antenna dilemma

oakleym82 · 08-19-2002

hi,

a few buddies and I are getting in to stumbling and we've been using the built in Onrico Gold antenna and the one for the Airport in the PowerBook that's built in, it's time for an upgrade... We saw the mag-mount at FAB, but then read a guys setup and he boasted about this 8db antenna, and said that the mag mount looses up to 3db just based on connectors and the metal magnet plate thingie:

http://www.hyperlinktech.com/web/hg2408u.html

Anyone have an opinion?

thanks

ted · 08-19-2002

I am not sure how much the connector and cable losses are for the 5 dBi antenna, but I am sure they are basically dependent on the antenna design, but the cabling itself. Therefore for any other antenna (inclusive that 8dBi one) with same/similar cable and connectors the losses should be comparable. I do not know why the mag mount should add to the losses, the 5 dBi from FAB antenna has a tiny ground reference plane above the magnet.

Now about antennas. Where the gain comes from? An antenna has no amplifiers or other active elements, so there is no "real" gain, except on cost of directivity. 8 dBi antenna has a narrower beam than that 5 dBi. Both are "omnidirectional" - but the radiation pattern is a more or less flat "donate". For higher gain it is simply flatter.

Result: For access points close to the horizont plane of the antenna you get 3 dBi more for the higher gain antenna, but for an access point ABOVE the horisontal level of the antenna the gain for 8dBi antenna falls more rapidly. Therefore, with that higher gain antenna you may actually get smaller signal strength from a building you pass at close (and where the access point is elevated above street level), whereas a signal from far away (on same level than the antenna) in an open space should be a little stronger.

My bet is therefore that the 5dBi antenna is a bit more useful for wardriving in cities, and it is also more car friendly to install.

renderman · 08-19-2002

I'll replay an experience;

Wardriving Vegas at DCX, I had my 5db mag mount and the CSIS agent in the back seat (ask later) had a 10db hyperlink. When we went through areas with large buildings (read: casinos) I was getting hits she was not, we tracked it down to the width of the radiation pattern because she started getting hits the same as I was.

When we got out on the edge of the city, she was getting AP's before I did. Her line of sight range was longer, but not very effective in cities.

Basically the 5db is a good size and style for urban driving. I've tested and I can usually cover about 1 block in either direction on a typical street with buildings , or 3-4 if there's a field in between or a 'line of sight hole' that the signal can cross.

It's your choice, but also consider that a higher gain means you will be able to detect AP's from farther away, but your GPS lats/longs will be at your current location, making tracking the AP a bit more difficult and your maps less accurate.

Just my $0.02, I could be totally wrong

Render

oakleym82 · 08-19-2002

no that makes total sense, thanks guys. We do a lot of suburban stumbling which takes us anywhere from housing communities to tall office buildngs... any way to incorporate both antennas (besides unplugging and replugging in)?

also, if anyone has experience with the PowerBook Airport, do you know if there's a way to add an external antenna? There appears to be a panel you can remove on the bottom of the laptop which exposes the NIC...

08-19-2002	#1 (permalink)
oakleym82 Registered Member Join Date: Aug 2002 Location: Northern Virginia Posts: 11	antenna dilemma hi, a few buddies and I are getting in to stumbling and we've been using the built in Onrico Gold antenna and the one for the Airport in the PowerBook that's built in, it's time for an upgrade... We saw the mag-mount at FAB, but then read a guys setup and he boasted about this 8db antenna, and said that the mag mount looses up to 3db just based on connectors and the metal magnet plate thingie: http://www.hyperlinktech.com/web/hg2408u.html Anyone have an opinion? thanks Last edited by oakleym82 : 08-19-2002 at 01:00 PM.

08-19-2002	#2 (permalink)
ted Stumbling on Join Date: Aug 2002 Location: Houston,TX Posts: 47	I am not sure how much the connector and cable losses are for the 5 dBi antenna, but I am sure they are basically dependent on the antenna design, but the cabling itself. Therefore for any other antenna (inclusive that 8dBi one) with same/similar cable and connectors the losses should be comparable. I do not know why the mag mount should add to the losses, the 5 dBi from FAB antenna has a tiny ground reference plane above the magnet. Now about antennas. Where the gain comes from? An antenna has no amplifiers or other active elements, so there is no "real" gain, except on cost of directivity. 8 dBi antenna has a narrower beam than that 5 dBi. Both are "omnidirectional" - but the radiation pattern is a more or less flat "donate". For higher gain it is simply flatter. Result: For access points close to the horizont plane of the antenna you get 3 dBi more for the higher gain antenna, but for an access point ABOVE the horisontal level of the antenna the gain for 8dBi antenna falls more rapidly. Therefore, with that higher gain antenna you may actually get smaller signal strength from a building you pass at close (and where the access point is elevated above street level), whereas a signal from far away (on same level than the antenna) in an open space should be a little stronger. My bet is therefore that the 5dBi antenna is a bit more useful for wardriving in cities, and it is also more car friendly to install. Last edited by ted : 08-19-2002 at 02:26 PM.

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08-19-2002	#3 (permalink)
renderman Drunken Stumbler Join Date: Jun 2002 Location: Anywhere but Utah Posts: 1,888	I'll replay an experience; Wardriving Vegas at DCX, I had my 5db mag mount and the CSIS agent in the back seat (ask later) had a 10db hyperlink. When we went through areas with large buildings (read: casinos) I was getting hits she was not, we tracked it down to the width of the radiation pattern because she started getting hits the same as I was. When we got out on the edge of the city, she was getting AP's before I did. Her line of sight range was longer, but not very effective in cities. Basically the 5db is a good size and style for urban driving. I've tested and I can usually cover about 1 block in either direction on a typical street with buildings , or 3-4 if there's a field in between or a 'line of sight hole' that the signal can cross. It's your choice, but also consider that a higher gain means you will be able to detect AP's from farther away, but your GPS lats/longs will be at your current location, making tracking the AP a bit more difficult and your maps less accurate. Just my $0.02, I could be totally wrong Render

08-19-2002	#4 (permalink)
oakleym82 Registered Member Join Date: Aug 2002 Location: Northern Virginia Posts: 11	no that makes total sense, thanks guys. We do a lot of suburban stumbling which takes us anywhere from housing communities to tall office buildngs... any way to incorporate both antennas (besides unplugging and replugging in)? also, if anyone has experience with the PowerBook Airport, do you know if there's a way to add an external antenna? There appears to be a panel you can remove on the bottom of the laptop which exposes the NIC...