How to Replace Me as FM Radio Antenna Booster?

wa8yxm wrote:
Re that folded wire dipole.
A folded dipole like that has an impedance of around 300 ohms
The radio is more likely "Something different" Coax is typically 75 (But not sure on auto radios.. Long mathematical story) Best reception requires a match.

If the antenna is a "Stubby" A longer antenna will help BUT if it's too "Tall" (Over 13') there is a chance it can be a problem going under a low bridge.

And for GDE trailer.. I did say they might not work.. I checked and you did a good job of explaining why.

Impedance mismatch on receive generally will not hurt reception performance very much if any.

In fact, you can plug a straight piece of wire 6" to 4' right into most antenna inputs and and get some sort of reception.

Car radios are an oddball on antenna impedance.

The coax used is 93 Ohm (RG-62) found HERE

"Product DescriptionCoax 93? RG-62A/U Type, 22 AWG solid bare copper-covered steel, semi-solid polyethylene insulation, bare copper braid shield (95% coverage), PVC jacket,CM"

The center conductor is also surrounded with Solid PE monofilament spiral around conductor.

It has been reported that typical car stereos antenna input impedance is around 100 Ohms and the typical car antenna has an impedance of roughly 36 ohms and 92 ohm coax is generally used..

Lots of impedance mismatches..

Most car preamps like the one you linked are 75 ohm which also represents a mismatch..

You are correct on folded dipole as approx 300 ohms, for that one I would be inclined to add a 300 to 75 ohm balum for a slightly better impedance match.. But, keep in mind, I was using that picture as a illustration of my struggles with indoor wire antennas which do not do very well for distance station reception.

As I mentioned, impedance mismatches on reception while not ideal generally will work OK with OK results..

Now if you were transmitting, that would be a hole nuther can-o-worms..