Part 15 it can't be legal because:

[edarmsttrong]

Someone needs to tell these guys Part 15 AM isn't legal....

http://www.iamradio.net/

Your half watt FM with a two mile radius is what's not legal.

Obivously...this was based on a hypothetical situation.

I was merely stating that if 'Part 15 can't be legal', someone should inform Radio Systems that they are selling equipment that does not comply with FCC rules. I don't believe it for a minute, but it appears that there are many on this forum who do.

 

[littlejohn]

>As someone that has a personal friend at the FCC in DC and many family and friends that work for the Federal government, I> take offense at his absurd accusations against reputable manufacturers and their customers. I think he needs to find a >better way to spend his time than to vilify users and manufacturers of peanut whistle AM transmitters.

>Understand?

Oooo, touched a nerve, I did. So I conducted an unscientific random survey (asked the next three folks in the industry I had occasion to speak with on one subject or another) for testimonials, Walker and Fry. I've never met either, so alls I can base opinions on are the URS and their posts here... Mr. Fry's seem to be rather more factual, and rather less negative. The URS concluded much the same.

I am, however totally whelmed that Mr Walker has Friends In High Places. I got a cousin who's a Notary Public, does that count?

 

[WCWalker]

>As someone that has a personal friend at the FCC in DC and many family and friends that work for the Federal government, I> take offense at his absurd accusations against reputable manufacturers and their customers. I think he needs to find a >better way to spend his time than to vilify users and manufacturers of peanut whistle AM transmitters.

>Understand?

Oooo, touched a nerve, I did. So I conducted an unscientific random survey (asked the next three folks in the industry I had occasion to speak with on one subject or another) for testimonials, Walker and Fry. I've never met either, so alls I can base opinions on are the URS and their posts here... Mr. Fry's seem to be rather more factual, and rather less negative. The URS concluded much the same.

I am, however totally whelmed that Mr Walker has Friends In High Places. I got a cousin who's a Notary Public, does that count?

They do say ignorance is bliss. ;D

 

[druidhillsradio]

They have a term in the U.S Navy for B.S. info. It's called "Bum Gouge." It seems that the haters of Part 15 radio don't want to be confused with the facts that the FCC certifies transmitters for both Part 15 AM and FM. They spend many hours studying in the "Library of Bum Gouge."

 

[rfry]

... It seems that the haters of Part 15 radio don't want to be confused with the facts that the FCC certifies transmitters for both Part 15 AM and FM.

Just to note that no-one rightfully deserves to be labeled as a hater of Part 15 unlicensed operations for facilities that truly meet the functional limits defined for such systems in Part 15.

More likely, the contests here arise between those who do NOT comprehend, promote and meet those functional limits, and those who do.

RF

 

[edarmsttrong]

Just to note that no-one rightfully deserves to be labeled as a hater of Part 15 unlicensed operations for facilities that truly meet the functional limits defined for such systems in Part 15.

I'm a Part 15 hater BECAUSE of those limits!

It's time to revisit some of Part 15 rules, and get real explanations from the people who create and enforce them, the Feds.

And, no...I'm not talking about the rules for the Part 15 4 watt TVBD coming to my neighboor's roof soon, blasting megabits of digital data to the town, killing my over the air TV reception.

I'm talking about the ones, that have been in place since the early part of last century, that limit a citizen's ability to use radio waves at a useful power level in a creative, civil, and respectable manner. Other countries have been able to do this, but we can't seem to do it here.

 

[Greg Strickland]

Well, during the amount of time the Part 15 debate has been going on, someone could have saved money and bought a small full power AM station. The ground lead thing is silly.

From the engineering side, if I were interested in this I would be focusing on driving a capacitive, low resistance load as efficiently as possible.
The goal is making an RF output stage that lifts this difficult load to a voltage corresponding to a high percentage of the 100 milliwatt limit.
i.e. can you make an output stage that delivers voltage across a near short circuit?

I think it would be more interesting and productive to work on a real radio station. There are plenty of licensed stations with poor ground systems and RF design. I mean meeting licensed efficiency, not exceeding it.

Also- a long "ground lead" does not seem useful to me. What is needed is an efficient ground plane. Imagine a standard broadcast ground system with a 3 meter tower. Now tune that. Instead, why not just go find a radio station that needs help or become an amateur radio operator. You can build backyard verticals that actually work in the ham bands since they are higher frequencies.

 

[Tom Wells]

Well, during the amount of time the Part 15 debate has been going on, someone could have saved money and bought a small full power AM station. The ground lead thing is silly.

From the engineering side, if I were interested in this I would be focusing on driving a capacitive, low resistance load as efficiently as possible.
The goal is making an RF output stage that lifts this difficult load to a voltage corresponding to a high percentage of the 100 milliwatt limit.
i.e. can you make an output stage that delivers voltage across a near short circuit?

I think it would be more interesting and productive to work on a real radio station. There are plenty of licensed stations with poor ground systems and RF design. I mean meeting licensed efficiency, not exceeding it.

Well, actually, most part 15 AM operators would have a hard time scratching up enough cash to pick up a distressed AM.
Here in Chicago there isn't such an option at all.

The physics of the goal in coupling the output to the (poorly matched) load always invites innovation, but
the " no free lunch " clause always seems to rear its head.

I can just imagine me going station to station, offering to audit their AM RF efficiency, grounding, shielding, losses...
I'd have more luck going door-to-door, offering to touch up undercoating dings on the bottom side of vehicles.
This is truly an out-of-sight out-of-mind issue, and one which MANY AMs have shot themselves in the foot with over the years.
Nothing is going to return us to the days of proper AM spectrum mangement and maintenance except a return to the equivalent of
a First Class license, and requirements that each station PAY for one.
Even then, owners would always be free to ignore the expensive advice of an engineer, many did back in the old days, too.

 

[rfry]

From the engineering side, if I were interested in this I would be focusing on driving a capacitive, low resistance load as efficiently as possible. ... Also- a long "ground lead" does not seem useful to me. What is needed is an efficient ground plane. Imagine a standard broadcast ground system with a 3 meter tower.

Interesting comments. The link below leads to an analysis of such a system, to give some perspective on this.

The r-f ground loss was set to 2 ohms, which is typical of a "broadcast type" system of 120 buried radials each 1/4-wave long. Transmitter output power was set to 85 mW, assuming a high-efficiency PA (not commonly used now in Part 15 AM txs). It was assumed that the transmitter could be adjusted to provide a 1:1 SWR match into the base Z of the 3-m whip without using a loading coil.

The 2 mV/m field needed to provide fairly good indoor reception to an average AM broadcast receiver in a quiet location is located at about a 320 meter radius from the transmit antenna.

Also of note is that the r-f bandwidth of this system would not permit an audio response that most radio listeners would accept (down 3 dB at about 600 Hz).

http://i62.photobucket.com/albums/h85/rfry-100/Part_15_AM_2-ohm_Gnd.gif

RF

 

[Greg Strickland]

Richard,

Thanks for running the study. I thought the loading coil or other matching network is where most of the loss would be, but based on your study it seems ground plane loss overwhelms everything with such a short radiator. One tenth of an ohm of radiation resistance in series with two ohms of ground loss is not good. The deal breaker is the low radiation resistance, it is like a low volume business trying to survive on a one percent profit margin.

It might be interesting to run it with a larger diameter antenna, like four foot wide tower section. That might reduce the Q and slightly increase electrical length.

 

[rfry]

It might be interesting to run it with a larger diameter antenna, like four foot wide tower section. That might reduce the Q and slightly increase electrical length.

Other things equal, the radiation resistance stays the same when using a 48" diameter radiator, but the input capacitance changes from 32 pF to 282 pF.

The added capacitance improves the received -3 dB audio bandwidth of the system to 5.1 kHz, but its radiation efficiency and distance to the 2 mV/m radius (for the carrier) stays the same.

RF