sharkfin question... can i add copper?

If you talking about just stuffing it in there it may block reception. Google Faraday cage. Soldering a length or coil of wire onto the end of the pcb board's antenna may help...or not.

 

When it comes to antennas, length counts a lot. That's the reason the OEM antenna performs better than the sharkfin. However, there are tricks usually involving loading the antenna or providing a good ground plane. I'm old enough to remember using tin foil on rabbit ears. As I remember it was flaky as all get out. A car is probably not a good platform! Best not to glue it down until you're done experimenting. Good luck.

 

As RonH wrote, length counts for a lot. All else being equal the sharkfin can't perfom as well as the OEM antenna for AM or FM reception. Stuffing it with brillo pads will probably make it worse.

The roof is a fair ground plane. You might improve the sharkfin a bit by moving it to the center of the roof, but I'd expect it's not worth the bother.

 

I figure the same argument applies here as with those cell phone "reception improvement" stickers - if adding a nickel's worth of foil or wire would make them work better, the manufacturer would already be doing it.

 

There are two things you want with an antenna.

First, it should be "resonant" over the frequency band you're interested in. This is usually done on FM but not on AM, because in order to make an AM antenna resonant, it would have to be very large. The exception is the old transistor radio ferrite antennas, which are resonant, but still a little bulky. On FM, size for resonance is achievable. The sharkfin, however is a little small, and would need a coil of some sort to make it resonant. As I haven't seen one I can't comment on whether they have done this.

The second important thing after resonance, is size. The larger the antenna, the more wavefront it intercepts or gathers. So a small antenna will gather a small amount of signal. There is no way around this. In the Prius, there is an amplifier, in the roof liner, I think. But you are still working from a low signal level, which will mean noise when it gets too low.

Reality bites. Sorry about that. When you install the sharkfin, you -may- be able to optimize its' function by making sure the ground point is well connected to the car roof. Short (no loops) connection straps may help here. Use something to reduce corrosion at the connection, such as silicone dielectric grease (it's clear). Other than that, there isn't much you can do.

 

I just got my sharkfin antenna yesterday, and when I looked at the underside of the sharkfin I had the same question as this thread title.

Here's a picture:

[imglink]http://priuschat.com/forums/attachment.php?attachmentid=16108&d=1246343772[/imglink]

As you can see from the picture, the copper, grid-like antenna wire is only on one side of the fin.

How come Visual Garage didn't extend that copper, grid-like antenna to the other side of the fin ... would not such a doubling of the copper wire increase the reception significantly ... should I try to do it myself (not with a copper scrubbie, but with something similar to the original copper, grid-like antenna wire)???

 

Hi Boo,

The copper scrubbie is a thing you clean grease out of pots with. These are randomly oriented copper ribbon, shaped like a sponge. They also come gold plated, although the plating is probably just "flash". Either type would screw up the tuning apparent in the Shark-fin antenna.

Having worked on antenna professionally, I do not have much good to say about the antenna you posted a picture of. So I wont. Does it work on AM at all ?

 

I'm sure from memory my shark fin has a lot more "stuff" inside it. There were 2 antenna in mine from memory and a small circuit board.

I can pick up a Victorian AM radio station on mine. Victoria is at least 200km away from here.

 

Well that would add 100% more copper, to that ridiculous little amount that is already in there, thus doubling the cost of that piece of crap!!!

As stated before, if you want more signal, put up more metal!
Brillo pads, with/without soap, do not count, shavings from a "Mill" do not count
Looking cool, and receiving stupid, just does not make RF sense.
I have been in the "RF" game for over 40 years.
Some laws of Physics you can just not violate and get good results!!!

 

donee and patsparks,

My sharkfin antenna is made by Visual Garage and sold by PriusChat Store and others.

It's the same one that's been the subject of many threads and posts here.

patsparks -- after posting the interior picture of my sharkfin, I found photos of the insides of other people's sharkfin antenna and they all looked like mine -- with the copper antenna grid on only one side of the fin. See, e.g., our friend, darelldd's sharkfin:

[imglink]http://evnut.com/images/prius/antenna/shark_fin02.jpg[/imglink]

So, I'm still wondering if I can improve the reception by just taping some additional copper wire to the end of the existing antenna grid and looping and taping that additional wire onto the other empty side of the fin. At minimum, I don't want to cause any harm.

 

I have that same sharkfin installed and I have NO PROBLEM with AM or FM stations, sounds just as good as the OEM antenna

-Matt

 

Boo, let us know how your reception is because I really would like to get one if it works well.

 

That's because you live in town and the ERP of the the stations you listen to have enough power to overcome the deficiencies if the "Sharkfin"
Try driving 40 or 50 miles out of town, and see how the reception is.
It all depends, on ERP, AM/FM, distance to transmission tower, what's between you and the transitter, and the type of receive antenna!

It's like walking into a forest and looking for a tree, your pretty much guaranteed your gonna find one. However walk up and over the hill into the desert 50 miles away, your not gonna get a lot of trees, just sand. The tree's you do find are all scrawny and crappy !!!

RF is simple!!

 

So KK6PD, what do you think of my idea of just attaching more copper wire (such as home radio antenna wire, speaker wire, lamp wire, etc.)?

Should it help?

Can it hurt?

 

Lets try a Positive approach.
What do I really need to do to "Sharkfin" antennas to make them more efficient.
If you follow RF theory, perfection would be a full wavelength antenna. The FM band in the U.S. is 88Mhz to 108Mhz. Thats a 20 Mhz spread of frequencies. For reference lets take the middle of the band, 98 Mhz. In inches, the a full wavelength antenna would be 120.489 inches long. Nice thing about RF is that if you start 1/2ing things, it still will work out rather well. So a 1/2 wavelength is going to be 60.244, and the most used auto wavelegth is 1/4 wave which woud be 30.122 inches. Measure the length of the copper circuit trace in the sharkfin, if it comes out to 12 inches I would be surprised.
At this point I have to add another variable into the mix.
Sorry, it's called Antenna Polarization.
In the early days of FM radio in the 88-108 MHz spectrum, the radio stations broadcasted horizontal polarization. However, in the 1960's, FM radios became popular in automobiles which used vertical polarized receiving whip antennas. As a result, the FCC modified Part 73 of the rules and regulations to allow FM stations to broadcast RHC or elliptical polarization to improve reception to vertical receiving antennas as long as the horizontal component was dominant.

To improve the antenna to 1/4 wavelength spec you should ADD aout 20 inches of copper in the pod. I would take some #20, or #22 Guage coated wire and glue it into the "Sharkfin in an up and down arrangement. High Temp Hot Glue would work OK. make sure you solder one end of the wire to the end of the trace on the copper foil. Do not overlap the wire, the spacing could be tight, but thats why your using insuated wire, that, and for corrosion protection. That should help with the range issue.
Note also the Prius has an RF pre-amplifier in the base of the existing mount. If the RF Pre-Amp goes south, so does radio reception.!! Its purpose is to amplify small RF signals. Make sure yor antenna extension does NOT come into contact with the chassis ground.

Somebody try ths, and take a drive that you nomally have a station you listen to fade away and see if this improves things a bit??

Here is the time for bonus science points folks, let's all play Mr Wizard!!!

 

Boo, that's funny, as I was composing, you post this!!!
Yes I think it could help quite a bit. be very inexpensive, and produce positive results!!

Lemme know how it goes!!

 

Boo, et al,

IIRC, there are two antennas (antennae?) in the SharkFin.

One, folded in a regular rectangular pattern, has been pictured.

There is I believe a second one on the small green circuit board affixed
to the flat after surface of the fin. This one is folded "fractal" style, and
looks for the world like an aquarium snail's feeding track.

Don't know which antenna is AM or FM.

Maybe one of the ee-smart members could confirm/deny/explain.