Reading about how they work and what they can do. Dig through the spec sheets and look at the applications notes. Skim the online catalogs to see what's available. Search Google of articles and photos of what others have done. Reverse engineer competitors products if available. Beg vendors for free samples. Somewhere along the line of such an investigation, some product ideas might pop into your head.
I do, but it's 1970's and 1980's vintage equipment. You can do quite a bit with old test equipment. Same with the easily affordable "toy" test equipment that is appearing for sale online.
I don't use an oscilloscope for RF over about 75 MHz. I do have a sampling plugin (that needs some repair) but a scope only gets you so far. My major test equipment for RF are:
- Spectrum analyzer with tracking generator and lots of plugins.
- Sweep generator, with lots of plugins.
- RF signal generator.
- Broadband noise source.
- Frequency counter with lots of plugins.
- Return loss bridge, single port VNA, or antenna analyzer.
- Dummy loads, attenuators, power dividers, directional couplers, tunable notch filters, coax adapters, patch cables, crimping tools, TDR for testing cables, calibrated loads, etc.
- RLC bridge.
- Laptop computah with as much design and calculation software I can steal err... find.
- Communications service monitor (optional) for NBFM work.
In the not so distant past, the shopping list for such equipment would be in the tens of thousands of dollars. Today, you can probably buy everything you need for working up to 2.5GHz for under $2,000 USD.
My $50 TinyVNA works to 1.5GHz, but is only accurate to about 100MHz. The Smith Chart display is useful for antennas.
Do you really need to fix it if the lower ranges are working? What are you planning to do above 10GHz? Talk to satellites?
If you can't handle the GHz stuff, buy modules for the mm wave frequencies that downconvert to something you can handle.
Learn to scrounge. Much of my test equipment came from thrift shops, who didn't know what they had, and eBay (which can be overpriced). All of it required repairs (usually electrolytics and tantalums). I also inherited some equipment from several aging ham radio operators.
I'm 72. The hand is still steady but the eyesight is rapidly deteriorating. So, I bought some microscopes: My guess(tm) is have about $350 invested in *ALL* the microscopes pictured. The most expensive items were replacement and additional objective lenses and eyepieces. Something like this would be ideal: You can also get a microscope camera that fits in place of one of the eyepieces. I bought a cheap one and regret it. Buy one that has a
0.5x lens.
Well, I tried and methinks that you're hopeless.
I tend to judge people by their willingness and ability to learn. What you've done is essentially announce that you don't want to try anything new and prefer to dabble in what you find comfortable. I realize that you probably don't care, but you just failed my litmus test.
It's also difficult to know that you've arrived if you don't know where you're going. Good luck doing what you enjoy so much.