Phasing aerials?

[Sleeper]

does anyone have information on phasing multiple UHF aerials together?

[JonoP]

Hi Sleeper, Thanks for your help. That's a pretty good site. I saw some info in this forum (general chat) About phasing aerials, I'm not sure if it's what your after but worth a look. This is the link that was posted in the chat. Cheers Jono.

http://www.repeater-builder.com/antenna/db-about-rf-communications.pdf

[Sleeper]

it kinda gives me an idea of how it all works, but i really need a stripped tot he bone explaination of how to do it and what i need

[robbo0419]

do you want one or do you just want info on how they work.

i have a phasing aerial that has 4 dipole aerials on it i will look tomorrow and see what frequency it is but i think it is uhf.

i am moving back to perth in a few weeks and it was going to be sold or thrown up the tip, but i may fit it on the truck.

[Sleeper]

what i'm aiming to do is attempt to phase 2 glassmount aerials on the back window of my car to improve thier rather woeful performance

[rebradio]

Yes, you can get an improvement over a single aerial by connecting two aerials 'in phase'. However the spacing between the aerials needs to be set correctly and the length of the cable an equal number of wavelengths (I.e in phase). The resultant radiation patern will be directional, not just a biger (higer gain) omnidirectional pattern and it is possible to 'steer' the radiation patern somewhat by altering spacing and phasing of the cables.
If you want to know more about the 'nuts and bolts' I would suggest you buy the ARRL Antenna Book. I have a very old copy (1974) and it gives quite a good description of how the radiation patter changes as you change the phase of the signal feeding the two antennas.

Good Luck,

Phill.

[RED]

I haven't really had net access recently and won't for a little while yet so i'm sending thanks in advance.

Does the cable running from antenna 1 need to be any set length (the co-ax running to the UHF) or can it be any length? The reason i ask is i had a minor under bonnet fire and some of the excess cabling has been burnt. Not to the wire, just the shroud. I wanted this removed before the fire but it's kinda bugging me now. I understand the importance of between antenna cable lengths but does the UHF-antenna co-ax matter?

Cheers

[digiteyes]

RED,

Are you talking about the same subject here (phasing two on-glass antennas) or something else?

On-glass antennas are the lowest-performing antenna you can use.

If it's better performance you want over a glass-mount antenna... use something better, like a ground-independent antenna.

What make / model antennas are you using?

What gain (if any) do they have?

Co-phasing antennas is an exacting science, often requiring critical alignment and yes, cables must be identical (as do the antennas). A phasing harness/power divider is required. Although essentially, this is just a coax assembly, it's basically a tuned circuit, so any changes to the cable lengths will affect it's performance.

Sleeper, there is no easy "stripped to the bone" way of doing it.

If you really want to do it properly, you must be prepared to study RF transmission principles and as rebradio has mentioned, the ARRL handbook is a good place to start.