Generally speaking....Can some please tell me what is the difference in anntenna types such as discone,ground plane,log periodic,yagi,beam,etc.
Wow!! Thats a whole lot of info to handle-way above my head. I want to put up an antenna in my attic or maybe on my roof. I have 4 scanners that I want to connect. I have 1 used for vhf high and 3 used mostly for 800 mghz. Ihave read the forums and everyone has a differt opinion. I really have no idea.Eh, you forgot to mention a ground plane antenna is an end fed vertical radiating element working against ground counterpoise. Large ground planes such as AM broadcast towers work against the ground itself while smaller elevated ground planes must have the ground raised up to the radiator. That's the function of the horizontal radial elements, an artificial ground.
By way of comparison the not mentioned thus far half wave center fed dipole is a complete antenna not requiring ground, it is its own counterpoise. On the other hand with a ground plane the ground counterpoise is the other half of the antenna making it complete. Imagine that broadcast tower with an equally tall phantom tower directly under it below ground and you have the dipole equivalent, the Earth being the opposite pole. Consider a magnet has two poles, so does an antenna.
Now don't confuse yourself here, all antennas including the discone and Yagi beam all work on the dipole (two pole) principle one way or another although it may not be apparent from their physical appearance.
Since you've already separated bands between radios, you're a perfect candidate for having each radio dedicated to a band, with band specific antennas. One for VHF, some for 800 and so on. Which ones you get depends on a lot of stuff. If you get everything OK already, then you don't need much. If you struggle to hear stuff over in the next county or something, then get something directional. If you struggle to hear something in all directions, then go with omni high gain. The thing to remember is that gain comes from stacking elements... Either horizontally (directional), or vertically (omni). Either way, the bigger the antenna, the better... In correlation to the wavelength of course. But comparing this ground plane to that one, or this discone to that one, is not going to be a huge difference.Wow!! Thats a whole lot of info to handle-way above my head. I want to put up an antenna in my attic or maybe on my roof. I have 4 scanners that I want to connect. I have 1 used for vhf high and 3 used mostly for 800 mghz. Ihave read the forums and everyone has a differt opinion. I really have no idea.
Any sugestions will be appreciated.
As Dave (DPD1) already mentioned, if you have multiple scanners to receive different bands, connecting one antenna to each scanner that is designed to receive that band will give you the best performance. But if you don't have the room or the funds available for that, the DPD LP antenna would be a good choice, although I'd recommend a rotor if you don't have one currently.Thanks for the help guys. I will try to decide on what to use hopefully soon.
WOW again.Over my head. I am only going to be recieving. After the last post maybe 200 is to much to spend an an antenna.Hi Chuck
If your looking to broadcast (transmit) all these antennas have different attributes as many have already mentioned. If you are looking to receive only there is no need for any of these fancy tennas.
If it is for a scanner all you need is a cheap discone as high as you get get it. Above 50mhz everything is line of site with the exception of periods of atmospheric transconductance. And then you may find after all that you will need to use rf attenuation. Most scanners are under $500 bucks and have limited ability for crossband rejection. Strong signals will swamp your receiver. The receivers in scanners are extremely sensitive and are designed to work with low gain antennas like the one that comes with the radio or mobile mounted tennas. If your looking to receive long distance signals you need to be in an area where signals coming into your radio are low. So you should be in a rural area to consider a high gain antenna on a scanner type radio. Reception is a whole different set of issues than transmission.
The higher you put the antenna the further away you should be able to hear above 50 mhz. The longer the bnc cable the more loss in the line. But that usually is the best mix for a scanner. A lower antenna and lower loss in the receiving bnc will surely swamp your radio with nearby strong signals.
If your on a second story or higher a small antenna is sufficient.
Tenna polarity is of little issue on a receiving antenna. Most signals arrive via mutipath distribution.
A 1S unit is = 6db change. A differnence in antenna receiving polarity results in only 3 db change 1/2 an S unit. Also half the signals reaching your receivers antenna cross polarized by the time it reaches it. Polarity makes little difference on receiving end.
Keep in mind tenna makers are no longer aloud to publish gain specs in ARRL publications because Hams have tested them and found they are all full of crap. An antenna has no amplification capability any how. Gain refers to signal level difference over at isotropic source. These are issues concerning mostly emmisions not reception.
There are very sophisticated techniques to increase reception signals and lower noise which require phasing dipoles and niose blanking dipole and rf mixer. Pretty much useless for most of us.
and your talking about receiving one a specific frequency using these techniques.
A transmitting antenna requires different designs because of how mother earth behaves on resonance throughout the emission spectrum. Earth is part of the antenna circuit and determines angle of radiation and absorbion characteristics. Its behavior varies tremendously depend what frequency you want to emit. Resonance is not a dire receiving antenna issue.
Some variations in design are focusing techniques such as beams antennas. All this has very little impact on reception antenna design.
There are exceptions here Extremely long wave or Microwave receiving antennas a satelite doppler antennas.
Receiving signals from moving satelites does require special receiving antennas. Receiving energy has no polarization and tend to roll 360 degrees. Signals are more focused and require tracking antenna mounts that have to lock on to the target satelite and move with it. And they use circular polarity antennas (dish antennas parabolic receivers). Any you cannot use a common receiver to track these signals. Special receivers capable of Doppler Shifting as the satalite moves.
Microwaves are highly focused and so are the antennas on the receiving end. Radar antennas fall into this catagory. Essentially requiring bore siting.
Very low frequency reception requires design techniques beyond using metal elements which would have to be miles long. Ferrite Inductive tuning is commonly used similar to an AM radio. Effectively making a tuning element look longer to rf energy than it really is.
Remember you are at he mercy of mother nature. Radio conditions vary everyday. They vary through out the day and tend to change dramatically through the evening and accross the seasons. Solar Flux and geomagnetic activity constantly changes the way signals propagate. Weather both local and distant can render some parts of the spectrum unusable at times. The Earths inner core tends to attenuater lateral low band emissions. Sometimes conductive wave guides form in the earths atmosphere allowing long distant transmission in the high bands which are normally line of site emissions.
The earth itself can be an antenuator or conductor depending on band an conditions your operating at.
VLF very low level signals can travel long distances in certain deep depths of the Ocean.
The are thousands of books on the subject of antenna enissions but not much on receiving antenna technology. There just isn't much too it. Unless your trying to do something very special.
Ken C. N2MAC
I use 50 feet of LMR-400 and it's a very excellent coax. RG6 is usually used for TV but it will work fine. It will have more signal loss than the LMR-400 though, but LMR-400 is also thicker and less flexible.Well: I think ? I have made up my mind to go with the DPD LP scanner antenna. 200 bills is alot,but it looks well made and the reviews seem good. Now I am loocking over coax and splitters.I've read LMR400 is real good,but pricey. I can probably get by with 50'.Was wondering how bad RG-6 would be since I have apartial rll left from a dish install. A stridesberg splitter is supposed to be tops,but also very pricey. Some posts I have read,guys have used an Electroline splitter and have had good luck.
That's more inline with my budget. Considering the RG-6 and Electroline to save money,but will wait and see what you guys have to say-good,bad,or ok.