Current Engineering Project

I keep this engineering notebook more for my own use more than for any other reason. It's invaluable when trying to find a solution to a problem I know I've solved before. You are welcome to browse though it to see what it takes to build a SETI station. Questions or Comments? Email me: Seti@SETI.Net

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Volume 11 Chapter 69

390 - Spectrum Analyzer on the Cheap - 2017-04-14

China has come through again.

For very little money you can buy the components to make a nice spectrum analyzer and noise source that doubles as a synthesizer and covers from 138 mHZ to 4.4 gHZ.

This is the lash up I used to chararize a filter I had in my junk box.

Professional looking output.

The modules are:

  • Spectrum Analyzer - Search EBay with '138MHz-4.4GHz'. It should turn up a bunch of listings. - Should be about $70
  • Noise Source - Search EBay with 'Noise Source Simple Spectrum External Generator Tracking Source' - Should be about $20
  • Pad - 20 dB or so attenuator needed otherwise the Noise Source output will swamp the Spectrum analyzer input

The Spec Ana also can be used as a synthesizer. Just the thing for antenna and detection logic testing.

When you get your Spec Ana. Download the software here

390 - Freeze - 2017-03-23

It's freezing.

The damn SpecAna is locking itself up and I am having a very hard time finding out why. I built a logging function into it and run it with EurekaLog to help narrow it down but still no joy.

It appears that the problem centers around the point that I clear buffers to be ready for a new run. I use:

 SetLength(bufFrame, 0);

in TfrmSpecAna.WMsetRun line (about) 778. The problem seems to be that *sometimes* it takes longer than 5 seconds to clear the buffer and reallocate it. Five seconds is the time out when Windows decides that an application is frozen and throws its own exception.

Trying this at the start of Create:

 procedure TfrmSpecAna.FormCreate(Sender: TObject);
  DisableProcessWindowsGhostingProc: procedure;
  DisableProcessWindowsGhostingProc := GetProcAddress(GetModuleHandle('user32.dll'), 'DisableProcessWindowsGhosting');
  if Assigned(DisableProcessWindowsGhostingProc) then

389 - Bad to Worse - 2017-03-15

I got the problem with the SpecAna down to a problem in the 25 MHz reference oscillator. The oscillator is a constant current saturated amplifier who's level is set by a DAC. This is referenced on:

  • Troubleshooting - Section 6.8.4 of Maintenance Manual VI (page 404 of the PDF)
  • Schematic - Maintenance Manual VIII Page 130 of the PDF

The trouble is the DAC itself is not part of the schematics that I could find (click here for a full size schematic).

Then after giving up on this problem, I put the unit back together and found that the +12 Power Supply had quit. So I opened it back up and dissemble it to get down to the power supply. Its buried in the center of four or five layers of circuit boards, cables, jumpers and other stuff (click here for full size JPG).

Getting the power supply out of there must be possible (it didn't grow there I'm sure) but I cannot figure out how. Not only that but I do not have a schematic that covers the power supply even if I coule extract is from the unit.

Stuck - Anyone have a power supply schematic?

388 - Spectrum Analyzer Repair - 2017-03-01

I have a very nice analyzer on loan to me from a local group but it has a problem.

This is what the instrument reports when connected to its Cal Output. It should read -10 dBm and 25 MHz. It does read -40 dBm and 29.107 mHz.

This is an Advantest R3365 but it is from the same line as these other models:

  • Advantest R3265
  • Advantest R3271
  • Advantest R3365 (The one I have)
  • Advantest R3371
  • Advantest R3271

First step is scrounge around the Internet to find the maintenance manuals. After a long search with a lot of dead ends I found a set with all the schematics - without them don't bother to try to fix something this complex. You may download them here.

387 - Time for a ToDo- 2017-02-19

In no particular order:

  • Scan chart improvement
  • Add antenna movement to list of discriminators
  • Self test with a noise generator
  • Burn the firmware of HackRF's to update and possible get rid of bug
  • Track ATA