Tag Archives: TomL

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):

Summary

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!

TomL

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Reminder: Comb Stereo Broadcast via Radio Gum Tree–June 18, 2021

A quick reminder that the rebroadcast of Radio Gum Tree Episode 2 will take place tomorrow: June 18, 2021 at 9:45 EDT (or June 19, 2021 at 01:45 UTC) on on 5850 kHz. You can find the program notes for these Test broadcasts at this web site address: www.radiogumtree.com/?p=54

Many thanks for putting together this Comb Stereo series, TomL!

For more information, check out TomL’s initial announcement.

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More Comb Stereo Broadcasts via Radio Gum Tree June 18 & 25, 2021

Many thanks to SWLing Post contributor, TomL, who notes:

Episode 2 of Radio Gum Tree will be rebroadcast this coming Friday night June 18, 2021 at 9:45 EDT on on 5850 kHz in case anyone missed it. Episode 3 should be on June 25.

You can find the program notes for these Test broadcasts at this web site address. I will not be archiving the broadcast on the internet due to music copyright concerns.

www.radiogumtree.com/?p=54

Many thanks for putting together this Comb Stereo series, TomL!

For more information, check out TomL’s initial announcement.

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Four weeks of Comb Stereo tests via WRMI!

Many thanks to SWLing Post contributor, TomL, who has put together a four week series of Comb Stereo tests that will be aired on WRMI. Here’s the full announcement:

Starting this Saturday June 5 at 01:45-02:00 UTC (Friday 9:45pm EDT), I will be conducting a four-week series of tests using Comb Stereo. The broadcast will be aired on WRMI on 5850 kHz and will only be 15 minutes long. It will feature two minutes of “CNN” news by a computerized voice (sorry, I am doing this on-the-cheap!). Then, what follows is about 12.5 minutes of music encoded with Comb Stereo.

For you, the listener, to hear the Comb Stereo, you will need to record the broadcast to your digital recorder or SDR software and then play it back through your Windows PC using the instructions at the bottom of this announcement. I welcome feedback regarding such things as, 1 – I heard the broadcast and recorded it, 2 – I tried to setup my Windows PC but could not get the CSDecoder and Virtual Audio Cable to work, 3 – I got those things to work and opinions about what the stereo sounded like.

To repeat, you will not hear stereo unless you send your recorded audio file through the CSDecoder.

Do not expect FM Broadcast quality since Comb Stereo is a rudimentary form of creating two-channel sound. For instance, you may hear the stereo separation waiver a bit, or the sound stage image may wander, or a slight hollow sound at times. Sure, OK, but this is also a chance to hear stereo from a shortwave broadcast. So let me know your thoughts by sending feedback to info@radiogumtree.com and I will tally up the results and post the findings here on the SWLing Post Blog.

Many thanks to Daz and Roseanna at Radio Northern Europe International for making the Comb Stereo available and to WRMI for the use of their transmitter.

TomL

P.S., please don’t mind the look of the web site at www.radiogumtree.com, it is still under repair and the web hosting company has to fix something or I end up replacing them!

RadioGumTree.com is a personal, eclectic look at Radio, Music, the Universe, and Beyond. For feedback or questions, please write to info@radiogumtree.com. For program notes, please visit the Blog section of radiogumtree.com for more details.

The broadcast itself will not be archived on my web site due to copyright concerns.

For Radio episodes that are encoded in Comb Stereo, go to this web site for instructions on how to install the Comb Stereo decoder: https://rnei.org/stereo/

For an example of a guided user install of CSdecoder and the needed Virtual Audio Cable on your Windows PC, go to this blog post: https://swling.com/blog/2021/05/guest-post-listening-to-comb-stereo-on-shortwave/

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Guest Post: Listening to Comb Stereo on Shortwave

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


Comb Stereo on Shortwave

by TomL

Comb Stereo is an old technique being implemented over shortwave by the main sound engineer (Daz) at Radio Northern Europe International (RNEI).  It ONLY works on Comb Stereo broadcasts which currently are RNEI, This Is A Music Show (WRMI), and one of the KBC broadcasts.  It works in real-time or for SDR recorded files, too.  It does NOT need a special HD/DAB+ radio.

A number of pluses for Comb Stereo on shortwave compared to digital:

“The bandwidth is the same as mono – So the SNR should be about the same as mono.

Selective fading doesn’t affect the comb bands much, so the balance is largely unaffected by selective fading notches.

The Comb Stereo artifacts are much like typical music effects of echo, chorus, fast reverb or room reflections.”

You can read about it here on Daz’ web site: homepages.ihug.com.au/~daz2002/tech/CombStereo/

You can also read Roseanna’s comment on the SLWing.com blog post: https://swling.com/blog/2020/04/rnei-now-broadcasting-in-comb-stereo/

An enhanced version is broadcast on WRMI for the RNEI time slot on Thursday morning (01:00 UTC) on 5850 kHz.  It sounds very good and is not a pseudo-stereo like in my previous article, Music on Shortwave.  For one thing, pseudo stereo is not real two-channel encoding and shifts vocals to one side, depending on which channels are chosen for high and low filters, which might get annoying after awhile.  What seems amazing to me is that I have been able apply some minor noise reduction in Audacity and the Comb Stereo stays perfectly intact.  It also still works after converting the WAV file to MP3 and sounds much like a regular FM broadcast.  Furthermore, it does not require a special patented transmitter or receiver chip.  It is compatible with regular mono transmitters.

If you want to try it, go to the RNEI web site; download and install the two files listed (VB Audio Cable and CombStereo Pedalboard x64):

https://rnei.org/stereo/

It is slightly tricky to setup and use or you will not hear anything (most Windows systems default to 48000 Hz these days).  Right-click on the lower-right taskbar Sounds settings.  Make sure to setup Properties – Advanced in both the VB-Audio Virtual Cable (Playback and Recording) and your output speakers (Playback) to 24-bit 44100 Hz processing.

Now run the app Pedalboard BAT file which corresponds to the broadcast you recorded (in this example “Start Comb Stereo for WRMI.bat”).  Set the Options – Audio Settings:

Since the VB-Audio Virtual Cable takes over your volume output, adjust the volume of your Speakers in Windows’ Sounds – Levels (or you can adjust the volume in the sound player you are using, too):

Play the mono WAV or MP3 file and you should be hearing stereo!

When you are done, close Pedalboard2 and then disable the VB-Audio Virtual Cable for Playback and Recording to get your Sounds back to normal:

I cannot demonstrate what it sounds like unless you have the VB-Audio Virtual Cable and the Comb Stereo app setup and working properly.  Here are snippets from recent RNEI broadcasts captured by my noisy porch antenna:

 

Here are links to the artists’ YouTube videos for comparison:

Kari Rueslåtten – https://www.youtube.com/watch?v=SFN4O3YrUG4

Ani Glass – https://www.youtube.com/watch?v=T63QS9enT-A

What is nice is that I can create a space-saving MP3 mono file and this setup will decode the stereo when run from the computer (sounds really nice on a stereo system with a subwoofer).  Unlike digital, this analog-friendly stereo seems mostly immune to fading, has a minimum of digital artifacts, and will not go silent and “drop out” like digital does for long, annoying periods of time.  It is not perfect stereo but audio players with features like Stereo Widener or Windows Sonic for Headphones can overcome some limitations.  Perhaps content providers should consider Comb Stereo for all their shortwave radio shows since it is perfectly compatible with mono AM transmissions!

Enjoying the Music,

TomL

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TomL’s guide to making and optimizing shortwave radio SDR music recordings

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

by TomL

I recently became curious about the seasonal music updates posted by Alan Roe.  It is a nicely detailed list of musical offerings to be heard.  Kudos to Alan who has spent the time and effort to make it much easier to see at a glance what might be on the airwaves in an easy to read tabular format.  I do not know of any other listing specifically for shortwave music in any publication or web site.  I especially like the way it lists everything in UTC time since I might want to look for certain time slots to record.  For some listings, I would need to go outdoors away from noise to listen to certain broadcasts.  Current web page is here:  https://swling.com/blog/resources/alan-roes-guide-to-music-on-shortwave/ .

As a side note, I have also found a lot of music embedded in the middle of broadcasts that are unannounced, unattributed, and not part of a regular feature program.  That can be a treasure trove of local music you might not be able to find anywhere on the internet.  It can be worth recording a spectrum of frequencies using the capabilities of the SDR and then quickly combing through the broadcasts at two-minute intervals (most songs are three minutes or longer).  In maybe ten minutes, I will have at least identified all of the listenable music that may or may not be worth saving to a separate file.

Whether at home or outdoors, I have wanted to try to record shortwave broadcasts of music using my AirSpy HF+ but never getting around to it until now.  There is a certain learning curve to dealing with music compared to just a news summary or editorial.  I found myself wishing I could improve the fidelity of what I was hearing.  From static crashes, bad power line noise, fading signals, and adjacent channel interference, it can be quite difficult to get the full appreciation from the musical impact.

I am starting to monitor the stronger shortwave stations like WRMI, Radio Romania International, Radio Nacional do Amazonia, etc.  These type of stations can be received in a strong enough manner to get good quality recordings (at least according to shortwave listening experience).  I am also finding that I appreciate much more than before the effort that these broadcasters put into creating content/commentary to go along with the music and little pieces of background info about the music or the artist.  I have also noticed how exact some broadcasters are in timing the music into the limited time slots.  For instance, Radio Romania International tries to offer one Contemporary piece of music exactly at 14 minutes, Traditional music exactly at 30 minutes, and a Folk tune exactly at 52 minutes into the program (whether in English, French, or Spanish), with nice fade-outs if the music goes too long.

One thing I ran into was to bother checking my hearing range.  If someone has impaired hearing, it does not make much sense to create files that have a lot of sound out of one’s hearing range.  I found this YouTube video (among a bunch of others) and listened to the frequency sweep using my Beyerdynamic DT-990 Pro headphones (audiophile/studio type headphones).   My hearing is approximately from 29 Hz through 14400 Hz.  Of course, the extremes fall off drastically, and as with most people, my hearing is most sensitive in the 2000 through 6000 Hz range.

Recording Workflow

Let’s assume that you already know how to record IQ files using your SDR software and can play them back (In the example below, I recorded the whole 49 meter band outputting a series of 1GB WAV files).  Then, when playing back to record to individual files, I have to choose the filters and noise reduction I want.  This gets subjective.  If I do not want to keep huge numbers of Terabytes of WAV files over time, I will want to record to individual WAV files and then delete the much larger spectrum recording.  You might tell me to just record to MP3 or WMA files because there is that option in the SDR software.  We will get into that as we go along.  For the time being,  I do not want to keep buying Terabytes of hard drives to hold onto the original spectrum recordings.

After lots of trial and error, I came up with this workflow:

  1. Record the meter band spectrum of interest using the SDR software.
  2. Record individual snippets of each broadcast in that spectrum to new individual WAV files.  This includes not lopping-off any announcer notes about the music I want to retain.  I also have to choose the bandwidth filter and any noise reduction options in the software.  Because I am not keeping Terabytes of info, this is a permanent decision.
  3. Take an individual recording and apply more processing to it.
  4. Convert the processed  recording to any number of final output formats for further consumption and/or sharing.
  5. Repeat steps 3 & 4 to take care of all the individual WAV files.

Step 4 allows me to create whatever file format I might need it to be: WAV, MP3, WMA, or even use it as background sound to a video if I so choose.  There are also different ways to create some of these files with different quality settings depending on what is needed.  I have chosen to listen to the individual WAV files for personal consumption but there may come a time to create high quality MP3 files and transfer those to a portable player I can take anywhere (or share with anyone).

The example below is a snippet from the latest Radio Northern Europe International broadcast on WRMI.  WRMI has some decent equipment and I like how clean and wide is the bandwidth of many of the music programs.  This is captured on the AirSpy HF+ using SDR Console V.3 with a user-defined 12kHz filter (11kHz also seemed somewhat similar sounding).

If you click on the ellipses, you can Copy an existing filter, type in a new title and change the bandwidth.  I also played around with the different Windowing types and found that I like the Blackman-Harris (7) type best for music and the Hann type for smooth speech rendering (the Kaiser-Bessel types can also have more “punch” for voice recordings).  Click OK TWICE to save the changes.

I also use Slow AGC and the SAM (Sync with both sidebands) to reduce the chance of distortion as the signal fades.  I found that trying to use only one sideband while in Sync mode would make the reception open to loss of Sync with the musical notes warbling and varying all over the place!

Noise Reduction

The SDR Console software has a number of noise reduction choices.   I tried NR1 through 4 and found the smoothest response to music to be NR1 with no more than 3 dB reduction.  More than this seemed to muffle the musical notes, especially acoustic instruments and higher pitched voices. Part of the problem has to do with trying to preserve the crispness of the articulation of the sound and combating shortwave noise at the same time.  At this time, I have chosen NOT to use any NR mode.  More about noise reduction below.

Generic MP3 sounds really bland to my ears, so creating higher quality files will be important to me.  I have been using Audacity which can apply processing and special effects to WAV files and export to any number of file formats.  WAV files are a wonderful thing.  It is a “lossless” file format which means that every single “bit” of computer input is captured and preserved in the file depending on the resolution of the recording device.  This allows one to create any number of those “lossy” output formats or even another WAV file with special effects added.  You can get it here:

https://www.audacityteam.org

One special effect is listed as “Noise Reduction”.  I literally stumbled upon it while reading something else about Audacity (manual link).  Here is how I use it for a shortwave broadcast.  Open the original spectrum recording (in this example the 49m band).  Tune about 25kHz away from the broadcast that was just recorded.  Remember, my hearing extends at least to 14.4k plus there is still the pesky issue of sideband splatter of bandwidth filters.  The old time ceramic and mechanical filters use to spec something called “skirt selectivity” -60db or more down from the center frequency.  This is still an issue with DSP filters even though they SAY they are measured down to -140dB; I can still hear a raspy sideband splatter from strong stations!

Find the same time frame that you recorded the broadcast and make sure it is the same bandwidth filter, AGC, and any noise reduction used.  Now record one minute of empty noise to a WAV file.  Fortunately on 5850 kHz, WRMI has no adjacent interference.

Now in Audacity, open the noise sample and listen for a 5 to 10 second space to copy that is relatively uniform in noise.  We don’t want much beyond that and we don’t really want noise spikes.  The object is to reduce background noise. In this case, I chose Start 39 seconds and End 44 seconds.  Choose Edit – Copy (or CTRL-C).

Choose File Open and find the broadcast WAV file in question.  Now click on the end-of-file arrow or manually type in the Audio Position (in this example 1 minute 15 seconds).  Now Paste (or CTRL-V) the 5 seconds of noise to the end of the broadcast file.  Now, while the pasted noise is still highlighted, go immediately to Effect – Noise Reduction and choose the button Get Noise Profile.  It will blink quickly to read the highlighted 5 seconds of noise and disappear.

Now select all with CTRL-A and the whole file is selected.  Go immediately to Effect – Noise Reduction and choose the parameters in “Step 2”.  Through some trial and error, I found 3db reduction has a noticeable effect without compromising the music.  I have used up to 5 db for some music recorded with narrower bandwidths.  Higher levels of noise reduction seemed to create an artificial flatness that was disturbing to me.  I also use a Sensitivity of 0.50 and Frequency smoothing of 0.  You can choose the Preview button while the Residue circle is checked to actually hear the noise being eliminated.  Press OK in order to process the noise reduction.  You should now see the waveform change slightly as the noise is filtered.  In a nutshell, I find this to be a better noise reduction than using 3db of NR1 in the SDR Console software.  Don’t forget to snip off those 5 seconds of noise before saving the file.

Pseudo Stereo

The SDR Console software has an Option for Pseudo Stereo (for playback only) and it can be useful for Amateur Radio receiving, especially in noisy band conditions when one is straining to hear the other person’s call sign and location.  There is a way in Audacity to add a fake kind of stereo effect to mono audio files.  I found a useful YouTube video that explained it very clearly.

I  do everything listed there except for the Reverb effect.  I find that too fake for my tastes.

I found the added 10ms of Delay on the right channel to be a little too much, so I use 9ms.

My High Pass filter settings are 80 Hz and 24dB/octave.  This is based partly on my hearing preferences as well as established industry standards.  There was a lot of science and audio engineering that went into creating the THX home theater crossover standard.  There is also science that says that anything below 200 Hz is omnidirectional.  The suggested 48dB/octave is too steep in my opinion.

My Low Pass filter settings are more squishy.  The YouTube video suggests 8000 Hz and 6dB/octave.  I feel that is too gentle a rolloff into the upper midrange.  I use 9000 Hz at 12dB/octave for very strong, high quality shortwave broadcasters like WRMI. For more constrained quality broadcasts, like due to limited bandwidth (Cuban broadcasters) or adjacent channel interference, I will decrease down to 8000 or 7000 Hz but still use a 12dB/octave rolloff.  This is subjective but it also means I am making a conscious decision to add that processing to the recording for future listening.

MP3 Quality

Typical MP3 files are a Constant Bit Rate of 128k.  Some interviews and voice-only podcasts are only 64k.  This is adequate but for recording detail in the music I prefer higher quality settings.  Frankly, with these days of 4G cell phone service and Unlimited Data minutes on cell phone plans, there is NO good reason to limit MP3 files to just adequate quality levels.  The typical MP3 file sounds limited in frequency range (muffled sounding) to me and very lacking in dynamic range (narrow amplitude).  This would include limits on stereo files which are about twice the file size of mono files.

I have tried creating WMA files and I actually like the quality a little better than high quality MP3 files.  The WMA files seem slightly more “airy” and defined to my ears.  But it is a proprietary format from Microsoft and not all web sites or devices will easily play them.  They are also a fixed standard and one cannot easily change the quality settings if forced to use a lower quality rendering.

There are many web sites talking about MP3 files, but I found this blog post helpful in summarizing in one paragraph the higher quality settings for a nice MP3 recording using VBR-ABR mode.

https://technical-tips.com/blog/software/mp3-encoding-right–1334

One Minute Samples

So finally for my examples.  Since most web sites still prefer MP3 files, I have created these using that  blog post’s suggestions.  Typically this is Min bitrate=32, Max bitrate=224, VBR quality=9, and Quality=High (Q=2).  Let’s see if you can hear the differences.  It would be much easier to hear if we were listening to WAV files, but those are way too big to post on this web site!  The software I used is Xmedia Recode and I find it easy to use.

https://www.majorgeeks.com/files/details/xmedia_recode.html


Example 1: No noise reduction in SDR Console, no further processing


Example 2: 3dB of NR1 in SDR Console, no further processing


Example 3: No noise reduction in SDR Console, Audacity Noise Reduction of 3dB


Example 4: No noise reduction in SDR Console, Audacity Noise Reduction applied 3 times (3db,0.33+2db,0.50+1db,0.80)


Example 5: No noise reduction in SDR Console, Audacity Noise Reduction applied 3 times (3db,0.33+2db,0.50+1db,0.80), Pseudo Stereo added


I would love to hear comments since I am new to recording music on shortwave and any further tips/tricks would be fun to learn.  Enjoy the music!

TomL

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Guest Post: Indoor Noise and Ferrites, Part1

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


Indoor Noise and Ferrites, Part 1

by TomL

My magnet wire loop antenna on the porch reminded me to revisit aspects about my noisy Condo that I still needed to understand.  Some RF noise I could control if I could find the right kind of information that is understandable to a non-engineer like me.  There is a lot written about the general problem of noise and radio listening, for instance this ARRL article with web links to research – www.arrl.org/radio-frequency-interference-rfi, but I needed to get more specific about my particular environment.

I had tried some common clamp-on TDK ferrites I had obtained from eBay a long time ago but they only seemed to work a little bit.  I have since found out these are probably the ones which are widely used on home stereo system connections used to reduce noise on those systems.  There must be a better way.

The more I researched topics, like a portable “Loop on Ground” antenna, or, using RF chokes on the magnet wire loop, it dawned on my feeble, misguided brain that I was wrongly thinking about how to use ferrite material.  For one thing, the material used to suppress RF noise is made with a certain “mix” of elements, like Manganese-Zinc, that electrically “resists” a specified frequency range.  Fair-Rite has a useful Material Data Sheets web page which lists the Types of ferrite material.  For dealing with noise (at the Source causing the problem), I needed to use the right kind of “Suppression” materials and proper placement.  So, it (partly) made sense why the TDK snap-on ferrites might not fully work to reduce certain noise coming from my computer screens, LED lights, USB devices, and cheap Chinese-made power adapters.

A very good  paper is by Jim Brown (K9YC) of Audio Systems Group entitled, “Understanding How Ferrites Can Prevent and Eliminate RF Interference to Audio Systems [PDF]”.  There is a longer paper speaking directly to Amateur Radio folks, but the Audio version is simpler and it uses some of the same  graphs and ideas.  I was drawn to the very detailed Impedance measurements of many different “Types” of ferrite material used for different noise mitigation.  I remember the traumatic pain of my college experience trying mightily to understand the Van Vlack Materials Science text book to no avail.  But Jim’s paper reminded me of the importance of using the correct type of ferrite material and in an optimal way that reacts favorably in the target frequency range to solve a particular noise problem.  So, what are my problem areas?

Shortwave Noise

Loop antennas have been what I have experimented with the most.  They do not pick up as much man-made noise (QRM) and they have a space saving footprint.  Fortunately, there is a wooden porch where these things have been tried.  I had successfully built a broadband amplified “ferrite sleeve loop” (FSL) in the past.  It was useful for a while but it fell into disrepair and also the Condo building has steadily increased in noise output.  The amplifier was just amplifying the noise after a while.  I also tried phasing two antennas but found the ever increasing noise cloud was coming from all directions and I could not null it out.  I even tried a “mini-whip” from eBay but that just produced a wall of noise.

I recently tested AirSpy’s YouLoop written about before, and the results were good.  However, it seemed obvious to me that it was too small as a passive loop to capture shortwave signals strongly enough without resorting to another amplifier attached at the antenna and would not improve the signal/noise ratio.  My current solution is a unamplified stealth magnet wire loop about 32 feet in circumference.  In that article, I mention things like common mode RF chokes at both ends of the antenna connection, horizontal polarization, and basically accepting that only the stronger shortwave signals will be received in a predictable manner.  I think for now, this is about all I can do for shortwave and mediumwave noise, as far as my own Condo-generated noise. Neighborhood noise is a different topic.

VHF Noise

I then started to isolate which devices caused which kind of noise when listening to my outside amplified antennas for FM/VHF and UHF-TV transmissions.  Many consumer Power adapters make a lot of noise from VLF up into UHF ranges.  One thing I did right was to try a 10 pack of these little miracle “Wall Wart” toroids from Palomar Engineers.  One by one, I put one of these small toroids (19mm inside diameter) on my home AC adapters as shown in the pictures, and the noises started disappearing.  It does not explicitly say, but I believe it is Type 75 material which suppresses the noise generating AC adapter (at very low frequencies) when wrapped 8 – 12 times.

Most egregious of these was my CCrane FM2 transmitter.  A strangled warbling sound kept emanating from the monitor closest to my laptop. Installing ferrites on the laptop and back of the monitor were not working.  I moved the FM Transmitter and noticed a reduction in noise.  So, I put one of these little toroids on the power input of the device and the noise disappeared.  Apparently, it was picking up noise from the monitor (as well as its own power adapter) and rebroadcasting it to all my other radios!  The strangled warbler is no more, I choked it (HaHa, sick bird joke).

While looking for the monitor noise, I put the eBay TDK ferrites on all the USB ports and HDMI ports.  This has helped greatly on VHF and confirms my suspicion that these cheap TDK ferrites are indeed a common type of ferrite material.  Some informative graphs can be seen in Jim Brown’s Audio paper mentioned before.  One example might be Figure 22, which shows the #61 Series Resistance which peaks around 100 MHz when using a toroid with three “Turns”.  More confused, I could not find a definition of a “Turn”.  Eventually, in his longer paper to Amateur Radio operators, he defines it, “…is one more than the number of turns external to the cores”.  Somewhere else he describes using many single snap-on ferrites being electrically equal to just one toroidal ferrite with multiple Turns.  And interestingly, more Turns shifts the peak impedance substantially lower in frequency.  So, using the graphs he supplies, one can target a noisy frequency range to try to suppress.

I then put 6 of the TDK ferrites on the VHF input to the AirSpy HF+.  Some FM grunge was reduced and was thankful for that.  The rest of the background noise truly seems to be coming from the outside picked up by the amplified antenna.

Also, I juggled a couple of the amplifiers around and now have separate VHF/FM and UHF/TV amplifiers which cleaned up the FM reception a little bit more – https://www.youtube.com/watch?v=zkDsy95et2w .

UHF TV Quality

On a whim, I put the balance of the TDK ferrites on the FM/TV splitter input cable, 10 in all.  The FM reception did not improve but the Over The Air UHF TV reception Quality improved noticeably.  My weakest TV station now has a stable Signal level and the Quality is pegged at 100%.  This is a nice surprise since it means that now all local TV stations on UHF will come in cleanly without dropouts and I can view all digital subchannels.  I was even able to rescan and added two more low-power stations never seen before. ?

LED lights

I have common LED lights hanging over a number of fish tanks and some grow lights over an indoor plant box and can hear this noise on upper shortwave and higher radio bands.  In a future article, I will explore RF noise from lights as its own special topic. For instance, why do some LED lights generate RFI and how to know before buying (I am using BR30 spot bulbs from name brands)?  Also, there is a new kind of LED “filament” light out now that uses much smaller LED’s on both sides of an aluminum strip, greatly reducing electromagnetic noise output (or do they??).  More questions than answers.

I will explore creating my own customized AC power cord attached to the AC power strips of the LED lights.  I will need to test this for safety and efficacy, so I will want to take some time to do this right.  The hope is that, using Jim’s info, I will be able to create a broad spectrum RFI suppression AC power cord and cost less than $30 each cord.  We’ll see.

Finally, I will look at “stacked” toroids using different mixes of ferrite Types, creating a custom RF suppression better than using just one Type of ferrite material, using AC cords as the main examples. For instance, the best set of graphs in Jim’s paper, in my opinion, are Figures 21 and 24 compared to each other.  Something I did not know before is that one can not only use multiple turns on a single toroid to get a lower, peaked frequency response, but also stack multiple toroids of the same Type to get a smoother frequency response.  Then on top of this, combine that set with other Types to create a customized frequency response curve.

Radios are quieter now.  Those pesky grow lights are still a problem as well as the upstairs neighbor’s lights which seem to be on a timer, making FM reception noisy again after 5pm!

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