Hi Scott and Dave,

I can see how Dave's point would be relevant in general, but if the same
antenna and orientation was used in both cases, it shouldn't matter.

Scott, the voltaqge relfection coeff for 36 ohm/50ohm mismatch is
(36-50)/(36+50)=0.16. If you square this (to get relfected power), you
get only bout 0.02, or 2% power loss. It is true that the voltage at the
load end is reduced about 16%, but the load impedance is also lower(36
instead of50) so the net result is that only 2% less power is delivered
than would arrive at a 50 ohm load. All in all, you have about 4% more
power arriving at the receiver with the matching.

As for the lumped elements, I must admit I haven't tried it, so it may
not be as hard as I thought. However, it is really easy and cheap to make
a little 1.5 inch long (1/4 wave for microstrip on FR4 PCB at 916MHz)
tran line on your board to match these impedances.

About the antenna impedance, there may be some complication that I'm not
thinking about, what I gave is a "textbook" example. However, for a
resonant antenna, there is no difference between impedance and radiation
resistance (except for the small amount of ohmic losses). How did you set
up your simulation? I used EZNEC the other day to check my calculations
for my project, and I got 36 ohms for a 1/4 wave monopole over an
infinite ,perfectly conducting ground plane. As long as the copper sheet
under your monopole is at least a good fraction of a wavelength, I think
it would give results pretty close to the infinite sheet. What did you
mean by surface area?

Sean


On Wed, 1 Aug 2001, David VanHorn wrote:

> At 11:55 AM 8/1/01 -0400, Scott F. Touchton wrote:
>
> >Prior to matching obtained about 700' range.. after matching, got about
> >850' or so.  Did the match on both the xmtr and rcvr.  Not sure of the
> >range implications, but at 36 to 50 ohms this would pick up about 20% lost
> >power.
>
> I don't know if this is relevant to your app, but a 1/4 wave radiates a
> significant amount of energy straight up. (along the long axis)  A 5/8 wave
> flattens this out.
>
> Depends on wether talking to spacecraft is what you're into :)
>
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