First Meteor Scatter Contact

Meteor in a Perseids shower, Wikipedia

It's not exactly ground-breaking in the Amateur Radio world, but I'm pleased to have made my first "meteor scatter" contact with another radio amateur.  Thanks to W4IMD, Peter in Georgia, who exchanged information with me over a path of about 1,100 miles on 50.28 MHz with about 50 Watts of power.  We used the software mode called "MSK144", developed by friend and colleague Joe Taylor (K1JT).

Meteors strike the Earth's atmosphere frequently, even in the absence of a big meteor "shower".  They generate a trail of ionization that lasts up to a minute or so (at 50 MHz), which is sufficient to exchange a bit of information between ground stations that have mutual visibility -- up to about 1,300 miles.

Strong meteor burst from N0TB in Minnesota displayed
on FlexRadio FLEX-6500 SDR transceiver

There are other worlds to conquer: working through Amateur Radio satellites or the ultimate in weak signals -- moon-bounce communication. All these have been done one way or another for decades, but they keep me learning new tricks!

First FreeDV on Flex 6500!

I'm giving an "SDR" talk in a few weeks, and I thought I should try out some new (to me) stuff.  My Flex-6500 supports FreeDV as a built-in "waveform" app with some help from the Windows PC.

Nothing was happening on the magic frequency, 14.236 MHz, so on a lark I gave a call.  To my surprise, I got a quick answer from Walter, K5WH, in Houston TX.  The band was up and down, but he was 90% copy at least, and I seemed to make the grade myself!

FreeDV (FreeDV.org) is an open-source digital voice system, designed especially for minimal bandwidth communications on the HF bands.  Voice fidelity isn't perfect, depending a little on current signal levels, but it's remarkably good for ~1.5 kHz (less than normal analog SSB).

Fun with WSJT-X

Since this weekend's ARRL 100th Convention, I've been trying out WSJT-X, the latest from Joe Taylor K1JT in his series of "Weak Signal" programs.  It supports the JT65 and JT9 digital modes, mainly for HF communications (1.8 - 30 MHz).  It's a more modern and user-friendly program than the original WSJT.

The JT65 mode, shown here as a waterfall spectrogram in the 17 M band, is Joe's classic mode.  It uses 64 tones plus a pilot to convey the digital message in a ~200 Hz band.  This selection is interesting, because the weak WSJT-X signal (JA1VGV) is hidden behind a strong RTTY station -- the two big vertical bars.  The JA station is -17 dB relative to the SSB noise level, while the RTTY signal is probably > 0 dB. 

A contact goes in 1 minute "chunks": sending for one minute (actually, 48 sec.) and receiving for one minute.  The divisions of transmit/receive are shown as red horizontal lines. (The waterfall is stopped for 48 sec during transmit.)

I use two power levels for JT65. Normal is 5 Watts.  When conditions are tough, I can ramp up to "QRO" -- 20 Watts.  To go higher than that is considered unsporting, I think!

JT65 is nice, but JT9 is better.  It uses the same message structure, but with only 9 tones that are spaced more closely.  JT9 is much more efficient in terms of spectrum utilization (by a factor of ~10), so it is clearly a better solution for crowded HF bands.  Unfortunately, most of the JT65 software now in use does not support JT9.  WSJT-X supports both.

Spectrum and Band Occupancy

Dan, KB6NU, has some good reasons to worry about 300-3000 MHz competition for amateur bands.
Image via Wikipedia
Right on.  At least frequencies below 300 MHz are under less pressure, which is a relief to us HF & 2M troglodytes.  Still, vigilance is required.  Support ARRL.

There is a problem with the VHF and higher bands that doesn't get a lot of attention.  Amateurs are not very good at utilization.  The bands are almost always completely empty, and this makes them targets for commercial use.  Around here in CT, the 2M repeater segments are mostly allocated and unavailable for new applications, but they are still unused most of the time.

Image via WikipediaBy contrast look at 14.070 - 14.073 kHz. I can often copy dozens of PSK31 QSOs in progress there in 3 kHz of spectrum.  Also look at the cell/CDMA bands that support 100s of "QSOs" in a few MHz all the time.  Hams do need to pay more attention to band occupancy.

BARTG RTTY Contest

I'm coming off the high of finishing the BARTG RTTY contest this weekend. I had a near 50 year record of not contesting (apart from a couple of Field Day "non" contests), but for some reason this was the time to dip a toe in. Upshot: > 440 QSOs in many countries. Finished up with a burst of Japanese stations on 20 M. (Japan has been very elusive from this QTH.)

Maybe it was partly because I've just been reading up on RTTY history.

Z100 -> P100!

After a little discussion with Jack Smith about the inner workings of his Z100 Tuning Aid (last post), one thing led to another.

The result is another little Python utility that does much of what the Z100 does, but in software under Linux.

The scoop and download are available here.

A Z100 Arrives

This is the Z100 "Tuning Aid" from Clifton Laboratories, as described by Jack Smith K8ZOA in the January/February, 2008 issue of QEX. I bought the kit and put it together as sort of a post-Christmas present to myself.

The Z100 is a pseudo-spectrum analyzer, using a simple zero-crossing detection and averaging algorithm as I understand it. It is intended to help "zero beat" a received CW or RTTY signal so that you can respond on the same frequency within a few 10s of Hz. (It's not zero beating really. With current rigs, you want to tune to a certain offset "spot" audio frequency that corresponds to your transmitter's output.)

A few notes on the Z100 so far

• Assembly was straightforward until it came to making the LED bar-graph indicator, which you must construct out of individual LEDs and spacers. Getting a neat result is tricky. I judge I managed it fairly well on the first try, but you need to read the instructions carefully. A number of hams have contributed handy alternative techniques that Jack includes in his write-up.
• Assembly of the board into the case, along with a clear lens and an optical filter film is the next tricky part. All in all the mechanical work with the LEDs and the case seemed overly difficult. It would have been very helpful if the filter film could be dispensed with -- e.g., if a neutral density Lucite lens could have been used.
• Operation (for an hour so far!): The Z100 is easy to connect and use. It does require reasonably strong CW signal (i.e. fair SNR) to make the CW note show up clearly out of the noise. I seem to work weak stations quite a lot, and the tuning aid may be difficult to use for them. A more intelligent algorithm would be able to pick a coherent signal out of the noise much better, but that would be beyond the capability of the simple PIC processor, I reckon. It would boost this kit well out of the $60 price category.
• Jack is to be commended for producing a very "open source" project. The PIC code is available for study and modification, and the QEX article and product documentation gives full design details. (A perfectionist might say that a true open source project should also distribute Gerber-type files for the PCB design, but that would be a quibble!)
  

This kind of tuning aid should be very helpful to any CW or RTTY operator. (I suppose it would make a reasonable guitar tuner, too...) In an age of DSP radios, this capability should have been incorporated into the transceiver itself, but alas this is not yet true of my radio.

Bandpass Controls for HF Digimodes

When working PSK31 or other "digimodes" on HF (high frequency) radio, we commonly use computer soundcards to analyze and transmit data. I like to use the Linux program fldigi for this, along with my Ten-Tec Orion transceiver.

The soundcard takes in the entire audio output from the Orion, typically 100 - 3,000 Hz. Fldigi (and similar software) allows you to point to a transmission of interest on a "waterfall" spectral display. This automatically sets the decoder to analyze data in a small band around the cursor using digital filtering.

This works well when the bands are relatively quiet, but when you have a band crowded with strong signals, the signal of interest can be strongly affected by "out of band" signals (but still in the 3 kHz audio region) that key the receiver's AGC (automatic gain control).

In this case, we need narrower IF (intermediate frequency) filtering than 3 kHz. Fortunately, a DSP (digital signal processing) rig like the Orion provides "infinitely" adjustable IF bandpass characteristics, so it is possible to "zoom in" on the signal of interest, largely rejecting any signals outside the small IF passband.

I have written a small Python/wxPython application "oFilter.py" that puts up a panel to allow Orion bandpass control from the same screen as fldigi. (Since fldigi communicates with the Orion via Hamlib at the same time as oFilter, there is a small potential for I/O conflict, but this is not a serious problem.)

Here are a few screenshots to show what is going on. Ultimately, it would be great to integrate the oFilter functions into fldigi or a similar program, using convenient mouse controls.

The PSK31 band at 14.070 MHz with many Europeans

coming in the 3 kHz default bandpass.

"Zooming in" the IF bandpass to 200 Hz,
more-or-less centered on the signal of interest.

Zooming in to a 100 Hz bandpass (minimum available).

The oFilter.py application.