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Author Topic: Build a very simple CW receiver using common parts  (Read 10011 times)
KK4MRN
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Posts: 92




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« on: December 28, 2012, 08:18:34 PM »

I have a challenge for myself to build a CW receiver for an HF band.  Maybe 40 meters? 

If that goes well and I learn my morse code well, then I want to eventually build a transmitter too.  So far, I have been giving myself goals.  Get the Technician License.  I did.  Build a crystal AM radio receiver.  I did.  Kind of worked.  I cheated by using my finger as ground.  I won't mention the number of tries I had to make building crystal radios for one to actually work. Then I hooked up a LM386 amp to it so I could listen via  speaker instead of crystal earphone - WOW, I pulled in a bunch of stations. 

Well, now I want to build a very simple CW receiver on a ham band using common parts.  When I mean simple, I really mean super simple.  And when I mean common parts, I mean parts that are not obsolete, can be easily found at your local radio shack. 

I looked over a ton of schematics on the web.  The "simple" CW receivers look complex to me.  Plus, many of them use parts that are not so common these days. 

I'm not interested in building a kit.  Maybe down the road I will build a kit which has all of the bells and whistles of a modern superheterodyne CW transceiver, but today I am interested in something I can actually build myself and get up and running.  Main reason, I'm on a shoestring budget for now. 

I have a ticket (ham license) but no radio.  I want to get on the air with my radio I built.  I found websdr.org online which allows me to listen to ham radio online, but nothing beats a real radio.  Plus, down the road, i want to actually make contacts which requires transmitting as well.

I do have a bunch of common components, such as, general purpose transistors like 2N2222, 2N3904, 2N4401, and a LM386 IC.  And I have capacitors and resistors via assortment packs.  I have magetic wire, hook up wire.  And I have germanium diodes, varactor diodes for the AM band, silicon diodes.

Even if I build the circuit, a bigger challenge is building the proper homemade coil(s) and antenna properly.

When I built my crystal AM radio earlier, I built a homemade antenna using 100 feet hook up 22# wire wrapped in a square loop.  Imagine a piano keyboard stand re-used as the holder for the wire for the loop antenna.   Then I have a coil for my LC tank which had 80 turns of green 26# enamled magnetic wire wrapped around a ferrite stick.  It picked up WRVA 1140 AM very well in Richmond, Virginia. 

Maybe this question is too big of a question to be answered, but I do hope to get some pointers in the right direction.  I "really" do want to get on the air using CW.  i am learning morse code, but my listing is like < 5 WPM now even though I know all the alphabet, numbers, some punt and pro-signs.  Maybe down the road, I will be interested in SSB as well or other modes.  For now, I am looking for the basics to get on the air.

Thanks in advance,
Daniel, KK4MRN
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JAHAM2BE
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Posts: 277


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« Reply #1 on: December 28, 2012, 09:11:28 PM »

Well, now I want to build a very simple CW receiver on a ham band using common parts.  When I mean simple, I really mean super simple.  And when I mean common parts, I mean parts that are not obsolete, can be easily found at your local radio shack.

I would say have a look at KE3IJ's web page. He has lots of schematics for simple regenerative receivers and one direct conversion receiver design. Many of his designs cover 40m. You might start with his "universal regen" and/or his "big loop regen" designs.

http://ke3ij.com/radios.htm

I built several of those projects and they all were simple and worked well.

If you want an even simpler circuit, you could try this ultra-simple regen:
http://www.afelino.net/crystoid.htm

For better performance, you could look up some of N1TEV's regenerative receiver designs.

When you're ready to go further, you might try some of the projects and ideas from the free online book "Crystal Sets to Sideband".

Personally, I like regenerative receiver designs, and some people do use them on the air (see for example the Yahoo "regenrx" group), but they can be touchy and hard to optimize and operate. For me, that's part of the fun. However, simple direct conversion receivers can likely offer better performance, and can be designed to be top notch performers if you're so inclined. YU1LM has some high-performance direct conversion receiver designs you might want to look at.

Have fun!
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WB6BYU
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Posts: 13331




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« Reply #2 on: December 28, 2012, 09:58:42 PM »

There are two basic approaches to making a simple CW RX:  direct
conversion or regenerative.  (They are actually quite similar, the only
difference is in the oscillator and detector circuitry.)

One thing to be cautious about, however, is in trying to reduce the
circuit to too few components.  This was a common approach in
the days of tubes, when an additional tube (and the required filament
current) was a significant addition to a circuit.  But another 2N3904
transistor or two really doesn't add to the cost of a circuit substantially,
and by using separate transistors for each stage it is much easier to
trouble-shoot, or to optimize each stage for one purpose.

A basic regenerative or direct conversion receiver will include an
optional RF amplifier, an oscillator, detector stage, and one or more
stages of audio amplification.  The oscillator determines the receive
frequency.  In the case of a regenerative receiver the oscillator
and detector often use the same transistor, but separating the
two functions makes performance more stable.

One of the first things to learn about reading schematics is to break
them into individual stages:  once you can do this, they make much
more sense, and seem less complex.  It also allows you to see how
you can modify them:  for example, you can use the oscillator from
one design, the detector from another and the audio stages from
something else entirely.  

In fact, this is the way I build receivers: each stage is built using
"ugly construction" on a small piece of bare circuit board and wired
together.  If I want to try a different oscillator circuit, I wire it up
on its own board and swap it out with the previous one.  I keep all
the pieces around, so when I want to build something else I don't
need to build all the parts from scratch - I just dig out the common
stages from my junkbox and build the couple more that I need.

Once I get it working to my liking, I build a copy of it into a
case that suites the end application.

As an example, I had a direction-finding receiver published in QST
(September 2005) that was intentionally made from simple, common
parts, most of which could be salvaged from an old AM broadcast
radio if necessary.  This was for 80m, and used a cascode RF amplifier
(two transistors), a diode mixer, one transistor oscillator, an audio
pre-amp, and an LM386 audio power amplifier.  This gave good CW
reception using an 6" diameter loop antenna attached to the receiver.
You can get by without the RF amplifier if you have a full-sized
antenna, but it provides a convenient RF gain control.  Each of these
stages was very simple, and used generic NPN transistors such as
the 2N2222, 2N3904, 2SC1815, BC547, etc.  True, some of the stages
might be a bit better using an FET such as the MPF-102 instead, but
the bipolar transistors provided adequate performance.  You can get
by with fewer stages, but none of them are particularly difficult to
build.

For each of the stages there are many different circuits that you
can use:  I borrowed the bits I liked form this receiver design
and that one.  You can do the same thing with a different circuit
for each stage and still get good performance.


Meanwhile, here are some resources:

http://www.qrp.pops.net/   is the QRP homebuilder web page.  Lots of good
info on circuits, construction, etc.

http://www.intio.or.jp/jf10zl/   JF1OZL has a lot of simple circuits to try, as well
as tips on homebrew techniques.  For example:

http://www.intio.or.jp/jf10zl/3trcw.htm  is a 3-transistor CW receiver for 15m
(though the relay switching necessary to do this makes the receiver complex.)

http://www.intio.or.jp/jf10zl/cmc.htm   shows how he builds each stage on a
piece of generic circuit board with pads.


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KA4POL
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Posts: 2027




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« Reply #3 on: December 28, 2012, 11:38:34 PM »

You see, there are lots of possibilities.
Of course, thinking of a CW receiver usually brings you to the good old circuits. I would like to add a modern thought though. If you are a member of ARRL, take a look into the January 2013 edition of QST. There you'll find a modern approach to receiving. It uses a so called DVB-T stick, which represents actually a SDR. Your part to build would be the up-converter to get the HF band into the DVB-T band. It is not a perfect solution but certainly fulfilling your goal.
Let me add, it is always great to see someone getting into the homebrew business. Good luck.
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WB6BYU
Member

Posts: 13331




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« Reply #4 on: December 29, 2012, 09:17:26 AM »

And here is a simple regenerative receiver from 7N3WVM:

http://www.qsl.net/7n3wvm/regen.html

This has an oscillator (regenerative) stage, an FET detector, an audio preamp
stage, and an LM386 audio amplifier.  In that respect it is very similar to
a direct conversion receiver.

You can use other common transistors like the 2N3904 or 2N2222 in place of
the 2SC1815, and an MPF-102 or 2N3819 FET in place of the 2SK168.


With a regenerative receiver you adjust the regeneration control (the 10K
pot in the upper left corner) to where the circuit is just barely oscillating
(for CW or SSB) or very nearly oscillating but not quite (for AM).  This
gives the best sensitivity to weak signals.

To change the frequency band of operation with this circuit, generally
you change both the oscillator frequency and the input stage by
adjusting the coil(s) and capacitor(s).  In this case, changing the
number of turns on the coil does both at the same time.  If you don't
have a ferrite bar antenna for SW, you can use an air-core coil and wind
a link winding around it for an external antenna.


And perhaps now you can see one of the advantages of building your
receiver in stages when you are experimenting:  the two audio stages
from this receiver can be the same ones you use in other projects.
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N1NQC
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Posts: 60




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« Reply #5 on: December 30, 2012, 11:49:51 PM »

Hi,

 I built the WN6Q " Almost  A Crystal Set MPF 102  for the B'cast  band and it  worked phenomenal ! I used a ceramic insulated   var cap w/ ball drive and very  light  coupling on the antenna.Got at least a beat  note  on around  98%  of ALL AM radio channels.

HF versions have  been built. A SUPER simple  radio and if coupled  correctly  onto a  good  long wire antenna , should work well.

K
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KK4MRN
Member

Posts: 92




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« Reply #6 on: January 09, 2013, 11:54:48 AM »

Thanks for all the replies.

I will try and build the 40m CW/SSB radio from here:
http://www.ke3ij.com/JFETrgn.htm

I wanted to build this on breadboards like I did for my crystal AM radio and audio amplifier, but I've read that with higher frequencies a breadboard will not work.  I might have to solder this on a perforated board.
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WB6BYU
Member

Posts: 13331




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« Reply #7 on: January 09, 2013, 12:50:31 PM »

The breadboard should be OK at 40m, though there may be some frequency shift as
the parts move around.  If you find you have problems, grab some bare copper board
and build it using "ugly construction", or add some pads and built it Manhatten-style.

That circuit assumes you already have an audio amplifier available, which is one
of the big reasons it can be so simple.

Once you get it working, consider modifying it to have separate regenerative and
detector stages (as is the case with the 7N3WVM circuit) and it should make it a
bit more stable.  I also might change the AM/SSB switch, as it doesn't appear to
allow adjustment of the regeneration in SSB mode.  (Try it and find the best settings
for each mode first.)
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VE3LYX
Member

Posts: 141




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« Reply #8 on: January 18, 2013, 07:45:26 PM »

A regen. very simple . hartley is the easiest.
Any triode tube. for 40 M 12 turns of hookup wire on a film canster or pill bottle with a loop twisted dead centre.
gridleak. 2.2 megs resistor, 150 pf cap in parallel. That goes to the grid of course. the other end goes to the top ofthe coil you just made . The loop goes to the cathode and the bottom of the coil goes to grd or B-. A tuning cap (whatever you have) goes accross the coil as well connected to the top of the coil and the bottom totally ignoring the centre tap . Sometimes a few turns (3 or4 wound on the end of the coil will do for antenna coupling.) If it is happy with that then one end of this loop is ground and other is antenna.  Not too close as regens are easily overloaded. 1/4 inch should be about right.  You need a RF choke in the plate lead to stop rf from getting into the power supply. Below that install the earphones  and connect them one end to the south side of the Rf choke and the other end to the wiper of the 100K to 250 K (whatever you have) pot. If you use 100K then add a 100k fixed in series with it .  One end of the pot connects to the B+ which should be not more than 110 volts . The other end goes to ground (B-) Power it up , adjust regen till you hear a hiss or definate change in sound with antenna connected. , hunt for a station. If you cant hear the BEEP add a bit more throttle to the regen pot till you do. I find batteries best for this type of radio. Ten 9 volts clipped together work wonderful and will last 6 months. The filiment battery will need recharging often so a small lawn mower battery and gel cel of the voltage  that your tube needs for heaters will do a great job. Now you have a working radio. If you live in a desert signalwise you may want to add another triode (or use a dual tube like 12sl7 or 12sn7 or 12axy etc) and couple the place where you now have the 2000 ohm phones to the grid thru a 01 cap and build a simple triode amp in that side. A good working regen well buiilt and well run will give almost anything else a run for its money. No BFO needed it is built in already.
I use a regen often for QRP vintage style QSOs. Am building another today as we speak for a 10M QRP AM station. It uses a 12ax7 in the regen. Simple , inexpensive and can hear anything. Takes skill to run but simple , practical radio.
Don VE3LYX
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N2EY
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Posts: 3894




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« Reply #9 on: January 23, 2013, 06:30:16 AM »

I think there's a much easier way that's being missed.

There are lots of QRP CW transceiver designs out there, using commonly available parts. Some are available as kits for not much money. Build one for 40 meters - just don't do the transmitter section.

73 de Jim, N2EY
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ZENKI
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Posts: 956




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« Reply #10 on: January 25, 2013, 05:19:53 AM »

KK7B,  R2 DC receiver. Its amazing! I think kits are still available from a company called Kangaroo or something like that
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VE3LYX
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Posts: 141




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« Reply #11 on: February 04, 2013, 06:34:44 AM »

I would question if that is easier as from my post above. a good working recvr can be built from that in 4 to 6 hours depending on work habits.  The Hartley design which it is doesnt require the fiddling a tickler coil one does and will work instantly.
In the past two weeks I built a two tuber from my brother from 01A tubes and the 10M one I had going yesterday.
Kit building may be fun for some but it is too much like paint by number for me. The more you build from your head(and heart)the more you learn. If you want a schematic I will draw you one. You could have a rx up and running by this aftenoon if you have any kind of a junk box. Or an old radio to steal stuff from.
It is simple.
Top of coil goes to grid thru a gridleak set up. (1 meg and 100 pfs paralleled) centre tap goes to cathode. Bottom of coil goes to B-. For 40M 13 to 14 turns. (2 turns per mcs ) and centre taped at the mid point.Tuning cap (any variable cap you have) goes accross complete coil (top end at the coil itself to bottom end of the coil (B-) Pill bottle, film canistor , tiolet papper roll , it doesnt matter. Any coil form of that approx size will work. Plate needs an RFC choke hooked to it. (15 feet of fine copper wire. (pick a gauge #22 , #24 #26 #28 #30  whatever) scramble-would around a pencil (or a wooden dowel of you want it fancy) A .01 cap of ANY description comes off from this choke's bottom (farthest end from the tube) and that can go to the grid of an audio stage. The RFC connects to a 500K pot wiper (centre terminal) the outside terminals go, one to B- and one to B+. At this point you have a functioning radio and could with a set of 2000 ohm earphones hooked betwee B- power and the B- terminal get it to work on a strong sigal.
The audio section  takes another triode (or triode section) and the 01 cap at the bottom of the rfc goes to the grid of that new tube or section. A grid resistor  5k  6.8k whatever  goes between the grid and ground or B- . The cathode needs a 400 ohm to 1k resistor(whatever you have) bypassed with a 10UF 35 volt electrolytic (positive terminal to the tube cathode)
Wire the plate to B+ and remove the headphones from bewteen the B- and Ps and place them between the cathode resistor and cap combo and ground or B -. Done  Turn it on and enjoy.  Antenna can come in by soldering a 4 inch chunk of hookup wire to the top of the coil and twisting a few turns of the wire from your actual antenna around it. A regen doesnt need much . A few feet of antenna is usually sufficient) Too much will shut it down. Or a couple or three turns of hookup wire wound about 1/4 inch from end of the coil with one end grounded. I would do the twisted wire first for my first build as it is fool proof. These little radios are addictive as they really perform.
After this , the old Doerle Twinplex is also a very good design and the Lindsay book on it is worth having. You may want it for you second one. It is probably the very best ever.
Go for it. You may be in doubt a bit and unsure at this point. Once you do it and have it working which could be a few hours from now you will never think about things radio the same. You will be sleeping with a grin all night!
Component values can and are always fudged from what is given to "What you have on hand." Very, very, rarely does this present enuf of a problem to stop your build from working.
Building on wood is fine although it is wise to shield at least the front panel with metal from behind even if it is just a cut up disposable pie plate or aluminum foil or whatever.
I mean you did say simple. Easily built. this is and will perform pretty good.
BTW putting the phones in the B- simplfies the build some if it is built on metal (because of grounded phone jack ) and removes the hi voltage B+ from around your ears. Personally I dont worry about that as it is a foolish concern but some do. B+ or B- , the phones dont know the difference and work the same in either. All they are doing is sensing the load variation between the radio and power supply as the set struggles to reach oscillation  but cant quite get there . the variation is produced by the antenna's input to the grid. The tail is really wagging the dog! A regen is simply a slightly underpowered oscillator with phones in the PS cricut sensing the load variation and a pot to control the B= to keep it just below oscillation.  Nothing more and nothing less.
To run. Adjust the pot till you hear a hiss or squeal. Then back it of til it is just on the edge of that. Tune for a station constantly adjusting the pot to keep it right on the ragged edge.  Have fun. These things are a blast  to build , to run and to use for QSOs. (CW or Am BTW. ) If you decide to go for it and have any snags at all, just ask. PM me or here and I will gladly help you over the bump.
Going to the shack to play with my 10m one right now.
Don Ve3LYx
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