Thursday, August 29, 2013

Radio-Sky Spectrograph

A beautiful solar storm.

Spectra displays sure have become popular.  When did you see spectra in the 1960s if it wasn't due to a rainbow or a mushroom?  Now our stereos and radios are very likely to have some sort of spectral display. Adding that extra dimension of frequency reveals patterns that cannot be discerned through a speaker or on a strip chart.   In the not too distant past, motors turned capacitors that tuned receivers that output spectra in terms of modulated light.  This in turn exposed a slit across  a slowly passing strip of photographic film.  Now we can simply? sample the entire HF spectrum with an insanely fast analog to digital converter, run it through a computer and, bang your done.  These new fangled technologies!

It was over 11 years ago that the Radio Jove Project received funding to develop a spectrograph that could be used to see Jupiter and Sun radio emissions in the HF range from 18 to 30 MHz  The device we built was designed by Richard Flagg and me over a period of more than a year.  We had earlier had produced spectra by sweeping a Icom R8500 receiver using serial connection to PC.  This actually produced some interesting spectra, but it was too slow to see the short duration S-Burst type of Jupiter radio emission. What's an S-Burst ?  According to the UFRO:

"The S bursts (S for Short) are very short in duration, have instantaneous bandwidth of a few kHz to a few tens of kHz, and drift downward in frequency at a rate of typically -20 MHz/sec. They arrive at rates from a few to several hundred bursts per second. In a 5 kHz bandwidth receiver they last for only a few milliseconds"

So we only had half of a second before the S-burst traversed the entire 10 MHz we were observing (18 to 28 MHz usually). By sweeping at 10 scans per second in the high to low frequency direction, we get at least 5 chances to see the S burst as it makes it's decent.

FS200 prototype.

Dick designed all of the analog electronics and I did the digital stuff and supporting software. Dick also built the spectrograph  (shown below) and he really did a beautiful job, that any geek would envy. Had I built it, would have looked more like the prototype shown above.  The result was a sweeping receiver that measured the radio energy in each of 200 channels about 10 times each second.  The more modern approach would of course be to use a software defined radio that samples the entire HF band simultaneously.  That would have been quite a challenge that long ago, so we took the more well trod path of sweeping a single channel receiver in the style of the older spectrum analyzers. We called the spectrograph the FS200, (Flagg-Sky 200 channels - which we named is a very self-congratulatory moment).  It was installed in the Windward Community College radio observatory on Oahu, Hawaii, and is still running non-stop today.

FS200B production model spectrograph with an automated step calibrator on the bottom panel. Everything can be controlled remotely via the serial port attached PC. From the front of the rack you just see an led, reset button, and perhaps a switch (can't remember). Basically, a DDS controls a receiver with a log detector. A micro-controller manages everything.

The results were beyond our expectations.  We could see Jupiter spectral emissions in detail that only the Nancay observatory in France could outdo. OK, I have no proof or even evidence of that, but it would be nice if true.  A second instrument was built and coupled to the then viable University of Florida TP array.  Unfortunately, thieves have since decided the unmanned observatory was more useful as a source of scrap metal than as a scientific facility.  Luckily the FS200B was saved and has been relocated. It is currently operated by Dave Typinski.  Dave, Wes Greenman, and Jim Brown have been putting instruments to use and producing spectacular results.  More spectrographs will be coming on line over time and of course the WCCRO machine is almost always available for viewing though it sometimes has interference issues.

A Jupiter noise storm showing intricate structure.
Several years ago Kazu Imai of Agawa Observatory in Kochi Japan commissioned me to modify the Radio-Sky Spectrograph software (RSS) to work with rfspace's SDR-14 software defined receiver.  Rfspace sharply foresaw that others might want to write programs for the SDR-14 and provided an easy to use ActiveX interface to the spectral data within. That made supporting their device possible. The Japan based SDR-14 is not available on line, but I mention it as a possible commercial device for people who would like to have their own spectrograph that works with RSS.  The SDR-14 no longer is produced, but occasionally you will see one offered for sale in the SDR-14 users group.

RSS in Client Mode. Four servers were available at the time this was copied.

But anyone can download and use RSS and link to one of several spectrographs that are available over the internet.  The software is completely free. RSS has Stand Alone / Server / and Client modes just like Radio-SkyPipe.   Of course, you need an SDR-14 or one of Richard Flagg's custom receivers to use the first two modes.  I will apologize beforehand that there is not much in the way of help available for users of the program.  Let me know if you get stuck on some aspect of the program.

Strong solar bursts.

More recently we developed a "stereo" version for looking at right and left hand signals simultaneously.  This project was commissioned by Dave Typinski and we really hope to see some great results from this device in the upcoming Jupiter season. 

Friday, August 16, 2013

A Beautiful Analog Voltage Meter

I do not remember when or where I purchased this meter but I always fantasized about using it as the output of some modern complex circuit. I suppose that might be called a vaguely steampunkish idea.  In any case, I feel compelled to share this elegant design with you.

This voltmeter covers up to 20 volts. Once zeroed, I found that it tracked very precisely with an applied voltage as measured on a DVM. What is unusual about the meter is the pointer which manifests as a floating triangle of light projected onto the vertical scale from behind.

 The light source is a 6 volt incandescent bulb.  I power it  with a 6.3 VAC transformer rated for a couple of amps.  I didn't measure the actual current but small power transformer gets quite warm! The bulb is very bright, making the meter difficult to photograph. In normal operation the meter would be in an enclosure and the light would be hidden except for the arrow image projected through the translucent linear scale.

This is what I saw after removing the numerous small screws from the side panel.

The light bulb is positioned above the image and passes through a crisp metal mask that forms the pointer arrow shape.  The beam reflects from a fixed mirror on the opposite side of the case.  The reflected light then passes through a focusing lens and onto a mirror that is attached to a typical galvanic meter movement. This tiny mirror rotates with the shaft axis of the meter movement.  The change in angle dictates on what portion of the linear voltage scale the pointer image falls.
To me this is a beautiful device.  I must find a use for it.  Unfortunately, it wastes a lot of power in that bright bulb.  Either I must find a very occasional use for the meter or find a way to reduce how much power it uses.  The scale would be perfect for measuring voltage from a PV system, but wouldn't it be ironic if the meter consumed all the power from the solar cells.

Notes on the DC-3G-90DB-V2 Attenuator

  I've been working on a simple step calibrator design for the Radio JOVE 2 project.  The attenuator will be controlled via the Radio-S...