Hi Folks,
I know there are several radio-smart people on this list, so I hope the
rest will forgive the noise as I pose a couple questions here.
The questions first; I'll provide background afterward.
I have settled on a digital FM transmitter chip (Silicon Labs' SI4721),
and a simple dipole antenna. Two questions arise from this decision:
1. The transmitter has a single-ended RF output, but will be fully
isolated from earth ground in operation (running on batteries or an
isolated AC/DC supply). A dipole is a balanced load, but since "ground"
of the radio circuit is isolated, can I just treat it as "balanced" and
connect the circuit ground to the other half of the dipole? Or do I
really need to use a balun for a proper balanced output? Coverage area
actually needs to be very small (< 100'), so I'm not majorly concerned
with impedance mismatch losses, etc.
2. I'll be using 1/2" copper pipe as the elements, held inside a larger
PVC enclosure. What's the best way to bond wires to the pipe? Should I
just solder them on? Tap a hole and use a screw to clamp them? Some
kind of shark-bite approach? Does it even matter at all?
Here's the background:
My church does a Christmas program called the Drive-Thru Christmas,
which is made up of five live-actor scenes distributed around our
parking lot. Guests are typically given a narration on CD which they
play inside their vehicles as they move from scene to scene. In order
to improve our social isolation this year, I'm doing some R&D on the
"talking sign" idea, using five separate short-range FM transmitters to
broadcast the scene's narration to the guest's FM radio in their car.
Each transmitter would broadcast on a different frequency, and some
system would step each transmitter through the list of frequencies in
time with the car's movement through the scene, so we can maintain our
5-car pipeline but not require the guest to re-tune their radios. We
tried using an internet streaming option last year (for folks with
smartphones linked to their car stereos) but that, I hear, was an abject
failure with many people unable to access the stream.
Well anyway, thanks in advance for any advice!
Cheers,
-Brian
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