Just realized that I have couple of AD8310 and AD8314 logamps in my stock :-)
Since I have the theoretical noise level of -130dBm @ 20kHz BW, the output level from preamp stage is ~-90dBm.. and the input range of AD8310 is from -80dB m (@ 50 ohms) to -17dBm..
So I need ~20dB additional gain.
I will also need a down-converter, because AD8310 fr cutoff is at 400MHz.
And ADC.. or some win app that measures DC voltage at MIC input of the audio card.
This configuration will be usefull as radiometer - the precise measurement of radio flux.
However, no spectrum analisys..
After some time, I am back to my radio-astronomy project..
Today I put together two amplifiers (total gain 60dB, NF= 0.5dB) and tried with Sun again.. no problems, signal was >5dB above the system noise floor.
Then I reduced the BW on my Spectrum analyser and tried with antenna pointed at zenith (where Milky Way was at that moment).
Results are summarised on the attached picture:
On the screen, two tracks are visible.
One is with spurious signal at -70dBm (internal spur, harmonic of reference frequency), another (in the centre of the screen) is clearly coming from outside (it disappeared when I switched off the power to pre-amplifiers).
After one hour, when Milky Way was not in the antenna field of view, this signal was also gradually gone.. visible on the screen as well, on the second track (there was some frequency shift during that time, this Spectrum Analyser is drifting a bit - I should have switched it ON much earlier, to allow more time to stabilise).
I am trying now to confirm what I saw.. I hope it's not some radio-amateur experimenting on same frequency..
I think I managed to convince myself I am actually observing the Milky Way at 21cm
The attached image confirms the statement.. The marked "bump" is Milky way, the other track was taken with antenna away (at zenith).
The sharp peaks are external.. the middle one is from my test generator set at 1.4204GHz, the others are of unknown origin.. but definitely from Earth.
In the course of the observation (2 hours, max hold), I noticed the peak frequency of the bump (marked) was changing slightly (lowering..).
All this is increasing my confidence in the setup.. I will be able to prove to myself that Milky Way is rotating
A very interesting result. I think the baseline raise around your marked peak is a good indication that what you are seeing is a source composed of lots of little sources. This is some indication that it might be extrasolar.
What is the BW of your SA ? From the header I read 50kHz span, which makes the marked source 1420.3125 MHz, with a span of about 8kHz across the shoulders.
With the galactic rotational velocity of ~100km/sec, we would expect that your detector would pick up the galaxy's hydrogen line anywhere between 1419.8MHz and 1420.7MHz depending on whether the bit you are pointing at is approaching us or receding from us (or not doing either). So what you show is consistent with the 21cm hydrogen line, with a bit of spread due to you sampling stuff around an area rather than a single star. The effective field of view of your radio telescope would be a good thing to know.
This is result of the second pass of the Milky Way (from last night, antenna was pointing upwards).
I am still not entirely sure about accuracy of frequency calibration (1.4204 is middle peak on the test track), generated by HP8922M, set to 710.2MHz.. so on the screen is first harmonic), but the two peaks of the 21cm signal are very obvious.
Guys,
I am trying to write a simple (Borland Turbo) pascal routine, which should read ADC values starting at specified time, with specified intervals between readings, for 24 sideral hours.
Before I went too far into that task (I am not a good programmer..), I would like to ask a question:
Does anybody knows of such source code?
It doesn't have to be pascal, anything else will do, as long as I have easy access to LPT port (on which my ADC is attached).
I know that SkyPipe supports ADC via LPT port but I do not have that particular ADC at hand.. and it has to be freeware.
Thank you in advance!
Currently I am thinking about PCF8591 (I2C bus), as I have it at hand.
And I already wrote the code for it (years ago), but I do not have a decent code for timer.
Actually, I worked out something today.. I can start (reading, or whatever) every second or every minute or every hour (by reading system clock via "GetTime" procedure).. but I still need to be able to program the start time, and more flexibility with interval.
Since you are using I2C, you could use something like the PCF85063A real-time-clock which has an alarm function. You set the alarm time and it pops up a pin. You can either do the sidereal to solar calculation or, since the osc uses the crystal in series resonance, pull it off frequency to run the clock at sidereal rate. The chip will keep time for years on a hearing aid battery.
After a lot of fiddling with various options, I decided the best approach to record data would be to control the HP8569B spectrum analyser via HPIB bus from built-in HP8922 IBASIC controller (I am using this machine as part of the system, because of its very stable and accurate time base).
However, I am having difficulties with programming this beast...
I am using terminal program running on PC (via RS232), and this is very uncomfortable, since there is no text editing capabilities in IBASIC controller.. so I have to re-type the code lines in full every time there is a syntax (or whatever) error encountered, and the IBASIC manual for 8922 is not written for beginners (which I am, after 20+ years not using it).
Is there anyone on the forum that might help me with this?
Thanks in advance!
EDIT:
I found that string variable accepts only 18 characters by default.
So, to proceed, I had to insert the following statement:
5 DIM A$[1923]
String variable A$ can now accept the full length of trace data from SA, and I can go on with developing routine for data collection in numerical form.
Then, next stage was a small IBASIC program:
5 DIM A$[1923]
6 INTEGER Ta(480)
10 OUTPUT 709;"TA"
15 ENTER 709;A$
20 PRINT "Trace transfer from 8569 finished"
30 PRINT "Printing numerical results.. "
50 FOR I=0 TO 480
60 J=4*I+1
70 Ta(I)=VAL(A$[J,J+2])
75 PRINT Ta(I)
80 NEXT I
200 END
The first test spectrum from SA (pilot tone at 1420MHz) in numerical form is attached below.
Use your favorite text editor on the PC and then do an ASCII transfer of the file with suitable (found by trial and error) inter-character and inter-line delays. Even the god-awful hyperterminal can do that.
PS. Thanks for nostalgic flash-back of writing data analysis programs on an HP-85. :-)
G'day Bojan, for info here's a different approach if you're open to alternative data collection/logging options?
I'm using a USB TV dongle with an alternative to skypipe (RTLSDR Scanner) which can be run from command line. I've found this pretty flexible and have it triggered using VBScript on a schedule from Windows task scheduler. Output goes to a csv file. It does generate a lot of data, but I read it into XL and reduce it with some VBA code.
Observation from early this morning, Crux region (with test signal superimposed).
Signal strength is celibrated to the antenna output.
I still have to figure out the antenna efficiency, to be able to express the vertical axis in terms of flux density.
Residual BW was 10kHz, digital averaging, sample detector.
Interesting signal capture, If that is from your spectrum analyser than you have a red shifted signal. Although that will depend on the calibration of the injected source signal though.
I think you may have more of a handle on it than me though.
Malcolm,
I have both red shifted and blue shifted signals :-)
On this particular spectrum, the 21cm line is pretty broad, spread across almost 500kHz BW, indicating velocities between ~60mh/s receeding and ~20km/s aproaching.
I am wandering now why on Earth I didn't start this or similar project earlier.. beinng RF design engineer
Probably because I had too much electronics as part of my everyday work..
Also, vintage (but GOOD) equipment is much more affordable these days..
HP8922 that I am using as time base and IBASIC controller was US$25k 20years ago.. and I've got it for $100 on internal auction in the company I worked for. Noone wanted it because it was too heavy and too specialised (GSM testset).. so I said to myself, what the heck... another box in my cubboard won't be a problem, and it may be used for soemthing one day
I have to 100% agree with you, hence the reason why I have started to look into 1.4GHz as well. My only problem is I am studying to further my existing qualifications as a Radio Technician doing and Electronics and Communication Degree and have really limited time available. I am also battling severe sleep apnoea too and have been temporarily prohibit driving and staying awake grrrr. At least I have my first appointment this week to get it resolved. My health frustrations as starting to get me babbling sorry.
This semester start next week and will start 3rd year course in Electromagnetics. Well in my line of interest.
I am really hankering for test gear and one of my greatest ambitions is a decent spectrum analyser but even though they are cheaper, they are still very expensive on a students income and my wifes disability support pension.
I also have to deal with my wife not understanding what I need. She looks at my current gears and quizzes why? Her disability makes it difficult to explain to her I wish my AUSLAN (Australian Sign Language) was a level 4 which doesn't exist in Australia.
!
I wish my AUSLAN (Australian Sign Language) was a level 4 which doesn't exist in Australia.
