Randys Bench

A repository for projects past and present

Leave a comment

Sky Wanderings

I finally had some descent skies the morning of June 25th (early morning 3am) and was able to do some more testing with the ASI120MC camera and Sharpcap software. Although the Moon was out in the Southwest (92% illuminated) the seeing appeared pretty good for this time of year so I gave it a go…besides I was already up anyway! As a target I chose the area around the star Mirfak in the constellation of Perseus situated in the northeast. This area is also termed the Alpha Persei Association. This association covers about 5 degrees around Mirfak. The image below comprises 75 light frames of 5sec each stacked in DeepSkyStacker. Mirfak is the bright star in the upper center of the photo…

Here’s the area covered in the excellent Stellarium sky simulator:

Hopefully I’ll get some more clear skies this Summer for imaging…We’ll see



Leave a comment

Re-imagining my Imaging setup

This will be a rather short post since I’ve been spending a bit more in the outdoor world now with summer here as opposed to my bench. I mean who doesn’t like to dig up weeds right? With that I decided to finally upgrade the Astro imaging camera I’ve been using for the last 12+ years. The LX converted Logitech QC3000 pro, once modified for long exposure capabilities it’s been a solid performer. However it was never originally designed for this type of application and is a bit noisy (hot pixels and background banding). Moreover the resolution leaves something to be desired. So I took the plunge for a rather moderately priced ZWO ASI120MC camera which I’m slowly putting into play.

And below is a shot of the mostly completed mount plate with the major pieces in place. Not the neatest setup but wanting to use the bits & pieces I’ve got…

Looking thru my bins and drawers for what was needed I ran across a photo of the moon I’d taken back in late ’71 or 1972 which I had completely forgotten. Taken on a city rooftop thru a Sears 60mm refractor and an old instant Polaroid camera it was the 1st astro image I’d taken. Extraordinarily poor by any standards  then and now…well here it is:

Looks like lots of camera shake….I guess one has to start somewhere.

I did get a chance, on a rather cloudy and muggy evening to capture a few image with the new setup. Mostly being anxious to give it a go and at least get some familiarity with the imaging software (Sharpcap) and get the finder scope properly lined up. Still have a bit to learn but did produce an image from somewhere in the Cassiopeia region:

The seeing on this evening was frightfully bad but that was fine…other chances will come…



Leave a comment

Compact Solar Spectrograph – Back to the Drawing (Card) Board

Based on my recent experiments…I’ve not been able to coerce the performance I was looking for with the current compact design. I thought I’d take small step in reverse and examine a more “traditional” layout approach which I had utilized on my previous spectrograph build.

The 1200l/mm reflective grating I’ve now used for many years

Here’s a few photos of the previous spectrograph build from about 2003 or so:

At the time the imaging camera was a long-exposure modified Logitech QC3000 which did a far job with it’s resolution limitations.

The 1st image shows the magnesium triplet (right of center). The horizontal lines shown in both images are known as “tranversalium” caused by irregularities along the slit edges.

The 2nd image shown below is that of the hydrogen beta line left of center…

Back in the 2nd half of the ’90s I used a homebrew Cookbook 211 camera as an imager for the spectrograph and was pleased at that time how well it performed for such a small monochrome CCD (192×165) image sensor. Here’s a PDF I created demonstrating it’s capability of imaging the solar spectrum.

But now back to the present…here’s the current mockup I’ve now built with the ever popular cardboard construction technique:

You’ll notice the use of a guitar pick to raise the height of the grating mount a slight amount! Whatever is handy… Below are some preliminary images of reference lamps used as part of the tests. 1st is a neon source:

Next is a compact fluorescent lamp:

So far so good with quite a bit more to do…See you next time

Leave a comment

Neon Wavelength Calibrator

Since I’ve finally started back to do some work on a sadly neglected project, the Compact solar spectrograph, I thought it time to put together a proper neon-based spectral (wavelength) calibrator for this instrument.

I researched a few designs for the power supply, including a older Forrest Mim’s engineer’s notebook 555-based design shown below:

As well I took a look at the internal calibrator incorporated in Shelyak’s Lhires III spectrograph design which is the one I decided on. This uses a UC3843 PWM controller which, coming from the power supply industry, I’d used in design’s back in the 90’s and became familiar with. This circuit incorporates both PWM regulation control and voltage multiplier circuitry to provide a DC output of 100V. It appears to work well with a variety of neon bulb types.

Here’s a look at the completed card assembly:

This will be a nice addition to the spectrograph redesign upcoming over the next few months. Here is a nice document describing the general attributes of neon bulbs and a few silly circuits as well…Neon Lamp Information. Below is a wavelength chart of the neon gas spectral signatures to give some idea of the calibration coverage one would expect. There’s also some finer lines in the deep blue and violet end of the spectrum:

And speaking of the spectrograph redesign underway, here’s what it look’s like at this stage of development:

Quite a ways to go yet….back soon




Leave a comment

Objective Prism Spectrography

One might think given the title of this post that there is a fundamental difference between recently presented posts on HF frequency analyzers and that of light frequency decomposition and analysis. In reality it’s really more a matter of frequency range and components needed to analyze the frequency content. Where as in the HF band we’re dealing with frequencies in the sub 100 MHz range, light frequencies occupy a significantly higher frequency segment of the electromagnetic spectrum, typically in the 400 to 750 THz range!

Back in July of 1998 I had the opportunity for a brief correspondence with the author of a particular Sky & Telescope article  published in May of 1983 concerning the hardware arrangement and procedures for capturing stellar spectra using an objective prism. This involves placing a 5, 45 or 60 deg. glass prism at the front of a suitable 35mm camera (or other) and lens. The camera’s shutter is opened and the object’s thin spectrum is allowed to widen using the earth’s diurnal motion (or varying the speed of mount’s RA clock drive). The use of an objective prism has been popular for a very long time due to it’s simplicity, light efficiency and it’s capability to capture a great number of stars in a single exposure. Excellent for sky survey purposes. Although Brent Sorensen’s May article was certainly not the 1st to be published in popular Astronomy magazines concerning this subject matter it (along with other’s)did manage to further my interest and improve the somewhat crude setup I’d had up to that point and proved to be a solid path in realizing an improved DIY system to explore the realm of stellar spectra.
The subject of the correspondence was, not only to express my appreciation for the article’s subject matter, but to ask if further images were captured which may have not been published in the original article. Turns out there were quite a few, and Brent graciously consented to place the negatives on loan to me. I had the negatives made into prints at a local camera shop and later scanned them into my computer.

Sorensen’s setup at Lake Afton’s Public Observatory Wichita, Kansas – Fall 1982

Below is a selection of these never before published prints using 45 deg and 60 deg prisms:

45 deg prism capture of Orion area

45 deg prism capture of M45 (Pleiades)

45 deg prism capture of  the Hyades (Taurus)

60 deg prism capture of Aldebaran (Taurus) 4min exp.

60 deg prism capture of pollux 3min exp.

60 deg prism capture of Sirius 3min exp.

Here’s an additional link for Brent’s followup article describing his reflection grating spectrograph

And I think that’s my story today…Randy


Leave a comment

Wrapping up the MC3356 Spectrum Analyzer

Oop’s! Well this time I managed a self inflicted circuit error. I was thinking I needed to invert the VCO sweep output hence adding an inverting x1 opamp to the VCO output…wrong. Due to the way the 1st mixer’s LO’s varactor is reversed biased the sweep polarity needs to be opposite of that of the X-axis sweep ramp. Works a lot better now. I’ve picked up another 30 MHz or so on the LO’s high frequency range. The occasional pitfalls of over-thinking…I’ve updated the Sweep generator/video amplifier schematic posted earlier. Below is the salient bit:

So what else…I corrected an additional error of judgement by removing the MC3356 IC socket I originally decided to use. By removing said socket I eliminated approx. 4.5mm of lead length and it’s accompanying inductance and parasitic capacitance(s). Makes for a tighter layout for those VHF frequencies involved in the SA design. Additionally I’m changing over the leaded radial caps I’m using around the MC3356 LO for SMT 1206 leadless components, and moving the varactor & L2 coil to a tie point directly to pin 3. I’d like to push the SA’s upper end as high as possible. Here I’ve picked up an additional 5-10MHz of frequency span.

At this point I’ve settled on an L2 coil construction of 2.5 turns of 3/16″ diameter. L2 constuction depends on your particular component layout. The tuning varactor remains a BB209 variety.

Lastly I played around with characterizing a few 10.7 MHz ceramic filters I’ve got in the bins to see if this is possible with this analyzer. Well it is as it turns out..kinda sorta. I built up a simple test fixture to accommodate these bandpass filters:

And here’s a few plots demonstrating the results of the tests:

Both of the above plots have an approximate resolution of 200 KHz / div. The vertical has not been calibrated as yet.
This has been a fun project and interesting learning experience. I’ll revisited this project once it’s situated in the chosen enclosure…

As always thanks for visiting…Randy

Leave a comment

Intermission: Thoughts on an Upcoming Bench Project

Back in the mid ’80s I had an opportunity to become somewhat familiar with a Tek semiconductor curve tracer we had on a back bench in our lab. This was a Tektronix Model 576 originally introduced to the market in 1969 at a touch over $2000…not cheap

I thought at the time how nice and useful a similar instrument would be on my home bench. Of course the price tag alone precluded such a commercial version as this. But, I did find a few projects in the Electronics magazines published back in the 60’s and 70’s at the local library. All well and good but in reality I didn’t really have the time or resources then to realize a homebrew curve tracer of a type I would find usable.

Here’s a few links to some semiconductor curve tracer projects and info back when:

1. Radio-Electronics November 1965 “Component Curve Tracer

2. Radio-Electronics December 1969 “Transistor Curve Tracer

3. Electronics World August 1971 “Transistor and FET Curve Tracer

4. Radio-Electronics June 1972 “Build a Transistor Curve Tracer

5. Popular Electronics June 1972 “Build a Versatile Semiconductor Curve Tracer

6. Radio-Electronics November 1972 “Using a Solid-State Curve Tracer

7. Radio-Electronics April 1975 “Using the Curve Tracer

8. ETI January 1979 “Curve Tracer

A slighter more current curve tracer project that caught my eye is located here
Popular Electronics’s May 1999 “Semiconductor Tester” project…

This project seems to be a nice compromise between functionality and versatility. But first there’s more work to do on the spectrum analyzer…

Next time…Randy