|
09-21-2007, 03:23 PM
|
#1
|
Remember, Safety Third
1973 27' Overlander
Catfish Corners
, Georgia
Join Date: Oct 2004
Posts: 5,720
|
Ohms…Ohms….Say it slowly…Ohms
A couple of questions about Ohm ratings.
First, does anybody know what the Ohm rating would be for radio antenna wire? After poking around at Radio Shack today, I’m guessing 50 Ohm. The reason I ask is that I’m trying to decide what to do about the radio antenna for the am/fm radio. The OEM connection came thru the television antenna, but unfortunately, I can’t repair that. The TV antenna works, but no luck with the radio.
I have a bunch of left over pieces-parts form the OEM setup as well as the remnants of two radio antennae that were mounted to the center and back vent covers up on the roof. Guessing that these were either CB or short wave. Just trying to decide what to buy to make it all work.
Second, what to do about the speakers. I seem to remember reading in a thread here someplace that modern speakers/radios use a different Ohm rating than in the early ‘70’s. And somebody mentioned that mixing old speakers with new radios could fry the radio??? The original speakers are still there, but I’m sure they are junk now, so they will have to be replaced. The original speaker wire is still there as well and looks to be in good shape. It appears to be about 14/16 gauge, stranded copper. That shouldn’t be a problem, should it?
As always, thanks for the help.
Jim
|
|
|
09-21-2007, 03:32 PM
|
#2
|
Rivet Master
1967 26' Overlander
Huntsville
, Alabama
Join Date: Dec 2003
Posts: 3,018
|
Radio antenna wire is usually 75 ohm coaxially wound. Keep in mind that 75 ohms is the impedance, which is the alternating current version of direct current's resistance.
Bottom line is that you can not verify a given setup with a run-of-the-mill ohmmeter.
Back when I was souping up car stereo, speakers were 8 ohm impedance. Nowadays, the standard is 4 ohm. Yes, you could cook a radio expecting 8-ohm speakers if you ran it at high volume for a while on 4-ohm speakers. Dinner-music-level volume should not be a problem.
Your speaker wire description sounds adequate.
Tom
|
|
|
09-21-2007, 03:50 PM
|
#3
|
Retired.
Currently Looking...
.
, At Large
Join Date: Jun 2003
Posts: 21,276
|
Jim, where is the radio located in your Overlander? Is it in the front overhead, or is it in a cabinet along the street side of the coach? I don't know if you've been following that closely, but I had good luck installing a car antenna on the side of our coach.
If you are replacing the radio, maybe you could pick up 4 new modern speakers to go with it.
__________________
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
Terry
|
|
|
09-21-2007, 03:55 PM
|
#4
|
Rivet Master
1977 27' Overlander
1954 25' Cruiser
1990 34.5' Airstream 345
VC Highlands
, Nevada
Join Date: Mar 2005
Posts: 2,151
|
Are you talking coaxual cable or the old twin lead wire. I had the old twin lead wires and that has an impedance of 300 ohms. You can use a BALUN (balanced-unbalanced) matching transformer to conect coaxual cable to the twin lead wire for a proper siganl to the TV/Radio.
|
|
|
09-21-2007, 04:03 PM
|
#5
|
Rivet Master
1967 26' Overlander
Huntsville
, Alabama
Join Date: Dec 2003
Posts: 3,018
|
Yes you can, but
Quote:
Originally Posted by Buttercup
... You can use a BALUN (balanced-unbalanced) matching transformer to ...
|
I tried that route in hopes of using my television's previously wired, 300 ohm flatlead. For whatever reason, I lost a lot of signal strength. Ended up having to run a new coax line for the television.
On a happier note, I doubt Jim's radio lead was wired with flatlead.
Tom
|
|
|
09-21-2007, 04:06 PM
|
#6
|
Retired.
Currently Looking...
.
, At Large
Join Date: Jun 2003
Posts: 21,276
|
Quote:
Originally Posted by TomW
=
On a happier note, I doubt Jim's radio lead was wired with flatlead.
Tom
|
The stuff I pulled out of our ceiling looked like standard radio antenna wire, I'm guessing Jim's is the same, based on the similar vintage of the trailers.
__________________
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
Terry
|
|
|
09-21-2007, 04:22 PM
|
#7
|
Remember, Safety Third
1973 27' Overlander
Catfish Corners
, Georgia
Join Date: Oct 2004
Posts: 5,720
|
Originally, there was flatlead coming from the TV antenna down to what I originally thought was a power booster of some sort. After consultation with my buddies here on the forum, I now believe that the “transformer” was in indeed a balun. I have replaced the flatlead with coax from the TV antenna to the interior of the camper to run my new HD LCD TV (GREAT PICTURE!), the flatlead was completely shot, apparently broken someplace inside the jacket, so it had to be replaced. You can read about it here http://www.airforums.com/forums/f450/hdtv-old-airstreams-34784.html if you need some late night reading material.
Now I’m faced with providing an antenna for the radio, hence the current question. I wanted to use some type of antenna like Terry found recently for his rig, but I can’t seem to find anything suitable. I’m also not really comfortable drilling new holes in the outer skin unless necessary. Since I’ve already got many of the pieces there, I just trying to put something together using new and old.
Jim
|
|
|
09-21-2007, 04:33 PM
|
#8
|
Remember, Safety Third
1973 27' Overlander
Catfish Corners
, Georgia
Join Date: Oct 2004
Posts: 5,720
|
Terry, I'm going to replace teh speakers with something modern (and that actually works!). And the stereo is in the front overhead, below the control panel.
Tom, you are correct. The wire that ran from the balun to the radio is some type of coax, not flatlead. It's really a strange looking setup.
Give me a minute to compose a reasonable description of it, you'll get a kick out of this weirdness. Back in a few.
Jim
|
|
|
09-21-2007, 05:05 PM
|
#9
|
Remember, Safety Third
1973 27' Overlander
Catfish Corners
, Georgia
Join Date: Oct 2004
Posts: 5,720
|
So the radio coax is really strange looking stuff. On the radio end, there is one piece of coax that presumably at one time had a standard radio jack on it (all hacked up now). So far so good, right? On the balun end, there were two pieces of coax that appeared to be cobbled into one cable going towards the radio. One cable appeared to acting as the center dielectric providing the signal a path from the balun to the radio, the other piece of coax appeared to be acting as the ground as it was soldered to the outside mesh shield of cable number two on the balun end, then ran towards the radio in a sheath that contained both wires. My assumption was that the two wires were joined inside that sheath and that one wire acted as the signal path, while the other provided the necessary ground/shielding to make a clean RF signal path. When I took the two apart, guess what? No connection between the two pieces of coax.
Strange, eh? All of this leads me to believe that either a) somebody got lazy at the factory, or b) I’m actually clueless or c) I just need to replace the whole run of wire with a little help from my friends here.
Thanks for the help guys.
Jim
|
|
|
09-21-2007, 05:13 PM
|
#10
|
Rivet Master
1967 26' Overlander
Huntsville
, Alabama
Join Date: Dec 2003
Posts: 3,018
|
1000 words
Jim,
Can you post a picture of the setup?
Tom
|
|
|
09-21-2007, 05:22 PM
|
#11
|
Rivet Master
Airstream Dealer
Corona
, California
Join Date: Feb 2002
Posts: 16,497
|
Quote:
Originally Posted by Jim & Susan
A couple of questions about Ohm ratings.
First, does anybody know what the Ohm rating would be for radio antenna wire? After poking around at Radio Shack today, I’m guessing 50 Ohm. The reason I ask is that I’m trying to decide what to do about the radio antenna for the am/fm radio. The OEM connection came thru the television antenna, but unfortunately, I can’t repair that. The TV antenna works, but no luck with the radio.
I have a bunch of left over pieces-parts form the OEM setup as well as the remnants of two radio antennae that were mounted to the center and back vent covers up on the roof. Guessing that these were either CB or short wave. Just trying to decide what to buy to make it all work.
Second, what to do about the speakers. I seem to remember reading in a thread here someplace that modern speakers/radios use a different Ohm rating than in the early ‘70’s. And somebody mentioned that mixing old speakers with new radios could fry the radio??? The original speakers are still there, but I’m sure they are junk now, so they will have to be replaced. The original speaker wire is still there as well and looks to be in good shape. It appears to be about 14/16 gauge, stranded copper. That shouldn’t be a problem, should it?
As always, thanks for the help.
Jim
|
Jim.
The antenna cable can be purchased with different "ohm" ratings.
The primary consideration for which rating to use, is not the antenna, but the radio.
Determine what the input antenna rating is for the radio.
That dictates the proper antenna, without guessing.
Andy
|
|
|
09-21-2007, 06:03 PM
|
#12
|
Remember, Safety Third
1973 27' Overlander
Catfish Corners
, Georgia
Join Date: Oct 2004
Posts: 5,720
|
Quote:
Originally Posted by TomW
Jim,
Can you post a picture of the setup?
Tom
|
No, I've already disassembeld it. I think Andy may be right, just look at the Ohms rating of the radio (if I can find it anywhere in the documentation) and go from there. I was really hoping to use some of the "left-over" parts to piece things back together.
Thanks for the help everybody.
Jim
|
|
|
09-21-2007, 06:19 PM
|
#13
|
Rivet Master
1967 26' Overlander
Huntsville
, Alabama
Join Date: Dec 2003
Posts: 3,018
|
Maybe in CA
Quote:
Originally Posted by Jim & Susan
... Andy may be right, just look at the Ohms rating of the radio (if I can find it anywhere in the documentation) ...
|
Jim,
I think most modern-day radios are set up for 75 ohm cabling. The Pioneer SuperTuner installed a year or two ago in my Airstream certainly was.
The spec sheet is attached below. Look at \FM tuner\Usable sensitivity & FM tuner\50 dB quieting sensitivity; both call out "75 ohm"
The factory-installed radio wiring in my Overlander plugged in to the new radio with no modification. And I have good reception.
Tom
|
|
|
09-21-2007, 06:23 PM
|
#14
|
Rivet Master
1967 26' Overlander
Huntsville
, Alabama
Join Date: Dec 2003
Posts: 3,018
|
Okay, so its unreadable.
Attached is a zoom-in of the above image.
Tom
|
|
|
09-21-2007, 06:51 PM
|
#15
|
Remember, Safety Third
1973 27' Overlander
Catfish Corners
, Georgia
Join Date: Oct 2004
Posts: 5,720
|
As Spock would say "scanning (my documents) now, captain".
Jim
|
|
|
09-21-2007, 07:08 PM
|
#16
|
Retired.
Currently Looking...
.
, At Large
Join Date: Jun 2003
Posts: 21,276
|
It's dead, Jim
Quote:
Originally Posted by Jim & Susan
As Spock would say "scanning (my documents) now, captain".
Jim
|
Transfer warp power to the scanners, we're not reading anything here yet.
__________________
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
Terry
|
|
|
09-21-2007, 07:22 PM
|
#17
|
Remember, Safety Third
1973 27' Overlander
Catfish Corners
, Georgia
Join Date: Oct 2004
Posts: 5,720
|
Scanning complete. There’s plenty in there about Heisenberg compensators, auxiliary power conduits, warp nacelles and general warp theory. But almost unbelievably, my documents are silent on the subject of Dr. Ohm’s theory. So, I’m going to assume two things. One, that the modern stuff is 75 ohms, and, two, since Tom had no problem with his setup, the old stuff is also 75 ohms.
Wish me luck, I’m going in.
Jim
|
|
|
09-21-2007, 07:29 PM
|
#18
|
Retired.
Currently Looking...
.
, At Large
Join Date: Jun 2003
Posts: 21,276
|
Quote:
Originally Posted by Jim & Susan
Wish me luck, I’m going in.
Jim
|
We'll maintain a transporter lock on ye'. Try no ta' get too wrapped up in the wirin', it messes with the pattern buffers.
__________________
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
Terry
|
|
|
09-21-2007, 08:29 PM
|
#19
|
Rivet Master
Commercial Member
Vintage Kin Owner
Naples
, Florida
Join Date: Dec 2005
Posts: 7,508
|
Lions and tigers and.........Trekkies.......... OH MY!!!!!!!!!!!
__________________
lewster
Solar Tech Energy Systems, Inc.
Victron Solar Components and Inverters, Zamp Solar Panels, LiFeBlue and Battle Born Lithium Batteries, Lifeline AGM Batteries
|
|
|
09-21-2007, 08:38 PM
|
#20
|
Remember, Safety Third
1973 27' Overlander
Catfish Corners
, Georgia
Join Date: Oct 2004
Posts: 5,720
|
As long as we keep the warp intake manifolds aligned to within 0.0001% of tolerance, we'll be fine. Carry on Scotty.
Jim
|
|
|
|
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
|
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
|
Recent Discussions |
|
|
|
|
|
|
|
|
|
|
|