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Old 2nd Sep 2017, 10:15 pm   #1
MrBungle
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Default Simple NE602 / LM386 40m DC receiver build

I've hit project overload. None of my larger projects seem to have any momentum so I have taken a few days out to build something a little simpler so I can practice copying CW and getting some real world on air experience so I can do the foundation test (finally!) and stop lurking as a listener only.

This is mostly stolen directly from Experimental Methods in RF Design by Heyward, Campbell, Larkin and is basically the same as the Neophyte and the Sudden receivers. There is no schematic for this and it was mostly made of junk and a few bits from RS and ebay. The capacitor combinations were found by attaching a DDS sweep generator with the marker output on the scope and adding capacitance until it peaked in the right place. Trimming is done on the front end filter with a trimcap and the VFO adjusted with the built in trimmers in the polyvaricons. Coarse/fine tuning is used. Next time I'm going to use varactor tuning and a ten turn pot. The polyvaricons are horrible. Q of the inductors may be spoiled by hot snot!

On air performance is, as expected, not fantastic but usable to copy CW and SSB. Sensitivity is pretty good, selectivity is not great and the noise is quite bad. Could benefit from a sharp CW bandpass in the audio stage. Antenna is simply a 20m long wire was strung from the curtain rail in the back bedroom diagonally through the house across door tops to the curtain rail in the front room. There is no counterpoise or grounding. A better antenna is being planned with SWMBO. She is harder than the council . Powered from 8xAA batteries. Only uses 6v internally so there is a regulator on the back. Consumes 13-20mA when running into a pair of hefty Sennheiser headphones.

The enclosure is the best bit (Takachi from RS) - I *really* like these enclosures and will probably build everything in them now! http://uk.rs-online.com/web/p/instrument-cases/3732233/ (scroll down for the series of enclosures. I think this is the YM-150 - I threw the label away!)

Sticky legends are falling off already - cheap label printers are horrible

Pictures below:
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Last edited by MrBungle; 2nd Sep 2017 at 10:21 pm. Reason: Terrible spelling
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Old 2nd Sep 2017, 10:30 pm   #2
Tyso_Bl
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Default Re: Simple NE602 / LM386 40m DC receiver build

Arggh put the lid back on!

Seriously I like it, It always surprises me with how much you can do with very simple circuitry,

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Last edited by Tyso_Bl; 2nd Sep 2017 at 10:31 pm. Reason: speeling
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Old 2nd Sep 2017, 10:54 pm   #3
MrBungle
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Default Re: Simple NE602 / LM386 40m DC receiver build

I always get the "what have i created?!?!?" moment. Then I put the lid on and all is well

It is quite impressive. Then again there's a lot of magic in those ICs. It feels slightly like cheating. Next time a double balanced diode mixer and discrete audio amp I think. I've got a copy of W1FB design notebook here with some ideas in it

Oh also a warning: green Omeg potentiometers are rubbish. Buying Bourns cermet one next time.
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Old 2nd Sep 2017, 11:50 pm   #4
kellys_eye
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Default Re: Simple NE602 / LM386 40m DC receiver build

There's a dead bug in your box. Was it 'free' with the purchase?

Nice little project - something for the winter nights for me. The case also looks very smart indeed.
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Old 3rd Sep 2017, 12:45 am   #5
Andrew2
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Default Re: Simple NE602 / LM386 40m DC receiver build

A nice project, and they work surprisingly well when you get them 'right'. I've been toying with the idea of making a DC receiver using a 602 with a cheap DDS local osc. At least it would avoid the drift and pulling that can plague these things.
Or possibly add a huff-puff stabiliser.
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Old 4th Sep 2017, 12:57 pm   #6
MrBungle
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Default Re: Simple NE602 / LM386 40m DC receiver build

I actually built this with a bench DDS to start with so it's definitely a valid approach. I haven't found this particularly drifty though. It's getting two upgrades though which I'd recommend for anyone else building one:

1. Frequency counter port.
2. Narrow bandwidth switchable audio filter.
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Old 4th Sep 2017, 2:23 pm   #7
Argus25
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Default Re: Simple NE602 / LM386 40m DC receiver build

Quote:
Originally Posted by MrBungle View Post
The enclosure is the best bit (Takachi from RS) - I *really* like these enclosures and will probably build everything in them now!
You are not alone there. I have built many projects into Takachi enclosures, mainly the previous generation designs they made. I picked up a number of them from Akihabara in Tokyo. They are outstanding examples of Japanese Engineering.

Also, if you have a project requiring complex punchings, rectangular etc and you want a run of them they will do it at their factory, Mr Takachi himself is super helpful. Be aware that the color they define as Bronze with their older enclosures isn't a metallic dark brown, its actually a dark green color.

A big part of any project (apart from the obvious electronic performance and specs) is the way the finished item looks, that is what people see, so it is always good to make it look as good as possible and those Takachi enclosures do that.
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Old 4th Sep 2017, 2:28 pm   #8
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Default Re: Simple NE602 / LM386 40m DC receiver build

Quote:
Sticky legends are falling off already
They stay on a bit better if you snip off the corners at 45 degrees for 1/16th of an inch or so.

It is great fun to build such projects, my favourite type is the one valve regen.
 
Old 4th Sep 2017, 2:33 pm   #9
MrBungle
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Default Re: Simple NE602 / LM386 40m DC receiver build

Couldn't agree more. I've already knocked up a load in another enclosure:

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Needs some holes to let the heat out a bit but I'm loathed to ruin it so just run it at 5W max
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