Author Topic: Regenerative Receiver Issues  (Read 511 times)

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Offline Mozee

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Regenerative Receiver Issues
« on: April 29, 2018, 05:03:30 am »
I was trying to build a Regenerative Receiver but It didn't work and I don't know what is wrong with it. The Base-Emitter junction of the BJT transistor with is connected to the base of the JFET by a 33Pf capacitor measures 0 volt! no bias is present and I am having doubts for the 1.1uH inductor located at the base of the JFET, probably grounding the base of the JFET and all the signals which is supposed to go to the base of the BJT transistor.
I took this video so please have a look. Also, the schematics are in the video as well.

Here you go https://youtu.be/5bnIffITJVI
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Offline Mozee

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Re: Regenerative Receiver Issues
« Reply #1 on: April 30, 2018, 02:27:20 am »
Also, I forgot to ask how to know is the reg. rec. is functioning correctly or not using an oscilloscope ?
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Offline JimRemington

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Re: Regenerative Receiver Issues
« Reply #2 on: April 30, 2018, 02:39:24 am »
Judging from the first 15 seconds of the out-of-focus, shaky video, the video is a useless waste of time. Please post a proper schematic.
« Last Edit: April 30, 2018, 02:42:34 am by JimRemington »
 

Offline Audioguru

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Re: Regenerative Receiver Issues
« Reply #3 on: April 30, 2018, 08:27:04 am »
It is a Mickey Mouse regen shortwave radio circuit. Does anybody use shortwave frequencies today? My grandmother had a shortwave radio that I heard its awful sounds about 65 years ago but it was not a regen, it was a real radio, a superhet.
 

Offline Mozee

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Re: Regenerative Receiver Issues
« Reply #4 on: April 30, 2018, 03:02:15 pm »
I am new to the entire RF thing! Would you recommend something that actually work!?
Ok how do I measure the frequrncy that my reciever is tuned to?
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Online Ian.M

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Re: Regenerative Receiver Issues
« Reply #5 on: April 30, 2018, 05:40:07 pm »
Start by posting the schematic + a well lit in-focus hi-res photo of your board.  Mark all the changes and substitutions you have made on the schematic.  Changing stuff before you fully understand it, other than for comparison as a scientific experiment (including logging all changes and their results in comparison to the original in your lab note book), is rarely a good idea.

Most regenerative receivers will oscillate if you turn up the regen control too far.   With the antennae disconnected (so you don't inadvertently transmit), 'sniff' around the regen section with the scope probe ground connected to its tip so you can use it as a RF magnetic field pickup.  Start with the probe away from the board and reduce the scope volts per div (increase input sensitivity) till the trace gets fat and fuzzy from ambient EMI and set the timebase to 1/100 of the period of the highest frequency you are interested in.   If you can get the trace to grow fatter by bringing the probe up to the regen stage and turning up the regen (which will have a 'snap' action - once it starts oscillating you will probably have to turn it down a bit to quench it) you can then increase the timebase speed  till you've got something you can trigger on and use the scope to measure the frequency.

I think your odds of getting results without a decent aerial (either a long-wire that's as long as you can make it, up to the wavelength of the bottom of the band you are interested in + a good RF ground - fat braid as short as possible to a well pounded in and watered ground stake *NOT* anywhere near the building's ground stake or any lightning conductors,   or a tuned open frame loop antennae) are minimal with all the environmental EMI in the average home nowadays.   

Your best bet is to turn fully off *EVERY* digital device you possibly can including portable ones, unplug anything with a SMPSU, turn off any LED or compact fluorescent lighting and any other fluorescents with electronic ballasts. (Old heavy magnetic choke ballasted fluorescent, and mains voltage incandescent  lighting is fine) then repeat your testing with only the *MINIMUM* itens of test gear you actually need switched on.
« Last Edit: April 30, 2018, 05:41:39 pm by Ian.M »
 
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