from what I've heard about antenna mounting, the antenna should definitely be above the metal of your roof (which is probably blocking the stations coming from that direction) |
The antenna is mounted to the eave right near the peak of the roof, so nearly all of it is above the roof. I was just wondering if anyone had any experience or knowledge of whether I would gain any range by raising it farther above the roof. |
Replace your antenna with a directional YAGI with a rotator such as an APS 9 or 13. Placementment of an omnidirectional is almost an oxymoron if one understands the machinations of FM. |
Some basic guidelines that apply to any antenna installation
1) "Height is might". The higher the antenna, the less obstructed the view that it has of incoming signals.
2) Antennas should be mounted away from nearby metalic objects, especially those of the same polarity ( vertical antennas don't like nearby vertical metal objects, horizontal antennas don't like nearby horizontal metal objects, etc... )
3) If an antenna is electrically shortened and makes use of a loading coil, the bottom of the loading coil should be located above the highest point of any support structure. In other words, the loading coil should not be blocked in any direction.
4) Base loaded antennas are the lowest in efficiency. Center loaded antennas are higher in efficiency and top loaded antennas are even more efficient ( comparing apples to apples ). Any antenna that makes use of a loading coil "typically" is of lower performance in terms of incoming signal strength and receiving bandwidth than a larger antenna that does not make use of a loading coil.
As a side note, the Magnum / Metz / Fanfare antennas are base loaded.
5) All antennas work better with a suitable "ground plane" or counterpoise below them. Antennas that do not have ground radials are more sensitive to their surroundings and feedline placement. In such cases, moving the antenna feedline a few feet can sometimes make a very noticeable difference in the quality of received signal.
As a side note, the Magnum / Metz / Fanfare antennas do not have a built in counterpoise. Performance can be improved if you can mount the antenna on a metal support post that is appr 90" - 96" tall. This is not a common length for pre-manufactured pipe or antenna mast, so you might have to cut to length. The support post or "mast" should be electrically coupled ( metal to metal with no insulating paint, etc... ) at the mounting hub of the antenna. If you can keep the mast electrically isolated from other metal where it is supported or mounted at its' base, the FM antenna will now have a tuned counterpoise of appr 3/4 wavelength to work off of. If you can't make use of a support post that long, use something around 30' - 32" long. This is appr 1/4 wavelength and may work "almost" as well.
6) No part of the antenna should be blocked or shielded by nearby metal objects. Mounting the antenna out in the open above all nearby metal objects would be optimum.
As a side note, the Magnum / Metz / Fanfare antennas make use of a metal shield around the loading coil. This is a horrible design and reduces the efficiency of the antenna in every measurable aspect of performance. Pulling the metal "can" around the loading coil at the base and replacing it with a weather-proof non-metalic / non-shielding material will increase the performance of this and any other similarly designed antennas.
7) Signal splitters absolutely kill the performance of any antenna. If at all possible, try to avoid using them. If you must use a splitter, use one splitter and route the cables from that point. One should never route the antenna feedline to a splitter, divide the cables from there, feed another splitter at a different location, etc... Even if it is more convenient and make use of less cable, the amount of signal degradation that takes place is very large. As such, ONE splitter is all that you are allowed, so make sure that you get one with enough taps to do the job. While i don't advise using a splitter with a bunch of extra unused taps on it, those that aren't being used should be terminated with the appropriate plugs. Most all of this stuff can be found at Radio Shack, Best Buy, Circuit City, etc... Bare in mind that there are differences in splitters, so look for one that offers the highest bandwidth possible. These are typically the lowest loss.
8) Vertical omnidirectional antennas can work very well for most applications. If you are in rough terrain, have a lot of nearby structures that block / reflect signal or are a great distance from the stations that you want to receive, some type of directional antenna should be used. If all of the stations that you would like to receive are located in one direction, you can simply orient the antenna in that direction. Otherwise, i would recommend using a rotor. This allows you to point the antenna for optimum signal strength simply by rotating an electrical switchbox mounted near the tuner.
Large directional arrays will always provide the highest signal strength, lowest noise floor, least amount of multipath, etc... but are sometimes overkill if living near a large city. In some cases, one may have to go to a large directional array with a rotor to avoid picking up nearby stations that are causing front end overload i.e. very strong signals swamping the tuner out. In such cases, turning the antenna AWAY from the strong signal may allow you to pick up stations that would otherwise be knocked out of the picture.
9) Never skimp on antenna feedlines. Cable loss can eat up a lot of signal. On top of that, all cables deteriorate with age, especially when exposed to sun, wind, rain, etc... It is better to spend a few dollars more when first installing than to have constant problems or have to replace the cable sooner than normal due to deterioration that has taken place.
10) All outdoor connections should be weather-proofed. The best solution that i've found for this is available from Radio Shack and is called "Coax Seal". It remains pliable, is easily removed, can be re-used and allows basic antenna maintenance without having dig through silicone caulks, etc... It is also far more durable and reliable than electrical tape, duct tape, etc...
Hope this helps... Sean
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Sean, thanks for the great info and advice. This is exactly what I needed. You've got me thinking now, but unfortunately I don't have enough knowledge to take the next step. I can certainly install a mast/counterpoise and 90" is not a problem. My next question is, would a properly sized whip without a loading coil be better? How long should it be? 1/4, 1/2, full wavelength? I presume we're talking about a wavelength of 3 meters. Would I use the same 3/4 wavelength mast/counterpoise? What about base termination and the connection from the base of the whip to the 75 Ohm coax? I assume a special geometry is required to maintain the impedance continuity at that point. Or can I just run the end of the whip right into a male coax connector and be done with it? I can machine just about any geometry that would be needed out of any material that is required, if necessary.
If there are any good practical texts that you can recommend, I would appreciate it. I have a good background in physics so I don't mind math. Thanks again. |
I suggest you consult:
http://www.antennaperformance.com/
great people to deal with. |
Ivan's suggestion is a good one, but not everyone can afford the types of antennas that they sell and / or want such a large directional antenna. All of the info that i've presented comes from both verifiable sources and well over 20+ years worth of reading and experimenting with RF / various antenna designs.
Personally, if i wanted the "ultimate" in performance, i wouldn't be looking at ANY Yagi antenna i.e. the design that Antenna Performance uses for their top models. The cubical quad is the only way to go IF looks and / or convenience are not a factor. While it is a higher maintenance design, the gain on the cubical quad is appr 66% higher than a Yagi of identical element count. As far as i'm concerned, a 66% gain in performance while retaining the same appr boom length is a "no-brainer".
As far as building your own antenna, modifying existing designs for better performance or optimizing the mounting location of what you already have, i would suggest picking up a copy of the American Radio Relay League's ( aka ARRL ) "Antenna Handbook". This book is worth its' weight in gold to those that like to tinker with such things. If you would like to do any of the above but don't want to become a long-term "antenna engineer" i.e. make the investment in this book ( probably well over $30 ), you can probably request a copy of this from your local library. This book has tons of different designs, explanations, formulas, etc... As far as the products that the folks at Antenna Performance make available to the public, i'm quite certain that the basic designs and the design principles can be found within this book.
As far as antennas go, my personal experimentation with both commercial and home-brew FM antennas has shown that a resonant 1/4 wavelength ground plane is hard to beat when mounted out in the open. As luck would have it, such a design is both easy to make and small in stature. If you've ever wondered why you can pick up stations in your car that you can't hear real well in your house, that is because the antenna on your car is pretty much what i just suggested i.e. a 1/4 wave resonant ground plane. Now picture the same antenna performance of your car mounted 20' - 40' higher with nothing around to obstruct the signal and you'll have some idea of what i'm talking about.
A 3/4 wave ground plane will also work well, but is both harder to make and support and three times as large. Any other wavelength will require more effort to build and will be more complicated to design. I'm specifically referring to the use of loading coils, baluns, etc... Such a design may not be as efficient depending on how those elements are constructed and implimented into the design.
There are many different ways to construct a ground plane, but the easiest is to have one vertical radiator for the "hot" with three or four radiators making up the "ground plane". If this sounds familiar, it is because it probably is. Such designs are very common-place and what were used for CB base antennas in the past.
For FM use, the vertical should be appr 30" long for "middle of the band" tuning. If you want better performance at the lower end of the FM band, make the vertical appr 32" long. If you want better performance at the top end of the band, make the antenna 28" long. The bigger the diameter of the element used for the vertical, the better off you'll be in terms of wide bandwidth and picking up more stations.
All of the ground radials should be of appr 32" long and should be fanned out evenly around the base of the antenna. The radials can be arrayed so that they stick straight out horizontally or droop at a 45" angle. One approach may work better than the other depending on mounting height, surrounding objects and the terrain in your individual area.
This design works FAR superior to the Magnum / Metz / Fanfare model and smokes several other commercially available models that i tested. The tuning of the antenna is far more resonant and maintains that tuning over a much wider bandwidth than the Magnum / Metz / Fanfare models. What this translates to in plain English is better reception with the ability to pull in more stations with a lower noise floor. After all, there is a reason why so many manufacturers choose this style of antenna in the communications market. Efficiency, ease of construction and "reasonable" size are three prime factors.
With the above in mind, it is beyond me why antenna manufacturers haven't produced such a design for the FM market ??? I had plans to do this very thing, but just haven't gotten around to it. I have built several prototypes, done a lot of testing and come up with a finalized design, but coming up with specific parts that i need to sell these on a higher volume basis has been a problem. I may still end up doing this if i can get my act together. Once again, i've got more projects to tackle than motivation to get them done. Maybe if i logged off the puter more often and..... : ) Sean
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Sean,
Excellent. I'm going to try this asap (which may be weeks) and put it as high as I can reasonably get it, and I'll give you feedback as soon as I get it running. One other question: Does the presence of trees have any significant influence on the signal? I don't want to bury it in a deep dark forest, but there are a few trees around the house that I'd rather not try to get above. (Not only to keep the tower height reasonable, but also to minimize the risk of lightning strikes.) Thanks again for the help. |
Most RF theory teaches that trees are relatively "harmless" in terms of signal blocking, but i'm not of that school. Since one can literally "load up" a tree and use it as an antenna ( if you know how ), it is obviously capable of absorbing and / or radiating signal. Having said that, i would not worry about it too much. Try to get the antenna into a place that is both as high and as open as is reasonable. There is always going to be "better", but chances are, this will be "good enough" for 90% of what you want to achieve. That last 10% is what costs so darn much to achieve.
Drop me an email when you get a chance. Maybe we can help each other out : ) Sean
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Sean,
I'm not questioning your knowledge. I just found APS easy to deal with (got an APS 9a for about $150) and 2 hours of a local installation professional's time to get great reception. If the cubical quad is a more advanced technology, that's part of the hobby and I am glad you opened our eyes to it. Ok, buddy? |
No problem Ivan. Sorry if i seemed defensive or came across as attacking you or your suggestion. I have NO doubt in my mind that using such an antenna as what you suggested would provide far better performance than the suggestions that i made. However, i also think that the suggestions that i made have the potential to perform quite well for a much larger percentage of FM users. Judging by many of the posts that i've read here and over at AA, my thoughts were that a large directional antenna array is well beyond the means or desires of most users. As such, i tried to provide them with an alternative means to good performance while keeping things very cheap and very simple.
As far as APS goes, i'm glad to hear that you are happy with both their products and customer service. I'm sure that there are interested individuals out there and hearing your words of support for both the product and company may help make up their mind to take the step to do business with them. My hat is off to anyone that can provide above average products and customer service. Sean
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I just find it a gas to tune in the station, and then look at the multipath meter approach zero as I move the rotator, pointing the APS9 to the station. |
Sounds like you are a "gadget master" like me if you get a kick out of doing something like that : )
I do agree that a big directional antenna is the way to go IF one has the funds, space and desire to do so. The quality and distance of reception that one can get out of such an installation is pretty remarkable. Sean
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Sean- There used to be a toney salon in Mass which featured Sequerra tuners. The owner had a demo where he would tune the rotator to various stations and show the display improving even if the station was transmitting off frequency .
I think that APS can be quite affordable esp if you are staying in the house and amortize the investment. |
