Category Archives: Radio Modifications

Icom IC-R72: a repair story

Icom-IC-R72-Front-Mehdi-Asgari In this post I’m going to tell you how I repaired my Icom IC-R72 receiver. Although it’s about a specific device, the logic and methodology applies to all radios.

I bought an Icom R72 from a friend for about $200. At first, I just checked 7.0MHZ (40 meter band) and 21.0MHZ (15 meter band) and it was OK. After some time, I tried to listen to some ham radio on 20 meters (14.0MHZ) and it was deaf! I checked everything: antenna connectors, balun…everything.

With some trial and error, I found out that it was deaf from 11-15 MHz. With the help of the members of “Icom R72” Yahoo Group, I found one of the usual suspects: bandpass filters’ switching diodes.

I took a look at the service manual and apparently this radio uses multiple bandpass filters for different frequency ranges.

Schematic-Icom-R72-1

As you see in the above picture (grabbed from service manual), one of the bandpass filters is for 11-15 MHz range–that’s the range where my radio was deaf.

Note that there are multiple ways to test that a radio is deaf at a frequency. One of the simplest ways: connect an antenna or even a long wire to the antenna socket of radio. The noise level should increase; if not, there’s a problem.

Schematic-Icom-R72-2

After testing diodes with a multimeter, I found out that D31 is faulty. Almost all multimeters have a diode-test functionality.

I replaced it. The original diode was 1SS53, but I used a 1N4148 which is very common and found everywhere. Now I have a working radio! 🙂

If you have a radio that’s deaf at a frequency range, there is probably a problem in bandpass filters.

Here are some internal pictures of my Icom IC-R72:

IC-R72-Internal-IF-Stage-Mehdi IC-R72-Board-1 IC-R72-Board-2 Icom-IC-R72-Open

I should thank my friend and electronics mentor, Saeed (EP2LSH) who always helps me in my electronics adventures.

Mehdi Asgari, the author of this post, is a regular contributor to the SWLing Post. Mehdi lives in Tehran and is an active member of the EP2C amateur radio club.

How to use the SDRPlay RSP as a panadapter

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SDPlay-RSP

In this post, I will show you how to use an SDR as a panadapter for a commercial communications receiver. I’m using an Icom R72 and a SDRPlay RSP, but you can do it with nearly all receivers and SDRs.

The Icom R72 is a double conversion HF (0-30 MHz) communications receiver.

A panadapter lets you see the spectrum of your receiver (it gives you a broader, higher-level picture of what’s around your tuned frequency). After using it, you’ll wonder how you’ve been using your receiver without a spectrum display! 🙂

Almost all the radios we use are of superhetrodyne type. To connect a SDR to the radio, you should first find its 1st IF mixer output (if it has more than one Intermediate Frequency stage).

To find it, the best way is to consult the service manual. The first IF of Icom R72 is 70.4500 MHz, so we can use RTL-SDR dongles too.

Here’s a part of R72’s schematics, extracted from its service manual:

IC-R72-Schematic-Mehdi-Asgari

Look at the R82 resistor; it’s located at the output of first IF stage, so I soldered a connector to its pins (its other pin is connected to the ground)

Between the R82 resistor and the output, we’ve added a series 470-ohm resistor (to prevent loading the IF stage)

Click to enlarge.

The other side of this connector is connected to the antenna input of my SDRPlay RSP.

Now I can view my spectrum on a PC.

Here’s a screenshot of CubicSDR on Mac OS X (you can use other apps like HDSDR, SDR Console, etc.):

CubicSDR-Screenshot-Mehdi

Although this post was about the SDRPlay RSP and Icom R72, this procedure can be done for almost any combination of receivers and SDRs provided that your SDR covers the frequency of first IF stage.

Also, don’t forget that you should tune the SDR to the frequency of IF–in this case: 70.4500 MHz.

Mehdi Asgari, the author of this post, is a regular contributor to the SWLing Post. Mehdi lives in Tehran and is an active member of the EP2C amateur radio club.

Best solution to restore a vintage plastic radio chassis?

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Friday, I brought home an untested, slightly grimy, Sony ICF-5500W. I purchased it through Goodwill for $20.

I crossed my fingers as I put three C cells in the radio and turned it on. Fortunately, I was rewarded with brilliant audio. I tuned the ‘5500W on AM/mediumwave and heard CFZM, 500 miles to my north, and Radio Reloj, 860 miles to my south. A quick scan on the FM dial revealed that I could also hear all of my local benchmarks. Whew!

Other than the dial needing a little calibration, and DeOxit on a few pots, it’s in excellent mechanical shape.

I started cleaning the radio last night using Q-tip cotton swabs and a vinegar/water solution.

I’d like to restore the hard plastic chassis’ original shine, though.

I was tempted to reach for some Armor All, but stopped myself short. I know it would give the ICF-5500W a nice shine, but would it cause any long-term damage to the black plastic or clear dial cover?

I know there are vintage radio restorers among the SWLing Post readership. Can someone offer advice on what’s the best product to use (or not use!) on my ICF-5500W?

If you have experience, please comment!

Jeff’s solution to increasing FM performance on the Sangean U3

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Many thanks to SWLing Post contributor, Jeff McMahon (at the Herculodge), who writes:

I upgraded my Sangean U3 with a male to female iMBAPrice 6 foot stereo audio extension cable 3.5mm, which I plugged into the U3’s auxiliary port.

The U3’s small stub of an FM antenna really needed some extra oomph. Now my U3 is picking up all my favorite stations, including the problematic KPCC 89.3 in Pasadena.

AM is as great as always. The sound is crystal clear on AM and FM. If this radio weren’t so big, I’d buy two more for the kitchen and my bedroom, but will have to be content to have one for my gym/office radio.

Thanks, Jeff! I might have to consider the Sangean U3–I hope a reader will let me know if one goes on sale.

Like Jeff, having a radio that not only performs admirably, but that can also withstand the attention of my kids, may be a great investment over the long-term! I’m glad such a simple addition to the U3 means that you can now hear your favorite Fm station, Jeff!

Now if Sangean only made a shortwave version of the U3–!

Simple hack: Changing the tuning knob on the PL-660

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Many thanks to SWLing Post contributor, James Patterson, who writes:

Has anyone ever thought of changing the Tuning knob on the PL-660?

Putting a larger knob on it makes for much easier turning instead of the very small fiddly knob Tecsun supply.

Finding the right plastic knob maybe a problem, needing to insert it over the tuner cam. But modifying another knob off something else is what I did.

Tricks of the trade!!

That looks like a very simple and effective mod, making the 660 more tuner-friendly for you! Thank you for sharing, James!

Bill’s simple Sony SRF-59 passive loop antenna modification

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In reference to our previous posts about the Sony SRF-59 ultralight receiver, SWLing Post reader, Bill Mead, writes:

“As someone who doesn’t normally open the backs of radios, this is my mod on my ultralight. All it takes is a bit of electrical tape to hold the belt clip on the loop.”

That is, indeed, a brilliant and simple mod. The SRF-59 inductively couples to the loop antenna, so no soldering is needed; simply tape the belt clip to the loop, making sure the position is convenient for tuning the SRF-59 and the loop’s capacitor.

You can find passive loop antennas ranging from $19 to $50 US. The Grundig AN-200 and the Terk AM Advantage are two models currently on the market. Here are a few places you can check prices:

Grundig AN-200: