She had your dark suit in greasy wash water all year

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An unidentified station was first noted at around 0330 UTC May 17, 2012, on 6990 kHz, sending three phrases over and over:

“She had your dark suit in greasy wash water all year. Don’t ask me to carry an oily rag like that. They used an aggressive policeman to flag thoughtless motorists”

I made this recording on 6990 kHz USB at 0041 UTC on May 17, 2012:

As of 2315 UTC on May 17, 2012, the station has moved to 6950 kHz USB, with the same repeated phrases.

Andrew Yoder reports hearing this same station on November 5, 2011 on 21450.7 kHz.

Some quick searches of the internet came up with something called the TIMIT Sentence Prompts.

According to Wikipedia:

TIMIT was designed to further acoustic-phonetic knowledge and automatic speech recognition systems. It was commissioned by DARPA and worked on by many sites, including Texas Instruments (TI) and Massachusetts Institute of Technology (MIT), hence the corpus’ name.

TIMIT consists of phrases of 630 speakers of of different sexes and eight major dialects of American English. The database is designed to assist in the development and testing of Automatic Speech Recognition systems.

There is an online listing of the phrases. According to that list, phrases 1, 2, and 437 are being sent.

Presumably someone is testing a system to perform automatic speech recognition on HF transmissions, and is conducting some real world test.

There is a thread of loggings of this station over at the HFUnderground Message Board.

I can only hope they don’t accidentally start transcribing 6925 kHz while Toynbee Radio is on the air. That could cause their computer to blow up, a la Kirk’s ability to make computers self destruct by confounding them with illogic on Star Trek.

Some online references:
The DARPA TIMIT Speech Database for MastersThesis
The DARPA TIMIT Acoustic-Phonetic Continuous Speech Corpus

UPDATE:
Still going at 1128 UTC on 6950 USB.

Construction of a Helical Antenna for SATCOM Listening

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Previously I wrote about the various kinds of transmissions you can heard on the 250 MHz SATCOM satellites. While you can pick these up with a standard scanner antenna, reception is much better with a directional antenna.

This page documents my project to construct a helical antenna for SATCOM listening, 240-270 MHz.

The antenna is based off the design found on this page, which has the specific dimensions and other technical details.

Here are the supplies:
Four 4 ft long strips of steel, four 5 ft long pieces of 1/2″ PVC pipe, one 5 ft long piece of 1 1/4″ PVC pipe for the boom, and window screening for the ground plane.

Here’s a close up of the flange and fitting for the PVC boom:

Here are the four steel strips arranged in the radial pattern:

Next I drilled four additional holes in the flange, so it could be screwed to the eight radials:

#10 hardware was used to attach it:

Here it is with the PVC boom attached, to see the overall size:

And now with the 20 supports for the tubing installed:

The tubing is 1/4 inch diameter:

Here it is with the 5 turns of 1/4″ diameter tubing:

The screening has been added to the reflector. It is sandwiched between the strips for support:

The [mostly] assembled helical antenna. The matching section is made from tin-plate and is cut to be a quarter of a turn, about 60mm wide. It’s soldered or bolted to the ground plane at the connector end, and supported by an adjustment screw at the other end. I’ve honestly not noticed much if any difference in the received signal, by fiddling with it. See http://www.uhf-satcom.com/uhf/uhfantenna.html for more details on the matching section.

Final assembly will be done outside, so everything is not tightly fastened yet:

Here it is outside, mounted on a SG-9120 motor. The motor uses the DiSEqC protocol for control, which is sent over standard coax cable. It is a standard in the satellite TV industry.

The motor is controlled by a Moteck digibox, which sits inside the shack:

Another view:

The angle of the motor is adjusted based on the latitude of the receiving site, so that as the motor turns the satellite tracks across the geostationary orbit.

Signal Levels of Radio True North’s May 14th Transmission on 6950 kHz

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The graph below shows the received signal levels of Radio True North, a pirate radio station from Canada, which transmitted on 6950 kHz on Mary 14, 2012. The signal faded in at around 0200 UTC, and the transmitter was switched off at 0702 UTC – that can plainly be seen on the chart:

You can also see that after the transmitter switched off, the received signal levels were about -85 dBm, that is the background noise level. At peak, the signal was about -75 dBm, just a hair under S9. The signal to noise ratio is the difference between the signal and noise levels, or 10 dB.

Here is a short recording taken at around 0516 UTC, so you can hear what this signal sounds like. Remember, it is around S9, but the signal to noise ratio, which is what really matters, is only 10 dB. We had rain/thunder storms all along the east coast during this time.

Signal to noise ratios were discussed an earlier post, coincidently enough called Signal To Noise Ratios. There’s some simulated SNR recordings there. The 10 dB example sounds very close to the RTN recording above.

RTN was using his “usual power” (we’ll be vague and say a few hundred watts). Had he been using a lower power level, say 10 watts, the signal to noise ratio would have been about 0 dB, if not negative. He’s using a delta loop antenna, and is about 4,000 km (2,500 miles) away from my location.

Here’s a graph of RTN’s carrier frequency, as measured here:

You can observe both the power on drift, and short term cycling (about every 10 minutes) due to most likely to something thermal, perhaps a fan.

UHF Pirates – 250 MHz SATCOM Monitoring

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UHF SATCOM refers to satellite repeaters that operate between 240 MHz and 270 MHz. To receive SATCOM, you need a receiver that can tune the frequency range in narrow FM (most modern scanners can do this). You also need an outside antenna, and possibly a LNA preamp.

The satellites in question are operated by the US military. They are essentially repeaters in geostationary orbit. Because they are open (no access control) they are often used by third parties, most often by people in Brazil. It is very common to hear Portuguese transmissions. One listener, who spent several years living in Brazil, described it as

Portuguese slang spoken by people who never paid attention in school

Back in 2009, 39 Brazilian pirates were busted, but the activity continues.

Here’s a recording of SATCOM pirates, and another recording of SATCOM pirates

255.550 MHz is very heavily used by the Brazilian pirates. As I am typing this, I am also hearing pirates on 253.500, 253.750, and 262.190 MHz.

There is an excellent breakdown of all of the 250 MHz SATCOM Transponders By Satellite

While you can start with a basic outdoor scanner antenna, such as a discone antenna or other scanner antenna, many serious listeners eventually build a directional antenna, such as a helical. I will have construction information about one that I built in a future article.

Next, since the signal levels are often very weak, the use of a LNA preamp is highly recommended. I built one of the Down East Microwave Inc. GaAs pHEMT pre amp kits, and find that it really helps a lot.

Digital Radio Mondiale

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Have you run across an odd sounding digital transmission in one of the SWBC bands? Possibly, you heard a DRM transmission. Digital Radio Mondiale (DRM) is a digital audio broadcasting technology that claims to provide FM quality sound over shortwave radio. It uses MPEG-4 codecs.

Here is an example of a DRM signal. This one is Vatican Radio on 17815 kHz at 1610 UTC on May 5, 2012. First, the digital transmission as you would hear it tuned on a regular SW radio: DRM signal

Below is a waterfall showing the DRM signal, between two traditional AM transmissions:

Comparing the transmissions, you can see how easy it is to distinguish a DRM transmission from a regular AM transmission. The signal intensity is pretty much constant over the entire 10 kHz bandwidth, and there is no strong carrier in the center, with the symmetrical sidebands around it.

Below is a zoom into the entire DRM signal:

And here is what the resulting audio sounds like, after being processed by DRM software: DRM audio

For this reception, I used a netSDR receiver with a 635 ft sky loop antenna, running the SdrDx software. SdrDx was set to USB mode with a 10 kHz wide filter, since the DRM transmissions are 10 kHz wide. The output of SdrDx was fed through Soundflower (a virtual sound device) to Dream, which does the DRM decoding.

Below is the main Dream window, showing some basic information about the DRM signal, such as the name of the station, target area, etc. This is all obtained from the DRM signal itself. The audio bitrate is also displayed. There is only one audio channel on this transmission, there could be multiple channels.

The next window shows some detailed information about the DRM transmission, such as the signal to noise ratio, various decoding parameters and settings, a graph of the SNR, etc:

One thing to remember about DRM, it is like most digital transmissions – all or nothing. If the reception quality of the DRM signal is poor, the audio will completely cut out. So when reception is good, you get great audio. When it is poor, you get nothing.

Another point, about Dream itself. It is the poster child of open sores software. There’s no OS X binary on the download site. Download the source code, hunt around for zillions of libraries, compile and link the app (Wait! You’re not a programmer, you just want to use the app? Tough luck, kid). Lather, rinse repeat.

I did find a binary download link for Dream for Mac OS X here. It’s from 2009, but it seems to mostly work.

There is a DRM encoder called Spark. I am not aware of any pirates that have tried using DRM in their transmissions. They’d need a transmitter that can handle very wide (at least 10 kHz) audio in SSB mode. There are some lower quality DRM formats that use 4.5 and 5 kHz wide transmissions, with resulting lower quality audio. It might be an interesting experiment for some of the the more technically minded ops.

A good source for up to date DRM transmission schedules is the Shortwave Broadcast Schedules app, available for both the iPhone/iPad and Android. DRM transmissions are identified with the word DIGITAL in the station name.

Lies, Damned Lies, and Receiver Images

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I have my SDR-14 receiver online, for some listeners to use. The other day, there was a logging of Trenton military aviation weather on 6950 kHz. I had not seen other reports of Trenton aviation weather on this frequency. And, since 6950 is a very popular frequency for pirate radio in the USA, this could cause some concern, as QRMing military stations is generally bad karma for pirates.

Here is a recording of Trenton Aviation as received on the SDR-14.

As it turns out, I had been running a recording of 6800-7000 kHz via another SDR, my netSDR. So I went back, and checked that recording at the same time the SDR-14 had picked up Trenton on 6950. Nothing. Nothing at all. And the netSDR is connected to a much better antenna than the SDR-14. Hmm. This is strange.

Last night, I was alerted that Trenton was again being heard on the SDR-14 on 6950 kHz. So I went and tuned in on the netSDR, and again heard nothing. I then decided to look for a schedule of frequencies used by Trenton, and found that they should be on 6754 kHz. I tuned in, and sure enough, there they were. Coming in very well, about S9+30 dB or so. Hmm… I did a quick calculation, and the difference between 6950 kHz and 6754 kHz is 196 kHz. 196 kHz, that sounds familiar. Why yes, that’s the I/Q sample rate of the SDR-14!

Now it all makes sense – the received signal on 6950 kHz is an image, a false signal generated by the receiver. It turns out that even SDRs are not immune to images. (Shhh… don’t anyone tell Al Fansome)

Images have been the bane of DXers for decades. They often manifest themselves as a particularly strong signal that is picked up on other frequencies. With an analog receiver, these frequencies are often offset from the actual frequency by the IF frequency of the receiver. With VHF/UHF radios and scanners, this is often 10.7 MHz, or close to that. In the case of the SDR-14, the image was located at an offset equal to the I/Q data rate. It was probably being heard on 6558 kHz (6754 kHz – 196 kHz) as well.

If you’re hearing an unexpected signal, one suggestion is to try another radio, ideally one with a different IF frequency. If you don’t hear the signal on the second radio, then it is most likely an image. Or your other radio is broken. But it’s probably an image. Ask another DXer if they can hear it, as well.

There’s a ham in Erie, PA that has been harassing the local club that runs a 2 meter repeater with claims of interference to the VHF marine band. The FCC has investigated, and found no interference. Multiple hams have contacted the Coast Guard and they have not had any interference issues. The only person who reports interference is the previously mentioned ham, who lives a few hundred yards from the building housing the repeater. I’ll close by noting that the VHF marine band is about 10.7 MHz above the 2 meter band frequency used by the repeater – 146.610 MHz.

Wolverine Radio SSTV

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Shortwave pirate radio station Wolverine Radio was on the air last night, with their typical excellent signal, excellent audio, and excellent programming. As is often the case, they finished their show with a Slow Scan TV (SSTV) image. SSTV is a way of sending an image using audio tones.

Here’s a video of the image, while it was being received. As you can see, it takes about 2 minutes to send a single image. Hence the name Slow Scan TV.

Here’s a larger video image, if you don’t mind rotating your head to watch it:

The image was decoded using the SSTV App for the iPhone, iPad, and iPod Touch which I will now shamelessly mention is

Here’s what the transmitted image looked like, by the way:

New version of SdrDx available, now for Windows also

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There’s a new version of SdrDx, the free app for RF Space SDRs (SDR-IQ, SDR-14, netSDR, etc): http://fyngyrz.com/?p=915

This version includes a lot of new features, including recording I/Q data directly to disk, so you can then play it back. Think of it as a VCR. You can, for example, record the entire 43 meter band (6800-7000 kHz or so, depending on your SDR model) and then go back later and run the I/Q recording back through SdrDx again. It’s awesome! Previously I’ve had to run SpectraVue under vmware to do this, now I can do it natively on the Mac.

I use a program I’ve written myself, that reads in the I/Q data file, and plots a waterfall for the entire file. I can then selectively demodulate what signals I want. I can record all of 43 meters overnight, then check in the morning to see who was on, and listen in. I don’t miss anything, nor do I have to choose if there’s two, or even three pirates on at the same time. I can listen to all of them. At some point I may release this for others to use (Mac OS X only) but it’s still pretty crude right now.

There’s lots of other new features and improvements to SdrDx, so if you have an RF Space SDR, go download a copy to try out.

GPS Disciplined 10 MHz Reference

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Some time ago, I wrote about the Rubidium reference that I connected to SDR. The reference supplies a very stable and precise 10 MHz reference clock to the SDR, so that the sample rate does not drift. Drift in the sample rate causes drift in the received frequency, much like drift in the various oscillators in a conventional radio causes drift.

Just today, I replaced the Rubidium reference with a GPS disciplined reference.

Here’s what I got:

The reference itself is the box in the center. To the right is the power supply, to the left is the antenna.

A GPS disciplined reference or oscillator uses timing signals from the GPS satellites to control,or “discipline” the oscillator built into the reference using a tracking loop. The 10 MHz output is continuously adjusted to keep it at the correct frequency, usually by making very small adjustments and using long time constants (averaging periods), typically around 100 seconds or more.

The 10 MHz output from the reference connects to an input on the netSDR. Internally, that 10 MHz signal is used to produce an 80 MHz clock that is used to drive the A/D sampling.

Here is what the inside of the reference looks like:

Here’s a plot of WWV on 10 MHz:

I believe the frequency shifts you see are due to doppler effects in the ionosphere.

Now I can figure out exactly what frequency Captain Morgan is on.

Excellent 43 mb Propagation, 10/11 mb Operators Put On Suicide Watch

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Old Sol has been quiet lately. Far too quiet for the 10 and 11 meter band guys. As I’m typing this, the solar flux is back into double digits, at 95. The Sun Spot Number (SSN) is officially 24, but you need to squint real hard to actually see any sunspots:

Sunspot SunSpeck group 1452 has pretty much rotated out of view, taking the meager solar activity we’ve had with it.

The NOAA/NASA/Space Weather prediction boys promise that we’re still a year away from the peak of cycle 24, and activity will increase.

Go up. Yes, it will go up any time now, just you wait. Hey! Look over there! Global Warming!

Meanwhile, back in the real universe, the background x-ray flux is at B1 levels.

So what does all this mean for us DXers? The lower solar activity has several major effects. First, the highest frequencies that can be propagated are lower, in many cases much lower. During a solar cycle maximum with high activity, the higher bands are often open 24 hours a day. With the lower activity we’ve been having, this is not this case. Yes, 10 meters is still open at times, but not nearly as much, or with the good conditions that have been experienced in the past. So operators and listeners need to move down to lower frequencies.

The foF2 frequencies are correspondingly lower, which means that a given band (including 43 meters) will go long earlier in the evening. Operators may want to adjust their schedules accordingly, and consider transmitting a little earlier to reach a semi-local audience. OTOH, they’ll end up reaching more distant listeners earlier in the evening as well.

Second, D-layer absorption is lower, due to decreased x-ray flux from the Sun. This means that lower frequencies are not attenuated as much, which is a good thing, since in many cases that’s all that is propagating. The last few days, I’ve been hearing 48 mb (6 MHz) Europirates fade in as early as 2 hours before local sunset. And once the Sun does set, their signal levels increase to really strong levels. Likewise, US pirates such as Wolverine Radio have been reported across the US and into Europe with incredible signal levels.

Third, the lack of major solar flares and coronal streams affecting the Earth means that geomagnetic conditions have been very stable. No geomagnetic storms means stronger signals, and less fading.

The net result is that reception conditions for 43 meter band pirates has been extremely good lately. Lots of operators and listeners have been taking advantage of the excellent conditions, loggings are way up.

There is a coronal stream expected to start impacting the Earth around the 13th or 14th of April, so we’ll have to see what effect, if any, that has on conditions. Until then, enjoy the great propagation!