Category Archives: How To

Guest Post: Recording Music on Shortwave Part 2 – Weak signal recovery

An example of an AirSpy SDR# software screen.

Many thanks to SWLing Post contributor, TomL, who shares the following guest post:

Recording Music on Shortwave Part 2 – Weak signal recovery

by TomL

The QRM noise cloud surrounding my condominium motivated my first foray into noise reduction software to find a little relief (Please refer to Part 1 posted here) using SDR recordings.  I was able to use the freeware software Audacity to reduce some of that type of noise to tolerable levels on strong broadcasts.  But what about non-condo noise, like out in the field??

NHK Japan

I took my trusty Loop On Ground antenna to the usual county park Forest Preserve which is relatively low in RF noise.  I did some usual recording on 25 meters and poked around for something being captured by SDR Console.  On 11910 kHz is NHK broadcasting daily from Koga, Japan.  It is hearable at this location but is always an S7 or weaker signal despite its 300 KW of power no doubt due to being beamed away from the Midwest USA.

I recorded it using the SDR Console 10kHz bandwidth filter and created a separate noise recording from a nearby empty frequency.  Here is the 2 minute portion of a Japanese music teacher. No noise reduction was applied:

I opened the noise and broadcast recordings in Audacity to see what I could do.  Part 1 of my previously mentioned post details how I apply the Noise file.  A big downside of using any kind of noise reduction software is that it is ridiculously easy to destroy the desirable characteristics of the original recording.  Applying too much noise reduction, especially in the presence of constant, spiky lightning noises, will create both digital artifacts as well as very dull sounding results.  So I used the Effect – Noise Reduction (NR) feature very carefully.

In this example, I used the Effect – Amplify feature on the one minute noise file.  I applied just +1dB of Amplify to the whole file.  Then I highlighted a 10 second section I thought was representative of the general background noise and chose Edit – Copy.  Then, I opened the broadcast file, Pasted the 10 seconds of noise to the END of the file and highlighted just the 10 seconds of noise. Then I chose Effect – Noise Reduction – Get Noise Profile button.  Amplifying the noise file by +1db does not sound like much but it seems to help according to my tests.  Anymore than this and the Noise Profile would not recognize the noise without destroying the music.

I used the NR feature three times in succession using the following (NoiseReduction/Sensitivity/FrequencySmoothing) settings:  Pass1 (3dB/0.79/1), Pass2 (2dB/1.28/1), Pass3 (1dB/2.05/0).  Part of what I listened for was choosing the Residue circle and Preview button for any music or dialog that was being filtered out.  If I heard something that came from the desired part of the recording in Residue, I knew that I hit the limit concerning the combination of Noise reduction and Sensitivity settings to engage.  I used those Residue & Preview buttons over and over again with different settings to make sure I wasn’t getting rid of anything wanted.  I also used the higher Noise reduction with lower Sensitivity to try to get rid of any momentary spiky type noise that is often associated with SWLing.

I messed around with a lot of test outputs of differing dB and Sensitivities and a lot seemed to depend on the strength of the broadcast signal compared to the noise.  If the broadcast was weak, I could push the dB and Sensitivities a little harder.  I also noted that with strong signal broadcasts, I could NOT use more than 1 dB of Noise reduction beyond a Sensitivity of about 0.85 without causing damage to the musical fidelity.  This was a pretty low level of nuanced manipulation.  Because of these minor level Audacity software settings, it dawned on me that it is very helpful to already be using a low-noise antenna design.

If the Sensitivity numbers look familiar, that is because I tried basing the series of Sensitivity on Fibonacci numbers 0.618 and 0.786.  Don’t ask me why these type of numbers, they just ended up sounding better to me.  I also needed a structured approach compared to just using random numbers!  Probably any other similarly spaced Sensitivity numbers would work just fine, too.

Now if you really want to go crazy with this, add Pseudo Stereo to your favorite version of this file (also detailed in Part 1) and playback the file using VLC Media Player.  That software has a couple of interesting features such as an Equalizer and a Stereo Widener.  You may or may not like using these features but sometimes it helps with intelligibility of the voice and/or music [VLC will also let you right-click a folder of music and choose to play all it finds there without having to import each MP3 file into a special “Library” of music tracks where they bombard you with advertisements].

You can also turn on Windows Sonic for Headphones if you are using the Windows operating system.  However, this can sometimes be too much audio manipulation for my tastes!

Here is the resulting NHK noise-reduced file with 9ms of delay with High & Low Filters:

Radio Thailand

Five days later I was out in the field again.  This time I found Radio Thailand on 11920 kHz finishing up a Thai broadcast.  It was a weaker S5 signal than the NHK example, so it would be a good test.

When I got home, I recorded the broadcast file at a Bandwidth filter of 8 kHz and using Slow AGC and the extra Noise file at 12kHz using Fast AGC.  In a previous test I had noticed a very slight improvement in sound quality in the way noise seems to get out of the way quicker compared to Slow AGC (which is usually how I listen to shortwave broadcasters).  I now try to remember to record the Noise file with Fast AGC.

Here is the original without any noise reduction:

This time the Noise file using Amplify +1dB did not help and I used it as-is for the 10 second Noise Profile.  I then tried multiple passes of NR at higher and higher Sensitivities and ended up with these settings the best: Pass1 (1dB/0.79/0), Pass2 (1dB/1.27/0), Pass3 (1dB/2.05/0), Pass4 (1dB/3.33/0).

As a comparison, I tried recording only with SDR Console’s noise reduction NR1 set to 3dB and got this.  I hear more noise and less of the music coming through:

Now for more crazy Pseudo Stereo to finish up the Audacity 4Pass version (nice Interval Signal of Buddhist bells ringing and station ID at the very end):


I do not understand why applying 3 or 4 separate 1dB Sensitivities of noise reduction is superior to just one Pass at 3dB Sensitivity (in Audacity) or the one 3dB noise reduction (in SDR Console).  My guess is that doing 1 dB at different Sensitivities shaves off some spiky noise a little at a time, somehow allowing for more of the musical notes to poke through the noise cloud.  Who knows but I can hear a difference in subtle musical notes and sharpness of voice and instruments.  Probably the Fast AGC helps too.

Music is a Universal Language that we can share even when we don’t understand a word they are saying. And there is more music on the air than I thought.  Some of these recordings sound surprisingly pleasing after noise reduction. The fake stereo is pumped through a CCrane FM Transmitter to a few radios in the home, or I can use the Beyerdynamic DT990 Pro headphones.

Enjoying the Music!


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Giuseppe’s improved read-to-go case for the Tecsun S-8800

Many thanks to SWLing Post contributor, Giuseppe Morlè (IZ0GZW), who writes:

Dear Thomas,

I want to share my latest version of my case / antenna for Tecsun S-8800 to make it immediately operational: simply open and listen.

In addition to the loop inside the case with a 3-meter wire at one of the ends that join two telescoping style whips of one meter each short-circuited to take advantage of the entire length. At the other end of the loop, a cable that goes to the ground of the variable capacitor.

I can tune the whole range from 3 to 16 MHz with truly amazing results.

You can see the video from my Youtube channel at the link:

Thanks to you and all the friends of SWLing Post.
73. Giuseppe Morlè iz0gzw.

This is incredibly clever, Giuseppe! AS I mentioned before, I love how self-contained this makes the entire listening station and I especially love the built-in antenna options! This is truly a shack-in-a-case!

Thank you for sharing this.

Click here to read Giuseppe’s other contributions here on the SWLing Post!

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Jock designs a Horizontal Room Loop to cope with reception issues

Many thanks to SWLing Post contributor, Jock Elliott, who shares the following guest post:

There’s a 50-foot antenna in this room. Can you spot it?

Got reception issues? An idea worth considering: the “Horizontal Room Loop.”

by Jock Elliott (KB2GOM)

When my radio room was in the front of the house (on the east side), it was easy to run a feedline to a large RF-hungry SWL dipole with various stubs and feeders.

Now, however, with my “shack” moved to the SW corner of the house, any attempt to mount an outdoor antenna of any significant length raised potential safety issues because of nearby electrical lines.

Monitoring VHF/UHF is no big deal because of high-performance scanner antennas. HF, however, presents challenges.

My main SWL receiver is a Satellit 800, which has the guts of a Drake R8 and also has a large telescoping vertical antenna. It works okay, but I wanted more signal. I had been looking at small loops and got some great recommendations on Radio Reference, but then I had a thought: what if I turned the 8′ x 12′ room into a giant horizontal passive loop?

Here’s a hint.

So I called a ham friend and ran the idea by him. “Sure,” he said, “give it a try.” He gave me 25 feet of 4-conductor phone wire. Before I could use it, I had to strip off the outer insulation so I could get at the four separate insulated wires inside. The better half helped. Once I had the four wires, I connected two of them together and ran the resultant 50-foot strand around the perimeter of the room by taping the wire to the top of window frames and hiding the wire on the top shelves of book cases. As a result, the horizontal room loop is near the ceiling, about 7 feet in the air, and the room itself is on the first floor.

With the loop in place, I hooked the ends to the clip-in terminals on the back of the Satellit 800.

There’s a switch on the back of the 800 that allows me to quickly compare the loop with the radio’s built-in vertical antenna. And . . . it works! It pulls in more signal than the vertical (as measured on the signal strength meter), but I have not noticed a dramatic reduction in noise. On some stations, the horizontal room loop brings the signal up to full scale, and then the sound is very agreeable indeed.

In all, I am pleased with the results.

For anyone who wants squeeze more performance out of their shortwave receiver, I can recommend giving the horizontal room loop a try. It’s not expensive; it’s relatively easy to do (and undo if you don’t like the results), and just might improve your shortwave reception.

If you are not blessed with a bunch of window frames on which you could tape the wire for your room loop, you’ll have to get creative, but with lightweight wire, you don’t need a massive support structure. Tape, map tacks, or even self-adhesive Velcro segments might work for putting your room loop in place.

I don’t claim that this is the “ultimate” SWL DX antenna, but it certainly improved my situation. Perhaps others have suggestions for improving it.

— Jock Elliott, KB2GOM

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Giuseppe’s Tecsun S-8800 aluminum case is a self-contained listening post!

Many thanks to SWLing Post contributor, Giuseppe Morlè (IZ0GZW), who shares the following video and notes:

I recently bought a Tecsun S-8800 to be used mainly on shortwave. I carry it in an aluminum case to use it everywhere:

Many thanks for sharing this, Giuseppe! I love the integrated antenna–so clever!

Post readers: Giuseppe has had issues with the S-8800 accidently turning on in the case. Can anyone describe the button combo needed to lock the dial and controls during transport? I checked the manual but have found no reference. Please comment if you can help!

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More Tecsun S-8800 hidden features/adjustments

Many thanks to SWLing Post contributor, Dan Robinson, who has recently been in touch with Anna at Anon-Co and discovered a few Tecsun S-8800 hidden features we haven’t mentioned in the past.

Anna notes:

There are some hidden features for this model that are worth mentioning, and are available on all S-8800 radios, also the pre-2021 ones.

Backlight setting

In power-off mode, press and hold [ 2 ] on the remote until the display shows “ON” or “Off”, this to change the backlight setting to always-on or auto-off. In the auto-off setting the backlight turns on after pressing a button or using a tuning knob, and turns off automatically after a few seconds.

DNR (Dynamic Noise Reduction

In the AM band (LW, MW, SW), first press and hold [ 4 ] on the remote to activate the possibility of this feature. The display will show “ON” or “Off”. Make sure that it is turned on. Subsequently, press and hold [ 6 ] on the remote until the display shows “ON” (DNR activated) or “OFF” (DNR deactivated).

FM De-emphasis Time Constant

While receiving FM broadcasts, long press [ 5 ] on the remote to adjust the de-emphasis setting to 50?s or 75?s.

Adjusting the signal indicator sensitivity:

1. Enter FM, LW, MW or SW band

2. Select a weak station.

3. Press [ 7 ] on the remote for about 0.5 seconds.

4. Rotate the main tuning knob immediately to adjust the bars of the signal indicator.

5. Press any button for confirmation or auto save after 2 seconds.

While making the adjustment in step 4, the value in the top-right corner of the screen changes. The factory default value is supposedly around “6” for FM and SW: 6, and around 16 for MW. The adjustment range is -99 – 99.

Add Seconds to the Clock

With the device turned off, press and hold [ 8 ] on the remote to add seconds to the clock. Press and hold [ 8 ] again to hide the seconds from the clock.

Adjust the FM soft muting threshold

While in FM, press and hold [ 9 ] on the remote for about 2 seconds until the current level (probably around level 5) appears in the main display area. Then adjust it by rotating the tuning knob and then press [ 9 ] again to confirm the setting.

Many thanks to Dan and Anna for sharing these tips!

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Videos: Nick explores synchronous detection and the Racal 6217

Many thanks to SWLing Post contributor, Nick Boras, who shares the following:

I was motivated by one of Tom Styles videos (hamrad88) about Sync detection to make one of my own. It is no secret that Tecsun offers Sync on several of their radios but only the 660 and 680 really work. My take on Sync is that the results are not consistent even on some of the highest rated Sync radios. While my video is not scientific or nearly complete, I think it gives a good representation of what we can expect from Sync for SWL.

[In addition] today was Radio Day, so I made another video on a very interesting radio:

Thought your readers might be interested.

We are indeed! Thank you for sharing these videos, Nick! That Racal, by the way, is a beautiful beast of a rig!

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Adid offers two simple mods for the XHDATA D-808 (or any portable radio!)

Many thanks to SWLing Post contributor, Adid, who shares two inexpensive mods he made on his XHDATA D-808 shortly after taking delivery of it in 2018. One is simply clear tape over the display to protect it from scratches. The second is applying three tiny drops of glue which create tactile points on the keypad for nighttime operation.

Thanks for sharing these, Adid!

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