Re: Test equipment recommendations

Robert D. Bowers
 

Digital scopes have some limitations - and to really use them effectively, you do need to know a little about how they work and operate.  That being said, they can be valuable too - even a 5mhz digital scope can work with audio (and to a lesser degree with RF - low frequency stuff).  A 20mhz would work for older radios (with a lower IF), but a 20mhz analog is far easier to use near the top end of its bandwidth than most digital scopes - and have a more accurate representation of the waveform at the upper end.  I'd suggest something at least 30mhz... if digital, go higher than that (better representation of the waveform).  For digital, a good rule of thumb is the bandwidth at least twice the signal you might want to check.

I've got a used analog (bought at a hamfest) which works good - yeah, there's a chance of a lemon but often they're quite rugged (and if they look good inside and out, you've got a pretty fair chance of getting a good one).  Usually a few simple tests can show if there are problems or not.  If it comes on, shows traces, and the seller can show a waveform (square wave is good), usually they're adequate for troubleshooting.  I think that there are lists on the internet that show what tests to do - and what sort of problems you're likely to find based on the make and model of the scope.  IME, the usual failure is dried-out power supply caps. 

Here is a list of suggested test equipment:
  1. A very good DVM - be prepared to spend a fair amount on this.  A cheapo model will work, but the better the model, the more useful you'll find it in the future.  (The one I have now - I've had for almost 10 years, and if someone hadn't torched my shop, I'd still be using models I'd had for years before that.)
  2. Make a RF sniffer probe for it.  VERY useful for troubleshooting radios.  You can use on-the-air signals or some other source (mentioned later).
  3. A directional wattmeter (aka SWR meter) - you can make one of these if need be - even make one that works with the DVM.  This is important - because a poor match puts transmitters in jeopardy.  It's not about "Maximum signal out!!!", it protects the finals from being overstressed!!!
  4. The next on the list: a 50 ohm dummy load.  VERY important - you can make one (just don't use wirewound resistors!).  I'd encourage looking at kits, by the way - if you have any experience at all with soldering (start with simple kits and you can develop adequate skill rather fast).

Less critical but worth having.  Kits, by the way, do work... and you might know someone who has an old scope lying around that they don't have a use for.  I've got a couple of pieces of equipment I built from kits - and have considered others.

  1. Here is where I'd put a scope - they may not be essential, but if you have any experience at all with them, they're that useful (make sure you have bandwidth in excess of the signal you expect to check).
  2. Almost as important - a signal source.  There are DDO kits available that are inexpensive and they do an adequate job (although the signal isn't that clean/pure).
  3. Make or buy a step attenuator (for the signal source) - if you don't luck out and find one.
  4. Here is where I'd put something like a VNA or other antenna checker.
  5. It goes on from there.  I'd even suggest something like a "grid dipper" or similar - they are VERY useful, especially when checking things like toroids and caps.  I used to have one - and miss it.
  6. Here's another good one - for checking many components.  It's called a "zener Sweeper" - and I used to have one.  There may be other little things like that.
  7. I thought I'd mention a RF bridge.  I bought a wide-band bare-bones one from China, and I'd previously built a dBm meter (combined chip and components with an arduino).  You can combine these with a DDO signal generator and do all sorts of neat stuff - even synthesize something resembling a dipper!
  8. The rest is per personal preference.  One more thing - don't stint on the soldering iron.  Get a good one (you don't have to break the bank to find a good one... temperature controlled and grounded).  Ditto for small tools - a good wire nipper is very important (especially for kits).

VERY important - do your best to get manuals (including service if available) for everything!!!  They can save tons of headache and heartache!

Good luck... and I hope this helps.

Bob

N4FBZ (First licensed 1980, General Radiotelephone {commercial radios} 1981.)


On 5/17/20 10:59 AM, ponton.leo@... wrote:

Very off topic. My mind is wandering since passing my foundation, getting my call sign and now waiting for a radio. The Baofeng I ordered at the beginning of April didn’t arrive (woop!) and I got a refund. The next day delivery FT-65 to replace it which I ordered on Thursday is coming on Monday. My uBitx is awaiting a despatch window. My CW isn’t good enough to use my Forty-9er yet. I can’t afford a FT-817.


So, I’m tinkering with circuits, arduino and so on. Of course whenever I google something there’s an oscilloscope in the article. Since I was a kid I thought I needed one but they’re pricey. Does anybody know....are those twenty-odd quid digital things any good? e.g. JYE Tech DSO138 Mini Digital Oscilloscope. I’ve heard good things about the NanoVNA and I wondered if these little ‘scopes are reasonable in the same way.

Or maybe I’d be better getting and old style big box scope from eBay and hope it works (“Spares only, turns on, but no way to test it” is the standard disclaimer)

Better still, what do people recommend for basic test equipment?

 

 


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