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Thursday, July 15, 2021

Mythbuster Video #5 -- More Listening on 75

at 5:47 AM
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7 comments:

  1. KE4NBB TedJuly 15, 2021 at 6:37 PM

    Nice job Bill! Looking forward to your next addition to this receiver. Forgive my ignorance but, what was the reason for halving the value of the cap in the amp? Thanks! Ted KE4NBB

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    Replies
    1. Bill MearaJuly 15, 2021 at 8:33 PM

      Thanks Ted. In the LM386, if you put a 10 uF cap between pins 1 and 8 you take the gain up to around 45 db. That is a lot. If you don't put anything there I think it is about 20 db. 5 db looks like around 30-35 db. At very high gain it can be hard to keep the amplifier stable -- it will break into oscillation and howl. So if you don't need all that gain, life is easier at lower gain levels. Bill

      Delete
    2. Bill MearaJuly 15, 2021 at 8:34 PM

      I meant "5 uF looks like around 30-35 db."

      Delete
  2. NevJuly 16, 2021 at 3:08 AM

    just for fun ... put the antenna after the filter and tune 75 & 20 at the same time!

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  3. UnknownAugust 8, 2021 at 12:45 AM

    Interesting that you like to listen on 75m AM through your SSB receiver. I often listen to those AM guys on the N1NTE KiwiSDR, there are some great conversations and quite a number of old and modded BC transmitters, and homebrew transmitters as well. Some of thise guys are hugely knowledgeable. It makes for good technical conversations.

    What about extending Mythbuster with a second IF filter, and a true AM detector? -- 3HN.

    ReplyDelete
  4. Bill MearaAugust 9, 2021 at 12:52 PM

    3HN: I would, but to tell you the truth, the AM signals sound just as good to me just by zero-beating the carrier and listening to the lower sideband. I know the AM guys wouldn't like to hear someone say that, but I think it is true. Also, I think that is why the Drake 2-B has a max passband of 3.6 kHz -- they must have figured that users would be listening to just one of the sidebands (but the Drake does have a diode detector). 73 Bill

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