I have a Wilson Electronics 801212 Cell Phone Signal Booster Kit for Vehicle w, Low Profile Antenna - for Multiple Users that I run in my truck and it works great. 4-5 bars of ATT GSM where I normally have zero or one. Question for the antenna gurus. Does the external antenna need a ground plane (ie: the metal roof of my truck) or can I attach it to the fiberglass top of an RV?
Not necessarily true unless it has a base loaded coil or no coil at all. Symmetrical center loaded coils don't need (and don't really want) any influence from nearby conductive metals. melbo's new toy looks like a center loaded coil (can't tell from the pic, but it looks like it.) If so, it'll work fine on the fiberglas pickup cap. The trucker's mount in melbo's post #3 is for use with the pictured base loaded coil on fiberglas truck cabs. Or, one could easily say I have no clue. See "The ARRL Antenna Book" if you can find a copy. Mine is 4th printing (1977) but the theory hasn't changed.
For a Cellular Antenna, or for that matter, ANY antenna, the necessity for an Antenna Ground, DEPENDS significantly on the design, and type of antenna. Most mobile 800 Mhz Cellular Antennas, use the Vehicles metal body as the Antenna Ground. There are a few, that are based on a dipole design, that require no Antenna Ground, as they are a balanced type antenna, and are self Grounding by design. This whole issue is almost mute, for 1800-1900 Mhz Cellular (PCS) Antennas as 95% of these, are by design, self Grounding. We are talking Vertically Polarized Mobile Antennas here. For Cellsite, or Base Station type Antennas, these are by and large are Panel or Patch Antennas, and by design, are self Grounding. Those that are Colinear Vertical Antennas do require a physical Ground connection to the supporting tower, but the size, or shape, of such a Ground, is not significant, at Cellular frequencies. Your Mobile CB Antenna will require significantly more Antenna Grounding consideration, than any Cellular Antenna of ANY type. Wilson Electronics makes some really good products, for both Cellular Bands, in their BiDirectional Amplifier, and Antenna, Product Lines. There are cheaper, off-shore products, but nothing as solid as a Wilson product. One thing to consider in mobile Cellular Antenna selection IS, that you may NOT want the highest gain Vertical Mobile Antenna you can find, for a Road Trip, as they will tend to have good Long Range reach, but the Cellsites are more than likely, on the top of the surrounding Hills, or Mountains, and if you flatten the Antenna Pattern doughnut with a High Gain Antenna, you will lose signal once the antenna angle to the Cellsite gets up passed 35-40 degrees above the horizon. NOT a good thing. 6 dbi of Antenna Gain is more than enough for most Mobile Cellular Antennas, and when your in the city, where the Cell sizes are a LOT smaller, they will work just as good. ...... YMMV....
Depends on where the feed point is. Is it end feed, or center feed, or shunt feed? You can not tell just by looking from afar. At cellular frequencies, it can be any of those, and at PCS frequencies likely it will NOT be end feed, unless it is a co-linear antenna, with multiple quarter wave sections with alternating phases. Dual band antennas will sometimes have both types in a single housing, with a duplexer section to couple them to the feed line. .......
I've shunt fed a tower and it is worked against a ground. Cells are duplex (talk and listen at the same time) not simplex (CB type transmissions) so dual band is a given; Ham repeaters use tuned cavities to block the transmit frequency from interfering with the receive frequency. I don't know how cell towers work; but I have worked on Ham 2 meter repeaters. For non-Hams, a common center fed antenna is a half wave dipole rotated 90 degrees. The length of a half wave dipole is calculated by dividing 468 by operating frequency in megahertz. For example, 468/7(MHz) = 66.86'. A cell phone would divide 468 by roughly 850 or 900 so the answer is a very small number. As the physical length of cell frequencies are very short rotating the dipole so it is perpendicular is easy. Plus a gain (gain improves receiving and transmitting by having the "multiple quarter wave sections with alternating phase" BT mentioned) antenna can be packaged in the OAL of the vertical element. As BT stated you can't know what (end, center, off centeretc.) feed it is unless you have a schematic. However, usually a lump in the middle means center feed.
True, but is melbo's question answered? (I still think that antenna doesn't need a metal cab roof for a ground plane.)
RF Ground is a very esoteric concept, especially when dealing with frequencies above say 450 Mhz. Since Cellular runs in the 800-900 Mhz band, and PCS runs in the 1800-1900 Mhz Band, most of the antennas designed for these systems are Balanced Antenna designs. This means that the RF Ground is inherent in the Antenna Design, and requires no external connection to a Ground-plane. As I stated earlier, many of the "Cellular" Antennas are Dual Band, (800-900, and 1800-1900) what the typical design has is two separate antennas, feed by a common Feedline, and housed in common structure. Case on point, would be a "Cellar" Antenna that mounts, with a "Thru the Glass" windshield, glued mount. No Metal connection to the antenna, at all, and a Capacitive Coupling between the Feedline, and the active Radiative Elements of the antenna. They work just fine, with no metal RF Ground. You just can't tell by looking, or even testing with an Ohm Meter. Many antennas will show a DEAD SHORT between the Center of the Feedline Coax, and the Ground, or Braid, but they still work, just fine at the RF Frequency, they were designed to operate at. In many cases this is a Good Thing, as the antenna will bleed off any Static, or Lightning, pulses directly to the Ground, because they are Grounded at DC, by design.
It would depend on which model he is looking at. Typically a vertical needs a ground plane; however, there are ways around it some as simple as rotating a half wave dipole 90 degrees; others use matching networks. Anyhow the easiest way to answer melbo's question was at Wilson's site. Although Wilson doesn't tell us the antenna's design they do provide installation instructions. (barring a typo )Models 301103/301125/301128/301703/3042202: "Wilson’s best-selling Magnet Mount Antennas improve signal on any vehicle with a steel exterior, including automobiles, pickup trucks, vans" Wilson Electronics Inc. This one: Fixed mount option 5/8 inch x 7 inch threaded mounting rod spans the distance between RV’s roof and headline Angled surface mounting kit included 5/8 inch threaded brass rod can be easily cut for various mounting depths No ground plane required Includes all mounting hardware Product Details This was the first "no ground (metal roof) required" I clicked on. There are others just look for no ground plane required. Wilson sells both ground plane required and no ground plane required antennas. The antenna in Melbo's link is this one: Product Details The specs state "Metal ground plane required (Minimum 3.5 in. Diameter) "
Not to speak for Melbo, but the Wilson Products, DO Work, and are the Standard by which most other competing products are measured. We use them extensively, here in Alaska, to make our Cellular Phones work where Cells are typically 30-50 miles in diameter. It often takes both a High Gain Antenna, AND a Bi-directional Booster Amplifier to keep any Bars, at all. ..... YMMV....
Tikka- there is never too deep an answer to a question. Your answer might make some one realize they don't know diddley-squat on a subject which will have value later. So, please don't dumb down your answers for the masses as we are all hereto learn little something new.
