antenna trimming?
in [Repair]
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From: Michael A. Terrell on 2 Dec 2009 22:28 Jeff Liebermann wrote: > > On Wed, 02 Dec 2009 10:11:04 -0500, Meat Plow <meat(a)petitmorte.net> > wrote: > > >On Tue, 01 Dec 2009 23:15:32 -0800, Jeff Liebermann > ><jeffl(a)cruzio.com>wrote: > > > >>On Tue, 01 Dec 2009 14:12:18 -0800, David Brodbeck <gull(a)gull.us> > >>wrote: > >> > >>>Michael A. Terrell wrote: > >>>> RG/62, 93 ohm coax. The same as what IBM used for their early > >>>> computer networks. > >>> > >>>I've got some 93 ohm coax lying around from when I used some to make a > >>>matching section. Never knew what the original application was for it. > >>> Very interesting. > >> > >>RG-62/u was used for Arcnet networking, > >><http://en.wikipedia.org/wiki/Arcnet> > >>and IBM 3270 terminal systems: > >><http://en.wikipedia.org/wiki/3270> > > > >Ahh, I love the smell of LANtastic over RG62A/U and TCNS in the > >morning. > > You might want to ease up on whatever you're sniffing. Arcnet and > 3270 used BNC connectors. What's a TCNS? > > My favorite gizmo was the passive hub. Huge amounts of cash for a > mysterious sealed box with 3 or more BNC connectors. I eventually > dissected one and was rather disappointed to find only a few > resistors. > > I'm still not certain that AM/FM car antenna coax cable is RG-62/u. I > haven't found a suitable car antenna to compare with the boxes and > boxes of RG-62/u I have left over from ripping out Arcnet systems > (Lantastic) and replacing them RG-58a/u (Ethernet and Novell). Whatever. I heard it from some Delco engineers who designed their car radios in the '70s, and saw it on plenty of car radio antenna cables in the '60s & '70s. The Delco engineers explanation was that a whip antenna for AM was used as a voltage probe, and 93 ohm coax had the lowest loss available. That made it easier to match to the tuned RF input. It was also cheap cable with a polypropylene tube to hold the braid and surround the zigzag center conductor. Compare that to a low loss teflon which can cost several dollars a foot. -- The movie 'Deliverance' isn't a documentary!
From: Jeff Liebermann on 2 Dec 2009 23:28 On Wed, 02 Dec 2009 22:28:14 -0500, "Michael A. Terrell" <mike.terrell(a)earthlink.net> wrote: > Whatever. I heard it from some Delco engineers who designed their >car radios in the '70s, and saw it on plenty of car radio antenna cables >in the '60s & '70s. Sigh. I never bothered to look. I just found a stainless car whip antenna with coax cable attached. The number on the cable is: 5PT3-30C LCN Google couldn't find anything. Both ends are soldered so I can't inspect the guts. The OD is 5.0mm, which is at one end of the range of RG-62a/u jacket diameters of 5.1 to 6.2mm. I would measure the PF/ft, but my destroyed my LCR meter is busted. It probably is RG-62/u but I'm still not convinced. >The Delco engineers explanation was that a whip >antenna for AM was used as a voltage probe, and 93 ohm coax had the >lowest loss available. Well, let's see. The cable is 4.5ft long. ohms pf/ft pF RG-62/u 93 13 58.5 RG-59/u 75 17 76.5 RG-58/u 50 30 135. Yeah, I can see the reason. The input tuning stage would never tune with that much capacitance. >That made it easier to match to the tuned RF >input. Well, it could be matched to almost anything. However, the low coax capacitance would give the trimmer in the radio a much wider tuning range. >It was also cheap cable with a polypropylene tube to hold the >braid and surround the zigzag center conductor. Compare that to a low >loss teflon which can cost several dollars a foot. They didn't PTFE when Bill Lear invented the first "Motorola" car radio. <http://en.wikipedia.org/wiki/Bill_Lear> Also, at 1MHz, the difference in cable losses between various dielectrics is zilch at 4.5 ft. They could have used aluminum foil wrapped garden hose, with a coat hanger as center conductor, and gotten the same cable loss. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com jeffl(a)cruzio.com # http://www.LearnByDestroying.com AE6KS
From: mm on 2 Dec 2009 23:52 On Wed, 02 Dec 2009 20:28:15 -0800, Jeff Liebermann <jeffl(a)cruzio.com> wrote: >They didn't PTFE when Bill Lear invented the first "Motorola" car >radio. Well, much of this thread is over my head now, sort of, but ftr, I was 40 years old before I realized why it was called "motor-ola" ><http://en.wikipedia.org/wiki/Bill_Lear> Interesting. For example: Learisms: # On electronics, "There's only one thing worse than an intermittent, that's an intermittent intermittent." # On weight reduction in the Learjet, "I'd sell my grandmother to save one pound."
From: Jeff Liebermann on 3 Dec 2009 03:44 On Wed, 02 Dec 2009 23:52:16 -0500, mm <NOPSAMmm2005(a)bigfoot.com> wrote: >On Wed, 02 Dec 2009 20:28:15 -0800, Jeff Liebermann <jeffl(a)cruzio.com> >wrote: > >>They didn't PTFE when Bill Lear invented the first "Motorola" car >>radio. > >Well, much of this thread is over my head now, sort of, but ftr, I was >40 years old before I realized why it was called "motor-ola" >><http://en.wikipedia.org/wiki/Bill_Lear> In the land mobile biz, it was called Rotomola. Search Google Patents for "William P. Lear" in order by date: <http://www.google.com/patents?q=%22william%20p.%20lear%22&btnG=Search%20Patents&scoring=2> There were radios fitted to vehicles before Motorola. However, they were big and bulky adaptations of console type radios. Together with the A, B, and C batteries, the radio usually more than one passenger seat. The antenna was usually a square loop about 4ft in diameter. It worked, but I wouldn't exactly call it practical. There are photos on the web, but I'm too lazy to look. By the late 1930's, components had shrunk sufficiently that to make a small radio. What Bill Lear did was make it fit in a package that was small enough to be practical in a car, which included the then unusual minimal rod antenna design. Here's the original car radio (mounted on the steering column): <http://www.google.com/patents?id=YeZ9AAAAEBAJ> <http://www.google.com/patents?id=OkluAAAAEBAJ> Incidentally, many police departments used AM frequencies at the top of the AM broadcast band for dispatch up to the early 1970's. In Smog Angeles, listening to the police on a tweaked AM car radio was common. -- Jeff Liebermann jeffl(a)cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
From: msg on 4 Dec 2009 15:50
Meat Plow wrote: > On Tue, 01 Dec 2009 23:15:32 -0800, Jeff Liebermann > <jeffl(a)cruzio.com>wrote: > >> On Tue, 01 Dec 2009 14:12:18 -0800, David Brodbeck <gull(a)gull.us> >> wrote: >> >>> Michael A. Terrell wrote: >>>> RG/62, 93 ohm coax. The same as what IBM used for their early >>>> computer networks. >>> I've got some 93 ohm coax lying around from when I used some to make a >>> matching section. Never knew what the original application was for it. >>> Very interesting. >> RG-62/u was used for Arcnet networking, >> <http://en.wikipedia.org/wiki/Arcnet> >> and IBM 3270 terminal systems: >> <http://en.wikipedia.org/wiki/3270> > > Ahh, I love the smell of LANtastic over RG62A/U and TCNS in the > morning. Do you happen to have any of the TCNS 100Mbit adapters? Michael |