Randys Bench

A repository for projects past and present

MC3356 SA Storage-Normalizer – Continuance

In the process of wiring up the AD/memory card I discovered a minor error in the schematic involving duplicate pin numbers on each of the four 74HC161 counters used. Two pins, being marked as pin10, it turned out that the S/bar input should be pin 9 as shown below:

I discovered an old Tektronix scope calibrator PCB I had received back in the late 80’s and thought it would be a nice addition to the SN project. This would allow a low frequency internal signal for calibration purposes. I’ll use a rotary switch to couple in int/ext signals to the A/D converter section. I completed the interface board as shown below. But for now the wiring continues…

Interface board – MC34074 & uA723 regulator

Back soon 73 Randy

MC3356 SA Storage/Normalizer – Beginnings

I decided as a first MC3356 SA addon to begin putting together Matjaz Vidmar’s, S53MV Storage-Normalizer project. It’s capabilities include storage up to 32mS of trace data (32K x 8 SRAM), Switchable analog & digital display capabilities and in particular allows for calibration data storage when used with a tracking generator i.e “A simple subtraction of the system response from the measured trace (DIFFERENCE) removes any system influence on the measured device response”

So as seen I’ve begun the A/D – memory card layout and wiring. Lot’s of wiring to go which is fine since the TDA chips won’t show up for 6-8 weeks anyway… Back soon 73 Randy


MC3356 Spectrum Analyser project – Addons

First a brief update on a few changes attempted in the SA. I replaced the 10.7MHz/IF amp card with one which incorporated an additional post filter IF amplifier (I mentioned this in an earlier post). Whether needed is still under test. I put together a simple 10MHz source to use as a calibrator (Internal this time). Turned out it’s a little weak above 50MHz so I plan to add an amplifier to it’s output for a little gain…In process.

Next I thought, what about some useful add-ons for the analyser? A tracking generator and a Storage-Normalizer came to mind. A few years back the designer of the original 100MHz Hobby Spectrum Analyser, Bob Kopski along with John Lawson published a simplified version of QST’s SA tracking generator. I ran across this back during the 100MHz HSA construction days and thought would be a great addition then and now. Here’s the schematic of this simpler and cheaper form:

And the Block diagram:

The original document can be found here
This TG could be built with only a few modifications to accommodate the MC3356 VCO range and low pass filter.This is a definite possibility for increasing the base functionality of the SA.

Next the 2nd addon I mentioned with that being a Storage-Normalizer. Again I ran across this design a few years back and is the brainchild of Matjaz Vidmar, S53MV. This addon compliments his own design of a +1GHz SA.
Here’s a link to the PDF describing his efforts…

The design does use a few now obsolete components such as the TDA8703 A/D converter and the TDA8702 D/A. However they are still available on auction sites etc.The remaining chips are easy to come by although I’m not sure about the uA723 power supply controller; I just happen to have a few in the bins. Besides passives & transistors here’s a short component list:

MC33074 (1) uA723 (1) TDA8703 (1) ADC TDA8702 (1) DAC
74HC164 (1) 74HC161 (4) 74HC00 (2) 74HC74 (1)
8MHz oscillator (1) 62256 Memory (1)

This Storage-Normalizer project might lend itself to the addition of an Arduino w/ serial comm to capture data to the PC….maybe. So at this point I’ll check some pricing on the needed parts and see where things go…
Back soon 73 Randy

Super-Earths Discovered Orbiting nearby Red Dwarf

The nearest exoplanets to us provide the best opportunities for study, including searching for evidence of life outside the Solar System. Astronomers have now detected a system of super-Earth planets orbiting the nearby star Gliese 887, the brightest red dwarf star in the sky. The newly discovered super-Earths lie close to the red dwarf’s habitable zone, where water can exist in liquid form.

Image Credit: Mark Garlick

The RedDots team of astronomers monitored the red dwarf, using the HARPS spectrograph at the European Southern Observatory in Chile. They used a technique known as “Doppler wobble,” which enables them to measure the tiny back and forth wobbles of the star caused by the gravitational pull of the planets. The regular signals correspond to orbits of just 9.3 and 21.8 days, indicating two super-Earths — Gliese 887b and Gliese 887c — both larger than the Earth yet moving rapidly, much faster even than Mercury. Scientists estimate the temperature of Gliese 887c to be around 70C.

For full Story visit ScienceDaily

73 Randy

Ocean Underneath Pluto?

A new study suggests that Pluto and other large Kuiper belt objects started out with liquid oceans which have been slowly freezing over time.

“The accretion of new material during Pluto’s formation may have generated enough heat to create a liquid ocean that has persisted beneath an icy crust to the present day, despite the dwarf planet’s orbit far from the sun in the cold outer reaches of the solar system.”

Image: NASA

This “hot start” scenario, presented in a paper published June 22 in Nature Geoscience, contrasts with the traditional view of Pluto’s origins as a ball of frozen ice and rock in which radioactive decay could have eventually generated enough heat to melt the ice and form a subsurface ocean.
“For a long time people have thought about the thermal evolution of Pluto and the ability of an ocean to survive to the present day,” said coauthor Francis Nimmo, professor of Earth and planetary sciences at UC Santa Cruz. “Now that we have images of Pluto’s surface from NASA’s New Horizons mission, we can compare what we see with the predictions of different thermal evolution models.”
Because water expands when it freezes and contracts when it melts, the hot-start and cold-start scenarios have different implications for the tectonics and resulting surface features of Pluto, explained first author and UCSC graduate student Carver Bierson.
“If it started cold and the ice melted internally, Pluto would have contracted and we should see compression features on its surface, whereas if it started hot it should have expanded as the ocean froze and we should see extension features on the surface,” Bierson said. “We see lots of evidence of expansion, but we don’t see any evidence of compression, so the observations are more consistent with Pluto starting with a liquid ocean.”
The thermal and tectonic evolution of a cold-start Pluto is actually a bit complicated, because after an initial period of gradual melting the subsurface ocean would begin to refreeze. So compression of the surface would occur early on, followed by more recent extension. With a hot start, extension would occur throughout Pluto’s history…

Read the full article HERE

Courtesy of ScienceDaily

73 Randy


The MC3356 Spectrum Analyser Project – A Summary

Originally conceived as a contest design submission by Albert Helfrick to RF Design magazine back in January,1988. the design fostered considerable interest among the amateur community around the globe. In particular, in the UK, interest was such as to spurn on an improved version. Combining Helfrick’s earlier more complex design published in QST and a few additional bits and pieces by Roger Blackwell, the updated design was published in November’s 1989 edition of Radcom magazine and insuing kit made available proved to be popular as an inexpensive alternative to pricey commercial spectrum analyser’s on the market then and today. However it really depends on personal needs and requirements (and budget!). Older commercial models are available relatively inexpensively on online auction sites as well as new very cheap ($40-50) model’s from a variety of vendors. The joy of building the instrument, regardless of it’s modesty, is in my opinion the very heart of amateur radio. The educational value is not to be under estimated with such a venture, as I know full well.
So today’s instrument, thou boxed up, Isn’t quite done yet. So far I’ve replaced the 5V card (78L05) with an adjustable LM317L implementation to give me some wiggle room to bias the Log amp and the 2nd mixer stage. The 1K pot is set for ~6.2V at the moment. Next is the finished replacement the IF amp & 10.7MHz ceramic 3-terminal filter. I added an additional IF amp stage post the filter. That will be put in place shortly. For now I put together a short video cruising thru my random wire antenna output. Not the highest quality video but the idea is there.


Again till next time 73 Randy

Boxing up the MC3356 Spectrum Analyzer Finale

Even though presenting a Boxing finale type post would be indicative of a job at-hand reaching a natural finish line, I’ve found that’s rarely the case. I suspect many projects in basements and labs are never fully buttoned up and stamped finished/done. It seems there’s always some mod/tweak or improvement which beckons us back. This SA project is certainly no different. I noticed in doing the post box testing that there’s simply a lack of gain in the IF circuitry. In particular, the loss of gain due to insertion losses from the final 10.7MHz ceramic filter. So the next change will be replacing the preamp/filter card with one that includes an additional gain stage. Not too bad…But after the boxing, testing went well on the whole. Here’s some pics of where things are currently:

Below is the card assembly that I’ll be adding the extra IF gain stage (Actually I’ll be replacing the whole card with a rebuilt one, the extra filter socket was not used and I’ll need the space)

See you soon 73 Randy

51-Pegasi – 1st Planet discovered orbiting a Sunlike Star

On October 6, 1995, astronomers Michel Mayor and Didier Queloz announced the momentous discovery of the 1st planet in orbit around a distant sunlike star. 51 Pegasi b has about half the mass of Jupiter. It orbits a star not unlike our sun.

October 6, 1995. On this date, astronomers Michel Mayor and Didier Queloz announced the discovery of the first planet in orbit around a distant sunlike star. They later published their finding in the journal Nature, in a paper titled simply A Jupiter-Mass Companion to a Solar-type Star.
The star was 51 Pegasi, located about 50 light-years away in the direction of our constellation Pegasus the Flying Horse. Astronomers officially designated the new planet as 51 Pegasi b, in accordance with nomenclature already decided upon for extrasolar planets. The b means that this planet was the first discovered orbiting its parent star. If additional planets are ever found for the star 51 Pegasi, they’ll be designated c, d, e, f, and so on. So far, this planet is the only one known in this system…

Read the full article here: https://earthsky.org/space/this-date-in-science-first-planet-discovered-around-sunlike-star