NOAA APT Decoding Success!

WHOO-HOO!

Got home from work and some errands just in time to catch the last "good" pass of NOAA-18 for the day.

I fired up my "Daily Driver" Linux box, and started the GPredict satellite tracking program. Since I already had the three operational NOAA satellites loaded, I saw that NOAA-15 was overhead, with NOAA-18 a minute or two behind.

Since I wouldn't have time to power up the Windoze 7 PC I normally use for my Ham Radio stuff, I took a chance and launched Gqrx, an SDR program that will work with either a FUNCube or RTL dongle. Since I already had the FCD plugged in, I set the mode to Narrow FM, and tuned to the NOAA-15 frequency of 137.620 MHz.

Since Gqrx either didn't remember the settings I used for the APT satellites, -OR- I had changed them, it took a minute or so to get them sorted out. There's an "APT" selection in the available filter parameters, but it's only 17.5 kHz, so I grabbed the filter window edge with the mouse, and stretched it out to 40.8 kHz, wide enough to cover all the "tracks" in the waterfall display, but not so wide as to let other signals in.

This screenshot was taken during the pass after I had everything set up, and was satisfied it was recording:

When the pass finally got weak, I stopped recording, opened Audacity, converted the stereo recording to mono, and resampled it down to 11025 kHz.

Then I fed it to WXtoImg, and it decoded clean!


This is the first decode, called "Normal":

The "steps" or "jumps" in the gray-scale data blocks along the edges are most probably caused by my manual adjustment of the Doppler as I was recording the audio.


Here's one in color, produced by using the information in each of the two pix above, along with certain data sent down:

For the sailors out there, here's the sea surface temperature:






And lastly, here's one called "Thermal":

There are a bunch more "Enhancement" options available on the version of WXtoImg that's on my Windoze PC, as that's a "paid for" registered version, while the Linux version is "freeware", and doesn't look like it even has a place to enter a registration code, so WYSIWYG!


I'll try to use the $20 RTL dongle on the next pass, about 40 minutes from now (0105 UTC), and see how that one receives. Since I now know how to change the "front end" sample rate on the RTL unit, I can cut down on the amount of spectrum it samples and converts, making it easier to tune the unit, and cut down on signals I *don't* want to receive.

I won't have time tomorrow to record any passes, as I'll be on the Battleship Iowa all day operating the Amateur Radio station for Pearl Harbor day, but I'm sure going to try and snag some nice, full passes on Sunday!

NOAA Satellite Recording Decoder Problem SOLVED! Well, solved for now........

Well, well, well.......

I "solved" my problem in kinda-sorta in a back-handed way, but at least now I know what I was doing wrong.

Earlier today I replied to Silicon Graybeard that I was going to try an old program I used to use to decode the audio recordings I made from the NOAA APT satellites. I tried installing WXsat on my Windows 7 PC that I use for my Amateur Radio activities, and it simply wouldn't run, regardless of whatever "compatibility mode" settings I tried. I then installed it on my Linux machine using Wine, and it ran!

The first snag I hit was that since this old program was meant for Windows 95, it couldn't handle long file names, and errored out when trying to load the recorded wave files I had. I renamed the files, and then the program informed me it could only handle MONO files. Using Audacity, I converted the recording to single track mono, and tried again.

It then threw another error, saying the files had to encoded at an 11025 Hz rate, which I remembered from looong ago, so back to Audacity to resample them from the 48kHz rate down to 11.025kHz.

Lo and behold, it accepted the file, and processed it, producing this image:

The right-to-left shift in image was caused by me doing something (I don't remember what) during the recording.

The "stripes" on the edges of the image are synchronization and telemetry frames, explained in this drawing:

Here's an image of both channels, which is easier to relate the above drawing to:

Switching to NOAA_IR (Infrared Mode), produced this image, where you can see the California coast down the approximate center:

SO....not having anything else to lose, I fed the  "remastered" file into WXtoImg, and it worked:

I still don't have the hang of flipping the images to "get them right", so until I get a longer recording, that shows more of the coast, I'm not sure what to do to "normalize" them so they look like I'd expect them to, like you're looking at a map in an atlas.

Now the interesting thing about this, is NOWHERE in the docs for WXtoImg can I find a warning, or caution, about how you have to feed the program an 11.025kHz, mono audio file, and in fact, all the things I found about "piping" the audio to the decoding program from the SDR receiving program via a Virtual Audio Cable say to leave things set at 48kHz.

It *might* accept a stereo file in some rate other than 48kHz, or it *might* accept a mono file at 48kHz, or it *might* require an 11,025 Hz, mono file, just like my "old" program.

Or, I *might* be able to get the SDR programs to save the audio from the dongle in the correct format of whatever, and not have to mess around converting the files after I've recorded them, I just don't know at this point.

And it's 2145 local time, and I have to be in to work tomorrow at 0600 for more training (we had Fiber Optic stuff today) and certification classes tomorrow, so good night, and hopefully I'll get a nice long pass recorded tomorrow so I can mess around with the decoding options now that I know I have something usable.

NOAA Weather Satellites and the FUNCube Dongle

SO.....When I got home tonight I decided to see if my FCD ("FUNCube Dongle) would work any better that the $20 RTL dongle I have.

The FCD has a much narrower bandwidth, about 80kHz, than the RTL dongle. The software I use with the RTL will allow you change the sample rate, which cuts down on the amount of spectrum it decodes, but I didn't see any difference in doing that.

I only had a couple of passes of the NOAA birds, so the only software I tried was SDR#.

The first thing I noticed was that it was very easy to set the filter bandwidth to include *only* the signal from the satellite. Doing this cuts out any strong signals that might degrade the desired signal, and it's always worthwhile doing if you can.

The screenshot below shows the received spectrum of NOAA-18 earlier today. If you look at the bottom pane of the display you'll see the "tracks" of the signal, and looking at the upper pane, you see the grey area corresponding to the receiver filter bandwidth, in this case about 50kHz:

All the extra area covered by the grey that doesn't have the "tracks" in it just allows unwanted noise to be recorded along with the signal.

Here's a shot of NOAA-15 a few minutes later after I adjusted the filter bandwidth down to 40kHz:

Notice how the grey area has narrowed, and includes just a bit of spectrum outside the "tracks". This is pretty much what you want, and is why my fellow Ham Operators love narrow filters when receiving weak signals; match the filter bandwidth to the incoming signal, and the extraneous crud gets cut off.

You can also clearly see the Doppler Shift causing the "tracks" to shift left-to-right as the satellite passes over. There's a single, bright, blue line running under 137.630 MHz, which is internally generated in the little receiver, and it doesn't change frequency, so it's a good fixed reference to compare the actual signal to, and observe the Doppler shift.

Now compare this to the next screenshot which I made over the weekend. This one was using the RTL dongle, with approximately 800 kHz of bandwidth in the display:

Quite a bit easier to determine what filter bandwidth to use when the display isn't crammed together so much! If I hadn't adjusted the bandwidth of the RTL unit for that particular pass, the display would have been about three times as crowded!

ANYWAY....today's experiment was to see if the FCD makes it easier to tune in the NOAA satellites (it does, although SDR# will let you adjust the bandwidth of the RTL unit), and to make an attempt to determine what a good filter bandwidth would be.

40 kHz looks about right, and that falls in line with all the things I've read about what filter bandwidth works best for receiving the NOAA APT satellites.

As far as using WXtoImg to decode the received signals.......well, still no joy. I'm going to take all the files I've recorded so far and run them through "xwxapt" on my Linux machine and see if I have any better luck. From listening to recorded APT signals at various places around The Web, mine sound at least as clean, and I'm pretty sure they should decode. I've done this before, with a Hamtronics R-139 receiver, a receiver specifically designed to receive APT transmissions, and it worked quite well with a homebrew turnstile antenna.

I just downloaded the older program I used to use "WXsat", and I'm going to give it a try, too.

And it looks like I might be cutting some PVC pipe this weekend to make another turnstile antenna........

A Warning About Our Loss of God Given Rights

Says it all......

NOAA Weather Satellites and RTL-SDR Dongles, Part II

Arrrggghhh!!!

I raised the antenna yesterday to 20', and now I'm getting a SOLID signal. Some directions I pick it up at 2*, and other directions from about 6*.

The spectrum display in SDR# looks solid, and I figured out you need the squelch DISABLED, other wise you get 'popping' noises that mess up the recorded audio, and the filter set to 48kHz.

Here's a screenshot of the last session I recorded:

The highlighted area of the spectrum is the filter width, and you can see in the display panel below it that all of the signal is within the filter's bandpass. I was cutting it off before, and losing some sync and telemetry information from the satellite.

With the antenna at 20', these birds are LOUD, well out of the noise by about 20dB.

With SDR# you manually have to adjust for Doppler Shift, but it's pretty easy to check it every minute or two, and 'nudge' the frequency a bit.

The recordings I've made so far sound great, BUT WXtoImg doesn't process them correctly. All I get is the proverbial "Black Cat In A Coal Bin" pictures, with a bunch of white noise thrown in for good measure.

So, I'm able to record the audio files, but I still have to figure out what I'm doing wrong to decode and display them.

I might have a sample rate error between how I'm recording them, and what WXtoImg expects, or some other problem. I'm still hesitant to setup my Virtual Audio Cable paths to feed WXtoImg directly, as if I mess it up, I'll wind up spending more time than I want to getting them squared away for use with my Flex 5000 SDR transceiver.

Oh, well.....I'm about done for this weekend.

See you all later.

Can't Fill Jimmuh Cahter's Shoes

Says it all.....

Saturday Morning "Get Yer Feet MOVIN!" Music

If this doesn't do it, maybe you're not among the living anymore!



Just got back from the World Famous W6TRW swap meet.

Got 200' of "550 paracord" for $10

Got 10 clipboards (nice ones) for $10

Bought a bunch of double-banana plugs-to-BNC adapters for $1 each

Bought 500 paper/plastic CD sleeves for $2

AND...bought a very clean Kenwwod R-2000 Communications Receiver for $75, an amazing bargin.

These are good little receivers, and the only thing "wrong" with this one is that the top shell of the case has the paint scratched up pretty badly in one place.

Since various vendors sell the correct color Kenwood paint in spray cans, it'll be a simple matter to pull the case, wash it, hit with my orbital sander, and respray it.

Now to get that antenna raised another 10' and continue with my FUNCube/RTL dongle experiments!

It's a beautiful day here in SoCal. Clear, cool, and there's a bit of snow in the local mountains.

Have a good day, everybody!

NOAA Weather Satellites and "RTL" dongles

This morning I decided to try and hear one of the NOAA "APT" satellites using the eggbeater I got going yesterday. I was going to raise it another 10', and anchor it to the eave, but it was raining all night long, and continued to rain until this afternoon, so I spent the time just using the antenna on a single 10' section of mast.

The NOAA "APT" (Automatic Picture Transmission) satellites have been around since the 1960's, and I used to record the audio from a modified scanner, and then process it with some free software, but I never had a dedicated antenna, so it was more for curiosity than anything useful.

This antenna works very well for receiving them, and they're LOUD! Unfortunately, the HDSDR software I use doesn't have bandwidth settings high enough to accommodate the wide signal the APT satellites use, so when I try and process the resulting audio file, I keep getting "Telemetry Not Found", and the program I use (WXtoImg) doesn't process the audio into a picture.

The SDR# software allows much wider received bandwidth, but by the time I finished messing around with HDSDR, all the high elevation passes were finished for today, so I'll have to wait until tomorrow afternoon to try recording the signal using SDR#.

There's a tutorial on the RTL-SDR webpage on how to use SDR# for APT reception, but I'm a bit hesitant about mucking around with my Virtual Audio Cable settings, as I use those for digital modes with my Flex 5000, and it took quite a while to get them set up correctly. I'm pretty sure I wrote everything down about getting it working with the Flex, but I'll have to go through the binder I keep for the Flex, and make sure I have the settings properly documented before I start trying to use VAC with another program!

Between the two programs, I prefer HDSDR, even though the documentation is scant. It just seems more friendly to use, and if they included some wider filter options for things like the APT satellites, it would be just a killer program to go with your $20 RTL dongle. There's a fairly comprehensive "HOWTO", but it's written for an earlier version. Just ignore some of the screenshots, read the verbiage, and you'll be well on your way to using it effectively.

This is from the first time I tried using it on the NOAA satellites:

And this is a pass of NOAA 18 as it went over:

SatPC32, my satellite tracking program is running in the upper left corner showing where the satellite was when I grabbed this screenshot.

Immediately underneath the waterfall display you can see the spectrum of the satellite transmission. It looks like the bandwidth should be sufficient, BUT, due to my excitement at seeing the signals this strong, I was messing with the settings while recording the audio, resulting in a file the WXtoImg couldn't read.

Sigh......maybe tomorrow.

Eggbeater Satellite Antenna Istallation and "Dongle" Success!

I spent most of today, up to Dinner Time, that is, refurbishing and installing the M2 Antennas EB-144 "Eggbeater" antenna that I had hanging in the garage rafters, along with one of my "spare" SSB Electronic 2 Meter preamplifiers.


This is the antenna, with the radial kit, after I cleaned it up, treated all the connections with an antioxidant:

I swept it over several frequency ranges, and was amazed at how flat this thing is. I almost thought something was wrong until I went significantly outside of the 2 Meter band, and saw a more "normal" sweep result, looking like a very broadband antenna.

An "Eggbeater" type antenna is, very basically, two vertical loops, rotated 90* to each other, and fed 90* out of phase to produce a circular polarization.

Each loop by itself would have an impedance of about 100 Ohms, and fed in parallel, that gives you 50 Ohms, a good match for commonly available coax.

Since satellite signals are fairly weak, a good low-noise preamplifier, mounted close to the antenna, makes a significant improvement. So, I pulled one of my "spare" preamps off the shelf, and mounted it in a Rubbermaid tote box:

The little box to the lower right corner is a Bias Tee, which I use to extract the DC power for the preamp from the incoming coax. There's a matching one down at the receiver where I insert the power. I usually run a separate cable for the power, but I wanted to try this since I have a bunch of those little AVCOM bias tees around. Yep, that's a good old PL-259 used for a power plug on the preamp!

I made up a cable connecting the antenna to the preamp input with a PL-259 on the antenna end, and a Type-N on the preamp end. Since this is going to be outdoors, I put a large piece of adhesive-lined heat-shrink tubing over the connection at the antenna, and shrunk it down:

After all the cabling was finished and checked, I tilted it up vertically, and cable tied the mast (a section of 1" rigid conduit) to a big aluminum saw horse I have:

Some of my other satellite antenna mounts are slightly visible behind this new one.



Does it work?

Well, for the first time I was actually able to copy two people having a chat on the VO-52 linear transponder satellite!

Looking at the middle panel of the display in the screenshot below, you'll see a red line, with a blue 'band' next to it. The red line is the center frequency, and the blue 'band' is the passband for an SSB conversation.

The top panel shows a "speckled" area, and that's the display of the two Hams I was listening to.

If you look carefully, you'll notice that there's a definite shift downward in frequency as time passes, indicated by the bottom of the display (newest information) being to the LEFT (lower frequency) compared to the top of the display.

This is the Doppler Shift, going LOWER in frequency as the satellite was moving away from me.

The sideways "Vee" to the right of the guys I was listening to is most likely somebody "ditting" their VFO to try and find their own downlink. Since the transponders on linear satellites use differnet uplink and downlink frequencies, most conversations are full-duplex, where you can hear your own signal coming back through the satellite, with a slight delay. Generally what people do is to find a clear frequency to listen on, and transmit a series of "dits" while adjusting the transmitter frequency back and forth until they hear their own signal.

The only other satellite passes that were "good" before I started this post were from FO-29, which has a UHF downlink, and this antenna doesn't work (well, actually the preamp filters everything out) on UHF, so I'm waiting until 0456 UTC for AO-73 to pass over, and maybe I can (finally!) capture some telemetry.

Tomorrow I'm going to raise this antenna to it's more permanent height of 20', and anchor it to the side of the house. The extra ten feet of elevation will get it above the ridgeline of our roof, and should make quite a bit of difference.

Hope y'all had a very Happy Thanksgiving!


WELL.....I didn't hear any telemetry, but I copied W9ND talking to several stations on AO-73, The Satellite Formerly Known As "FUNCUBE-1"!

This time all the activity is on the right side of the top display, and you'll notice (well, some of you will....) a curving, slanted line near the top of the display. This was somebody "swishing" their VFO trying to find themselves, and they "swished" right through the conversation I was listening to, and it was neat to see it even though I've heard it many times when operating satellites.

2110 local time here, and I'm going to hit the rain locker, and then hit the hay.

Good night, all......

Happy Thanksgiving!

May you and your families enjoy the day.

We're having my wife's oldest son over, and I'm going to work on getting the Eggbeater antenna up and operational.

I'm going to redo all the bolted and screwed together connections with some Penetrox, and then weatherproof them with some electronics grade RTV.

Then I'll mount the antenna and preamp on the mast I bought today, and enclose the preamp in a Rubbermaid tote box I picked up.

Hopefully by this time tomorrow I'll have a better antenna installed for the "Dongle" project that I've been reporting on.

"RTL" Dongle with HDSDR

Well, having played with both of the dongles, and most of the available free software, I've come to a few conclusions, so far.

The FUNCube dongles have a restricted bandwidth, with around 80 kHz of useful display.

This is both good, and bad.

It limits you to how much spectrum can be observed at any one time, which makes it easier to spot a signal in the relatively narrow transponder passband of a satellite (50 to 100 kHz, depending on the satellite), but it sucks for using it as an ersatz spectrum analyzer to see what's popping up in the section of spectrum that you want to monitor.

It also helps cut down "image" frequencies as far as I can observe. (It's probably what's called "aliasing" in digital sampling and Digital Signal Processing, but I'm a Radio Guy, so I'm calling it an "Image"!).

It's also NOT enough to decode Broadcast FM Stereo by a long shot, or even Broadcast Mono, if that's important to you, but then it was never designed to do that, so I'm sure not crying about it now that I know the limitation.

The "$20 RTL" dongles do about 2 Mhz of bandwidth (mine does about 2.15 MHz), which makes sense, as they were designed to receive Digital Television signals.

This is almost twenty-seven times the bandwidth!

It receives FM Stereo very nicely using SDR#, and not so well using HDSDR. HDSDR was coded for "Communications" use, so the demodulators, even the "FM Wide" can't cope very well with Broadcast FM.

BUT....it dows a bang-up job of observing a 2 MHz slice of spectrum, as seen in this screenshot:

The display is centered on 162.550 MHz, which is the strongest of the NOAA Weather Radio broadcasts here.

To the left are the other NOAA broadcasts at 162.400, .425, .450, .475, .500, .525, and ,550.

Off to both the left and right, you'll see some broad, blue bands in the waterfall (top) display. From a casual glance, considering their bandwidth (over 100 kHz), I suspect these are FM "images" caused by the poor filtering in the front-end of these little receivers. Somewhere around here I have an FM band-reject filter, and if I can find it, I'll stick it in and see if this goes away.

Almost all the way to the left, you'll see some activity, which turns out to be the railroad frequencies. There's  quite a few "RailFan" websites out there, and some people are fascinated listening to trains. I prefer to listen to aircraft, but to each his own.

Above the NOAA channels are various services listed as "Mobile", but since I don't usually explore this part of the spectrum, I'm not sure what's up there. I just picked this frequency to center on as I knew NOAA was there.

Here's a shot of 2 MHz worth of the FM band out here in L.A.:

And here's what 2 MHz wirth of the 2 Meter Amateur radio band look like:

So, to wrap up tonight's "experiments", I'm getting more comfortable using these little guys, and learning more about each of them, and the different software available for them. They both have their pluses and minuses, as does the software.

I suspect, and I've read, that to get the best performance out of them they both need some front-end filters for whatever band you want to use them for, but then you can say that about almost any receiver made.

More to come......