This is the current state of the test equipment in use and being built for SETI Net.  It covers  the Tektronix 475 oscilloscope, the build up and debug of a crystal controlled Weak Signal Source , maintenance on my HP 141T Spectrum Analyzer, construction of a Varactor Tuned Oscillator (VTO) for the water hole and a Noise Com signal source.  

Tektronix 485 Oscilloscope

This is a prime piece of equipment in the lab.  It is needed for most operations in the shop and it has failed. I found that the 'A' Channel vertical input was locked in the 'AC Input' position and the 'B' channel locked in the 'DC Input' position.  It looks like I will have to open it up and see if I can fix both rotary switches.  Since I depend on this instrument for most tasks I must keep it in top running condition. 

1/18/98 - I have pulled the cover off the 'scope and started removing the knobs in an attempt to get down to the AC/DC input switch.  These pictures will help me put it back together in the right order when I find the problem.

Tektronix 475 with the cover and front bezel removed.

Volts/ Division with plastic ferrules showing

Close up of the finger switches causing the problem.  A little white grease on the cams that control these switches put it back in working order.

Ready to go back to work 1/26/99

Weak Signal Source

The next order of business is to get the signal source kit received from Down East microwave running. 

Kit with probe leading to Spectrum Analyzer

This was completed in about 4 hours of work but doesn't seem to work.  To test it I need a Spectrum Analyzer running.  I have a Tektronix 555 dual beam scope with a 1L20 spectrum analyzer plug in on one side but I am not sure how well it works.  I am going to try to resurrect a VCO that I built some years ago that covers 1.42 GHz to use as a test source for the spectrum analyzer.

So - I found that I had to fix a dual power supply to run the VCO to test the spectrum analyzer to test the weak signal source.  I have backtracked quite a bit this weekend.

1-26-99 - Power supply repaired.  Needed a LM317 variable three terminal regulator replaced.  Now I can go on to get the VCO running.

1-27-99 - VCO seems to run and spectrum analyzer can show VCO output.  Connected the Weak Signal Source and found that the first stage seems to work as well.

Screen shot of Weak Signal Source oscillator only at 1.42 GHz.  Now I can connect the remainder of MAR amplifiers and finish the kit up with a battery pack and enclosure.  

This was the last user of the Tek 555 and its plug in spectrum analyzer.  shortly after this the power supply on the main frame crapped out and I junked the whole thing.  I switched to my H/P 141T Spec. An. and it is in daily use now.  p.s.  The only thing saved from the 555 was the Spec. An. plug in.  Anyone want to trade??

2-6-99 - Finally got it running.  Turned out to be a through hole that the solder didn't flow through and some adjustment needed on the oscillator.  I also realized that I need to use a counter to set the output frequency to the right point.  The crystal is cut for 118,367,150 Hz and the filters select the twelfth harmonic:

     118,367,150 X 12 = 1,420,405,800 Hz or 1.420 GHz

Finished and working...

8-1-99 - Tuning Problems.  The Weak Signal Source didn't seem to start on 1.42 Ghz every time.  Most of the time it would start on one of the lower harmonic multiples.  I adjusted the coil on the Local Oscillator and it seemed to be better but still not 100%. Anyone have an idea?

Water hole Varactor Tuned Oscillator (VTO)

This is a piece of general purpose test equipment that supplies a signal between 800  and 1700 mHz so the upper part of the curve covers the water hole at 1420 mHz.  The output frequency is set with a tuning voltage that works out to be +23 Volts for 1420.  

The unit was built around a H/P Agilent  VTO-8090  oscillator and a +15 volt three terminal regulator (7815).

The HP link shows a different case arrangement but the one I used was found in my scrap box and seems to work fine.

The PC board material was obtained form Gateway Electronics in town and is designed to be worked by hand with a X-Acto knife.  You simply cut through the copper and peal back the unwanted area.  Just the thing for a one of a kind simple build up.

Rear

Shows surplus case and hand worked PC board.

Font 

Front shows the 15 volt regulator, and 0.1 bypass caps around the unit itself        

Finished

The final unit with SMA connector.

The thumbnail below shows the Volts/Frequency curve that was printer out and pasted on the finished unit.

Volts in / Frequency out curve

You can print out this curve and past to the cover for later reference.

Noise Com Signal Source

Many times you will need a broadband signal source to perform A/B type testing (what is the pass band of this flee market filter etc.) and for gain testing of purchased amplifiers.  The following module was built using  a NoiseCom NCC503/15 noise source for this purpose.  It produces white gaussian noise over the 200kHz to 2 GHz range with a flatness of +/- 1.5 dB.

503 Base

The base diagram of the 503 noise source for reference

Install a +15 volt regulator (7815 family) put the board with the 503  in a utility case,  add a SMA connector and you are ready to go.

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