Aerial's ain't aerials...Or are they?

[Spimon_NH]

I need a new aerial. A tree *may* have claimed a chunk of my aerial .
I'm confooosed and don't know which one to get!
(Had a search but couldn't find a lot of relevant info. Sorry if it's been covered)

1. None of the fibreglass ones say what material the core is made from. In theory there's a hierarchy of effective materials (starting with gold etc..). In reality does it make a noticeable difference?

2. My understanding of Gain is this... Aerials aren't powered independantly so cannot 'add' energy to the signal. Any antenna connected to the same radio will receive and transmit the same energy. The higher the gain, the more concentrated the transmission will be in one direction. The compromise is a lack of signal in another direction. Is this correct?
The first aerial on the site below is 6.5dB but still seems to have a fairly broad transmission pattern. Is there any reason not to get a 6.5dB aerial?

3. 470mHz is about a 640mm wavelength. What sort of fraction of a wavelength is the most effective aerial length?
I'm lead to believe that shorter aerials (1/4 wavelength) are more effective in places with more 'stuff' such as trees, buildings, etc.. Longer aerials (3xwavelength etc) are better in open areas (deserts).
I use my radio everywhere. I guess mostly highway cruising in a convoy, in forests, on beaches. Is there a good compromise?

Is there anything else I should consider? It's for a GME TX4000 radio and will be mounted on the side of my bonnet (the gap between the bonnet and the quarter panel).

The ones I'm considering are on the site below. The 1st, 2nd and 6th packages.

http://www.prestigecom.net.au/default.a ... openmenu=3

[DamTriton]

2. My understanding of Gain is this... Aerials aren't powered independantly so cannot 'add' energy to the signal. Any antenna connected to the same radio will receive and transmit the same energy. The higher the gain, the more concentrated the transmission will be in one direction. The compromise is a lack of signal in another direction. Is this correct?
The first aerial on the site below is 6.5dB but still seems to have a fairly broad transmission pattern. Is there any reason not to get a 6.5dB aerial?

You are correct about the higher the gain the more concentrated in one direction at the expense of another direction.

The antennas give a donut shaped in the vertical plane, and the "gain" an antenna has influences how the energy is directed. ie in a big, roughly equal horizontal and vertical "figure of eight" on it side ("0 dB gain), or a heavily flatened version having more horizontal power that vertical power ie
.________..________
(________X________)

(> 0 db gain) increasinly flattened the more gain you have.

The effect of this is that lower gain (3-4.5dB) antennas are better for short distance "convoy" operations (less interference from distant vehicles) and operation in hilly environments (due to better vertical spread), whereas higher gain (>~6 dB) are better for long distance communication on the open road "speed camera dodging" operations (sorry RN ).

Chrome CD 900 would be the best option, gives you a choice of antennas depending on what you are doing

[rockrover]

ok heres my opinon <<<< note opinon...depending on the surrounding terrain of where u use it but if u live and drive the mountains a bit id take the 4.5 any day over the larger gain also buy a steel whip type less likely to get the chop in trees also the 6.5 if u live in say a medium built up area is a great choice and on the flat 9-12 db Gain would be the weapon of choice i personally carry a 6.5 in my car and run a 4.5 neva know when ill need it also if u want to get more affective range use the bigger coaxial cable RG213U lot less db los over the distance u run it good site check it out
http://www.gme.net.au/land/antennas/choose_antenna.php
Cheers Bourkey

[rockrover]

GME AE409L 6 & 9 DB Antenna
6 & 9db Gain antenna
Fold Down Adapter
Antenna is removable from base
Ground Independent
Supplied with 3.6m Coax Cable & Connector

Our Price: $75.00 (Including GST)

i have 1 of these sittin in my shed if u want it altho ur in syd i unno bout shipping but its there if u want it and i have a few other types sittin around too
Cheers Bourkey
ps advantage of these is u acan fold them down when in the bush and they still work well i have 1 on my 4b atm

[ferrit]

ive got two of the RFI CD900's and im VERY, VERY happy with them- they perform well in the mountains and scrub, and very well on the deserts too.

[Spimon_NH]

Thanks for the replies. At the moment I have (or had) a GME AE409L. I'm happy enough with it, but its the only one I've ever used to I don't know what I'm missing out on, if anything.
Still deciding if I'll use the same again or try something different.

[cookiesa]

If your after better range in all conditions perhaps now is the time to revisit the mounting location before you decide on the antenna. If I read correctly your right on one side of the vehicle and if that is also towards your front corner then your limiting the antenna ability dramatically

(unless of course you are using ground indeoendant antenna, although I believe they still benefit from a nice big reflective base under them, just not as important)

You might get a bigger improvement looking at this even if it means a cheaper antenna cause you have spent a few dollars on getting the mounting better.