Home-made antenna
Hi all,
Brand new to the forum (and iBurst), but let me share what I've learnt from some late night reading (and playing)... All related to WiFi, but could be applicable...
Basically the antenna on the iBurst UTC (PCMCIA) is a dipole and a 1/2 wave monopole on the UTD. Someone mentioned the internal "25 dBi" antenna - this is incorrect - the power output of the unit is 25 dBm - you'll be lucky if the antenna gives you 2 dBi.
Using the following technique, you could boost the signal by using a parabolic reflector:
http://www.freeantennas.com/prod01.htm
By doubling the dimensions, you should be close enough to the correct wavelength.
Try this link for a helical antenna:
http://www.wireless.org.au/~jhecker/helix/ The wavelength applicable is 0.167m for 1797 MHz(
http://www.csgnetwork.com/freqwavelengthcalc.html)
Both these antennas are directional - and I understand that iBurst works better on omni because the towers will "hand you off to another" in certain conditions (mmmm - maybe explaining the dead-link problem and why ping re-establishes the path). However if you're barely reaching one tower, maybe a bit of directional help could be a good thing.
The trick with dB values is that they are logarithmic. For each 3dBi change, you double or halve the signal strength:
http://www.moonblinkwifi.com/dmystifying_the_db.cfm
Now you know why a 21 dBi parabolic grid is such a wonderful thing!
Look at this link:
http://www.wppltd.demon.co.uk/WPP/C...bles___Connectors/rf_cables___connectors.html
RG178 has an attenuation of 1.5 dB per meter at 1800 MHz. This means 3 dB every two meters - so for every two meters of cable, you lose half your signal. RG58 has a loss of 1.1 - so save your bucks and pull out that old Ethernet cable from the box in the garage!
If you look at those losses, a much more effective idea is to take the UTD and put it in a waterproof box and mount it on the roof (mom's tupperware is real handy - but a proper box with a seal is better). With an ethernet cable you can do this up to 100m away. With USB, you can go 5m, or 10 if you put an active hub in-between (long story - don't try a 10m USB cable). Run low-voltage from the transformer to the box to be safe (wouldn't want rain on the 220v!) but use thick flex if you're going far and use compression glands and silicone to make sure things are watertight. This way you get good line of sight to the tower without the cable losses.
Are there any RF guys active on the forum? I'm not an RF engineer and wouldn't want to mislead you. With cables and stuff I've had joy at
http://www.hiconnex.co.za/ (Midrand) but haven't asked them if they stock the particular connector - skeeve posted that its a SMK TS6 (
http://www.mybroadband.co.za/vb/archive/index.php/t-16314.html).
Please let me know if anyone tries any of this and how its working. I'm getting 90-100% off the Bryanston tower, so I'm not that fussed to fiddle at the moment. I did a test at a buddy of mine's house close to Xtreme 16 and the signal there continuously went from 100% to 0 and back and we couldn't get it stable - so maybe I'll give it another shot there.