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Author Topic: Measuring transmitters with an oscilloscope  (Read 5208 times)

Offline makeRF

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Measuring transmitters with an oscilloscope
« on: September 10, 2013, 0137 UTC »
All,

I just posted a write up about measuring transmitters with an oscilloscope.  A good one for beginners out there that want to get down some basics.

Essential Equipment: Measuring RF Circuits with an Oscilloscope
http://makerf.com/posts/essential_equipment_measuring_rf_circuits_with_an_oscilloscope

As always, comments and feedback are welcomed!

Offline moof

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Re: Measuring transmitters with an oscilloscope
« Reply #1 on: September 10, 2013, 0232 UTC »
I wish I knew how to use an oscope. I depend on jamming the output into a meter and tweaking the coils.  A rat shack meter made for the cbers will give you a close reading. Get something else if you want better than within 25%. If you blow it up you are out 40 bucks. It has a 20 watt scale and I have found it to be a good indicator. Not super accurate but what's a dummy to do?

Offline ff

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Re: Measuring transmitters with an oscilloscope
« Reply #2 on: September 10, 2013, 0259 UTC »
Not super accurate but what's a dummy to do?

Don't get so down on yourself Moof.  I did it just like you for many years before I got my first scope.  Your way might not be as accurate, but you get the relative indication which is what you really need anyway.  Channel Z has built a bunch of first class transmitters and unless his status has recently changed, he doesn't own a scope either.  Where a scope really is useful is building switch mode transmitters like the LULU and the Commando.  It's much easier to find the Class E operating point when you can simultaneously look at the waveforms of the MOSFET's gate and drain.  But many have done it successfully without a scope too.  If you do get one someday, makeRF's article is a really good place to learn the basics.
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Offline makeRF

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Re: Measuring transmitters with an oscilloscope
« Reply #3 on: September 10, 2013, 1316 UTC »
Moof, I agree with ff...  Don't get down on yourself.  I consider myself just a step or two above novice, and have only recently started understanding this stuff more.  I'm a software guy who was always interested in electronics, but never had any formal training.  Lots of reading and experimenting for years got me somewhat competent and building some basic circuits.

As for the oscilloscope, I've worked for years blind on these designs.  It's sometimes tough to know why something isn't working without a scope.  Usually a small tweak will make things magically start working, but it's difficult to pin down what the tweak should be without the ability to debug with the scope.  Purchasing one is an investment, but worth it if you can squirrel away enough cash.  And they are easy enough to use...  At its most basic functionality, hook up your leads and press the Auto button.  This will get you close to where you need to be to see if your circuit is oscillating.

But, you definitely don't need one to experiment...  Especially if you can find some decent schematics.  Just make sure you plug the parts in correctly (something I often do wrong) :D

Offline RadioAnarchy

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Re: Measuring transmitters with an oscilloscope
« Reply #4 on: September 10, 2013, 1504 UTC »
several months ago, some rain water leaked through the roof and ceiling on to
my old B and K scope.. it blew out the high voltage circuit when I turned it on.
I had it for 20 years or more.

so I went on craigslist and found here in my area a Tektronix 465M for
225 bucks. . . this is the military version of the old famous 465B that I have
used back as a technician years ago, working at various places.
 both of these scopes were very
costly back then.

so you can get you an old analog CRT scope for cheap nowadays,
and they are good for RF.

that is how I learned, by reading books, and then going on the internet to learn,
then try to design, build, and look at the signal on the O-scope and blow stuff up.
.them IRF510 can just pop and smoke sometimes.

and the only book that really tells you how to design is

Solid State Design for the Radio Amateur - by Hayward    

and I have some other book "RF Circuit Design"  that is good also.

« Last Edit: September 10, 2013, 1506 UTC by RadioAnarchy »

Offline makeRF

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Re: Measuring transmitters with an oscilloscope
« Reply #5 on: September 10, 2013, 1512 UTC »
and the only book that really tells you how to design is

Solid State Design for the Radio Amateur - by Hayward    
I also recommend Experimental Methods in RF Design by Hayward.  The Solid State book I believe is no longer in print, and the Experimental Methods book is the updated version.  The nice part is you can pull docs from decades ago and they still apply today.  Analog radio is a century old technology, and not much has changed since the early days.

Offline redhat

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Re: Measuring transmitters with an oscilloscope
« Reply #6 on: January 09, 2014, 2037 UTC »
In case anyone else is interested, this site gives a run down of transmitter modulation checks with a scope.  In practice, I have a selection of RF samplers that fit in my bird for envelope sampling, but you could do just as well with a T-106-2 torroid with 20 turns terminated by a 10 ohm 1W resistor to feed your scope. 

http://www.nu9n.com/scope_your_audio.html

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Offline olddxer

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Re: Measuring transmitters with an oscilloscope
« Reply #7 on: January 12, 2014, 1055 UTC »
RH,
That is a great site. I have used his method for several years now.
Anan 8000DLE, Drake R8B, NRD-515, Perseus SDR, a bunch of Hammarlunds, Inverted V multiband dipole

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