaining a license for a "real radio station" is helpful, and I trust others will consider your suggestion.

But, there are folks, such as I, who just use part 15 for personal uses around their property. When I want the thrill of hammering the ether with lots of power and being heard worldwide I turn on my ham set. This also is fun.

Sometimes, playing with my 55 year old model train (1952 vintage American Flyer) is fun even though it doesn't deliver a ten thousand ton payload of coal.

But, in my case with part 15 there is a payload. It is that I can stream audio from the internet or from my vast and excellent computer based audio library and listen on a very cheap receiver anywhere on my property (IPod is too much trouble) and I could care less if anyone else listens. Toward this end, I want to produce a clean signal which provides adequate range. Also, I am interested in the theory and practice as an end unto itself. Recognizing that others may want to squeeze as much range as possible from their transmitters on the assumption neighbors will listen, and who care about doing so withing the rules, I try to offer theory and practice based technical guidance on this board. You are free to dismiss this as wasted effort such as "playing with a model train" but perhaps others don't.

I am not interested in owning a "real radio station" or even one that ranges a few miles. Yes, part 15 is my toy, but for almost 50 years this toy has been fun for me and it provides a nice way to investigate technology and it meets my personal needs by providing a way to listen to decent programming as I wander about my estate.

My ten minutes of fun began in 1959 and hasn't ended yet. Guess it doesn't take much to keep some people happy, huh?

Toys are necessary.

Neil

 

[SUPERCASTER]

Your original claim was that a center fed conductor...does not radiate. No. ... This is false.

The far-field radiation envelope of a tee antenna in the link posted earlier shows that there is no radiation from the horizontal wire. And this envelope is very nearly identical to that of a vertical monopole using 120 buried radials each 1/4-wave long, which shows that the radials do not radiate, either. These are facts of physics that really aren't open to debate.

Maybe if you downloaded the demo (free) version of EZNEC, and constructed/analyzed a simple model of a center-fed wire it would help you see the reality of this. I'd be glad to work with you on this if you wish. You can contact me through my website http:rfry.org.

Otherwise both Neil E and I have tried our best to explain this, and if we've had no success, then probably there is no point in pursuing it further with you. Hopefully the information has been useful to others.

//

GiGo
http://en.wikipedia.org/wiki/Garbage_In,_Garbage_Out

I can find no reference to "Tee antennas" either in the topic of this thread

Part 15.219(b) rule

or in Hamilton's original post.

Your frequent posts about Tee antennas, are simply a midirection, (red herring=something that distracts attention from the real issue).
http://www.m-w.com/dictionary/red%20herring

 

[Tom Wells]

I see the back-and-forth over cancellation and currents, and it reminds me of arguments back in radio school.
The same points (arguments) were made, and the instructor said BOTH viewpoints were valid.
The seeming disparity is WHY radiation occurs. If there were no L or C component to the radiator, we'd just be disappating heat.

 

[SUPERCASTER]

Once upon a time, I had a conversation with a friend about part 15 AM. A good man and the Engineer
in Charge of a midwest FCC field office. He told me about a low power AM that had strapped on to a
tower. The ground strap went through the tower.

He told me that because the tower was pre-existing it was fine. The key was pre-existing.

Thanks for the anecdote. Once again it appears this was a matter of discretion. In the rules there is no mention of "pre-existing".

Neil

"Pre-existing" might be proof that the tower was an "incidental radiator" under Part 15, as opposed to an "intentional radiator" to which other regulation applies.

 

[Tom Wells]

100 mw on AM with 10 feet of antenna is kind of like playing with my old electric train. Fun
for about 10 minutes. Then, time to pull the plug and put the toy away.
If you guys are for real about wanting to own a station, your last chance may be right now.
You don't have to spend thousands on lawyers and engineers. Study and do it yoyurself.
File with the FCC for free.

Not everyone, despite the title of this board category, is interested in part 15 radio to "serve the community". Some are, and that is fine, but some aren't. Your input about obtaining a license for a "real radio station" is helpful, and I trust others will consider your suggestion.

But, there are folks, such as I, who just use part 15 for personal uses around their property. When I want the thrill of hammering the ether with lots of power and being heard worldwide I turn on my ham set. This also is fun.

Sometimes, playing with my 55 year old model train (1952 vintage American Flyer) is fun even though it doesn't deliver a ten thousand ton payload of coal.

But, in my case with part 15 there is a payload. It is that I can stream audio from the internet or from my vast and excellent computer based audio library and listen on a very cheap receiver anywhere on my property (IPod is too much trouble) and I could care less if anyone else listens. Toward this end, I want to produce a clean signal which provides adequate range. Also, I am interested in the theory and practice as an end unto itself. Recognizing that others may want to squeeze as much range as possible from their transmitters on the assumption neighbors will listen, and who care about doing so withing the rules, I try to offer theory and practice based technical guidance on this board. You are free to dismiss this as wasted effort such as "playing with a model train" but perhaps others don't.

I am not interested in owning a "real radio station" or even one that ranges a few miles. Yes, part 15 is my toy, but for almost 50 years this toy has been fun for me and it provides a nice way to investigate technology and it meets my personal needs by providing a way to listen to decent programming as I wander about my estate.

My ten minutes of fun began in 1959 and hasn't ended yet. Guess it doesn't take much to keep some people happy, huh?

Toys are necessary.

Neil

My part 15 follows the same form as Neil's, but I have only been operating it since 1988.
I would not want a low-power FM. We have a full dial here in Chicago. I am sure no LPFMs will be shoe-horned in here.
I don't really even think music sounds as good on FM as AM ( at its best, not the current hobbled AM).
I enjoy listening to and maintaining the best sounding AM signal I can hear on a transmitter of my own design and construction.
If I want to hear true hi-fi AM, it's up to me. Very few AMs have full fidelity anymore.
And if I am playing unique, interesting content, why shouldn't the neighbors be able to listen?
Some of my neighbors have parties that can be heard farther than my flea-power AM, and I have no choice but to hear their music.

 

[rfry]

['ve seen a counterpoise used on a Kinstar-type antenna where a wire is strung among the poles. But how would a counterpoise be implimented on a unipole? Would this be similar to a folded unipole?

Any form of broadcast vertical monopole could use a set of 6 or 8 radial wires each about 1/4-wave long, elevated 10-15 feet above the earth in place of the conventional set of 120 buried radials. The fields measured from both of those configurations are very nearly the same, other things equal.
//

 

[Hamilton]

I’ve been reading the posts and have some thoughts, to the many who have no idea what these people are talking about go to ARRL.org and get the ARRL amateur radio handbook It has a great short course on electronics and antennas and you can learn at your own pace.
Guys, I am curious what you think about signal polarization, specifically in relation to frequency. I have found in the field that in for Part 15 AM that using a standard 3 meter antenna for the transmitter and a 1-2 meter antenna for the receiver the orientation of the antennas seems to make no difference I can see either for the transmitter or receiver. I assumed it was because the antenna was so short in relation to the wave.

 

[Black_Shire]

I’ve been reading the posts and have some thoughts, to the many who have no idea what these people are talking about go to ARRL.org and get the ARRL amateur radio handbook It has a great short course on electronics and antennas and you can learn at your own pace.
Guys, I am curious what you think about signal polarization, specifically in relation to frequency. I have found in the field that in for Part 15 AM that using a standard 3 meter antenna for the transmitter and a 1-2 meter antenna for the receiver the orientation of the antennas seems to make no difference I can see either for the transmitter or receiver. I assumed it was because the antenna was so short in relation to the wave.

How far apart were your Rangemaster AM transmitter and your AM receiver (what kind of receiver was it, by the way?) when you conducted these tests?

Ham radio operators who engage in 160 meter band (1800 kHz - 2000 kHz) mobile operation (using vehicle-mounted whip antennas that are mounted atop big loading coils) often refer to their physically-short 160 meter band antennas as "leaky dummy loads."

I suppose there is some antenna length below which a physically-short antenna begins to approximate an isotropic radiator, where no one polarization is more prominent than another. (Even a horizontal 1/2 wavelength dipole antenna radiates some vertically-polarized radiation off its ends.)


-- Black Shire

 

[rfry]

I have found in the field that in for Part 15 AM that using a standard 3 meter antenna for the transmitter and a 1-2 meter antenna for the receiver the orientation of the antennas seems to make no difference I can see either for the transmitter or receiver. I assumed it was because the antenna was so short in relation to the wave.

Even though the far field radiated in the horizontal plane by a 3-m Part 15 AM vertical monopole is vertically polarized, some field may still be produced in a cross-polarized receive antenna depending on the geometry of the path, the presence/performance of incidental radiators and other factors. Cross-polarized Part 15 AM antennas generally show less discrimination for shorter paths -- especially in the near fields of the antennas.

Vertical polarization is used for daytime broadcast purposes below about 2 MHz, because the groundwave field that provides this service has much less propagation loss along the surface of the earth for vertical polarization than for horizontal polarization.
//

 

[Hamilton]

I was testing at about 1/4 mile using a frequency selective meter. So it sounds like what you are saying is that the signal gets bounced around a bit, making it likely that (at a distance) what I was getting when I was testing with the transmitter and receiver at different polarizations was twisted and bounced signal reception.

I had wondered if a part 15 antenna could be a “point source” radiator, since it was so short in relation to the wavelength.

 

[Tom Wells]

I was testing at about 1/4 mile using a frequency selective meter. So it sounds like what you are saying is that the signal gets bounced around a bit, making it likely that (at a distance) what I was getting when I was testing with the transmitter and receiver at different polarizations was twisted and bounced signal reception.

I had wondered if a part 15 antenna could be a “point source” radiator, since it was so short in relation to the wavelength.

It must begin to approximate a point source, but in the same way an amoeba is a point source.

I think the far field is an amalgam of all the various conductor/current fields, and moving/changing any of such relatively short
conductors has some affect, but not as with 1/4 wave and up radiators.
The fractional wavelength also means far more energy returns via the "short path" and is effectively cancelled from radiation,
just as woofers can not load bass into the air without a baffle, or lengthening the path betweem front and back of speaker.
Pt 15 AMs are like the 6 x 9 inch speaker sitting out on the rear window deck of a car, unmounted.
They can't really "hook" into anything with such a tiny grip on it.

 

[rfry]

Pt 15 AMs are like the 6 x 9 inch speaker sitting out on the rear window deck of a car, unmounted. They can't really "hook" into anything with such a tiny grip on it.

Really, these are not parallel situations. An unmounted (unbaffled) speaker has uneven frequency response, because the acoustic wave from the rear of the speaker cone is reflected from the environment, and at some frequencies tends to cancel the acoustic wave from the front of the speaker cone. This is most noticeable at lower audio frequencies.

OTOH, the radiation pattern shape of a 3-m Part 15, ground-mounted vertical monopole is very similar to that of the 1/4-wave monopoles used by licensed commercial AM stations -- the main difference being in the lower peak gain of the Part 15 monopole due to its very low radiation resistance along with the higher losses typically present in the loading coil and r-f grounds they use.

//

 

[Tom Wells]

If the speaker is in relatively free space, there is nothing to reflect from, thus frequencies are not being cancelled.
Rather, the bass frequencies, which "bend" more easily take the "short path" just around the front-to-back avoiding "work".
If you place your ear near the speaker or edges you will hear these sounds are present, just not able to do work.

The speaker's own electrical impedance/response has not changed, except for an infinitesimal increase/decrease of inductance depending on whether a good baffle (analogous to a good RF ground) is loading those frequencies into the system to do work (radiate).

I certainly agree that the ground-mounted vert monopole pt 15 is the IDEAL, and radiates a pattern exactly like a bigger antenna,
with the inefficiencies you cite, but all antenna compromises involve accepting such losses upfront.

In the same way, a single speaker, properly mounted on a huge infinite baffle puts ALL its movement into moving air.
As I find sense in all your other engineering opinion I've read so far, I'm surprised you don't see these both as
an issue of self-inductance/capacitance and electrical transducers in an impedance-matching problem.

Are you sure you don't see a parallel in terms of power transmission?

 

[rfry]

Are you sure you don't see a parallel in terms of power transmission?

Thanks for your comments. I just wanted to point out that a 3-m Part 15 AM antenna is not even close to a point source of radiation, and in fact has a radiation pattern very similar in shape to all MW monopoles up to a height of 1/2 wavelength.

I didn't quite get the analogy of a Part 15 AM antenna with a speaker, but I guess that is my failing.

//

 

[Tom Wells]

I see the moderators sweeping up hasty words before others can be infected by them.

I am gritting my teeth about the noise like others, but let's not let our strong feelings squelch discussion.

We can disagree without name calling. Let's use constructive commentary.

I think the people involved in this thread are all pretty well informed, and their words deserve respectful disagreement,
even if someone's (anyone's) comments seem excessively authoritative.
I believe anyone this far along in this discussion is enough of an authority to be afforded respect.

 

[Marathon Don]

I see you guys are still here. I'll check back later.