Tag Archives: Software Defined Radio

Chris tracks down sources of radio noise

Many thanks to SWLing Post contributor, Chris Smolinski, who shares this guest post from his blog, RadioHobbyist.org:

Yet Another !&*%$! Noise Source

The past few days, I have noticed higher than usual noise levels, generally on the lower frequencies, and particularly on the longwave band, including the 285-325 kHz DGPS band, where I run nightly SDR recordings, to later process the data and decode and detect DX DGPS stations using my Amalgamated DGPS app.

Thinking back to what new electronics devices have been added to the house, two came to mind, a new cable modem, and a new ethernet switch. The switch is up here in the shack, so it seemed to be a likely candidate. The switch is a D-Link DES-1008E 8-Port 10/100 Unmanaged Desktop Switch. It uses a mini USB port for power, using either the included AC adapter, or power from a USB port. When I installed it, I decided to not use the AC adapter, but rather a USB port on my UPS, figuring it was better to not add yet another potentially noisy switching power supply to the mix.

The test was easy, I just unplugged the power to the switch. Sure enough, the noise vanished. Great, the switch is a RFI generator. Or is it? As another test, I plugged it into a port on a USB hub. No noise. Hmm… so it seems that the noise is indeed from the USB port on the UPS. I did not notice any increase in the noise floor when I got the UPS a few months ago, but It’s something I should look into again, just to be sure. The UPS is a CyberPower CP1350PFCLCD.

Here’s a waterfall from the SDR, showing the DGPS band, 280-330 kHz. You can see where I changed the power to the switch from the UPS USB port to the USB hub, the bottom part of the waterfall is when the switch was still powered by the UPS (click to enlarge it):

I still have a noise source just above 305 kHz to hunt down.

Update

I decided to see what I could do to improve things, and reduce the noise floor.

Here is the baseline, after no longer powering the switch from the UPS:

First, I relocated the AFE822 away from the computer and rats nest of assorted cables behind it, powered from an HTC USB charger:

The squiggly noise around 305 kHz vanished!

I then switched to an Apple USB charger / power supply, as their products tend to be a bit better made:

Another improvement, the overall noise floor is a bit less now.

But can we do better? I then switched to an older USB hub for power to the AFE822, that I thought might be better filtered:

I then changed to a linear supply plugged directly into the AFE822. I don’t notice any obvious improvement? Maybe it even looks like a little more noise? Difficult to tell. You can see a DGPS station popped up on 304 kHz while I was switching things around, between the last two tests, it was likely Mequon, WI.

Thank you for sharing this, Chris! I find a wideband spectrum/waterfall to be such a useful tool for tracking down sources of noise. Not only can you “see” the noise, but you can measure its bandwidth and identify what portions of the dial it affects.

Follow Chris at RadioHobbyist.org.

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Oxford Shortwave Log: transatlantic MW DX catches with 200 metre Beverage – part 2

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Hi there, here is the second set of reception videos for my transatlantic MW DX catches using the 200 metre Beverage antenna. Most of the signals originate from the United States and Canada, however, there is also a catch from Mexico – XERF La Ponderosa – which is a personal first and another from Bogotá, Colombia – Verdad Radio. I hope you enjoy them. Please do not hesitate to contact me if you would like further details regarding the Beverage design and/or construction. in the meantime, thank you for watching/listening and I wish you all great DX!

Clint Gouveia is the author of this post and a regular contributor to the SWLing Post. Clint actively publishes videos of his shortwave radio excursions on his YouTube channel: Oxford Shortwave Log. Clint is based in Oxfordshire, England.

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Oxford Shortwave Log: transatlantic MW DX catches with 200 metre Beverage – part 1

New Beta version of SdrDx allows for AFEDRI AFE822 two input phasing

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Many thanks to SWLing Post contributor, David Goren, who shares this tip from Chris Smolinski at Black Cat Systems:

If you have an AFE822 Dual Channel SDR, and a Mac, run, do not walk, to the SdrDx website, and download a copy of the beta version. It now lets you phase the two inputs, much like using an external phaser such as the MFJ-1026. Great for nulling out another station, or noise/QRM. I have some descriptions of how to do this, along with some recordings, and the relevant links, in this HFU post. I believe a Windows version will be out shortly.

Chris’ post on the HF Underground goes into more detail and includes audio samples:

A few months ago, I picked up an AFE822 dual channel SDR, one of the reasons was to experiment with using it as a phaser for MW DXing. It was a bit of a daunting task, having to essentially write an entire SDR app. I then realized I could instead write a “black box” app that sat between the SDR and the SDR app, which would take the pair of I/Q channels from the SDR, and adjust their relative amplitude and phase, and combine them into a single I/Q channel, and send that on to the SDR app. I played around a bit with that, and was quite impressed with the results. I passed on the general idea to the author of SdrDx, who has implemented it in a beta of the app, which is nice because now it is all self contained, rather than having to use my kludgy app in the middle Grin

There’s gain adjustments for each RF input, as well as a phase control, an invert switch to flip the phase 180 degrees, and switches to zero either of the RF inputs, useful when first roughly setting up the gains.

I am quite impressed with how well it is working. As an example, here is a recording of 1680 AM from earlier this morning. I toggled the invert on the phase control a few times, so you can hear reception flip between the two dominant stations on that frequency.

This is going to be really nice for MW DXing. SdrDx is for both Windows and the Mac. If you’ve been considering getting an SDR, this feature alone in SdrDx is reason enough to get an AFEDRI AFE822. If you do buy one, be sure to let Alex of AFEDRI know the reason is because of SdrDx, we need to support the authors of third party SDR apps we use, and let the hardware manufacturers know how important they are.

The URL for the SdrDx page is http://fyngyrz.com/?p=915

The download link for the beta (Mac only right now, once this is confirmed to be working well, I am sure he will update the Windows version) is http://fyngyrz.com/beta.zip

Some more tests, this time on some local Graveyard channels.

1230, getting rid of WRBS:

1240, getting rid of WJEJ:

How to use the phasing adjustment with SdrDx, an AFE822 SDR, and your Mac.

Download the Mac beta (Windows version coming soon) of SdrDx: http://fyngyrz.com/beta.zip
If you have not used SdrDx before or recently, first download the stable version, and run that: http://fyngyrz.com/SdrDx-AA7AS-Light.zip
SdrDx page: http://fyngyrz.com/?p=915

Familiarize yourself with SdrDx if you have not used it before. You need two antennas of course, one plugged into each of the AFE822 inputs.

To use phasing:

Click on the PHA button, turn on Dial Channel Phasing Mode. Click OK to close the window.

Click the Run button to get the SDR into Run mode. Tune in whatever MW frequency you want to use. Ideally one with two stations you can hear at the same time. Graveyard channels are great for this. Be sure to put the SDR center frequency offset from that. For example if you want to null 1300 AM, make the center frequency 1305 or something like that. Or the I/Q imbalance will cause problems.

Click the PHA button to open the phasing window again. You want to keep it open now.

Make sure the Invert checkbox is off, the Both Channels On radio button is on. Set the Phase slider to the middle, both Gains to zero, far left.

Adjust the first Gain slider to bring the signal level up to a reasonable level. S9. S9+10, whatever you want. Make a note of it.

Click Chan A Muted

Now adjust the second Gain slider to bring the signal level up to where it was before with the first RF input. The goal here is to make the signal levels about the same, so you can begin the process of nulling out one of the stations, with some chance of it working.

Click Both Channels On now, so you have both RF inputs active.

Adjust the Phase control, until you notice a dip in the signal strength. Try to get it centered in the dip as close as possible.

Then adjust one of the gain sliders, I usually use the one with the largest value to make things easier, to increase the dip in the signal strength.

Then go back to the Phase control, and try to increase the dip. You may now notice the dominant station starting to be nulled, by listening to it.

Then, like washing your hair, lather, rinse, repeat. You have to iterate back and forth many many times. Eventually, if your two antennas produce different enough signals for the two stations, you will be able to null it out. There are cases where you cannot null out one station, because the antennas produce the same signal for both of them. So nulling out one also nulls out the other. But this is rare.

You can click in the invert checkbox, and reception should switch to the other station. Listen to some of my recordings to hear this in action. You are changing the phase by 180 degrees when you do this.

Most impressive, Chris! Wow–I think this feature alone could make the AFEDRI AFE822 an invaluable tool for the mediumwave DXer. Those audio samples are amazing!

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Mark’s Global Spectrum Project MK2

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Many thanks to SWLing Post contributor, Mark Fahey, who shares the following:

It’s been a fun weekend getting the first two remote modules for the Spectrum Project MK2 together. These modules tune into and then digitally preserve broadcasted human communication; music, discussion, culture for future generations to study and ponder.

This initial version of the hardware provides 0-30MHz with four (simultaneous) independently configured receivers that are controlled remotely from anywhere on the planet. The first of the modules will be installed near Vladivostok in Russia’s far east and the second is planned to go to one of the “stans” in Central Asia, most likely Kazakhstan.

The hardware includes a KiwiSDR 0-30MHz SDR 4 channel receiver AM LSB USB CW FM plus GPS for precision timing and location information. A BeagleBone Green is the CPU and the compact 100KHz-30MHz active antennas we are using are precision built by RA0SMS in Irkutsk, Siberia, Russia.

(Note to fellow SDR geeks – the WinRadio Excalibur running on the iMac [above] is not part of the remote system – it just happens to live on my assembly bench).

Remote Module #1 prior to sealing.

This first generation is built to connect to a wired internet connection and power supply. The hardware includes a KiwiSDR 0-30MHz SDR 4 channel receiver AM LSB USB CW FM plus GPS for precision timing and location information. A BeagleBone Green is the CPU and the compact 100KHz-30MHz active antennas we are using are precision built by RA0SMS in Irkutsk, Siberia.

Remote Module #3 and later will support solar power and a 4G/ LTE connection so the devices can be located anywhere on the planet that has reasonable cell phone coverage.

Remote Module #2

This is Remote Module #2 sealed and ready for connection to a network and power supply. The hardware includes a KiwiSDR 0-30MHz SDR 4 channel receiver AM LSB USB CW FM plus GPS for precision timing and location information. A BeagleBone Green is the CPU and the compact 100KHz-30MHz active antennas we are using are precision built by RA0SMS in Irkutsk, Siberia.

Remote Module #3 and later will support solar power and a 4G/ LTE connection so the devices can be located anywhere on the planet that has reasonable cell phone coverage.

Don’t forget you can tune into the prototype system now up and running near Sydney Australia. Point your browser to http://mediaexplorer.ddns.net:8073

This is simply amazing, Mark. I can’t wait to try out the receivers in your Spectrum Project MK2 once they’ve been deployed and implemented. We’ve talked about this concept before, but what I love about Mark is he simply pulls the trigger and makes it happen as soon as technology has made it possible to implement.

Mark: please keep us posted with your updates!

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HDSDR publishes a new Beta release

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Many thanks to SWLing Post contributor Mike Ladd who notes that HDSDR has just published a new 2.75 Beta release.

Mike included the screenshot (above) which includes the following release notes:

Click here for the HDSDR website and to download the new Beta release.

Thanks for the tip, Mike!

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Oxford Shortwave Log 200 metre Beverage antenna: further MW and SW reception videos

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Hi there, further to my previous post regarding the initial testing of the Medium Wave Circle-design 200 metre Beverage antenna at the woods in Oxford, UK, I am pleased to share further reception videos for both the medium wave and shortwave bands. For medium wave, I operated the FDM DUO via a laptop and the FDN-SW2 software, recorded the entire band at the top of the hour and retrospectiively analysed the signals. For shortwave I utillised the FDM DUO as a standalone receiver, routing the audio via the excellent Bose Soundlink Mini 2 speaker.

As a quick recap, the antenna was terminated at the ‘front end’ with a 650 Ohm resistor into a 1 metre-long, permanent copper earthing rod that I had previously driven into the ground, away from the route taken by the general public. The actual wire was orientated in a generally westerly direction, and thus nulling signals propagating from the east. At the receiver end, I utillised my self-built transformer, wound for a 50 Ohm input impedance (14 turns on the primary), thus making the entire set-up suitable for the Elad FDM DUO. It was quite a pain to set up, taking over an hour to deploy, however, the results were very promising. A scematic diagram follows below.

Links to the next group of reception videos follow:

The reception from VOCM St. Johns, Newfoundland & Labrador and WRCA Waltham, Massachusetts was unprecidented and another indication that the 200 metre Beverage configuration is demonstrating excellent SNR performance. Similarly, the reception of Radio Nacional Brazilia was an improvement on any signal I’d previously recorded with any receiver or antenna. Finally, the signal received from Radio Huanta 2000 – one of the more exotic stations on the Tropical Band and rarely heard in Europe – delivered discernible audio with this set-up, whereas previously I had only ever observed a carrier. All-in-all a very pleasing result, with more reception videos using this antenna set-up to follow in the coming weeks.

Right now I’m uploading SW and MW reception videos to my YouTube channel, recorded during my two week trip to Pará in Northern Brazil – it was really interesting to check out what can be heard on the radio in the middle of what is a very remote area of tropical rainforest. I hope you find the time to take a look. In the meantime, thank you for watching/ listening and I wish you all good DX.