jon928se

its likely that the capacitor does a couple of things.
A series capacitor acts as a DC block, its good design to prevent dc into a signal path. you can live without it, if it does only dc blocking, but you risk your radio electronics (only slightly, but I would avoid touching the antenna while wearing nylon underwear).

End fed antennas tend to be high Z (impedance) so the capacitor is part of the circuit to get it to match the radio usually in conjunction with an inductor or resistor. Its more often an inductor than resistor as its more efficient. The impedance of the inductor is frequency dependant and its value is chosen to be the best compromise for the intended frequencies its designed to receive. In addition it will act as a static drain to get rid of the dc.

Mrs Jon929se

LT Texan

ditto.

Bypass it with a bit of wire. plug it in and see how it works.

VehiGAZ

Oh WTF?? Is it a resistor or a capacitor???

If it's a resistor, wouldn't it be 120 ohm instead of 180 ohm?
Brown = 1
Red = 2
Brown = 10x
Grey = 8 = ???? Uh-oh.... who put an extra band on there??
Gold = +/- 5% tolerance

I think it is a 8100 pF capacitor with a +/- 1% tolerance. In all the color-coding guides I've found, resistors are marked with 4 bands and capacitors with 5 bands. I see 5 bands... gold-gray-brown-red-brown (read from gold-to-brown for caps):

Gold = bypass or coupling (from Ed Scherer's post)
Grey = 8
Brown = 1
Red = 100x
Brown = +/- 1% tolerance

Oh wait!!! Maybe it's the elusive Flux Capacitor!!

As for the practical application, I received my coax connectors yesterday, so I will test whether I really need the resistor or not over the weekend. I am in the middle of installing new door speakers right now, which is requiring a TON of preparation work first, like disassembling the OEM grills for re-painting, re-gluing the door panel upholstery, fabbing and installing new aluminum speaker plates behind the panels, Dynamat, plastic-weld filling and re-drilling mounting tabs on the OEM tweeter cups that the !(#@%$&! hacks who installed the current system drilled out on me, etc, etc...

Ed Scherer

You really need to test the damn thing (assuming it's still somewhat functional) and find out for sure what it is so we can finally drive a stake into this thread.

And, yeah, that crud might just be soldering flux, so maybe it is flux capacitor. Or a totally fluxed up capacitor, anyway.

LT Texan

does it really matter?

Just bypass it with a bit of wire, plug in the lead and see if it works better.

VehiGAZ

It certainly does if I need to replace it, which is why I started this thread int he first place.

I will get my MM and soldering gear off the boat, test the whatever-it-is as best I can (but I will not be able to test it for capacitance with my MM), put a new male connector on the coax wire this weekend, and report back.

VehiGAZ

Weirdest. Advice. Ever.

John Speake

My bad, yes, 120 ohms. I've never seen an axial lead capacitor looking anything like that one.

Ed Scherer

You know, with all the uncertainty around that potentially dangerous little component, I think you should play it safe and not do any further work on any part of this system unless you're safely ensconced in a Faraday cage.

Ed Scherer

There's a five band code for resistors, too, allowing for one more (than the four band code) decimal digit of precision to be specified.

So it might be a 121 × 0.01, i.e. 1.21 ± 5% Ω resistor (if that fourth band is silver; if it's gray, then we're talking 12.1 GΩ, which is pretty damn unlikely; maybe it's green, for 12.1 MΩ, which also seems unlikely).

Seems kind of weird to use that that much precision when specifying the resistance of a 5% tolerance resistor, though.

VehiGAZ

Where do you think I'm typing this from?!?!

Thanks Ed! My cousin (an EE/ME/PE) came to the same conclusion you did. He found this site that lets you input the band colors and it spits out the rating (fourth band must be silver, not gray) and he came to the same conclusion that it is a resistor of 1.21 gigawatts - a Flux Capacitor!

J/K - I mean 1.21 Ohm of course.

So even though we now know that it's a resistor, what does it do? My cousin's guess was "to get the correct impedance at the radio." Any other guesses while we wait for this weekend's tests?

docmirror

I've seen caps like that before. If it's an impedance matching resistor it should be from the center conductor to the shield, to account for the input impedance of the first stage of the amp. I can't see how having a resistor in series with the center conductor would work unless it's a J-pole(folded dipole) type in a single cased package. That would explain a resistor in there, but what a whacky way to make an FM antenna.

Oh well, measure it with a ohmmeter and put us out of our suspense. If it's a cap, and you have an old analog meter you can test it's general capacitance by setting the meter on it's lowest ohm scale, then watch the meter needle as you touch the leads to each side of the cap. The needle will deflect quickly toward a short, then it will deflect back toward open circuit on a logrithm motion. This is the current inrush to the cap, and the saturation as the needle goes back toward open circuit.

jon928se

You haven't met my wife - Rhonda the amazing static electricity women. She managed to fry a car immobiliser key just by keeping it in her coat pocket.

She also muttered other stuff like band pass filters that went over the top of my head.

VehiGAZ

It's not. See for yourself - it is in-line on the central filament. You don't have to believe me - believe the picture.

Considering the wacky way our beloved Porsche engineers designed the windshield washer system (I challenged friends at work to draw out a washer hose system with the number of Y-splits and check valves the 928 has, and they couldn't!), wackiness is no argument against the possibility! Nevertheless, I don't think that's the case. This is just the coax wire connecting the antenna to the head-unit.

I will tomorrow. MM is on the sailboat, which has much worse electrical problems than the shark, about 35 min away at the marina. So is my soldering iron and supplies, which are also needed to attach the new plug.

I only have a cheap DMM without a capacitance test function, so I don't think I can test it. And don't forget - it looks fried, so I don't think I'm going to be able to figure anything out about it no matter what I test it with.

Considering we can't figure out if it's a cap or a resistor, the antenna had BETTER work without it...

docmirror

I wasn't questioning you, just pointing out where a impedance matching resistor would be in circuit. I agree it is in series with the center conductor.