You can think of gain as being somewhat like a telescope; It effectively "amplifies" the amount of signal coming in to the receiver.
Don't confuse the LENGTH of the antenna, with the antenna's HEIGHT (above average terrain) - two separate issues.
Antennas are not so much a "device" as they are a "system". I am not sure if the spider antenna you speak of is a base antenna or mobile. Base antennas typically have radials that act as a ground plane. Mobile antennas use the metal of the vehicle they are mounted on for a ground plane. If you're trying to raise a mobile antenna, it won't work (or work well anyway).Question I am using a spider antenna and I have it sitting on top of a 20 foot PCV pipe. I cannot seem to pick up any better then with the Rubber duck antenna that came with the radio.
My translation of your statement is that these trunked systems are 800MHz. That makes me wonder what kind of coax you are using from the antenna to the scanner. If you're just using "any old coax" that could be your problem. A common problem is the length and type/quality of the coax between an antenna and receiver. Longer coax = more loss. To get the benefit out of raising your antenna you need coax that will not add more loss than you will be gaining from the increased height.most everyone in my area is trunking.
The typical reason for grounding is lightning protection. Otherwise you're just waving a metal device out in the sky, asking for it to be hit, and have the voltage travel directly to your radio. A ground plane is needed (see above).Do I need to ground the antenna for better reception.
More details would help. What is the antenna model, is it a base antenna? What frequencies are the systems on you want to receive? Next I'd check the RR DB for transmitting locations of those systems to determine their antenna height. Your antenna has to be high enough to "see" theirs over the curvature of the Earth for reliable reception.Change the PCV to a medal pole of what antenna would you say to use? I can only pick up my own county trunking and not the next county over.
AHA! You brought up a very valid point. Thank you.Don't confuse the LENGTH of the antenna, with the antenna's HEIGHT (above average terrain) - two separate issues.
LENGTH of antenna affects what frequencies it is tuned for. The longer antenna is typically better suited for lower frequencies. They are often designed with coils so as to have good coverage in several bands.
HEIGHT is significant. This is why "broadcasters" spend lots of money to build tall towers and/or put their transmitters on mountain tops. Elevation is key "seeing" to the curvature of the Earth and maximizing coverage area.