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.

Wednesday, April 3, 2013

Chart Your Solar Panel Voltage

A friend of mine gave me some of his old photovoltaic, (PV), solar panels.  The frame they were on had disintegrated and they had not been used in a long time.  I was thrilled to have them.  I decided it would be good to characterize them simply by following their voltages over a few days.  I laid them out in the yard and ran a cable back to my shop a few feet away.  The series connected voltage measured with a DVM showed it to be in the expected range, never to exceed about 20 volts. 

A new life for some old PV cells.

An old, junker laptop was available, so I combined it with a LabJack U3 - LV  analog to digital converter (ADC)  and my Radio-SkyPipe data logging program. The LabJack is really more than just an ADC. While here I am only interested in measuring the voltage from the panel the LabJack U3 can detect digtal states on some of its inputs and can output both digital and analog signals.    The input range for the U3-LV (Low Voltage) is 0 to 2.4V in the singled ended configuration so I needed to reduce the voltage from the panels to fit in this range.  A resistive voltage divider was called for.  I decided to just use a 5K pot (variable resistor) instead of a calculator and a couple of fixed resistors.  Using the pot has the advantage that it can be changed if you would like to alter the range or compensate for a impedance other than that presented by the LabJack analog input. 

LabJack U3-LV fed from a pot used as a voltage divider attached to the PV panel output.
Before hooking anything to the LabJack input:  The outer terminals on the pot should temporarily go to the positive and ground of a regulated variable DC power supply.  I adjusted the power supply to 20V and then the wiper arm of the pot so that it read 2.4 V.  Only then connect the wiper arm to the LabJack analog input. You may need to slightly retweak the pot after the connection is made.

This arrangement means that when read by the ADC,  20V will be produce a reading of 4095.  Each step from zero to the full input voltage is 20/4096 = 0.0048828125 Volts.  Forgive the ridiculous precision.  I wanted to read the voltage in volts, not the number of 0.0048828125ths of a volt, so I used the Equation feature of Radio-SkyPipe that allows you to apply a function to the data read from the ADC. The Equation function is simply X*0.0048828125 .

It would be a simple matter to extend the functionality of this arrangement so that it could function as a Battery Charge Controller.  I mentioned above that the LabJack U3 has a number of digital ports.  We can use one these output ports to toggle a relay that connects the panels to the storage battery.  Hidden away in the Radio-SkyPipe program on the Misc. tab of Options, you will find the Triggers button.  You may configure triggers that are activated by incoming chart data (in this case the PV output voltage).  These triggers effect real world outputs, like the LabJack output we are using to control the battery charging relay.  When the PV voltage drops below some minimal charging voltage, the relay opens disconnecting the voltage source from the battery. The photocells actually can draw current away from the battery when they are not adequately illuminated. A diode in series with the + line from the panels can also do the job at the sacrifice of the 0.7V or so that drops across the diode junction.  A second Trigger may be configured to remove the PV charging voltage when it exceeds a limit corresponding to overcharging.  Overcharging can seriously affect battery life.  I am no battery expert, so I will leave it to you to research the voltage thresholds you want to use.

Whether or not you use RSP as a charge controller, it can be informative to monitor the voltages in your PV system over days or even over seasons.  This information can be helpful in making adjustments that optimize your energy collection and usage.

Wednesday, February 27, 2013

Radio-SkyPipe Update 2.5.0

Here is the URL to the Radio-SkyPipe update you will need to use the UDS serial port communication channel. A full installation of this version is not yet available.  If you do not already have Radio-SkyPipe II, you should go here and get your free copy, and then do the update below.

I have opened up the UDS feature to free version users! 

Tuesday, February 26, 2013

Arduino and Radio-SkyPipe

A New Start

 This is my new effort at blogging.  This will replace the Radio-Sky Journal which I never was able to be productive at.  I am hoping for better now.  My current intent is to make this blog more than just an amateur radio astronomy place.  All sorts of amateur science will be incorporated.  This can run the gamut from biology to hardware hacking.  Sometimes, content will be directly related to my products, however, often it will not. 

Arduino and Radio-SkyPipe

Lets get started with something I am really excited about, connecting Radio-SkyPipe (RSP) to Arduino devices.  I will describe the details of the project on a static web page, but let me introduce you to the basic ideas here.  Radio-SkyPipe is my data-logging PC based strip chart program..  It is written in VB6 which for now still seems to work on Windows computers.  Originally, the program only allowed for input via the sound card or a homebrew analog to digital converter connected to the parallel port (remember those?).  In 2009, I created a open source protocol for other devices to send chart data to RSP.  I called this the UDS (User Data Source) model.  The protocol requires the recognition of few commands and proper formatting of the data being sent to RSP for plotting. 

For every UDS that I had created, I wrote corresponding UDS executable program that stood between the data collection device (usually an analog to digital converter or ADC) and RSP.  I was using whatever protocol was native to the device to communicate with it and translating to feed RSP.  The data flowed between the UDS execuatable file and RSP over a simple TCP connection in which the UDS exe acted as a server. 

Last year I began working with Arduino hardware for a privately contracted project.  We ended up abandoning Arduino because of speed concerns, but I was taken by these devices and all of the inexpensive hardware that could be easily interfaced to them. Several weeks ago I received an email from Jonathan Rawlinson regarding a project he was working on in which he was communicating with an Arduino to Radio-SkyPipe not by the serial line directly but via a TCP-RS232 converter program.  The Arduino was handling the protocol and the converter program simply acted as the TCP route to RSP.

I decided to use a little different approach than Jonathan and to generalize the code so that it could be used by anyone writing an Arduino sketch (program).  I decided it was a practical thing to remove the TCP-Serial converter program and talk directly to the Arduino via its com port connection.  So RSP now has a com port associated with it and may exchange UDS commands and data over the serial connection without the aid of TCP.  If you have a TCP UDS, don't worry.  Both connection types are supported.

The old UDS method is shown on the left. RSP 2.5.0 provides a direct connection via a serial port to devices like the Arduino.

  The hookup details and code are given here.  I am sure that improvements can be made and that many different approaches could be taken to facilitate the UDS protocol in Arduino.  I welcome your contributions to this effort.