Radio Antenna Connection

With the AM radio not working I started troubleshooting. Radio, speaker, and antenna were checked on a bench prior to installation, unfortunately I did not check the AAR antenna extension. Bottom line is it appears the extension is my culprit where the pinned connector was able to come free from the 90 deg connector that attaches to the coax wire, breaking the connection.

The plan was to simply strip the wire back, insert it in the tip and resolder, but as with many things a full dismantling added to my confusion.

Attached you can see the pieces in the order they were removed, there appears to be a resistor/filter of sorts, and as best I can tell it had a very small integral wire attached to it on both ends. One end running into the RCA style tip that was soldered and the other being soldered to the center wire of the coax cable, when assembled the connection between the coax cable and the resistor would be shielded by being inserted into the black plastic tip of the 90 deg fitting.

So does anyone know what this resistor/filter is?
What’s it’s purpose?
Do I need it for the radio to function properly?
And where do I get one if needed?

Thanks

I would guess with an AM radio and a fiberglass hood YES it is need for your particular car.............as an owner of a car with a (lift-off) fiberglass hood that the original or second owner moved the antenna to the right rear quarter panel because of RF interference using what appears to be an AAR rear mount antenna lead, which might also have that resistor in it? You could also just add an inline resister to what you have too?

So I’m having trouble finding things on the internet that address this issue but did manage to find this thread that appears to be a similar issue/question where many with better electrical backgrounds have offered their input. In their case it appears to be a Porsche with a short cable run, or certainly shorter than an AAR with multiple antenna cables would have. So I don’t think it’s purpose would have to do with the fiberglass hood, but maybe optimum frequency tuning (link below)

https://rennlist.com/forums/928-forum/579218-purpose-of-resistor-in-coax-antenna-wire.html

Honestly I was able to follow most but not all of the dialog. Of course they never really solved the mystery of resistor or capacitor, and their image clearly has a more traditional look than the image I posted.

As for one being in the first run of antenna cable from the rear quarter heading forward I have no idea. I suppose it’s possible that all MOPAR antennas have this and maybe I’ve never had a need to cut a connector apart to find out. It may make an interesting junkyard trip to find out, but wouldn’t solve my mystery of what exactly it is and getting a replacement, unless of course I could salvage one from another assembly.

The search continues

Wow I read the entire 50 + posts.......and still is it a resistor or capacitor......my vote it's a resistor and only from knowing how the Germans (re., TUV) are real strict about RF. Something to check out would be owners or forums with those well known vintage fiberglass sports cars "Vettes", didn't a lot or most of them have rear mounted antennas? Be interesting to see what Corvettes used for antenna coax.......with or without a coax resistor/capacitor?????

LOL, I read them all as well, some interesting ideas/theories. If I understood correctly the argument for a capacitor was linked to the short cable length and/or a power wire running along side the cable and not my issue at all. The idea with the resistor being used to dial in the optimum frequency appears most plausible.

I’m still curious if ALL antenna cables have this installed. Just don’t have a spare wire to cut up and find out.

Good thought about checking the Vette forums

That looks like a 150,000 ohm resistor to me, radio guys use those as bleeder resistors. Go to RF parts.com and look around. A ham radio site could help you on what value you need, seems like it would block signal to me, it depends on the coax cable resistance and radio power. You can test a cable for a resistor with a cheap multimeter.

I just measured a 3 foot extension and it was less than 1ohm. I can't fathom a car radio working with 150,000 ohms so I did a little research. On the Electronics Point website it explains that with long car antenna cable lengths the capacitance increases, so they add a capacitor to bring it back to spec. I assume that is why it is there, not to block anything.

And the capacitor/resistor debate continues . . .
I tried testing the small Cyanide pill looking piece but it appears to be broken internally.
As you mentioned, I checked the full cable run less the ??? piece pictured, 3 ohms. What I don’t know is if the first run of cable from the rear mount has one of these installed or not.
I have a feeling I’ll be visiting the salvage yard in an attempt to find a suitable replacement, or at least one that can be tested to determine with certainty what it is. And of course the issue may be that this is unique to extension cables only????

Best I can tell you is the long cables have them, and your total resistance from radio plug to antenna mast should be 5 ohms or less. I am told nissan roof mount antennas have them, I would imagine any long cable would have one.

So I decided to head to the junkyard and see what I could find. After driving 45 min I pulled up to the front gate to find the entire yard clean, not a single car!! They had a banner hanging stating they had moved and to call. Only after calling do I find they have moved another 30 min further and won’t be open for several hours due to a staffing issue.

THIS SUCKS, now and for future runs

You do know you can buy a reproduction kit for that. If you don't care about perfect original you could use a cable from a 50s gm car about $25, it appears 521 restorations sells a mopar base with the screw on cable style that gm used for $29.95. I would not drive all over for that kind of $$.

I just can’t bring myself to add a piece thats blatantly incorrect, but I get where many are temped.

So I ran to a junkyard and cut several connections from standard antenna cars, obviously there is little chance of finding an AAR with the extension lying in the scrap yard these days. Not a single one had a resistor/capacitor.

I trimmed back a new section of the original cable, reattached the original connectors and checked for continuity (tone) and ohms (3.2). Reinserted into the radio and everything works. Go figure !

Good to hear, you could try a 750 picofarad capacitor if you have radio tuning problems, if it works and brings in stations I would leave it, I am sure somewhere you can buy what you need and it plugs right in, but where. If you ever get by a truck stop with a good cb radio repair shop, I bet they would know.