Toni wrote:
. . .
There are many classes of helix antennas, and all the "normal" helix
antennas you will find have dimensions comparable to a full wl if not
greater.

Quadrifilar helices typically have four twisted half wave elements. The
length for 1228 MHz would be somewhat less than 4.8 inches. Twisting
would make the assembly less high that that, and fattening the elements
or plating them on a dielectric substrate would further shorten them.
This is consistent with the antenna of an older GPS unit I had.

My doubting on pocketable GPSs antenna's efficiency is based merely on
their size. They are about 1/10 wl long. The only other antennas of
comparable size I know are loops, isotrons, fractals, CFA, EH and CB
sticks and, except for tuned loops, we know how they are treated
whenever they appear in this forum.

It's possible to make an electrically small antenna that's quite
efficient. Typical examples are the small transmitting loops made by AEA
and MFJ, or the shortened, top loaded verticals described by Jerry
Sevick, W2FMI, in a series of articles in the '70s. What you can't make
is a short, efficient, broadband antenna. But GPS antennas don't need to
be broadband. And for that matter, they don't have to be that
electrically small.


The difference is that the helix is quite directional.


The ones used in GPS receivers are exactly the opposite. They should
ideally have a "half orange" radiation pattern, as they should be able
to follow a satellite from horizon to horizon all over your head.

This describes the approximate pattern of both quadrifilar helix and
patch antennas, which is why those are the types which are commonly used.

. . .

Roy Lewallen, W7EL