Antenna mod

<div class='quotetop'>QUOTE(Doc Willie @ Aug 25 2007, 03:44 PM) [snapback]502059[/snapback]</div>

Well,

I guess you guys are awake. Hi. But I wasn't. That would be huge on 97 MHz.

But the issue is reflections off canyon sides, and mountains out west where the other poster is from. Its a completely different propagation situation. And FM is elliptically polarized, so reflections would have opposite sense of circularity.


That probably does not apply to a New York state propagation enviorment. Where best on-horizon gain is going to be best, with simple vertical polarization.

 

Fin works for me.

 

OK. so some of this is explained (once ya look up the terms, etc.) but I still get to complain that my wife's '93 dodge caravan (18 MPG! but only used rarely) doesn't drop the local FM station in the places that my lovely Prius does with it's stock antenna.

 

Lest it be overlooked, the Prius' antenna is amplified with some circuitry
imbedded in the conical base piece. Because the Sharkfin hooks to the base,
its signal is amplified also.

I tried to find, but was unsuccessful, a different amplifier that could be
mounted up near the sock location behind the overhead liner. It would have to
be quite small.

 

I fought that for years on my road trips. I finally broke down and got Sat radio. Once you hear how clear it is all the time there is no going back. I can drive from Mexifornia to Montana and listen to the same station.

 

If you want to mess with the antenna there are two things you must take into consideration.

1. The antenna is "tuned", that is, matched to the amplifier inside the headliner. So if you change the antenna in -any- way you have to think about how you are going to re-tune the system. This may be possible with an adjustment on the amplifier (I haven't looked at it so I can't be sure it has an adjustment).

2. The signal -any- antenna collects is directly proportional to the size of the antenna, assuming it has been "matched" as above. Think of it this way, the signal you are trying to receive is an electromagnetic field, like an invisible sheet of paper traveling perpendicular to the ground. The more of that sheet your antenna wire intercepts, the higher the signal strength you will see.

So, as long as you keep it matched, a longer antenna wire will give you a stronger received signal.
The spiral wire -inside- the insulation on the Prius antenna is for matching. It DOES NOT increase the amount of the signal intercepted. It just matches better to signals requiring a physically longer antenna wire. In effect, it's a "stubby" antenna.

There is more complication yet. There is polarization. But most broadcasters transmit signals that are polarized in such a way we don't have to worry about the orientation of our receive antennas. Except for AM. It is vertically polarized, so you want your antenna as vertical as possible for maximum received signal. Unless it's a ferrite loop antenna, in which case you want it horizontal, but now we're getting technical.