antenna signal booster

Discussion in 'General Electronics Chat' started by adamclark, Jul 11, 2014.

  1. adamclark

    Thread Starter Member

    Oct 4, 2013
    this is not an automotive mod... with that said, I need to build a signal booster for a car radio antenna.. Not a powered antenna, I have one of those.. I remember in the 80's I could just buy one, but now they seem extinct... could anyone please point me in the right direction to build one of these please.. thank you... its just a small circuit you plug your antenna into and then plug it into the radio... powered antenna do not work the same way for some reason...
  2. adamclark

    Thread Starter Member

    Oct 4, 2013
    ok.. I found a schematic,, just have a few questions... im going to show the instructions and schematic then ask my questions... heres the instructions....
    Assemble the circuit on a good-quality PCB (preferably, glass-epoxy). Adjust input/output trimmers (VC1/VC2) for maximum gain.
    Input coil L1 consists of four turns of 20SWG enamelled copper wire (slightly space wound) over 5mm diameter former. It is tapped at the first turn from ground lead side. Coil L2 is similar to L1, but has only three turns. Pin configuration of transistor 2SC2570 is shown in the fm antenna booster schematic............ My questions are as follows..
    1. how do I assemble input coil L1 and tap it at the first turn?
    2. what is a 5mm former?
    3. how do I adjust coil L1 and coil L2?
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    I'd be looking at a MMIC
  4. adamclark

    Thread Starter Member

    Oct 4, 2013
    whats an mmic? im really looking for the easiest way to do this and im getting familiar with various ic's and tne normal components.. ive completed a few peojects now just asking simple questions.. I have no problem doing the legwork myself just need a good push in the right digestion,,thanks for the help..
  5. adamclark

    Thread Starter Member

    Oct 4, 2013
    is there an easier way to assemble the schematic I posted? im pretty confident I can put that one together,, just don't under stand a couple parts of it
  6. bertus


    Apr 5, 2008

    Info on the MMIC can be found here:
    #5 - RF Components
    The ERA and MAR are MMIC components.

  7. yourownfree

    Active Member

    Jul 16, 2008
    I looked at your schematic and it really isn't suited for automotive use. The reason is you have two tuned circuits that must be tuned to the frequency you are wanting to hear and no others. if you want to hear the other frequencies you would have to re-tune again. what you need is an active antenna amplifier with no coils or if it has coils, remote tuning using varicap diodes. Best if you just use either a simple one transistor unit no coils that need tuning or use a mars circuit amplifier. It looks like a transistor with three legs but is a powerful chip amplifier. It can boost the signal around 15 db. Just follow the rules of the power source for the ic. I think it is around 3 volts. Check out those circuits and for a simple one I have included this link. Uses an easy to find mpf102. No tuning so all you need to do is get a motorola jack and plug, that's what they call it, and simply plug the antenna coax into the jack and the then get a piece of coax and attach the plug to it. so that you can plug the plug into your radio and other side of the coax goes to your booster. You can use any jack for that side or hook up direct. To get a motorola plug visit your automotive junk yard and snip off the coax from an old car antenna and take the jack from an old car radio. It can either be on all the time with a power switch or use a dpdt switch to turn it on and off. When in off position you bypass the circuit to run normal through your antenna to your radio. that way you can hear the difference it makes or be able to turn it off if you dont need it. Sure the coil ones are better, but more of a hassle. If you only want to hear one station then that is fine. By the way a former is just something to wind the coil on until you wind it, then take it off. Like use a bolt or screw for your form, maybe a pencil, depends on the diameter of the coil. Once the coil is wound remove it from the former(screw or bolt). Then once project is finished adjust the input coil for most gain the adjust the output coil slightly less than full gain or the circuit could become unstable and oscillate. Set it for the frequency you want to hear. Then turn the unit off to go to other frequencies in normal position. You could place a resistance across each coil to broaden the tuning so it wont be so precise. That you will have to play with. It will lessen the gain but you will be able to cover a wider frequency range. I would start with 100 - 1000 ohms. here is mpf102 circuit