sharkfin question... can i add copper?

Thanks KK6PD.

I measured the length of the copper circuit trace in the sharkfin, and it came out to 29 inches!

Given this measurement, how many inches of #20 or #22 coated wire would you add?

 

Yes, you are right. There is a second antenna (or something else?) in the small green circuit board folded "fractal" style, and looks as you described (or like cloud ears or clover). You can see it in this photo from darelldd:

[IMGLINK]http://evnut.com/images/prius/antenna/antenna_shark_fin04.jpg[/IMGLINK]

I too wonder which is AM and which is FM. My guess is that the first one that is folded in a rectangular fractal pattern onto one side of the fin is the FM antenna, and that the second one that is embedded fractal style in the green circuit board is the AM antenna.

 

Boo, well I stand amazed and corrected... RF wise you pretty much have a 1/4 wave antenna in that package.

There are several thoughts that come to mind,
1- Make the system a 1/2 wave antenna. Add the same length of fine guage wire to the other side and solder one end of the wire to the end of the circuit trace. Just like a Smith & Wesson beats a Full House, a 1/2 wave antenna is better that a 1/4 wave antenna.
2- Remember the Polarization note I mentioned, it's the way the antenna reacts to signal Polarization. Not much you can do about that. Idealy a Horizontal antenna would work geat, but it's not easy going H and achieve a circular pickup pattern, which is what you would want. Most cars with whip antennas are in the Vertical position. That along with the car shell which acts as the ground half of the antenna system make up what is known as a "Ground Plane" antenna. Equal receive ability in a 360' pattern around the vertical element of the antenna. The stock Prius antenna, being at a slant, really has an eliptical, egg shaped receive pattern. I believe the strongest point would be facing front!
3 The fact that the receive circuit trace of the antenna in the "Shark" is so close to the metal of the roof ground plane, as oppsed to the more vertical stick antenna may play a part in the receive issue. Proving that woud involve raising the "Shark" antenna off and above the roof by at least 6 inches, but then it would look like a Aerodynamic Camel's Hump and rather stupid!
If I wanted to test the RF Pre-amp, first I would pick up a simple car whip antenna, then find a weak station with the original car antenna in place, note how bad it is, distorted, fuzzy, etc., then pull the motorla plug that has the car's antenna out of the radio and plug in the whip. Stick it up in the air and see what difference it makes. If you hear a big difference, BAD RF pre-amp perhaps! No difference Good amp. If you had access to a RF Spectrum Analyser, you could see the level of the signal coming off the antenna and make a very valid comparson. I have one, but no "Sharkfin to experiment on. That would be an interesting test!

 

KK6PD,

Yes, there are 21 of those long bars that range from approximately 0.75 to 1.5 inches each; then there are 21 of those short bars that connect the long bars, and each of those short bars is approximately 0.125 inch. Hard to measure exactly, but I think the total length of the copper circuit trace is 28 to 30 inches.

I think I'll try your suggestion #1.

That approx 29 inch circuit trace is embedded into or glued onto the fin plastic and it's all covered with clear tape. I don't have a soldering iron, so I'm just going to lift the clear tape at the end of the circuit trace, place the end of the exposed new wire onto the end of the circuit trace, and then place the tape back down. Then I'll bring the new wire to the other side of the fin, approximate the fractal design of the original circuit trace, and then tape the new wire down with gaffers tape.

I still wonder why Visual Garage didn't do this in the first place -- putting a connected duplicate circuit trace on the other side of the fin and thereby making it a 1/2 wave antenna.

* * * * * * * *

I'm not going to be able to really test if this attempted DIY wave doubling will improve the range of the antenna. (I live in Manhattan, so it'll be hard to test the range of the antenna unless I drive out about a hundred miles or so, which I'm not planning to do.) About the most I can do is test to see if this DIY wave doubling doesn't screw things up.

* * * * * * * *

Thanks for all your help.

 

I get FM reception further out of Adelaide with my shark fin equiped Prius than I get with my standard antenna equiped Holden Commodore.
Maybe it's always a better day for radio when I take the Prius out of town.

 

Results of Adding More Copper

I just finished my DIY attempt to improve the reception of the Visual Garage Sharkfin Antenna by doubling the length of the copper circuit trace of the original antenna and thereby increasing the antenna's wavelength spec from 1/4 to 1/2.

What I Did:

1. I cut an approximately 30 inch length of 18 gauge lamp wire.

2. I stripped the insulation on one end of the lamp wire so that I could connect the copper end to the end of the original copper circuit trace.

3. I crimped the lamp wire into a pattern similar to the repetitive, fractal pattern of the original copper circuit trace.

4. I took this crimped lamp wire and stuck it onto 4 inches of gaffers tape, and then I sealed the crimped lamp wire with clear packaging tape.

Here's how this lamp wire addition looked like:

[imglink]http://priuschat.com/forums/attachment.php?attachmentid=16363&d=1246840418[/imglink]

5. Then I connected the ends of the lamp wire addition and the original copper circuit trace by lifting the clear tape off the end of the original copper circuit trace (the entire copper circuit trace is covered with clear tape), laying the copper end of the lamp wire addition over the end of the original copper circuit trace, and placing the clear tape back down.

Here's how it looked like with the lamp wire addition connected to the original copper circuit trace:

[imglink]http://priuschat.com/forums/attachment.php?attachmentid=16364&d=1246840418[/imglink]

Then I taped the whole lamp wire addition to the sharkfin shell.

Test Results:

1. I live in Manhattan approximately one mile from the strong radio broadcast antennas on top of the Empire State Building. So, except when I travel at least 75 miles out of town, I typically receive a strong signal from the many stations with broadcast antennas on the Empire State Building.

2. But there are several local college radio stations with weaker broadcast antennas located on campus. I did my weak signal tests with the Fairleigh Dickinson University radio station located around 12 miles from me.

3. With the strong signals from the stations broadcasting from the Empire State Building, I could detect no difference between:

(a) the stock whip antenna,
(b) the unmodified sharkfin antenna, and
(c) the sharkfin antenna modified as described above.

4. With the weak signal from the Fairleigh Dickinson University radio station:

(a) I could receive a weak but listenable signal with the stock whip antenna,
(b) I could only receive a faint but unlistenable signal with the unmodified sharkfin antenna, and
(c) I could not detect any improvement in reception with the sharkfin antenna modified as described above -- the unmodified and modified sharkfin antenna sounded the same.

Conclusions (suspicions really, given my DIY modification and limited testing protocol):

1. I suspect that the reason why Visual Garage produced a 1/4 wave antenna instead of a 1/2 wave antenna is that given other limitations inherent with the sharkfin antenna design, increasing it to a 1/2 wave antenna would produce no or little improvement in reception.

2. Because I could detect no difference -- whether good or bad -- between the unmodified and modified sharkfin antenna, I'm going to keep and install the sharkfin antenna in its modified 1/2 wave form. I figure it doesn't and can't hurt.

* * * * * * * *

I welcome any comments before I go live with my modified sharkfin antenna next week.

 

Boo, well done! I kind of suspected that might happen. It is interesting in how the stock whip faired in the test.
I suspect that is beause of the vertical eleent inherent in the design in a Ground Pane antenna system. So I guess the rule of thumb for "Sharkfin"antennas is...
"If you in the city and so is the transmitter you probably going to be OK!!!
If you want to receive distant Lo power FM, This is not the antenna for you.
Whie I happen to like the design, beause of RF rules, I prefer the whip!!

 

Thanks again KK6PD for all your help and guidance.

I'm going to stick with my sharkfin antenna because it looks great and works fine for me given that I rarely venture far away from New York City. But if I ever move outside of New York City or other major city, I can always switch back to the stock whip antenna if necessary.

BTW, I read somewhere that most stock whip antennas these days are 1/4 wave. But I think that back in the day when antennas were commonly embedded in windshields or other car glass, that those antennas were full wave -- about 120 inches of antenna wire.

 

I had the same antennae when I had my Prius too, and had great reception from it!!!

 

I heard its not worth the price and works like crap I bought a shorty annt. and i lost no reception

 

FYI, here is the formula to determine wavelength from frequency. I'll use the words rather than the symbols,

wavelength (in centimeters) = 30,000 divided by the frequency (in MegaHertz/Mega Cycles per second)

So for an FM band antenna you would divide 30,000 by 98 to get 306.1224 cm or 120.5" For the standard 1/4 wavelength mast used on autos, divide by 4 and you'll get 76.556 cm or 30.125"

For an AM band (.6 - 1.6 MHz) antenna, divide 30000 by 1.1 and you'll get 27,272.73 cm or 10,737.3" for the wavelength and 2,684.325" for a 1/4 wave antenna.

BTW, for any CB users, you'll see that 108" whip antenna is 1/4 wavelength for the CB band.

 

Re: Results of Adding More Copper

Nice job. I'll take an empirical test over a formula any day. BTW, it's not how long the antenna wire is (no jokes, now), it's the effective length; meaning how much wire intersects the wavefront. Take a couple of yards of wire and roll it up in ball and you will get the same performance as a wire the size of the ball. Look at the shark fin zigzag antenna. If the signal is coming from the side, it sees an antenna the length of the zigzag pattern. If the signal is coming from the front, the effective length is the width of the pattern. These dimensions are significantly shorter than the quarter wave length which is why it does worse than the whip. There are details, of course, having to do with the fact that the pattern actually intersects the wavefront in multiple places due to its extent, but generally, details smaller than 1/10 of the wavelength don't matter. You could have gotten some gain with your add-on if you had separated it from the OEM pattern by a significant distance, such as laying it out lengthwise but then it would have extended outside the fin.

Also, the reason a 1/4 wave vertical whip mounted on the roof does better than one in free space or mounted on the bumper is that the metal roof acts as a reflector, effectively doubling the length.

 

Re: Results of Adding More Copper

Technically, the roof/fender/trunk etc. is the Ground Plane for the antenna, not a reflector. Think of it as a dipole antenna with 1 element at 90 degrees to the other element.

Now, would the liquid copper paint used for repairing defroster traces work in lieu of actual copper wire?

 

Re: Results of Adding More Copper

I am impressed with the creativity and craftmanship shown (and pics are great). I saved the orig antenna in case I wanted to go back, because it was better reception. These days, I tend to get my favorite stations on iPhone (when out of range) and this can go to speakers if I ever find my patch cord.