AM Directional

The first one is rather simple. If you examine a copy of the ARRL antenna book or similar reference, you will note that a ground mounted vertical antenna will exhibit a slightly directional pattern in the direction of the best ground. So, if you were to install a number of radials on the ground stretching in the direction you want to maximize your signal, it might help. However, many variables are at work here; if the ground system is already pretty decent or you have high conductivity soil, it might not make much of a difference. I would expect the effect to be rather small in any case-- perhaps 3 dB at best.

The second legal way is to install an additional transmitter in the direction where you need more signal. There are some questions about whether it is acceptable to synchronize them and I will not go into that, but it has been established that you can use more than one transmitter. The problem is, of course, that you need to find a location where you are permitted to install it. If you have a friend or neighbor in that direction, you might be able to work something out. If you are not going to synchronize, you will probably need to set it for a different frequency to avoid interference, unless it is far enough away that the signals from the two don't interfere with one another.

My understanding from OET is that any attempt to create a directional array by installing passive elements will be considered non-compliant, and will likely result in a citation. Incidentally, another enforcement action was posted just today.

I couldn't find anything about an FCC enforcement action today. Where did you find this?

Where they always are:

http://www.fcc.gov/eb/FieldNotices/2003/DOC-295641A1.html

Enjoy!

"Incidentally, another enforcement action was posted just today."

There were several, none of them having anything to do with what this board is about, the linked NOUO said:

"The field strength of the signal on frequency 1580 kHz was measured at 350,000 microvolts per meter (uV/m)"

or over two thousand times typical Part 15 levels - I doubt that was caused by a directional antenna, or an excessive ground lead.

What on Earth does that have to do with low power radio?

Anytime there is an enforcement action, I would think that it is something that people would be interested in knowing about.

Wouldn't you want to know about that?

What is the problem?

Pie

Because I'm in a similar situation, I've done a fair amount of research on the problem. My conclusion is that there is no legal way to extend Part 15 AM range by D methods which wouldn't benefit the same by ND methods.

But there is, as they say, more than one way to skin a cat. For me anyway, the best solution is to move the TX/antenna system to a site with a better shot at my listener base (in my case, my boat), and operate it remotely from the studio via internet radio/wifi. IOW, I'm using the internet sort of like a repeater. Requires wireless internet, modem/router, computer or Barix Extreamer for audio.

There are other methods for P2P, where system costs can vary wildly. One of the best analog systems is the MicroTek MiniLink, but you need a fair chunk of moolah to purchase it and put it into service:
http://www.surveillance-video.com/ml-5-8-txm.html?productid=ml-5-8-txm&channelid=BIZRA

"Wouldn't you want to know about that?

What is the problem?"

Quite frankly, I hardly think you really need an explanation, your posts here indicate that you are a highly intelligent individual who has plenty of knowledge about the subject.

Unfortunately, some of your posts also suggest that you have an agenda to discourage our visitors from experimenting in low power radio and that is unacceptable. If you are asking for examples, your recent post with nothing more than "Incidentally, another enforcement action was posted just today." is exactly the kind of nonsense I am referring to.

Do not waste my time with any "but I was only trying to educate, inform, blah, blah. blah…" response - you're smarter than that and so am I.

One more time with feeling, the purpose of this private web property is to encourage and foster experimentation in low power radio.

Posting "Incidentally, another enforcement action was posted just today." without making it clear that the enforcement action has nothing to do with low power experimentation is interpreted by me as an attempt to discourage participation in experimentation and to scare users into believing there is something wrong or dangerous about legitimate experimentation within Part 15 guidelines.

For the record, this is the second time I have had to speak to you about this. Your informative and knowledgeable posts are always welcome. If you continue to post information that appears to me to be discouraging, you will be banned.

I hope that answers your question.

Well put! I could not find anything on the FCC website pertaining to enforcement action involving Part15 either, as referenced in the earlier post.

Thank you for the ideas and I'm relieved that the enforcement is not a part 15 situation.

My ignorance allows me to dream about things that don't exist. I'll pose an idea, and instead of trying it in real life, I hope you'll save me the trouble by explaining why it won't work.

Two pieces. A 10' vertical copper pipe 1 1/2"-diameter NOT electrically attached to the TX but securely grounded to the earth. The pipe has a vertical slit about 1/4" wide down one entire side, except at the bottom, top, where the pipe would be left uncut for stability.

INSIDE the pipe but electrically not attached to the pipe is the 10' vertical antenna wire, looking through the slit "window" toward the direction of choice.

Cast your vote now.

Well, here's my "guess" about this:

The dimensions of part 15 AM antennas and grounds are very small compared to the wavelengths we use and therefore do no lend themselves to designs which work at UHF or VHF frequencies. These directional designs depend on dimensions where the phase difference in signals can add or subtract and usually require spacings of multiples of 1/4 wavelength. Though such schemes will work at BCB frequencies, the dimensions get rather big.

Your idea about the "slot" antenna in interesting and such things are used in aircraft and radar but again the dimensions are such that wavelength effects are critical. Interestingly a slot antenna appears electrically as a dipole and radiates with the same pattern.

Now for your idea. It appears to me that there will be little radiation through the slot but huge capacitive coupling between the center wire and the pipe, thus the pipe will act as if you had attached it to the transmitter output terminal and it will become a radiator. Unless I am missing something here this would not be worth trying.

Neil

Could a part 15 am station take advantage of the same properties found in a beam antenna system?

I feel like this would work but is not compliant.
Years ago when I was still tickling the nether on 11 meters (c.b. radio) I had trouble hearing a friend 25 miles away. She lived in a low lying area surrounded by hills. A few of my friends and I set out to build a three element quad antenna (beam).

Well it started out three elements, but as we left his property to transport the beam to my house we clipped a tree and the director was damaged. We were going to replace the director and continue on our way to my house, but time was against us and sunset was creeping up on us. After some quick calculations we did away with the director and kept the driver and reflector. The idea was to direct the power in one direction as well as receive in the direction we were looking.

The antenna worked well but rejection of other stations was a science I would have to master on my own. Had we more time the antenna would have performed far better if it had a director, driver and reflector.

The reflector being the back of the antenna was passive in the sense that it was only meant to bounce the signal from the driver into the direction you wanted to send the most energy.
It also acted as a wall , rejecting signals behind the reflector.

Could this set up be replicated on the ground with carefully placed elements? They would not have to be physically attached to the transmitter or the antenna system. If you could calculate the wavelength needed to place the director and reflector elements you might be able to send more energy in the desired area.

One of my crazy ideas.
I just think this would be a cool weekend project, if nothing else a learning experience.

If you can recall the dimensions of the CB beam you will note that they were on the order of 1/8 to 1/4 wavelength at 27 MHz. These antenna arrays work because of the physical relationship between the elements and the signal wavelength.

Indeed, your idea is used on the AM BCB by stations which use directional arrays. Usually the auxiliary towers are actively fed with RF which is phased such that this in combination with the distance between towers yields the desired pattern.

Could this set up be replicated on the ground with carefully placed elements? They would not have to be physically attached to the transmitter or the antenna system. If you could calculate the wavelength needed to place the director and reflector elements you might be able to send more energy in the desired area.

The answer is yes but for the director or reflector to work there would need to be a significant signal induced in them by the radiator. This seems unlikely given the weak field strength at the distances involved, though the principle of superposition still applies and there could be some directional effects produced. The big problem, as I see it, is the dimensions involved in such an array.

Also, bear in mind that the length of the passive elements needs to be long at BCB frequencies.
Neil

Earlier the idea of synchronizing 2-transmitters with one of them closer to the desired direction was proposed to create what would be a signal lengthier than it is wide. Of course these transmitters would be in positive phase, one to the other.

What if the farther transmitter were synchronized 180-degrees out-of-phase with the forward transmitter. Would this improve the directional thrust or simply throw-away the back field?

Carl,

If you were observing a peak in the pattern then reversing one transmitter's phase by 180 degrees would cause you to observe a null.

Here's a way to imagine what happens with two transmitters phase locked (but not necessarily in phase). Suppose we ignore the signal strength for now except to assume that you observe equal strength from each transmitter and antenna. Imagine a line between the two antennas and that you are standing on this line beyond both antennas so you can see both. Now imagine that the electric field of each antenna is at peak positive at each antenna at the same time and the distance between the antennas is 1/2 wavelength. You are close to antenna B so you see the positive peak from B but by the time the signal from antenna A reaches you it has shifted in phase by 180 degrees due to the time and distance traveled (1/2 wavelength) and you see this wave at its negative peak. If the signals are equal strength you will observe them cancel and you will be in a null with no signal. (If you were standing off the line in a position where you are the same distance from A and B then the signals would add and you would be in the major lobe.) Now, go back to the line where the signals canceled and invert antenna A's phase and you will see it at a positive peak coincident with B's positive peak and the signals add and you will be in a major lobe. This rather grossly illustrates how the direction of the major lobe can change with phase and distance.

This effect applies wherever you are standing. Both waves will add according to the original phase at the antennas as well as their phase shifts due to the distance and time to reach you at your distance from each radiator. This addition will produce different strengths depending on the phasing. This is how the patterns develop.

I hope you followed this since it is intended to give you some physical feel for how directional arrays function.

Neil