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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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13th Mar 2019, 12:38 pm | #1 |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,061
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2N3819 MW mixer circuit problem
Here is a jfet mixer circuit I am trying to use as a building block for an AM radio. I have built a separate local oscillator circuit that is working fine but the issue is that as soon as I connect it to the mixer circuit, the oscillator stops oscillating down from 3 MHz to zero.
Can anyone please advise what the issue could be ? |
13th Mar 2019, 12:51 pm | #2 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,339
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Re: 2N3819 MW mixer circuit problem
If the oscillator stops working as soon as you connect it, I would suspect an oscillator problem rather than this circuit.
Can you post the oscillator schematic as well? |
13th Mar 2019, 12:53 pm | #3 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,868
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Re: 2N3819 MW mixer circuit problem
The local oscillator, whatever it is, will see a rather low impedance ( 220 ohms//1/Gfs) and it all depends on the oscillator circuit and its drive capabilities. You need an oscillator or buffer compatible with that load.
David
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13th Mar 2019, 1:24 pm | #4 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
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Re: 2N3819 MW mixer circuit problem
Agree. stuff another 2n3819 follower after the oscillator. I usually have one as the oscillator, then a buffer 2n3819 and then a 2n3904 "power amplifier" but I'm driving diode mixers which require a bit more grunt.
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13th Mar 2019, 1:33 pm | #5 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,339
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Re: 2N3819 MW mixer circuit problem
Here is a circuit that sounds similar to what your are trying to do.
Ignore the frequencies it is set up for, they can be changed. |
14th Mar 2019, 5:06 pm | #6 | |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,061
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Re: 2N3819 MW mixer circuit problem
Quote:
The buffer circuit has not killed my oscillator so I seem to be heading in the right direction. Last edited by Jolly 7; 14th Mar 2019 at 5:16 pm. |
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6th Apr 2019, 5:49 am | #7 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,339
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Re: 2N3819 MW mixer circuit problem
Here is a dual JFET mixer that may be of interest:
https://zl2ctm.blogspot.com/2017/09/...iguration.html |