Most young folks listened on small transistor radios by the early 60’s or on car radios, yes. Emphasis on mid-range frequencies. But by mid-50’s “high-fidelity” all the rage (monophonic) then stereo by late 50’s and finally FM multiplex stereo transmission by ’61. So in the home environment, our parents were interested in “hi-fi” and the recording engineers catered to that market. Even in Rock ‘n roll – “wall of sound” 360 stereo effect on many 60’s recordings, lots of reverb, etc. Obviously analog recordings but very wide frequency range possible using RIAA curve –to fit the physical LP vinyl record - the playback equipment decoded that (bass boost/treble cut) but could get 20-20000 Hz response recorded. What was limited was “dynamic range” i.e ratio of loudest to softest sounds due to physical size of record – irrelevant in digital providing enough bytes available. Also signal to noise ratio limited – lots of tape hiss- original master recordings on open reel tapes. Can be processed by modern digital technology to remove hiss – Dolby noise reduction early version -made cassette tapes hi-fi. Early FM car radios all monophonic. Factory FM stereo car radios not available until 1968 for Chrysler Corp., in the Imperial. Carl From: dplotkin@xxxxxxxxxxxxxxxxxxx It is said that most mid century recording engineers had the ultimate goal of making a record sound as good as possible on a Delco radio. Most of the country was listening on one. It is interesting how sensitive and high definition (to use todays term for high fidelity) our old radios are. Based on the above from the experts i have to assume I need to trim my radio to work with the new antenna lead given my car was delivered with a front antenna. Thanks for the education. Danny Plotkin -----Original Message----- Carl is 100 % correct ; and the cables are very important ; the AM band in such that the cable capacity to ground ( made minimal by that fine wire drawn into a tube loose .. it is not coax cable ) —can be made part of a resonant circuit in the input of the AM tuned antenna coil , why you adjust that trimmer to peak at 1400 . The AM band when tuned by capacitors is using like 350-370 uuF The capacity of the cable is on the order of tens of uuF . So we can live with that . But at FM frequencies that is almost a dead short to ground , the total tuning range of FM capacitors for tuning is only 10-30 uuF . 30 in the cable would kill it . So other approaches are used , —in cars generally FM is almost always essentially untuned “ low impedance” wideband input to amp and very sensitive FM front ends. To send high frequency like FM over longer distance , the cable requires “ matching “ the impedance of the coax ( like RG-6 catv ) 50- 75 ohms or like 300 ohm twin lead and a matched 300 ohm antenna too . ( the old folded dipole ) . But then you may need an amplifier at antenna or an antenna with known matched ohms to avoid losing signals . Note that as Carl says , the wavelength of FM is like 30” almost the same as the cable length in the car from radio to antenna . AM is closer to 500 - 800 feet wavelength , 10 feet of cable is ok then, does not even look like a cable to the AM , just a capacitor that can be tuned out . This stuff gets way more complicated , ( band width front end design etc) but getting back to what to do , they used to sell like a thin wire in scotch tape you stick to windshield , very short wire to radio , for FM ; I think some GM have that . Or shortest wire you can to AM mast pulled to 39” . Yes it works — if not right , but not as well . I bought some 70’s era Motorola and Sparkomatic FM to AM converters trying to keep 300 F radio . Sort of work , but nowhere near modern FM . And as Carl alludes to — AM radio performance today in a new car is a joke compared to our tube radios when working right . They are well designed —there will be solid stations end to end if radio is perfect at night . Tubes are almost never ever bad , (!!) but corrosion in tube sockets is common . wiggle back and forth or even better toothpick and silicone grease on each pin put back in . Loose antenna connection / corrosion in antenna base also kills it . Check with ohmmeter —- pin at end of cable to mast should be almost zero ohms. Plus today heavy interference in AM band is the rule , automatic volume control in our radio hears that noise , thinks it is a station and cuts sensitivity way back ... Try engine off in the country some night . Like it was ... Other stuff goes wrong —-too long for here , worst is mice piss from on top through vent holes ruins the PC card and some fine wire coils ; not uncommon if stored . In Boston we listened to WMEX ( Arnie Woo Woo Ginsberg , )but it faded later in night , but WPTR Troy NY , 50 kw clear channel would start coming in , even better than WMEX . In 57 dodge , essentially same radio . I Hung around Big Burger Ranch , every one there ( 40 cars?) has PTR on by 11pm . Was just like American Graffitti very single night ! Just too many chevy guys.. smile. There is a station in Toronto , some guys’ personal thing , about 720 AM plays great 60’s music . Sky bounce might let you hear that at night , generally 200-500 mikes away ! Otherwise AM is lame now. The 30” length (actually closer to 31”) is a compromise for the middle of the FM frequency band (98Mhz in the USA) where that length matches one-fourth of the wavelength. Lower frequencies like 88 MHz would match to an antenna a couple inches longer and higher frequencies like 108 MHz would match to an antenna a couple inches shorter. The radios have sufficient sensitivity that a precise match isn’t necessary. I used to design and built my own yagi FM antennas in high school for “DXing” which is the arguably nerdy hobby of picking up distant radio stations. FM signals are at a high enough frequency (located just above channel 6 on the old analog TV lower band) that the signals tend not to bounce off the atmosphere and are restricted to somewhat “line of sight” from the transmitters, with some exceptions due to weather conditions. Those exceptions are called tropospheric ducting or tropospheric propagation, when the FM and old analog TV signals would sometimes strangely travel for hundreds of miles for a few minutes or hours. AM signals, on the other hand, are at a much lower frequency (KHZ vs. Mhz) with very long wavelengths that will bounce off the atmosphere at night, every night, allowing one to hear stations from Mexico and Cuba that are allowed to transmit at up to 10 times the power of US stations. Back in the day folks would listen to AM stations from across the country at night. Hence, some stations were “clear channel” at night so they could be heard many hundreds of miles away. In Chicago, we could receive stations from Canada, Mexico, Cuba, the Caribbean, and from Boston (WBZ), New York (WABC), New Orleans, Dallas, and many other locations. I liked KAAY 1090 in Little Rock, a great rock ‘n roll station in the early 1970’s. The AM car radios of the day were highly tuned RF amped circuits with exceptional sensitivity and selectivity for long distance reception. All, of course, before the days of digital tuners. Anyway, when Chrysler introduced the AM/FM radio for their cars, a Delco model of very high quality (January of 1963 for Chrysler) the antenna was front fender mounted (no power option), standard on New Yorker Salon and optional on other models. It may have included a fixed length antenna of 31” (can’t remember offhand). The AM only radios were matched to the antenna via an antenna trimmer adjustment for maximum reception, with the antenna set a 40”, regardless of front or rear mounting. Carl Bilter From: Bob Podstawski FM antenna should be 30” for max reception. Cables are shielded and are of no consequence in my understanding
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