Tag Archives: Test Equipment

My Spectrum Analyzer Addiction (and Education)

I recently returned to amateur radio after a 50+ year absence, and have been assembling a collection of vintage radio gear, and vintage and more modern test instruments to maintain this gear. While I have a long, strong background in electronics and am familiar with and have used a wide range of test instruments over the years, prior to a few months ago I had never seen a spectrum analyzer and was only vaguely aware of their purpose and functioning. While cruising the classifieds at eHam, QRZ, and QTH a few months ago, I happened to notice an Agilent 8560E spectrum analyzer in working condition for sale at a very low price. After doing a little research online, I emailed the seller with an offer at an even lower price, and he accepted my offer. A few days later, this beast arrived, all 40+ pounds of it. It did not come with a user manual, but I was able to purchase one on eBay and did enough reading to figure out how to fire the SA up and do a preliminary checkout. Sure enough, it worked just like the manual said it should, and was in very good cosmetic condition, with just a few minor battle scars on the case. This instrument listed for about $50,000 in the mid-eighties when it was in production. So, with this acquisition, I thought I was set for life as far as SAs go. Wrong!

A few months later, I was cruising the classifieds again, looking for some Collins S-line gear and happened across a listing for a Tektronix 495P spectrum analyzer which was described as “works and looks like new,” and, again, at a tiny fraction of the $30,000+ original selling price around 1990. I was skeptical of the “looks new” description, but “new” is good, so I asked the seller to confirm this. He emailed some details of the history of the instrument and more photos, all of which convinced me that he was accurately representing this instrument. The “want” side of my brain quickly overcame the “need” side and I emailed an offer which he accepted. As before, a few days later, this beast arrived in the original Tektronix shipping carton, weighing 70 lbs; this weight included the SA, hard copy user and service manuals, and a few accessories. And it did, indeed, look like new. Turns out some branch of the U.S. government had purchased a bunch of these, sealed them in new, unopened cartons in humidity resistant packaging, and stashed them in a warehouse for years, finally offering them for sale as surplus much later, when the seller I purchased from bought one. And after reviewing the manual and stepping through the initial checkout chapter, I found it did work to spec. Now I was really set for spectrum analyzers! Wrong!

A few weeks later, the guy I bought this one from emailed and told me he had another Tek 495P that “almost works,” and which he had acquired for parts, as the 495P has not been supported by Tek for many years. Then he made me an offer I couldn’t refuse: he would give it to me if I would pay the shipping cost from CA, about $70. How could I possibly say “no”?  Here we go again! It took him three months to get around to shipping it, but eventually a 50 lb package arrived. Having seen quite a few “parts” 495s for sale on eBay, I wasn’t expecting much. But, I was pleasantly surprised. While it could not be accurately described as “looks new,” it was quite decent for an instrument manufactured in 1991 (according to the Tek inspection tags inside), and, it worked! Well, … sort of. In stepping through the initial checkout section of the user manual, it displays traces that resemble the illustrations in the manual, however, according to the messages displayed at boot up (this is a microcomputer controlled instrument), it thinks it is a 492AP model SA rather than a 495P. The 49x series of SAs share a common base of microcomputer code, with the specific model type selected by DIP switches on a memory board. There is enough functionality that I decided to try to fix it rather than use it for parts, and I am now launched on that path.

This is an amazingly complex instrument. The two-volume service manual runs some 700+ pages. Fortunately, the problem I am seeing is in the microcomputer controller subsystem, where I am somewhat competent, and not in the analog/RF subsystems, where I am not. This repair effort has travelled an interesting path, along which I have met (online) some helpful and accomplished people and found a number of resources I was not previously aware of. One of these is the [email protected] forum which is mainly focused on keeping vintage Tektronix gear running. This has been a great learning experience and I am confident the fix is close at hand. We’ll see! Still much to learn, however.

My cup runneth over with spectrum analyzers. I’m not sure if there is a 12 step program for SA addiction, but I may need one. I find myself still eagerly looking at for sale listings. I am thinking that I should at least have one of the modern Rigol SAs to balance out my vintage collection. Sure seems rational to me!

Rick, K8EZB

Feb 18 DSO138 Kit Building Tips

Hi DSO138 kit builders,

I wanted to share some tips to follow for our 18 Feb Kit Build from 1-4pm. As I already built my own kit, I wanted to share some advice.
I know not all of you can attend, but for those of you who can, please read below. I’ll also post on the website along with some pics.
  1. Make sure you bring a magnifying glass AND a multimeter. Also, might help to bring an LC meter too (though I didn’t have one at the time) The color bands on the resistors are particularly impossible to see, so I had to measure the resistance of every one. I even did it 2-3 times to make sure I was right.
  2. To test your kit at the end of the night, you need to supply it with power. You can do this 2 different ways. The first is bringing a 9V battery along with 9V battery leads terminating at the end of a female port as shown below. The second is grabbing a power adapter rated for no higher than 12 V again terminating on a female port with pic shown below.
  3. You might want to bring a small Phillips head screwdriver (for eye glasses) in order to perform probe calibration.
  4. If you want, bring your laptop so you can download some signal generators (using your sound card) in order to play with the oscilloscope. In order to do this, I ended up using a BNC to an audio adapter which I purchased off of Amazon Prime. I’ll bring mine in case you don’t have one
  5. If you have a standalone signal generator, please bring it, along with BNC wire connections for the o-scope.
DSO138 kit power supply port
DSO138 power supply port
9V battery adapter
9V battery adapter
12V power supply (stolen from a Linksys router) with port (top-middle)
12V power supply (stolen from a Linksys router) with port (top-middle)

In order to do some testing, we are going to want to use either signal generators that club members graciously bring in, or you can use your laptop’s sound card. To that end, Mike (K1WVO) suggested a really nice link to do this.

I’ve tested most of these and they work fine on my scope.

If I have any other thoughts, I will update this post.

Thanks and 73,

Brian, AB1ZO

Show Your Love for Amateur Radio on Feb. 14

February 14, 2017, now represents two important days: Valentine’s and Nashua ARC’s Feb Tech Night! Nothing else says love like telling that special someone — you want to solder some electronics 🙂

Back by popular demand (and good reviews from others) is our kit building night. Everyone had a blast on Election Night building the Pixie kits, and on V-day, we are going to work on a DIY oscilloscope known as the DSO138. (It is mere coincidence FYI that our kit building nights have fallen on holidays, of sorts).

The nice thing about this kit, of course, is being able to visualize some of the basic waveforms used in electronics. The kit does come with a square-wave test signal, but we will also have a signal generator present to visualize more complicated waveform.

Building this kit is an excellent opportunity to hone those soldering skills, brush up on electronics theory, and add another fun toy to your growing (or perhaps overflowing) collection. The price point is definitely fair for an oscilloscope and may help you figure out if you’ll want a more sophisticated one down the road.

We had about 15 people last time, so I think this time, it’d be great to expand that number to 20 (or more)! Buy a kit here, and join us in February! Looking forward to seeing you.

Brian, AB1ZO

Inexpensive DIY Digital Oscilloscope Kit

I came across a DSO138 DIY Digital Oscilloscope Kit (SMD Soldered Version) on the Internet recently that looked like a fun project for the kids and me to work on together.  The price didn’t seem bad at $24 w/free shipping.  I ordered the optional clear acrylic case to go with it for another $7.50 more.

Basic specs (from the supplier site):

  • Maximum real-time sampling rate: 1Msps
  • Accuracy: 12Bit
  • Sampling buffer depth: 1024 bytes
  • Analog bandwidth: 0 – 200KHz
  • Vertical Sensitivity: 10mV / Div – 5V / Div (1-2-5 progressive manner)
  • Adjustable vertical displacement, and with instructions
  • Input impedance: 1MΩ
  • Maximum input voltage: 50Vpp (1: 1 probe), 400Vpp (10: 1 probe)
  • Coupling modes: DC / AC / GND
  • The horizontal time base range: 10μs / Div – 50s / Div (1-2-5 progressive manner)
  • With automatic, regular and one-shot mode, easy to capture the moment waveform
  • Available rising or falling-edge trigger
  • Adjustable trigger level position, and with instructions
  • Observable previous trigger waveform (negative delay)
  • Can freeze at any time waveform display (HOLD function)
  • Comes with a 1Hz /3.3V square wave test signal source

It came in the mail this weekend.  In the box was the case kit, bag of parts, main board, display board, test cable, assembly checklist, and a basic how to use guide:

Oscilloscope Kit

Oscilloscope Kit Oscilloscope Kit

Oscilloscope Kit Oscilloscope Kit

Oscilloscope Kit Oscilloscope Kit

Oscilloscope Kit Oscilloscope Kit

I plan to post updates on the build experience with photos along the way.  Stay tuned!

Wayne,  AG1A