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 Post subject: Built LM386's Regen He Posted
PostPosted: Sep Wed 27, 2017 3:18 am 
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Location: Lafayette, LA.
Howdy Folks,

I just finished building LM386's regen receiver he posted awhile back. Listening to 40 mtrs, but the signals are all "warbled." Guess I'm going to have to lock the thing down mechanically :D. Also going to try to add a varactor diode for fine tuning, but I"m thinking I can get away with using a reverse-biased 1N914 or some other diode I pull out of some junk piece of electronics :D. Should be good enough for a few KC's of tuning.

I'd also like to install an external antenna, but not sure where I can attach it and not screw with regeneration. I think I'm going to try and attach it to the coil and cap via a gimmick or small-value cap (3-7pF) and see if I can get away with that :D.

Now I'm going to see if I can build a simple IRF510-based xmitter. I'm going to see if I can use WA6OTP's PTO to transmit. Unfortunately, I don't know if my version will have the mechanical stability to pull it off. If that winds up being the case, I'm just going to say to heck with it and throw an SI5351 at the thing :D. I'll let you guys know when I'm done, and maybe you guys will be able to hear me on 40 CW and we can work each other :D.

Here's a pic of my completed receiver:

Attachment:
regen.jpg
regen.jpg [ 70.53 KiB | Viewed 919 times ]


At the bottom is a wallwart filter, which includes a full-wave bridge rectifier that is bypassed at RF, and it has two outputs: 12 and 5 volts. Going to add a LM317 for 3V as well. In the middle is a 2N3904 driving an LM386. Need to get it off that damn breadboard. Tired of all the loose connections :D. At the top is the regen itself.

BTW, I'm copying the W4 and W5 call areas no problem. What I want to do is see if I can pick up stations much further away by adding a longwire antenna run around the shack.

73,

Randy AB5NI

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Last edited by ab5ni on Sep Sat 30, 2017 6:50 am, edited 1 time in total.

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 Post subject: Re: Built LM386's Regen He Posted
PostPosted: Sep Wed 27, 2017 5:33 am 
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Who or what is the "He" you refer to?

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 Post subject: Re: Built LM386's Regen He Posted
PostPosted: Sep Wed 27, 2017 5:50 am 
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Howdy Peter,

Pbpix wrote:
Who or what is the "He" you refer to?


"LM386" is a user here on ARF. He posted a very simple regen schematic, and it was too simple to pass up, so I built the thing :D.

Attachment:
Favorite regen 2.jpeg
Favorite regen 2.jpeg [ 25.77 KiB | Viewed 901 times ]


73,

Randy AB5NI

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 Post subject: Re: Built LM386's Regen He Posted
PostPosted: Sep Wed 27, 2017 9:38 pm 
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Joined: Aug Tue 16, 2016 10:01 am
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Hi Randy
Too much antenna is bad with this and any regen (loads the detector).
Try a turn or two on the rod, one end grounded the other to the antenna, thru a small cap if its a real long wire, I had a few yards straight up on this little circuit, the performance vs component count is great (intercontinental).

PS. Love the Cartman avatar!

Jon.


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 Post subject: Re: Built LM386's Regen He Posted
PostPosted: Sep Wed 27, 2017 9:59 pm 
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Howdy Bro :D,

Brother Jonathan wrote:
Hi Randy
Too much antenna is bad with this and any regen (loads the detector).


Yeah, that's what I was figuring as well.

Quote:
Try a turn or two on the rod, one end grounded the other to the antenna, thru a small cap if its a real long wire, I had a few yards straight up on this little circuit, the performance vs component count is great (intercontinental).


I've always been really into simple radios, especially if they perform decently. If you can get decent stability on the things, the cost vs. performance ratio can be staggering. Not only that, but building your own radios actually teaches you something, and I'm all about learning new things on a daily basis.

Anywho, what I think you're saying to do is add a two-turn link at the ground end of the ferite rod, and then add a small coupling cap if my longwire antenna is really long, which will load the circuit. Gotcha. I'll try it out and let you know how things work out.

Quote:
PS. Love the Cartman avatar!


I'm a computer guy, love Cartman, and that's a picture of him from the "Make Love, Not Warcraft" episode. I played WoW on and off for many years, so I figure my avatar is appropriate. LOL!

73,

Randy AB5NI

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 Post subject: Re: Built LM386's Regen He Posted
PostPosted: Sep Fri 29, 2017 6:32 pm 
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Howdy Guys,

Update:

I was powering the regen with 12 volts, and the excess heat on the transistor is causing drift and making the received signals "warbled." I calculated a dropping resistor to supply 9 volts, but it's still drifting and sounding terrible :D. NOTE: these issues have nothing to do with the actual design of the rig, and they're more than likely caused by me trying to add modifications to a circuit that works fine when powered by a 9V battery :D.

I'm going to see if I can just use 5 volts, which is regulated via a 7805 on the wallwart filter, and see if that will be enough to power the regen. If not, I'm going to try 6 volts, and 1-volt increases until she plays well. I'm also going to add more bypass caps as well to make absolutely sure nothing is traveling up the 12V and 5V rails. The 12V rail is bypassed at RF, but I need to bypass at audio, too.

The overall goal here is going to be using the receiver with a homebrew CW transmitter. I'm going to use an el cheapo IRF510 with current-sense protection and adjustable output. I'm also thinking about powering the IRF510 with 24 volts for better output when band conditions call for it, too. The long-term objective is to also add an audio transformer and modulate the IRF510 and put out a small AM signal :D. Hopefully, some of you guys will hear me on the AM windows on 40 and 80. LOL!

73,

Randy "AM BIG GUN!" Jouett AB5NI :D

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 Post subject: Re: Built LM386's Regen He Posted
PostPosted: Sep Fri 29, 2017 9:42 pm 
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ab5ni wrote:
Howdy Guys,
I'm going to see if I can just use 5 volts, which is regulated via a 7805 on the wallwart filter, and see if that will be enough to power the regen. If not, I'm going to try 6 volts, and 1-volt increases until she plays well.

Randy "AM BIG GUN!" Jouett AB5NI :D

Hi Randy:
I've found that I can keep rasing the 7805 voltage by adding a forward biased diode to the center ground leg of the 7805.
Each diode will raise it .7v.
I've used it w/5 or 6 diodes adding 3.5 -4.2 v to make 8.5 or 9.2 volts to run one off my 9v battery powered DMM meters for years..

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 Post subject: Re: Built LM386's Regen He Posted
PostPosted: Sep Sat 30, 2017 2:22 am 
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Hi Peter,

Peter wrote:
I've found that I can keep raising the 7805 voltage by adding a forward biased diode to the center ground leg of the 7805.
Each diode will raise it .7v.
I've used it w/5 or 6 diodes adding 3.5 -4.2 v to make 8.5 or 9.2 volts to run one off my 9v battery powered DMM meters for years.


Nice. I'll try that the next time I'm I need that kind of thing. Fortunately, it looks like the 7805 has enough voltage to allow the Radio Shack generic multi-pack transistor to oscillate. I chose one that has an HFE of 308, which allows the thing to oscillate quiet easily and pick up stations really well when on the verge of oscillation. It still drifts a tad, and I thought I was copying 40 and I'm actually copying 80. LOL! Going to have to add a bit more series capacitance to bump it up in frequency a tad. I also measured the inductor, and it's 10.3 uH, which should be good.

Main problem I'm having (besides drift) is VERY distorted audio when copying SSB, no matter what voltage I use. The funny thing is that AM broadcast stations sound fine. It's only on SSB that the audio really sucks. It could be that transistor. I'll swap it out and see how she plays.

73,

Randy AB5NI

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Last edited by ab5ni on Sep Sat 30, 2017 7:04 am, edited 1 time in total.

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 Post subject: Re: Built LM386's Regen He Posted
PostPosted: Sep Sat 30, 2017 2:43 am 
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ab5ni wrote:
Main problem I'm having (besides drift) is VERY distorted audio when copying SSB

Randy AB5NI

Assuming that you are not using Varactor tuning which can cause this effect, there are a couple of things that you can try.

1. Divide the 1M self-bias resistor into two equal parts in series and add a 1 uF filter cap from their junction to ground.

or

2. Remove the regen control and connect the top end of the Collector load resistor to the supply voltage. Disconnect the top end of the 1M bias resistor from the Collector and connect it to the wiper of the regen control.

or

3. Do not use a Collector load resistor, but connect the Collector directly to the supply. This will minimize any changes in Miller capacitance which can occur from the detected audio. Use the modified regeneration control as above.

Take the audio output from the Emitter through a 10 mH choke into the capacitively coupled audio amplifier. The choke prevents loading of the oscillator. The value of the Emitter resistor may have to be increased to get more audio.

or

4. Connect the Gate of a common Drain JFET to the hot end of the inductor. Connect a 47K bypassed resistor to ground from the Source. Take the audio from the Source. This acts as a high impedance detector and the oscillator becomes only a Q multiplier rather than also being the detector.


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 Post subject: Re: Built LM386's Regen He Posted
PostPosted: Sep Sat 30, 2017 6:40 am 
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Howdy LM386,

LM386 wrote:
Assuming that you are not using Varactor tuning which can cause this effect, there are a couple of things that you can try.


I have yet to add the varactor for fine tuning. I do have some air-variable caps that can do the job of sufficient value. Because these caps are getting to be very rare, I've been trying to not use them and save a few for horse trading or a care package to a close friend. I should be able to just reverse bias a 1N914 and get the range I need for fine tuning, I'm thinking. Once I get the rig working properly, I'll add it and let everyone know how shes plays with the change.

Quote:
1. Divide the 1M self-bias resistor into two equal parts in series and add a 1 uF filter cap from their junction to ground.

or

2. Remove the regen control and connect the top end of the Collector load resistor to the supply voltage. Disconnect the top end of the 1M bias resistor from the Collector and connect it to the wiper of the regen control.

or

3. Do not use a Collector load resistor, but connect the Collector directly to the supply. This will minimize any changes in Miller capacitance which can occur from the detected audio. Use the modified regeneration control as above.

Take the audio output from the Emitter through a 10 mH choke into the capacitively coupled audio amplifier. The choke prevents loading of the oscillator. The value of the Emitter resistor may have to be increased to get more audio.

or

4. Connect the Gate of a common Drain JFET to the hot end of the inductor. Connect a 47K bypassed resistor to ground from the Source. Take the audio from the Source. This acts as a high impedance detector and the oscillator becomes only a Q multiplier rather than also being the detector.


I'll try the listed methods and let everyone know what worked. I'll go in sequential order. I'm having a lot of fun messing with my first regen ever, LM. Thanks for posting the circuit :D. My long-term goal is to see if I can get the rig to copy signals on 80 and 40, and to make it stable enough to pipe into my computer and copy the various digital modes and rtty. I love history -- archaeology and anthropology as well -- and I want to know what it was like to be a ham in the 1920's that used a regen as their main receiver. Now I'm probably going to want to build a legit replica of such a setup from the 20's :D. Yet another item to add to my build list! LOL!

Anywho, if I can get all of that to work, I'll be a happy camper. Wish me luck! :D

73,

Randy AB5NI

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 Post subject: Re: Built LM386's Regen He Posted
PostPosted: Nov Sun 05, 2017 3:13 pm 
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I have built regens for many years, and they have all had this problem to one extent or another. Basically what you are hearing are capacitive changes in the transistors junction being applied upon the tank circuit.

I have built this circuit and found that although it worked well on AM signals, for SSB it pulled and warbled quite a bit. Decreasing antenna coupling should help, but only slightly.

Again this seems to be a drawback of any circuit that heavily couples the tank into the active device. Even the Kitchen circuits have this problem, and tube regens,too.

Tired of encountering this problem, I set out to improve the situation, and still keep parts count low. I had success, and end result was a regen that sounded like a DC receiver on all but the very strongest signals. Using a JFET with VERY light coupling to the tank ( 1 to 3 pf), and biasing the device differently was the key. While this lowered efficiency on AM it greatly increased performance on SSB and CW, which is what I was after.

This is a total of 7 or 8 parts working into 32 ohm phones. Running a dipole for 75 of course. http://v8.tinypic.com/player.swf?file=vgriue&s=8


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