Ferrite bar antenna for car radio?
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From: Mike on 15 Sep 2005 21:02 On 13 Sep 2005 21:28:11 -0700, wrongaddress(a)att.net wrote: >Any idea the best way to couple a ferrite loopstick antenna >to a car radio input for AM reception? > >I experimeted using a 6 inch loopstick (230uH) and 365pF >parallel tunning cap from antenna input to ground (chassis) >with reasonable results, but I'm wondering what the best >approach is. > >The tuning is very broad and I don't get much of a peak >when adjusting the capacitor, but all the local stations >come in. > >How should I wind the loopstick for best results? > >-Bill I bought this new microwave oven that trashes every AM radio in the house while it's running, So I built a Shielded loopstick antenna for my old RCA Radiola. It is untuned, Faraday shielded, and I used a mosfet amplifier with the drain capacitor coupled to the external ant input to the set. No impedance matching to speak of, but it works really well! No noise from the microwave and it picks up more stations than I care to listen to. Mike
From: wrongaddress on 15 Sep 2005 23:01 > You forgot Hugh Hewitt. > you must be in the LA area, Right ? Yes, I'm in the LA area, I can walk to Disneyland. I have a year round pass. I forgot a couple others in addition to Hewitt. Kevin James late at night on KABC. Also, Doug McIntyre and Bill O'Reilly in the morning on KABC. -Bill
From: Keith Williams on 16 Sep 2005 09:41 In article <1126750523.480728.54940(a)g43g2000cwa.googlegroups.com>, wrongaddress(a)att.net says... > >> You still listen to AM ! ? > >> Awesome. > > I used to listen to FM music when I was a teenager, but nowadays, I > just listen to right wing AM talk shows: > > Michael Savage > Larry Elder Didn't know he had a radio show. > Rush Limbaugh > Shawn Hannidy Hannity - like the TV show, not the radio version > Michael Medvits Medved - not my style. > Dennis Prager Didn't know he had a show either. > Al Rantell ? > Bill Handle > etc. G. Gordon Liddy And don't forget Phil Hendrie. ;-) I've become hooked on Bill Bennet's "Morning in America". XM dropped the show 9/1 so I had do buy a subscription (via the internet) and an MP3 player with an FM modulator to get my daily fix. :-( -- Keith
From: wrongaddress on 17 Sep 2005 22:52 John Woodgate wrote: > I read in sci.electronics.design that wrongaddress(a)att.net wrote (in > <1126672091.043123.283820(a)f14g2000cwb.googlegroups.com>) about 'Ferrite > bar antenna for car radio?', on Tue, 13 Sep 2005: > >Any idea the best way to couple a ferrite loopstick antenna to a car > >radio input for AM reception? > > > >I experimeted using a 6 inch loopstick (230uH) and 365pF parallel > >tunning cap from antenna input to ground (chassis) with reasonable > >results, but I'm wondering what the best approach is. > > > >The tuning is very broad and I don't get much of a peak when adjusting > >the capacitor, but all the local stations come in. > > > >How should I wind the loopstick for best results? > > You need to tap down the coil or wind a secondary winding on the rod. > The car radio antenna input is a lowish impedance, not 50 ohms or > anything like, but much lower than the resonant impedance of your tuned > circuit. But if you tap down too far, you will need to retune the > loopstick for each station. > > Experiment with taps or secondary windings. Alternatively, you could put > a larger fixed cap in series with your 365 pF at the earthy end, and > connect across it to the antenna socket. You might try a number of > values from 1000 pF upwards. > -- > Regards, John Woodgate, OOO - Own Opinions Only. > If everything has been designed, a god designed evolution by natural selection. > http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk Yes, a separate short winding on the loopstick improves operation. The main winding is about 80 turns, and I added another winding of about 20 turns feeding the antenna input. I get a sharp peak on weak stations, and it picks up stations I can't get in the car, so it seems to be working better than the normal car radio setup. There are 8 tunable coils inside the radio which is a Ford modle from 1980s. I tried tuning a couple coils near the antenna input, hoping to improve it further, but didn't have much effect. I might try adding or subtracting a few turns from the secondary winding to see if I can improve it further. -Bill
From: John Woodgate on 18 Sep 2005 02:47 I read in sci.electronics.design that wrongaddress(a)att.net wrote (in <1127011945.038647.221590(a)g43g2000cwa.googlegroups.com>) about 'Ferrite bar antenna for car radio?', on Sat, 17 Sep 2005: >I might try adding or subtracting a few turns from the secondary >winding to see if I can improve it further. 20 turns does look too many for an 80-turn primary. If you have a standard 93 ohm input impedance in the radio, the load on the primary is 93 x (80/20)^2 = 1488 ohms. If your 365 pF cap tunes the primary to 540 kHz (I don't remember the lower bound of the AM band in US, but it's around that frequency), it has an impedance of: 1/(2pi x 540.10^3 x 365. 10^-12) = 807 ohms, so your circuit Q is only 1488/807 = 1.84. Try 5 turns, would round the ground end of your coil. You have grounded the frame of the variable cap to the case of the radio, haven't you? -- Regards, John Woodgate, OOO - Own Opinions Only. If everything has been designed, a god designed evolution by natural selection. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
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