Re: Cool cheap oscilloscope for troubleshooting

Robert D. Bowers
 

One of my dream purchases for radio is a functional spectrum analyzer that is reasonably accurate.  I use a dongle right now as a 'poor man's spectrum analyzer", although it has some serious limitations - like taking things in a 1mhz 'bite' at a time, plus compression of the signal makes db measurements only an estimate at best.  It works for checking for deviation or for spotting unwanted signals, but not that well.

The bottom end of my dongle is also around 25mhz... I have some parts to cobble together an up-converter, but haven't had the time to work on that (first I need to get my old HF rig going again).

I know that there are some kits out now (plus units from China) that work, but their price is outside of my reach.  Maybe things will get better!

Bob

N4FBZ

On 7/31/19 10:43 AM, Ashhar Farhan wrote:
An easy way to extend the upper frequency range of an oscilloscope is to use a 'down converter' - a diode mixer driven by a VFO, like a direct conversion receiver. The mixer output is fed to the oscilloscope.
About ten years ago, I wrote in a blog post that serious homebrewing needs a good scope. I must revise my claim. You need a spectrum analyzer of some sort. The reason is that our work is frequency domain.  Our circuit blocks are filters, mixers, amplifiers and oscillators. All of them have inputs and outputs specified in terms of frequencies.
It is this realization that led to the development of antuino. But that is a separate post..

On Wed 31 Jul, 2019, 6:10 PM Roy Appleton, <twelveoclockhigh@...> wrote:
"Of all the cheap oscilloscopes we have tested, we are the most impressed with this DSO188. Despite the small dimensions, the scope is easy to operate and the oscillogram is easy to interpret. It is easy to live in practice with a service life of about ninety minutes with one battery charge.
The only unfortunate thing about this beautiful device is that the DSO188 cannot be used to reliably measure the numerical values of the input signal. The manufacturer should have omitted this option, because a measurement function that is 'for reference only' is not very useful in practice. "

Roy 
WA0YMH

On Tue, Jul 30, 2019, 1:50 AM Tom, wb6b <wb6b@...> wrote:
Hi,

Anyone looking for a low cost scope to trouble shoot (a least audio and low frequency such as encoders) parts of their UBitx, these little oscilloscopes were on sale. I bought one. It only has a 1 Mhz bandwidth, but that is better than the 200 Khz bandwidth on many of the other cheap tiny scopes. 

So far I've liked it and have use it for observing some pulse width modulate signals where the frequency and duty-cycle readouts were handy. It is totally isolated when running on its battery. That is a nice feature. 

I have another radio with an intermittent causing both the transmit power and receive signal strength to abruptly change. Am planning to make an RF detector probe with a diode and capacitor and just leave this little scope attached to various points in the RF chain to see where I see the signal change in step with the change in my transmit power or S meter on receive (particularly the background noise floor on the S meter). This little scope won't take up a bunch of room while doing these measurements and may provide me with a little more interesting information than a DVM. 

https://www.banggood.com/DSO188-Pocket-Digital-Ultra-small-Oscilloscope-1M-Bandwidth-5M-Sample-Rate-Handheld-Oscilloscope-Kit-p-1315186.html?rmmds=home-mid-relatedViewed&cur_warehouse=CN

Here is a review on a site that specializes in trying out low cost Chinese electronic gizmos. Not sure if my later model is calibrated better than the one he tested, but did not strike me as really bad. 

https://chinese-electronics-products-tested.blogspot.com/p/dso188-matchbox-scope-tested.html

Tom, wb6b

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