Three Transistor Short Wave Radio

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Introduction: Three Transistor Short Wave Radio

About: All project articles are being moved to www.netzener.net. I am no longer responding to emails from instructable.com. Eventually this account will be deleted. Please visit www.netzener.net for the latest p...

Step 1: Obtain Components Listed in the Assembly Manual Parts List

Review the parts list and obtain the components indicated. Everything but a few pieces of hardware are available on Amazon or can be obtained directly from the suppliers indicated at the bottom of the parts list.

Below are a few notes regarding the parts used for the radio:

  1. The transistors for the radio can be purchased from Amazon or Radio Shack (assuming they are still in business in your area). I highly recommend the excellent Joe Knows Electronics semiconductor kit. It includes the transistors you need for this radio project and over 150 different types of transistors and diodes for just $22. And it includes a set of documents that are really good reading for the beginner. Check out www.joeknowselectronics.com. You will not be sorry.
  2. The resistors for the radio can be purchased from Amazon or Radio Shack. Radio Shack has a good selection of 1/4W resistors in a big 500 piece bundle for about $15.00 if you have a store nearby. Joe Knows Electronics also has a nice 800 piece package of 1% resistors for $12.00 if you don't mind ordering online. Joe's is a really good and well organized kit even if 1% resistors are a bit of tolerance overkill for this radio project.
  3. I strongly recommend ordering NP0 ceramic disk capacitors from Mouser or Digikey as they will far outperform most anything you can get on Amazon. The Joe Knows Electronics capacitor kit is an extremely good buy for every other capacitor at 645 pieces for $13.00. Don't bother with Radio Shack for capacitor kits as they are mostly junk values you will never use.
  4. I purchased several crystal earphones from AmplifiedParts on Amazon and they work great despite the poor reviews. Whatever quality problem they had in the past seems to have been ironed out. The crystal earphone comes with a 1/8" mono phone plug so I added a 1/8" mono phone jack from Radio Shack. The phone jack is also available from various sellers on Amazon.
  5. The variable capacitor (and a lot of other rather old and interesting parts) can be found at Uxcell (via Amazon) which seems an unlikely domain for radio stuff but they do have a lot of radio stuff that's interesting. I've created a diagram of the variable capacitor here that will help you figure out how to wire it in the radio.
  6. The case for the radio I built is a Hammond 1591GSBK ABS Project Box from Amazon.com with a piece of vector breadboard cut to fit on the top and spray painted with high temperature automotive flat red. I like the look of red on black, and the red color of the breadboard matched the red color of the original pbox kit. It's completely up to you how you want to house and color the kit you build.
  7. The knobs I used are Radio Shack knobs I've had in inventory for decades. Use anything you think is cool that will fit on the pot/varicap shafts.
  8. You will need to be creative on how you mount the variable capacitor on the vector board. I used a piece of 1/32" sheet metal cut to size with a Dremel tool grinding wheel and then drilled the holes to mount the variable capacitor with a power drill. Then I bent the end of it 90 degrees to form an L shape.
  9. You will need to be creative on how you mount the tuning knob to the variable capacitor. The shaft on the varicap is only about 1/4" long so you will need something to extend it. I found a plastic cylinder with a hole drilled through it that was about 1" long at my local Ace Hardware store. They have a really nice selection of odd hardware that is very useful.
  10. The 2-position barrier strips are available from Amazon or from Radio Shack in a pack of four. These are a great value at the price so if your local Radio Shack hasn't yet been turned into a Sprint cell phone shop you should definitely buy all of the packs on the peg. I know I did.

Please Note: I have no business relationship with any of the above vendors. Nothing of financial value was exchanged for my recommendation. None of the above vendors provided compensation of any kind during the creation of this project. I will not be compensated in any way if you choose to build this project or purchase components from any vendor I recommend. I simply had a good experience with the vendors I recommend and believe you will too.

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74 Discussions

Kit of VHM and AM radio just ordered.

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Here is image of it in action with 9 volts not 3 volts!

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Very interesting. A small IC like a single OP amp can amplify sound more effectuvely than 3 transistors. In fact IC radio with three transistors in it works like that.

I've received a few requests to see if it's possible to resurrect the old Science Fair Globe Patrol 4-Band BC/SW radio, an example of which can be found at the URL below:

http://www.qsl.net/kc6vdx/gear/globe.html

I've determined that it is feasible to construct a receiver using a similar RF design but with the following changes:

1. The tuning section will use different component values in order to make use of the same variable capacitor specified in the Three Transistor Short Wave Radio.

2. The band spread capacitor will be replaced with a 1N4001 diode tuning capacitor. I could not find a volume reseller for the 12pF band spread variable capacitor.

3. The RF transformers are no longer available from any source so I've redesigned these using hand-wound toroid core inductors and 30AWG magnet wire. These aren't all that fun to wind by hand but they work really well.

I really don't like the transformer coupled audio amplifier in the old design. I think it's inefficient and just not all that good. But it is possible to replicate it with transformers still available. I could redesign the AF stage with a direct coupled transistor amplifier. Or just use the well-known LM386 with a gain of 200. If anyone has a strong opinion on that, let me know.

I've constructed and tested a rough prototype for the broadcast band which seems to work well. It tunes 550Khz through 1.6Mhz. The diode "varactor" band spread seems to work really well for tuning above and below the center frequency. It's range is currently +/- 45Khz at 1Mhz. A photo of the prototype is shown below.

When I get the design into a state in which someone else can build it, I'll publish an article on it.

radio.jpg

Nice project. I remember getting a Radio Shack kit when I was young and found myself years later wishing I knew what happened to it. I'm pretty sure I was picking up air traffic control communications at the time. I recently tried to make a shortwave/VHF radio following instructions from a Youtube video, but I haven't been able to get it to work. Not sure what I did wrong but the instructions were not very clear. I would love to try your design, but can you tell me if it would work with powered speakers instead of the crystal headset, or would that feed back power into the circuit? How could I prevent that? I like the idea in the other design of using a 9v battery in order to be able to use regular headphones or plug into a computer to make recordings. Thanks for any suggestions!

-Matt

7 replies

The output of the 3 Transistor SW Radio is designed to drive a high impedance crystal earphone, but it is possible to attach an external amplifier to drive a speaker. As long as the external amplifier input impedance is around 20K Ohms, there should be no problem driving a speaker or set of dynamic headphones.

If you would like to build your own amplifier, download the LM386 IC data sheet from TI at:

http://www.ti.com/lit/ds/symlink/lm386.pdf

Construct the "Amplifier with Gain = 20" on Page 6 excluding the 10K volume control. Attach Pin 3 of the LM386 to the earphone output connected to Q3 and the amplifier ground to the earphone ground. The amplifier can be powered from the same 9V battery used to power the radio.

The input impedance of the LM386 is 50K Ohm which is perfect for the output of the radio.

Thanks for the kind comments and I'm glad you liked the article.

Let me know how things go for you should you decide to build the radio.

Thanks again!

NetZener

Thanks for the reply and advice. I'm currently collecting the parts list from Mouser. It's been a bit of work narrowing each part down to the right specs from the thousands of results you get from each part search, but I'm fairly confident in my choices up until the Mylar Capacitor. They seem to be calling it by a different name. Will this one work?: http://www.mouser.com/ProductDetail/Nichicon/QYX1H...

Also, I'm assuming the voltage rating on the capacitors and resistors is not so critical. Am I correct in that assumption? I'm finding parts ranging from 1kV to 500V. I'm trying to stay at the smaller end, and away from AC ratings. Is that good enough? Thank you again sir.

-Matt

You are absolutely correct that voltage ratings in this project are not critical. For capacitors in general, lower voltage means smaller size. A 50V rating with 5% or 10% tolerance Polyester Film (Mouser 647-QYX1H104JTP) will work just fine. I should probably have used the correct name for the capacitor dielectric material. Mistake on my part I think.

In this project the voltages are very low so anything above 15V will last.

Most common coupling capacitors today start at around 50V and go up from there. I find that the 50V variety are pretty cheap and are small enough to fit the layout.

Aluminum electrolytic filter capacitors, however, can be rated all the way down to 4V which are typically only used for 3V power in digital circuits. Electrolytics with 16V, 25V or 50V ratings will work just fine.

Resistors can be 1/4W or 1/2W and are large enough to easily work with on a breadboard. Current consumption is very low so even 1/8W will work but those are tiny and their leads are fragile.

NetZener

Thanks again for the info. Sorry to keep bugging you, but I now have everything sitting in the cart on Mouser except for the 140pF Variable Capacitor. I'm not clear on if I need to find something labeled exactly 140pF (which Mouser doesn't have) or if I can get anything that has 140 in the range? For example: 10pF to 150pF, or 12pF to 180pF. Once I get that out of the way I'll be ordering and starting the build as soon as everything is shipped. Thanks so much for all your help!

-Matt

Not bugging me at all. Glad to be of some small assistance to you.

I would recommend the variable capacitor from Uxcell (www.uxcell.com) available from their web site or on Amazon. Last time I checked neither Mouser or Digikey carried these.

The Uxcell part number is a13091000ux0626. It's $6 for two plus shipping. I've ordered quite a few items from Uxcell and their shipping is very quick for items in stock. Items they have to order internationally take longer. The variable capacitors I ordered took only a few days. The only challenge is extending the capacitor shaft so that a suitable knob can be attached. I usually look for something in the junk box that can be made to work.

The description states 20pF - 126pF but in my measurements the capacitance is a little higher than published and there is a trimmer on the back that can be used to increase capacitance by 10pF. I didn't have to use the trimmer. It worked great out of the box.

NetZener

Just one more question. Is there something on Uxcell that would work for the 0.047uf multilayer capacitor? I can find .047uf and I can find MLCC's, but not in the same product at once. I've already placed my order with mouser and I'm trying to keep shipping to a minimum. Unless Mouser has a 140pf Variable capacitor that I could use, I will have to place another order with mouser and one with Uxcell. Thanks again

-Matt

No problem. A 0.047uF capacitor can also be stated in nano-farad units or pico-farad units. So 0.047uF can also be referred to as 47nF or 47000pF.

I used a MLCC (Multi-Layer Chip Capacitor) because that was what was in my Joe Knows Electronics Capacitor Kit. But you can use almost any small capacitor type such as ceramic disk or polyester. Capacitor type isn't critical.

Uxcell offers an MLCC capacitor via part number a14070900ux0094.

They also offer a polyester capacitor via part number a14062700ux0358.

I like the polyester capacitor the best because it is closest to the original design and has much longer leads for you to work with.

The only thing is... Uxcell doesn't sell these in small quantities. It's around $6 for 50. But you might be able to use them in other projects in the future. It's always nice to have extra.

NetZener

This is probably one of the best shortwave radio projects I have found.

I have built AM and FM radios but it is shortwave that interest me the most.

I have just ordered the transistors as they are a type that I don,t have.

I may build it dead bug style instead of using the perf board or vero board here in the UK.

Great article ,I hope you do some more

All the best

John

1 reply

Many thanks for the comment and I'm glad you enjoyed the article. Dead bug style on single-sided PCB will work really well. Probably better than the perf-board for hand capacitance.

I can't take full credit for the design and layout as that was originally a product of Radio Shack in the US. But it was a lot of fun redesigning the radio to use parts still available from retailers.

Thanks again for the very kind comment.

NetZener

0
user
DHeigh

2 years ago

Thank you.
I have been regretting not buying a "Globe Patrol" when I was younger for decades. I love the portability of the design (small case & battery powered).

Please consider using a low-profile case, similar to the cases Ramsey kits uses for their SW kits. It might make a good update - especially for campers like myself.

0
user
DHeigh

2 years ago

Can you do anything about resurrecting the "Science Fair "Globe Patrol" regenerative radio"? It was more complicated, but more capable too.

1 reply

Oh, yes. Great question. It will not be difficult to redesign the circuit using modern parts. I've been thinking through the easiest way to replicate some of the coils and assembly steps. And I've been reviewing manufacturers of multi-position rotary switches to see how close I can stay to the original design. Instead of air variable capacitors, I can refactor the design to use varactor diodes and potentiometers. That would give the finished radio a similar look and feel, but varactor diodes are mostly SMT components these days which are hard for the average builder to solder. The challenge is making sure that the parts I specify will be available for at least 3 to 5 years so that folks who are interested in building the radio won't be disappointed by unobtainable or hard to handle components. The other challenge is making sure the project doesn't turn out to be so complicated that folks would rather just read about it than try to build it themselves.

But yes, I am very interested in seeing the Globe Patrol radio or something very much like it making radio sounds again.

NetZener

hi @netzener I am considering building this as a physical accompaniment to a paper i'm writing on diy radio making culture (past & present). Could you tell me if this variable capacitor would work for this project? I'm hoping to buy everything i need from one source. http://www.digikey.ca/scripts/DkSearch/dksus.dll?Detail&itemSeq=182012689&uq=635809659825808438

2 replies

Woops the url got cut off. http://www.digikey.ca/scripts/DkSearch/dksus.dll?Detail&itemSeq=182012689&uq=635809659825808438

Could you send me the Digikey part number? The URL displays "Page Not Found" due to limitation on the length of a URL in the comments section.