On the two threads comparing the AMT3000 to the new AMT5000 I used my ram-shackle window-frame antenna, which showed only that the AMT5000 goes a farther distance than the other one, but it did not show how far it can go with a much better antenna.
Meanwhile, still living in an imaginary world where an antenna can be built into the house in some way to radiate indoors and outdoors with some efficiency, I “decoupled” from the window and tried another approach.
I moved the AMT5000 1.5-feet to the left on its shelf, ran a 5-foot lead-in wire out a tiny hole at the base of an east facing window, found a corner where the clearance from ground to overhanging roof was exactly 10-feet, cut a 10-foot long bamboo pole supporting a 10-foot vertical wire, secured it in a standing condition right up against the window but electrically insulated, attached the lead-in at the lowest-point of the antenna, and tried to find peak. No luck.
So I put the 20 pF capacitor in line with the lead-in at the transmitter and found peak within toroid position S3, then went 1-full turn CW for that resonant spot.
R1 = mid
peak current = .5345
resonant spot current = .2465
Jumped in car and tuned radio to 1550 kHz, left the driveway onto the street and the signal went from full to weak background and didn’t even get halfway across the street. At the intersection no signal. On the next block it came back very briefly and was gone as I moved on.
Lesson: Though not perfect, the original window antenna works better than a 10-foot vertical wire against the back of the house.
No Ground Plane Is No Ground Covered
If there was a ground radial system, or even a few ground wires strung out away from the vertical, it would have worked a bit better most likely.
RFB
Ground Yes
The same ground wire has been used in these tests, about 150-feet run out from the basement up the full length of the backyard and the other direction follows the I-beam in the basement, thick gauge copper.
One thing I’ve found, to echo
One thing I’ve found, to echo some others from another thread, is that what you expect to happen in Part 15 rarely does.
I recently dug up a Landmark FM-350 from my storage area that I don’t even remember purchasing. It’s FCC certified with a supplied dipole wire antenna and a coax feedline with an F connector(don’t ask me how they got it past certification). I put the wire dipole inside a bamboo stick, and leaned it vertically up against the side of my house – the signal went a lot farther than it had a right to.
Well, I thought, if I get that kind of range with the bamboo pole leaning up against the back of the house (ground level), imagine how much further it will go with the stick up on the roof. So I extended the feedline a bit with a dual female connector and about 10 extra feet of coax, throw it up there (I’m in a small bungalow), it’s leaning on the slope at the back of the house, and lo and behold, the signal goes about half the distance!
So who knows? In my case, I figure it’s because the dipole was predominantly horizontal, which made the signal’s polarization horizontal, while the car antenna is mounted vertically. I’ve read somewhere that the signal loss in such a situation is quite large (20db?, too lazy to look it up right now).
Bottom line – you won’t know unless you try it out.
Off Shoot Antenna
Carl,
You are killing the antenna performance by placing it right up against the exterior wall. The fact that you still need the 20 pf series capacitor confirms the antenna capacitance is still way above normal for that length of wire. By placing the wire right against the wall, you are creating a capacitor between the wire and the stucco mesh. This is shunting the signal to ground instead of radiating the signal. The wire mesh, as I said previously, may be either grounded directly by a connection somewhere around the house or be grounded indirectly by all the AC wiring along the exterior walls which will add up to a large capacitor to ground. I would not expect the wire mesh to contribute anything positive to the signal radiation.
Your transmitter is grounded not only directly to your long ground wire ground, but also indirectly to the AC line via the wall adapter and likely directly to AC ground through the audio shields to a computer or other audio source that has a 3 prong AC plug. So if you follow the signal circuit: RF exits the transmitter antenna terminal, goes to the antenna, gets shunted to ground by the antenna’s proximity to the wire mesh, and then goes back to the transmitter ground via AC ground connection (direct or indirect). If this shunting capacitance is 4000 pf, it is just like connecting a 25 ohm resistor across the transmitter and ground terminals. This shorts out almost all the transmitter RF output. This is a high impedance point and the RF voltage at the antenna terminal would normally be around 165 V peak and the current would be very low at 50 mA peak. A 25 ohm resistor across the output would almost completely kill the output. The series 20 pf cap would remove the 25 ohm short as seen by the transmitter, but the signal is still shorted on the other side of the added capacitor. The result is, the transmitter tunes, but the signal still won’t be radiated by the antenna. The 50 mA peak current will still flow in the ground paths resulting in all the signal being radiated by the power wiring.
Your off shoot antenna would work a lot better if you could get the portion of the outside wire antenna away from the wall by several feet. Get as much of the wire on the outside as possible. Place the transmitter on the window sill and run the wire horizontally (90 degrees to the wire mesh) out the window with minimum wire inside. On the outside, you could continue to run the wire horizontally for about 3 feet and then 90 degrees up the bamboo pole. Or, you could run it at a steep angle from the window sill to the top of the pole. The pole should be at least 3 ft from the house. You should not need the series capacitor with the AMT5000 when the antenna wire is spaced away from the wall. In fact, you can used the fact that it tunes without the capacitor to confirm that you have minimized the capacitance between the antenna wire and the stucco wire mesh.
You won’t need to be concerned about running any portion of the antenna indoors for indoor reception. You will get more than enough indoor signal from the AC wiring. Shoot for maximizing the amount of the antenna wire outside the house.
In general, any experimental antenna needs to be outside the house and at least several feet away from the stucco wire mesh.
Off Shoot Antenna (more)
Carl,
OK, if you were able to wade through my previous post and make any sense out of it, here is some more information that likely will add confusion, if there wasn’t enough in that post.
By some inference and calculations, it looks like your offshoot antenna has reduced the huge 4000 pf capacitance of your window frame antenna down to something like 60 pf. This is still outside the tuning range of the AMT5000, but you were able to tune with the toroid tap at S3 instead of S5 indicating much lower capacitance on the far side of your 20 pf capacitor.
Now for the added confusion. Even if you re-configure your bamboo pole antenna as I recommended in the last post, you still may not be able to achieve better range than with the window frame antenna. The reason is that your original range was almost certainly due to power line radiation ONLY. The recommended antenna wire location will divert RF signal from the power lines in favor of the antenna, BUT… The antenna is till in a very poor location, being still very close to the house (3 ft or so) which is not a good place for an antenna!
I think relocating the antenna away from the house by 3 ft would be a good experiment and I would like to see your results. Get rid of that 20 pf capacitor! But, I’m not sure you will actually get better range.
The holy grail is to locate the transmitter/antenna out in the clear with a good ground radial system underneath. Performance of such a setup is predictable and should result in at least 3/4 to 1 mile range. As an aside, the signal received indoors from such a setup may even be stronger than you have now provided the antenna is somewhere close by, like 20 to 50 ft. This is from experience, not calculations.
Time to Reorganize
I appreciate, Phil, your detailed account of the science behind my antenna trials. Time for a serious outdoor antenna.
Tomorrow I’ll survey the scene and figure something out.
Window antenna
Back in 1980, I wrote an article about a window antenna I used routinely for ham radio for the ARRL Antenna Compendium, Vol. 2. I was living in an apartment at the time, and using a window antenna was the only option I had. Carl, don’t be intimidated by ex-spurts with a business motive from relying on your own experiments. It was a comparative test, and whatever characteristics the window antenna had applied to both transmitters.
Window antenna
Ermi,
I know you’re trolling here, just chomping at the bit to get me to reply. Well, here’s my reply. I have been ignoring your noise in the background, and I think everyone else is too.
Seek And Ye Shall Find
“Carl, don’t be intimidated”
I doubt he is intimidated by the messengers.
Perhaps creating new wear paths in the carpet bouncing back and forth between a quick make-shift “proper” antenna and his current working antenna (window frame).
I believe Carl’s tests using the window antenna is viable as well, simply because the window antenna is the current working antenna his station relies on.
Only Carl knows how long the outdoor antenna will be ready. So in the meantime, the comparison testing into the existing antenna was worthwhile IMO.
Compensating for excess external influences on the window antenna with the capacitor is no different from tuning out unwanted resonances on a long wire or dipole or any other kind of antenna. That is part of the reason why Carl got increased coverage from BOTH the 3K and 5K units, if I understood his testing after installing the capacitor. And the 5K unit did demonstrate an improvement over the 3K into the same antenna with the compensating capacitor.
RFB
I Remember!
“Back in 1980, I wrote an article about a window antenna I used routinely for ham radio for the ARRL Antenna Compendium, Vol. 2.”
I remember reading that article! And it was very informative and the ideas presented worked incredibly well.
I also tend to agree regarding the intimidation factor brought on by aggressive sales tactics.
Why build and learn on your own when you can just pull it off the store shelf eh?!
Let’s just forget how to hunt, fish, camp. Why go through all that trouble when we do not have to investigate and discover how. Just buy your way through knowledge. Graduate on American Express I suppose.
“It was a comparative test, and whatever characteristics the window antenna had applied to both transmitters.”
Indeed. The test used the same antenna with both the 3K and 5K, and Carl even discovered how to tune out the excess capacitance and get better performance from that window antenna from both the 3K and 5K unit.
Regardless of the type of antenna, the test did demonstrate the improvement.
Not everyone is going to have the option of building this so called “perfect” Part 15 MW antenna. There is NO such thing as a “perfect” Part 15 MW antenna….PERIOD!
More marketing wording to those who are not very well versed in the manipulation art of the English language. Many lawyers know what that means..as do many business operators relying on publication or social networks for their advertising medium.
CAVEAT EMPTOR!!!!
RFB
I appreciate you remembering
I appreciate you remembering my article, RFB.
I found that PhilB tries to maintain a civil tone most of the time, but sometimes his inner bully comes out.
Position Paper
I don’t see the reason to impugn the effort or intentions of the rare person who develops an entirely new niche for the part 15 transmitter market. Here is my position in this flack attack.
The AMT5000 is exceptional and meets my expectations entirely. I’m going to get the outdoor unit or, if available, one of the custom enclosures.
I have no doubt the theories put forward regarding the limitations of what I now call the Wintenna (window antenna) are genuine and carefully deliberated technical findings, with no sales undertow.
Pulling a million miles away from this particular dispute, I will say that the fatal weakness of AM Part 15, the flaw that will keep it from spreading popularity, is the awkwardness of the antenna requirements. The only solution to this would be attractive, integratable indoor or window mount antennas that could be added to the home decor. If that is technically not feasible then Part 15 AM will remain a fringe hobby.
The mission and purpose of the testing I did was to demonstrate the AMT5000, not to prove or disprove my Wintenna. But I will come to the defense of my “invention.”
The Wintenna does exactly what I need it to do. It puts a strong signal everywhere in the yard and indoors. That was my goal. But for distance into the surrounding neighborhood it is deficient and there is no argument over the fact that a well located stick with radials would do much better “long-throw” of the signal.
It would be very interesting at this time to have the opportunity to see the window antenna designed by you, Ermi Roos. Perhaps you are the original inventor of this concept. If possible, please publish your information.
Delayed Response
Phil, I just now found your second message OFFSHOOT ANTENNA (MORE).
Three feet out isn’t much, but for Part 15 it’s like a mile because of the transmission line length from a house-bound transmitter. But never mind all that, here’s a new idea.
There is a spot about 12-feet from the house where I can easily erect a bamboo tripod, then work out all the other details.
November.
Hi Carl. My recent
Hi Carl. My recent experiments with that FM antenna showed me another issue with Part 15, at least AM, and that’s the noise factor. I admit that I’m a bit more privileged in using FM in Canada, since we’re allowed 4 times the field strength (that FM-350 I was using I remember now was trimmed to Canadian specifications), but I’d almost forgotten how much of a pleasure it was to listen to Part 15 FM signals. When the signal could be heard, it was all there, as opposed to AM, where noise starts at a relatively short range, and just increases. Plus there are so many more factors for interference using AM.
The average individual doesn’t understand the miniscule power levels that are being used in AM, and I always get questions like “Well, why can’t I receive it” or “You mean it only goes a mile” or “Gee, I was only and it was awfully noisy” or “I couldn’t get it on my [home] stereo [when the home stereo was a cheap portable]”.
Overall, I suspect a listenable signal, which I always talk about, for the average listener is much less noisy than what I’m willing to tolerate to listen to my own radio station.
So even if the AMT5000 surpasses the Rangemaster (which is what I use currently) in testing (and that remains to be seen), and even with an ideal antenna and ideal terrain, Part 15 AM still remains problematic.
A bit off topic, but perhaps a reality check.