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 Post subject: LOW NOISE SW REGEN RECEIVER
PostPosted: Jun Mon 24, 2019 6:41 pm 
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Joined: Feb Sun 16, 2014 10:03 am
Posts: 39
Inspiration for this receiver i get from my old buddy from TRB forum
QRP-Gaijin where he post about low noise regen receiver.
Instead of using FET..which is good option for low noise receiver
I use low noise RF BJT transistor and one 2N3904 as oscillator/ regen-detector.
This oscillator can be replaced with FET transistor but then for stable
oscillation require larger voltage about 6V.
Heart of circuit is Hartley oscillator in well known shape.
Feedback from emitter to coil tap.
Preamplifier transistor should be RF transistor with low noise like
BFR91A, 2SC3355, BFR93 or even excellent BFG65.
Coil is a air-type with 15 turns over paper tube 21 mm.
Tap is after 4 turn.
For different SW range use different coil configuration and
recalculte value for tuning variable capacitor.
If you use one fixed capacitor of 25pF you can use varicap diode
like BB910 in combination with 33pF cap.
With R5 varable pot adjust regeneration level changing bias of transistor Q2.
You can increase value of cut-off capcitor from 5nF to 10nF to get 16kHz.
After variable pot you may add simple audio amp with two transistors.

PS: something went wrong when i post this topic because is double
i apologize for that ..
Here is version with varicap tuning and with audio part with 2 transistors
first is NPN and second is pNP.
use what you have at hand.


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