Quasi-SDR Telescope

[John101]

Background

Wandering the ‘www’ a few week back, I ran across this…

[26 January 2014]

Jupiter Season Passes Midway Point

Jupiter was at opposition (the point where it is on the direct opposite side of the Earth from the Sun) on Jan. 5th, 2014. Jupiter is currently well placed for evening observing. The conjunction in 2014 will occur on July 24, 2014. If we assume that the observing season ends about two months before that, we have until approximately May, 2014 for our current Jupiter watch.

So I said to myself, since you’ve collected more radio ‘stuff’ over the years than optics why not build a radio telescope and hear what this is all about?

Believe It Or Not:  in the mid/late 1950s one of the best grades I got in high school was on a radio telescope research paper.  We lived in southern West Virginia at the time Green Bank was coming into focus.  Even though a ham at the time, I have never tinkered with a radio telescope.

So, I went back to the www (to search for dreams that fit budget and experience) to find a thread on Stargazers Lounge that referenced the Ten-Tec 1056 short wave radio. This triggered the conclusion that hay I probably have enough stuff on hand to build and ‘blog’ (if that is the right term) ‘our’ radio telescope here on SGL.

Our radio telescope?  What an excellent point in time for a grand daughter, now in high school, who received a Ten-Tec 1056 for Christmas a year ago, to get more involved with the astronomy resources here on SGL.  She lives out in the country with very low ambient light and low RFI. In addition the house sits on several open acres perfect to erect a phased-dipole antenna farm. What else can Gramps ask?

First… I must thank and apologize to Marcus (screen name: schorhr)

Thank you; it was your post with reference the TenTec 1056 that set our project in motion.  Apologize; for I only have one spare 1056 kit to offer.  I did not realize at that time two radios would be required for quadrature (I/Q) output.

Our-Quasi-SDR Telescope

A quasi-experiment is an empirical study, cause, effect and consequence

SDR (Software Defined Radio) Telescope

Block Diagram

            tba, with  gain/loss signal levels

Antenna

            Phased 20 MHz dipoles

            Radio Jove RJ1.2 Antenna Manual 2012

Power Splitter

            MiniCircuitLabs, ZEC-2-1 from ham fest years ago

Band Pass and/or Band Reject Filter-s

            Coax Quarter-wave Stub

            Tuned via MFJ-259

            ARRL Handbook

Pre-Amplifier

            tba, bone yard promises hamfest gold

Local Oscillator

            N3ZI  DDS2

Quardrature Hybrid

            tba

Detector

Two modified TenTec 1056 direct conversion short wave radios

SDR Software

            C#  (pronounced C sharp) 

            and/or

            SoftRock

Data Management / Storage Software

            Audacity         

Display System

            ARGO

            SpectrumLab

PC

            DELL Notebook

With exception of  antenna, coax, enough connectors and quadurature hybrid all else is on hand (i.e. compensated :>)) and has been used on the air by me in pasted years but never configured into a radio telescope.

This experiment is  “our” first radio telescope!!!

So, first quasi experiment… scratch build a quadurature hybrid !!!

[John101]

QuadratureHybrid-coming-to-life

[Gasman]

Looks very interesting John! Would be good to checkout another part of the EM spectrum ;-) look forward to seeing the end result.

Steve

[John101]

The prototype 90 degree hybrid turned out a delight.

Target frequency was 20.2 MHz. The math calculated 73.5 pF for caps, best on hand was 100 pF so it came to resonance tad low at 18.6 MHz, but, close enough to start receiver modification and single channel on the air test. So I have to assume the toroid-core and turns ratio was near dead on.

[John101]

The LO and 90* Hybrid and TenTec 1056#1 play together so well I need a front end 20 MHz band pass filter (BPF) and provide some means for calibration. 

Image,  just-finished broadband signal (noise) source and with good ham fest pads and known power meter prove within +/- ½ dB, for my guess-ta-mation of 3% repeatability.

What’s Next?

Define a 20 MHz BPF, first shot will be a ¼ wave stub. Advantages; so easy to build and tune, up to 50 dB notch or peak, disadvantage; fixed bandwidth and skirts, skirts are not exactly brick wall

Define broadband minimum discernable sensitivity(MDS) i.e how much preamp will I need?

Define and build a narrowband signal source for phase calibration (through two radios)

[John101]

Scheme change…

Why modify a faultless SWL receiver when you have enough pieces parts in the ham fest bone yard?

Image:

Very top center;

Un-modified TenTec 1056

Lower left corner, bottom poke board;

Extra-terrestrial receiver (ETR#1) comes to life

Lower left, middle two poke boards;

QRP transceivers from previous experiments, one, a 30-meter ham band (10.106 MHz), who’s LO just happens to double into 20.2 MHz and my first ET frequency of interest!!!

[John101]

_{Progress to date:}

_{Finally on the air (so to speak) for a ‘test drive’;}

_{One working broadband calibration noise source with power meter}

_{One working ET receiver with quadrature LO option}

_{One oriented (north/south lQQking) and pruned (20.2 MHz) antenna}

_{One full wave feed line with power splitter ready}

_{And with some application software running;}

_{IrfanView (a free download for image and sound card construct) and I are old friends, THANKS again Mr Skiljan for keeping such a delightful piece of work up to date!}

_{SpectrumLab (visual, time (waterfall) and frequency domain plus I/Q and digital demodulation) with BITE (built in test equipment) THANKS to DL4YHF and at a couple decades work in progress. WOW!!! What an outstanding free download, but, at my age and retirement date (been out of the engineering loop since 1997) made for quite a learning curve.}

_{Delighted to find SpectrumLab and my note book soundcard run well in stereo-mode :>))}

 _{i.e. I/Q demod (and I’m sure I’ve only scratched the surface here).}

_{Test drive?}

_{Of course I will need two receivers, two antenna and two feed lines for full up galactic interferometry and aperture synthesis observations.  Plus a narrowband CW source for phase calibration.}

_{73 es Good DX}

_John

_N3AAZ

 

[John101]

My QSD/SDR-Telescope Update

Most electronics is poke-board (image) but play very well together, I am still tweaking some of the gain circuits for ‘flattest’ bandwidth. Like optical telescopes pollution is a problem, in this case, radio frequency interference (RFI) from both terrestrial and adjacent components (block diagram) contaminate the outcome. Steps must be taken to shield corrupt circuits from domino effect.

SpectrunLab has quite a learning curve (my age is reflected in this loop) but wow I’ve only scratched the surface I’m sure!  Sweet!!

[John101]

A work in progress,

so this blog is a bit rough at the moment

My gain in knowledge since this venture started reveals a

WOW Factor and Aha-plateau…

Revised objective,

Mulit Mode Radio Telescope (block diagram);

QSD…Quadrature Sampling Detector

SPS…Stepped Power Spectrum

Fringe…Interferometry

SD…Software Defined

Spectrum Lab (thanks DL4YHF) will allow

diverse mode and almost real time data contrast via,

an onboard Plotter and/or

IrfanView imaging (thanks Irfan Skiljan) and/or

port to MS-EXCEL and all it’s magnificence

Image;

SA-612, Gilbert cell mixers, blocks 9 es 11 built on RockMite (thanks K1SWL) PCBs

Cost as of project start;

Less than $10.00 (two 10 foot PVC pipes for antenna support)

All material for this project was used for other projects and/or

from ham-fest / bone-yard archive

John

[John101]

!oops dupe image :>(

[7170]

Delighted to find SpectrumLab and my note book soundcard run well in stereo-mode :>))

 _{i.e. I/Q demod (and I’m sure I’ve only scratched the surface here).}

Hi John, am I correct in saying you're using your laptop to record the output and analyse in SpectrumLab?

If so I would say do some testing of the sound card in your laptop. In my experience laptop soundcards don't appear to be shielded well and if you turn input levels up you can often get a lot of noise from the laptop internals or picked up from something close by. I have a SID detector setup and had to use an old desktop in the end as my laptop's soundcard picked up too much interference which could be seen on SpectrumLab even though it sounded absolutely fine in normal day-to-day use.

Another good tip is to take the output of the plotter and load it into excel and graph there with a moving average to smooth the curves out if you have a high sample rate.

[John101]

Thanks 7170 …

Yes you are correct; SpectrunLLab (thanks DL4YHF) runs my laptop stereo soundcard in I/Q SDR mode and ports to EXCEL.  SLs Plotter Watch List, while running its own analysis, plots events. With IrfanView (thanks Irfan Skiljan)s ready to capture an image of the moment!

HamRadioDelux (thanks HB9DRV) runs a second USB port for narrow band FT-817 receiver control

And thanks too for bringing up a good point…

Radio frequency interference (RFI) can be a BIG pain in the … ‘ham shack’

Image 1

Clamp on ferrite beads corral the greater part of common mode RFI problems

Image 2

And incredible job directing ‘wished-for’ RF current down the coax center to let the outer shield achieve its intended task  –and-in-addition-  keep common mode current coming from the shack getting back on the antenna i.e. to help exterminate the domino effect

John

N3AAZ