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Old February 22nd 05, 07:43 AM
 
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Thanks for all your responses, good stuff here.

Rich, I am using TX modules from Liapac which specify a 50 ohm load.

So putting it all together (I think) by bending the antenna (both 1/4
and 1/2) I am messing with its impedance and subsequent matching? So I
would be better off with a straight 1/4 over ground plane if I had the
choice.

From reading I've done I think that a bend from vertical to horizontal

(closer to ground) would be decreasing the antenna impedance, does that
sound correct? Would I benefit from adjusting (extending) the antenna
length slightly (I don't think so because it would no longer be at
wavelength, but I am not sure?).

Ken said ... "If I've read what you wrote correctly, the antenna spends
more of its length parallel to the surface of the PCB than it does
running 90 degrees away from it"... Actually it's about half and half
(feed up 15mm , loop around the case, up - {clear of case} 130mm).
Note the horizontal loop does not cross over itself.

Sort of like this (~~ is horizontal loop) side view.

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feed

I understand that more of the radiation is perpendicular to the wire in
the 1/2-wave (than 1/4 wave), broadly speaking how will the bend('s) in
the aerial effect radiation pattern (I understand this is tough to
answer)? I can't fit a full loop inside the case.

I have no rf test equipment so can only use trial and error, thanks
again to all who responded. As I said it actually works fine it's just
I don't like not understanding the reason its working, and would like
to make any small changes that may improve performance.

Thanks Again