listen to shortwave broadcasts on an am radio

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Listen to Shortwave Broadcasts on an AM Radio http://www.instructables.com/id/Listen-to-Shortwave-Broadcasts-on-a...

1 von 11 26.10.2012 17:47

The larger radio is my Sangean ATS-803A shortwave receiver. The smaller radio in the foreground is atravel alarm/AM-FM radio from the late 1980s. I converted it to receive shortwave frequencies between 4and 9 MHz and used it that way for a while. You can make a like conversion on an AM radio you own.

For those with a deeper interest: Once while vacationing in Oregon I heard a broadcast from RadioAustralia about a radio operator on a naval ship who learned to recognize the "fist" or touch of wirelessoperators from other ships before he heard their call signs. When WW II was about to break out theGerman radiomen ceased using their call signs to hide the identity of their ships and their location, but heknew each one from his distinctive "fist" on the Morse code key. The radio signals also modulated in adistinctive way when a ship was transmitting from one particular area. Not only could he identify theGerman ships from the way the radiomen tapped out their Morse code, but he also knew exactly wheresome of the ships were located at the time. This is just an example of things you can hear on shortwavebroadcasts.

Step 1 Not as popular as before


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Shortwave frequencies bounce off of the ionosphere and return to earth halfway around the world. It iseasy to receive broadcasts from another continent; depending on conditions, time of day, signal strength,and target area for the broadcast.

Pictured is the Passport to World Band Radio. A new edition is published each year. It is a yellow pagesguide to international broadcasts.

Unfortunately, shortwave broadcasts are not as available as a couple of decades ago. This is due tobudget cuts and the Internet. Now you can download Podcasts from many national broadcasters. ThesePodcasts are in FM quality and without the static interferences associated with shortwave broadcasts.Still, there is a certain romance from listening to a radio signal from the other side of the globe.

Step 2 Open your radio

Select a radio with analog, not digital, tuning. Open the back of the radio. Look for the ferrite rod antennaand the condenser or capacitor tuning block. The ferrite rod is the black rod with flesh colored wirewrapped around it. (See the top of the photo.) The tuning block is the translucent plastic block you seewith trimmer screws on the back surface of it. There are solder tabs around the tuning block. A boom boxworks better for this project than a small radio because the much larger ferrite rod pulls in a better signal.


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Step 3 Magnet wire

Get some magnet wire from an old motor, ballast, or transformer. Or, you can buy a set of small spoolsfrom Radio Shack. #26 is about the right size. The pencil included in the photo is for scale better toperceive the size of the wire. Cut a piece about six inches long and scrape about 1/8 inch or more bareon each end.

Step 4 Loosely wrap seven turns of wire

Wrap seven turns of magnet wire around the flesh-colored coil on the ferrite rod antenna. The turns canbe a little loose. Spread the turns out as evenly as possible over the length of the flesh-colored coil.

Step 5 The circuit


4 von 11 26.10.2012 17:47

Sep 30, 2012. 5:15 PM

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BigBadgers2001 says:This is brilliant. I have dug out my old Realistic DX-350 and started listening to SW. It is fascinating.If I did this to a AM radio for my kids to play with, would there be a way to make it switchable topreserve AM functionality or does the loose coil adversly effect the AM signal?

Below is an electrical diagram of what you are trying to accomplish. The easiest radio for this conversionhas only an AM band. Then you can solder the ends of the wire you wrapped to the tuning block terminalswhere the very fine wires from the flesh-colored antenna coil attach to the tuning block. It is a little morecomplicated when the radio also has an FM band with additional connections to the tuning block. The trickis to find the two tabs on the tuning block for the AM band. A good clue is when local AM stations are nolonger heard as you tune across the radio dial. Attach ten to twenty feet of wire to one end of the smallcoil you added. This will lay across the floor as an antenna. Close the back of the radio.

It is possible that a radio you have will not work with this conversion. I have just such a radio, but havealso successfully converted several other radios.

Reception is generally limited to hours of darkness. Evening will be the best time. Tuning can be difficult.Stations may be no more than a blip on the dial, requiring a constant gentle pressure from one side or theother on the knob or wheel to hear the broadcast. A smaller radio may require earphones in order to hear.A boom box will be easier to tune and to hear without an earphone.

I knew a Chinese couple and offered to convert their boom box's AM band for shortwave. I finished theproject and gave it back to them four days before the massacre at Tiannamen Square happened. Everyevening after they closed their business they were glued to their radio. Radio Taiwan gave accuratereporting. Radio Bejing glossed over the story and played classical music. Both had relatives in Bejing(Peking). Not only had I experienced a success with the conversion, but I helped out this couple and theywere very appreciative.


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Phil B (author) says:I expect you could put a switch on the coil windings you add. Try disconnecting one leg to see ifthat works. If it does not, try disconnecting the other end of the coil and see if that works. Add asingle pole or a double pole switch according to what you find.

You will need to help your kids understand tuning an SW station on a modified radio like thisrequires a lot of patience because a signal is just a blip on the dial.

I do not listen to much SW radio now because broadcasts I would want to hear are available nowas Podcasts I can hear on my schedule in much better quality than I got with SW radio.

Thank you for your comment and for looking. I hope you and your kids find enjoyment and successin your efforts.

Chakazuluu says:Wow you brought back some memories. When I was in elementary school (I am 70 now) my fatherhad an old stand up Philco Am and shortwave radio. I sandwiched a piece of aluminum foil betweentwo pieces of card board with two screws connecting the two antennae wires and put it under thedial phone we had. It brought in some amazing frequencies.

I think I will do this with an old AM radio I have. Thanks for the memory.

Phil B (author) says:You are four years older than I am. We had a similar radio, but ours was a Zenith. For whateverreason, I do not remember ever getting a shortwave broadcast on ours. At the time I do not think Iknew to attach an external antenna. I am guessing that what you did coupled with the telephonelines by capacitance to make use of them as an antenna.

Thank you for looking. I hope you are able to make your old AM radio receive some shortwavebroadcasts. I think I may have mentioned it worked pretty easily on one radio, but not so easily onanother radio I still have.

Shortwave has been a lot of fun. Regrettably, the band is not nearly as full in recent years,although at night I still hear a number of things in Spanish. Radio Havana broadcasts in English andthere are some Christian broadcasters. I miss things like Radio Canada, Radio Austria, RadioAustralia, etc. Thank you for looking.

Chakazuluu says:Now that you mention it ours was a Zenith also I thought it was a Philco but when you mentionedZenith suddenly the memory came back. I got the aluminum foil antennae idea from a short blurbin Science and Mechanics.

Phil B (author) says:If you go to this link, I think the radio shown is very close to the one we had, if not identical toit. Several details I remember correspond. I am not sure of other details.

Chakazuluu says:Oh my goodness I can't believe this it is precisely the same radio we had. It is like you tookme back in time and opened up a flood of memories that was seemingly forgotten. It is like adoor to the past has been opened and I can see situations and occurrences clearly that wasfuzzy and inconclusive. I need to ponder on this for a bit.


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Miketan323 says:Its weird, I'm picking up stations in the 10-15 kHz range. Hmmmmm...

Phil B (author) says:Good for you. It is working. You have shifted your radio's frequency range to the 10 to 15 MHzrange. My experience with my radio was the 4 to 9 MHz range, as best I could tell. Perhaps it is adifference in radio circuitry.

onlinemastering says:I have to admit being a bit of a "anorak" myself and still like to tune round the SW bands at night. Iespecially like it as you do not know what new ethnic music you might discover next, veryentertaining.cheers

online mastering

Johenix says:Recognizing CW operators by 'FIST' dates back to the American Civil War (War of NorthrenAgression) when a Confederate telegrapher spotted the strange sending of a Union intercept tapoperator and sent: "Get off the line you damn yankee!"

elias.alberto says:I have a huge digital Aiwa stereo on my living room, it can tune Am, FM and SW but I've never beeninterested on SW. Gonna attach its antenna and try to listen to it sometime. :)

charlieb000 says:i have a car radio i bought ages ago but never installed. it is not PLL, but very simple. it has littlecoils soldered into the board near the tuning cap but no ferrite. it also has a few (maybe six) metalboxes with painted ferrite inside. how can i convert this? it would make an excellent reciever as thetuning knob is really geared down and takes 16-20 turns to go accross the band. i guess i can do itas instructed with some ferrite, but the tuning cap has six pins and i dont know which to join to it.

Phil B (author) says:I do not know enough about car radios to say if it is possible. You can, however, order ashortwave converter for your car radio. Here is one link. But, it is not cheap--about $165.

nutsandbolts_64 says:I found this i'ble just in time. I have an on-going project on pause so I think I'm gonna turn it into ashortwave radio to pick up my friend's Morse code.

Phil B (author) says:It should do that for you. This makes an interesting receiver. But, it is not always a greatreceiver. I hope it does what you need.

nutsandbolts_64 says: If I can find it that is.


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gccradioscience says:I used to get SW stations back in 1991 with a cheap $20 radio, but the radio fell apart, but I havekept in touch with the world. The radio was a portable Windsor TV/AM/FM/Weather radio. I alsohad a friend that was picking up shortwave broadcasts on his AM/FM clock radio until I told him toput the ferrite rod back in place. It was a new come back experience. Now I feel I mightexperiment again.

Phil B (author) says:Thank you for trying this modification and reporting back that it worked for you. It makes a crudeshortwave receiver without some of the circuit refinements in modern receivers, like spurioussignal rejection and phase locked loop (PLL) controlled tuners. Your friend's experience with thepresence or absence of the ferrite rod on his clock radio is interesting. The early 1990s was theheight of my shortwave listening experiences. The number of stations I am able to receivecurrently is only a shadow of what was available 20 years ago. But, I now download Podcastsfrom some of those same stations and convert them to CDs I can play in my car. My aim was toimprove at understanding spoken German. Although I miss the shortwave broadcasts, the audioquality on the Podcasts is far superior to anything I ever heard on shortwave. (During the firstGulf War I once heard a news item on shortwave that did not make the news reports in the USAuntil two days later!)

gccradioscience says:I tried it, it works very good, except it drifts alot, it takes patience to tune and experimentation. Ialso used one of my indoor shortwave radio antennas. What a great way to get access to worldband on a radio you do not use. Great Job!

static says:For whatever reason I was lead back to this instructable, so I thought I would search out and postsome links for the noobs. I did find a schematic for the typical transistor radio herehttp://my.integritynet.com.au/purdic/am_rec.htm . Go here to find the link to part 2 it's in the leftcolumn as you scroll down the page. You can read the USN electricity and electronics trainpublications here http://www.tpub.com/content/neets/http://www.tpub.com/content/neets/ Thedocuments can be downloaded free as well, but I can't find my bookmark for doing so. OK here itis, this will keep nerds busy for awhile.

static says:Came back to get an url I failed to bookmark, and notice errors in my post, Exclamation deleted.

Read the USN training docs here http://www.tpub.com/neets/Download them here http://www.tech-systems-labs.com/navy.htm

Infinitevortex says:Very interesting Instructable! How does the addition of a seven-turn winding on top of the existingantenna enable shortwave reception?

Phil B (author) says:Reading about tuning circuits, also known as tank circuits, answers the question. A tank circuit is avariable capacitor in parallel with an inductance (coil of wire). At a specific frequency aninductance has a unique amount of resistance, also known as reactance, to a signal currenttraveling through it. Reactance from a capacitor works to cancel the reactance from an inductor.Turning the shaft on a tuning capacitor changes the capacitive reactance presented to the signalcurrent until the point is found at which the capacitive reactance cancels the inductive reactance for


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that frequency. At that point all frequencies above or below this signal current frequency areattenuated, or blocked. Only the desired frequency passes to the rest of the radio circuit. Adding afew turns to the coil on the ferrite rod changes the inductance so that a different frequency passeswhen the tuning capacitor is in a particular position. In this case, seven turns was about the rightamount to throw the range of frequencies that can be tuned into the 4 MHz to 9 MHz shorwaverange. I like to think of the front wheels on an automobile. Let us say both have a serious amountof toe in. The left wheel wants to push the car to the right. The right wheel wants to push the carto the left. At some position the steering wheel is able to make the car go straight down the road.Change the toe in on either wheel, and a new position on the steering wheel needs to be found forthe car to travel straight.

riverreaper says:(removed by author or community request)

static says:Repost to correct a typo. What they had you construct was a common mode choke. To chokeany RF on the outside of the coax braid, so it wouldn't act as a radiator. Sometimes it helpswith RFI problems, sometime it doesn't. Yes inductors(coils) do many things, our modern worldwouldn't exist without them. so it would act corrected to so it wouldn't act.

Phil B (author) says:Radio experimenters sometimes add coils to antennae to preselect the desired frequency andattenuate undesired frequencies. This is supposed to be a helper for the tank circuit and maymake it possible for weak stations to be received. It does not change the range of frequenciesthe radio can receive. The inductance I added to the tuning or tank circuit had the effect ofchanging the range of frequencies the radio could receive. So, it is not quite the same as whatyou did.

66411 says:Another good way to learn about tank circuits is to build a spark gap Tesla coil, by changingthe length of the primary coil, you change the frequency that it generates. For maximumefficiency, you want the capacitor and coil to resonate at the same frequency. I find that thiswebsite offers a good explanation on the operation of a Tesla coil.

static says:Then again the coil diameter. wire size and spacing/pitch as well as the capacitor values alleffect the resonant frequency of tank circuits. No doubt some where on the web are goodtech training videos that illustrate well what's going on in a tank circuit, and component valueply into the whole thing. The old black and white army/navy films help out a lot.

Phil B (author) says:Thanks for the comment and the information. Tesla coils have always seemed interesting,but I never pursued them.

Infinitevortex says:Thanks, thats fascinating! I'll have to investigate those tank circuits further. In this example, theadded coil is in parallel with the existing one. Would it make any difference if the seven turnswere in series with the coil?


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Phil B (author) says:I am glad my feeble explanation made sense to you. Watch out, though. Soon you will bestealing time from your other responsibilities to read tattered electronics books you found indark corners at libraries and bookstores. On garbage day you will sneak around yourneighborhood looking for discarded electronic devices that you will carry home under your coatso you can hide them in your room until you think you are alone and have time to coax out theirsecrets. Adding a coil in series would change the inductance, but perhaps not as much or in thesame way. I do not know.

Infinitevortex says:Thanks. I already have an old Beta VCR under my bed, (in addition to a lot of assortedcomputer and electronic junk)!

Phil B (author) says:If you "rescue" any old TVs from the curb for parts or experimentation, be very careful. Thetube acts like a large capacitor and holds a deadly charge for a very long time. Get somegood instruction on how to discharge it safely. On the bright side, many TVs have a smallfuse on the circuit board. There are folks who discard a TV without checking to see if theproblem was only an inexpensive fuse.

Infinitevortex says:That's good advice. Be careful with CRT computer monitors, too, as they also contain largecapacitors. Thanks for the fuse tip. It just might come in handy some time!

Phil B (author) says:If you liked the way tank circuits work, have you ever read about superheterodyne radiocircuits and why they are superior to tuned radio frequency or regenerative radio circuits?I really enjoyed learning about superheterodyne circuits.

Infinitevortex says:I believe I did ,once, but I didn't really understand what the book was talking about.Recently, I was given a large quantity of old electronics books which I hope to gothrough when I get the time.

Phil B (author) says:At the risk of boring you with unsolicited commentary, a tuned radio frequency settunes in a station, strips audio away from the radio frequency and amplifies it to makesound. A TRF circuit is fairly easy to build, but it works pretty well at some radiofrequencies while not working very well at others you may want to tune in. A guynamed Armstrong solved the problem when he came up with the superheterodyneradio. It adds something called a beat frequency oscillator. Imagine you hear a musicalnote. It has a frequency. Suppose a second note is played at the same time. Onebeats against the other and the two blend together to make a sound at a frequencydifferent from either of the original two. Suppose you could manufacture andmanipulate a frequency to beat against the frequency of the radio station you want tohear so that the combination of the two frequencies always resulted in the same finaloutput frequency, regardless of what station you want to hear. You could then build allof the detection and amplifying stages of the radio to handle this one frequency veryefficiently. You could do this because you are changing the beat frequency as you tunethe radio so that the combination of it and the station's broadcast frequency is alwaysthe same. That is why modern radios have two sections in the tuning condenser. Onesection tunes the tank circuit and the other tunes the beat frequency oscillator.


10 von 11 26.10.2012 17:47

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Aug 17, 2009. 10:10 PM

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static says:Actually the second capacitor section tunes the local oscillator. While the localoscillator output frequency beats against the frequency of the desired signal tocreate the intermediate frequency, the Beat Frequency Oscillator, serves anotherfunction. While every superhet receiver has a least one local oscillator very few havethe BFO. Only receivers that are constructed with CW (Morse code) and simple(poor) Single Side Band reception in mind, have the BFO. While these simple tricksdo allow a medium frequency broadcast band receiver receive broad cast signals inthe short wave bands, it's a trial and error process, where what works on radio maynot work on another.

Infinitevortex says:Very interesting, and it wasn't boring. Thankyou!

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Author: Phil B

I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing posting things I have learned and done since I got my...

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11 von 11 26.10.2012 17:47

listen to shortwave broadcasts on an am radio

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