First homebrew transciever - not working

Discussion in 'Homebrew and Kit Projects' started by S52Y, Dec 28, 2016.

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  1. N7EKU

    N7EKU Ham Member QRZ Page

    Hi Pampi,

    I looked some more at your past posts and see on page 2 that you gave some RF probe measurements of you VXO. Those all look good to me and are similar to what I have measured, so I think that your VXO is operating well.

    One thing to look at, is the the lm386-1 should not be run at over than 12VDC. What is your supply voltage?

    Here also is a list of DC voltages for my lm386. Note that some measurements may be different than your as I am using the datasheet's "AM Receiver" circuit.

    Pin Vdc
    1 1.4
    2 0.0
    3 0.0
    4 0.0
    5 5.9
    6 12.0
    7 6.1
    8 1.4

    Also for reference, with the volume set midway, the receiver is consuming about 35mA of current.

    Hope this can help us figure out your receiver.


    VK4FFAB likes this.
  2. N7EKU

    N7EKU Ham Member QRZ Page

    Just a bit more info,

    I finally put the antenna bandpass filter on my receiver here. I found that it is a pretty strongly peaking filter, and I had to use a trimmer capacitor, and remove a couple turns from the toroid in order to get it peaked in the 40M band. Once it was all adjusted though, it is nice as it removed a lot of common-mode noise (hum) and AM broadcaster interference.

    So, it could be that you need to adjust your filter. A trimmer capacitor is the easiest way, but you can also add/remove windings from the toroid and/or compress/expand the windings on it.

    I also found that the mic amp needs a bit of work as the original design (at least with the transistor that I have in there now) sets the collector at 1VDC which is resulting in distortion and low output. I will study it more and see what I can come up with.

    Cheers and 73,

    VK4FFAB likes this.
  3. N7EKU

    N7EKU Ham Member QRZ Page


    I worked a bit more on the mic amp and it's quite a bit better now. Also, I will probably lower the gain on the lm386 because it's really got too much now at 200 with the cap bypassing pins 1 & 8.

    But as the OP has stopped responding, I will not post further here but will try to work on getting my web page organized and will post anything more there. OP -- just email me via my QRZ email address if you want to converse further.



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