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  #61  
Old 24-02-2015, 01:43 PM
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Astrogeo (Tony)
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Originally Posted by mswhin63 View Post
I have an L Band Up Down Converter I am looking at using as it has up to 45db gain. Place a LNA and should start something
Hey Malcolm can I ask what type the LNA is? Is it a bought one, or homebrew? Sounds meaty with 45db Gain. I've been thinking about how to improve that component of my rig and have done some searching but not sure of the best approach since I'm scanning a broad freq range (25-88MHz) ta
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  #62  
Old 24-02-2015, 02:08 PM
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This is not an LNA, instead it is a amplifier with a downconverter more of a mid stage amplification and converter stage. It still requires a Low Noise Amplifier in front to give it its initial sensitivity.

As it is an intermediate restage amplifier it can have multiple stages to provide 45 db of gain.

I picked to up at an auction. The only unfortunate part is that the impedance is 75 ohms, but it should be rectified with a very simple impedance matching network to provide me with the 50 ohms that I'd like.
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  #63  
Old 24-02-2015, 02:40 PM
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Very simple matching cicuit I am using is 1/12 wave circuit, described here:
https://www.cv.nrao.edu/~demerson/twelfth/twelfth.htm
It is not broadbad, but loss is very low (0.5dB in my case)

This circuit is also used to power my LNA (that is why those additional coils and caps are there).
I am also inserting the pilot signal there (via side SMA connector, open) with -33dB coupling, for frequency check.
The reason for all this is, 75-ohms cable (RG6) is very low loss and good quality.. and available at Bunnings.
50-ohms cable (RG58) is much more expensive and not so good at those frequencies (1.4GHz).

I cut this PCB with scalpel...
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Last edited by bojan; 24-02-2015 at 02:58 PM.
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  #64  
Old 24-02-2015, 03:13 PM
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Thanks for the info, things are going to get a little bit busy at the start of semester so I may need to put off this project again until the next holiday break.

I am not sure if I will end up using the up down converter, I thought it was a good alternative to use that and a much lower frequency spectrum analyser like the RTL system.

This is just an easy and quick way to get started with limited funds. Still enjoying your efforts and watching this post very closely.
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  #65  
Old 25-02-2015, 05:51 PM
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Initial scan started, using listing as follows below..
Hopefully tomorrow I will have a first scanned band, 7.5° wide, at DEC -70°.

Program listing:
10 DIM A$[1923]
20 INTEGER Ta(480)
30 Interval=300!Interval in seconds
40 Test_duration=24!Observation time in hours
50 Test_duration=Test_duration*60*60
60 Test_end_time=TIMEDATE+Test_duratio n+Interval
80 LOOP! start of the loop
90 Int_end_time=TIMEDATE+Interval
100 Curr_time=TIMEDATE
110 PRINT "Current time = ";Curr_time
120 PRINT Date;Time
130 OUTPUT 709;"TA"
140 ENTER 709;A$
150 PRINT "Trace transfer finished"
160 PRINT "Time = ";Curr_time!Timestamp
170 FOR I=0 TO 480
180 J=4*I+1
190 Ta(I)=VAL(A$[J,J+2])
200 PRINT Ta(I); !Printing track to terminal via RS232 in the same line
210 NEXT I
220 IF Curr_time>Test_end_time THEN GOTO 290
230 REPEAT
240 Curr_time=TIMEDATE
250 UNTIL Curr_time>Int_end_time
260 PRINT
270 PRINT "Interval Loop finished"
280 END LOOP
290 PRINT "END TEST"
300 END
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  #66  
Old 26-02-2015, 10:47 AM
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A problem occured in midnight:

It seems that HP8922 internal clock went bacwards 24 hours.. thus disrupting the scan.

Does anybody know anything about this strange behaviour of the RTC ?

In manual I found reference to internal clock:

TIME
Description Sets/queries the TIME of day for the instruments clock.
Syntax CONFigure:TIME?
CONFigure:TIME <real> [:INUM]
Options Refer to Appendix A.
Format = HH.MM in 24 Hour format.

DATE
Description Sets/queries the current DATE for the internal clock
Syntax CONFigure: DATE?
CONFigure: DATE <integer> [:INUM]
Options Refer to Appendix A.
Format = yymmdd

But, whatever I type as command, all I am getting is syntax erro message.. very frustrating..

Last edited by bojan; 26-02-2015 at 02:10 PM.
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  #67  
Old 27-02-2015, 06:56 PM
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Problem solved with the following statements, specific to HP8922

120 OUTPUT 814;"CONFATE?"
130 ENTER 814;D$
140 OUTPUT 814;"CONF:TIME?"
150 ENTER 814;T$
160 PRINT "System Date & Time",D$,T$
170 PRINT "TIMEDATE = ";Curr_time

All this was actually in the manual.. but it was not cleat to me until give it some more thought.
Now I have time stamp. The format of the returned value is strange, but consistent.

System Date & Time +22715 +1.95300000E+001

This means:
The date is Feb, 27, 2015
Time is 19:53.
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  #68  
Old 27-02-2015, 09:08 PM
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Quote:
Originally Posted by bojan View Post

System Date & Time +22715 +1.95300000E+001

This means:
The date is Feb, 27, 2015
Time is 19:53.
US Date system and no colon implemented in the ASCII character set.

Well done, you have done really well and I am so happy to see red and blue shifting in you data.
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  #69  
Old 01-03-2015, 06:22 PM
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Work continues..
But I have a lot of RP *Radio-Pollution)

I thought noone is permitted to transmit on this frequency..
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  #70  
Old 01-03-2015, 07:41 PM
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This signal I am getting from the direction indicated by red circle
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  #71  
Old 01-03-2015, 08:19 PM
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Nice stuff, is that further red shifted than before?
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  #72  
Old 01-03-2015, 08:40 PM
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Yep..
But I think this is associated with MW.
There is also a signal from LMC earlier, it is in the collected data but I can't find it now.
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  #73  
Old 01-03-2015, 11:25 PM
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still a very good result well done
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  #74  
Old 05-03-2015, 05:28 PM
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I wanted to share with you guys the forst results of my work, just one scan, actually a band of sky 7.5° wide at DEC -53°.
On this graph, the horizontal axis is velocity, vertical axis is signal level at antenna output, and "series" is time, or AR.

All features parallel with X or Y axis are external or internal interference..
only that red, random-like blob at the roughly middle of the graph is actually Milky Way signal.

I have a huge work on my plate to do to sort this out properly.. but I am really excited about it.
I am aware that this is a far cry from a "real" scientific work.. but still it gives me a taste of what professionals could be doing and what this is all about (at least I think so.. ).
Anyway.. my journey into amateur radio astronomy has just begun ..
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  #75  
Old 05-03-2015, 06:33 PM
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Really nice! Definitely things are speeding up at your end.
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  #76  
Old 06-03-2015, 07:34 AM
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Yep..
Data are pouring in now, and I am wandering how to process all that properly. Mainly data reduction.. removal of known external interference.. and finally, presentation of the information.
There is a lot of info on this here:
http://www.haystack.mit.edu/edu/undergrad/srt

However, I do not want just to follow somebody else's example...
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  #77  
Old 17-08-2017, 04:16 AM
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Interdigital Filters

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Originally Posted by bojan View Post
After some time, I am back to the project :-)
Filter is tuned on the frequency, but I am still not happy with response - it is not flat (ripple is +/-1.5dB, and the attenuation is 3.5dB.. too much for placing this filter in front of the LNA.. so it will have to go after.
Getting there..
Hi Bojan,

Saw your note on the problems you are having. I've built a few of these now and have some observations. (Mine are 1275MHz centre frequency). If you use the Butterworth routines, then the bandwidth tends to be fine. The tapping points I have have found to be a bit too low. The rods seem to me to be slightly too short, as the tuning screws (I use 6mm screws for 6mm rods) are a long way into the case, when the design does not recognise the need for screws. The two characteristics that strongly drive passband attenuation are bandwidth and case depth.

By the time I add in 0.2dB for connector losses (not included in the design tool), then the passband attenuation is not far off.

I have discovered "Dishals tuning method", this is great for these filters, but you do need to be able to measure reflected phase. All you do is terminate the filter with a 50ohm load, wind in all the screws to short the resonators. Then using a VNA or similar, back off the first screw and watch for the phase flipping from -ve to +ve and lock off the screw at 0deg at your centre frequency. Move to the second screw and back that off until the phase is at 90degrees. This is an inverter, so the input impedance should be 0 + J50. If all is well you move onto the 3rd screw and back that off until it is at 180 degrees, then the input impedance will be 50 + J0 and the resonators are all bang on the desired resonant frequency. What is likely to happen, is that the input impedance will be off, but you will have a good guide on how much adjustment is necessary.

The issue I have, is on my current filter, I cannot get the last rod adjusted to resonance, once I've sorted what causes that, then I'll have good grip of these things.
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  #78  
Old 17-08-2017, 06:15 AM
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Hi Steve,
Welcome to the IIS forum and thank you for your comments... yes I have access to Agilent E5061B here at work, and will certainly try your method at first occasion
My conclusion after playing with this filter (4 resonators) at home (I have SA with tracking gen and reflectormeter bridge) was coupling was too high

In the meantime I build another one (3 resonators, 10MHz, see here).
Interestingly, this one has too low coupling, and losses are also too high.
I even used copper sticky tape inside but the result is still not good enough for my taste.
Next I will try with thicker rods, they are easy to replace.
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  #79  
Old 17-08-2017, 08:33 AM
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Which is the most up to date thread on this?

Malcolm
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  #80  
Old 17-08-2017, 08:57 AM
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Which is the most up to date thread on this?

Malcolm
The other one (version 2) :-)
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