Ferrite bar antenna for car radio?
in [Design]
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From: wrongaddress on 14 Sep 2005 00:28 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
From: Pooh Bear on 14 Sep 2005 03:05 wrongaddress(a)att.net wrote: > Any idea the best way to couple a ferrite loopstick antenna > to a car radio input for AM reception? You still listen to AM ! ? Awesome. Most poor ppl I know use wire coathangers to replace the car aerial when the original gets trashed by kids or whoever.. Graham
From: Dave on 14 Sep 2005 03:12 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 > IIRC the normal approach if you wish to make it tuneable is to have a large winding which is tuned with the cap, and a smaller winding with less turns, so there is an impedance transformation. I suspect very much depends on the device used as the front end - whether it is a high Z fet or a lower impedance device. It sounds like the Q is low if the tuning is broad, but do you really want the hassle of returning the capacitor every time?
From: John Woodgate on 14 Sep 2005 03:40 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
From: Robert Scott on 14 Sep 2005 09:05
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? Why bother with "best", unless you mean "easiest". There is no sense in trying to improve sensitivity beyond the point where you can hear the background RF noise. And on the AM band there is a lot of it. The radio itself is probably already doing as well as it can using selectivity to limit background noise. So if you connect the loopstick antenna any way at all that produces enough signal to hear the background hiss, then that is good enough, and no further overall improvement can be had by improved impedance matching or tuning. To check if your connection is adequate, just turn up the volume until you hear a good deal of hiss, while tuned to a frequency where there is no local station. Then disconnect the antenna completely. If the hiss drops to almost nothing, then you have as good an antenna as is possible. But if the hiss remains the same or drops only a little, then that hiss is coming from the radio itself, and a better antenna match could improve things. -Robert Scott Ypsilanti, Michigan |