Use of Oscilloscopes in Radio Repair, building, testing and Troubleshooting - Page 1
Forum section: electronics / rf-microwave

author: vinlove
author_rank: Frequent Contributor
timestamp: February 18, 2020, 03:47:33 pm
content: What are the uses for the scopes in RF gears, and how have you used them on your repair, building, testing and troubleshoot and maintenance work on RF gears?

author: vinlove
author_rank: Frequent Contributor
timestamp: February 19, 2020, 08:14:39 am
content: No one uses oscilloscopes for / with radios & rf sets?

author: dzseki
author_rank: Frequent Contributor
timestamp: February 19, 2020, 08:38:28 am
content: While oscilloscopes are multipurpose instruments they are best in showing how is the actual signal looks like vs time. In radio this is less important. Spectra, actual frequency is more important.That said a decent digital oscilloscope can be useful at lower bands as well (<100 MHz) knowing its limitations, but at higher frequencies oscilloscopes loosing ground quickly (better said the price of the scopes skyrockets).A spectrum analyzer and a signal generator are the de facto standard instruments for those who inclined in higher frequency radio stuff, a network analyzer is very nice to have too.

author: 9aplus
author_rank: Regular Contributor
timestamp: February 19, 2020, 09:39:26 am
content: Just google for:"osciloscope component tester"that is most useful tool for my taste...

author: bd139
author_rank: Super Contributor
timestamp: February 19, 2020, 10:17:50 am
content: Hardly use mine for RF work. Mostly just use a DMM and RF probe for signal tracing / peaking.A decent signal generator is a better investment IMHO (Marconi 2019 / HP 8640 or later etc)

author: vinlove
author_rank: Frequent Contributor
timestamp: February 19, 2020, 10:47:45 am
content: Yeah, my 50mhz Rigol DSO is not being used that much, and recently I was given an old Heathkit OS-2 and Telequipment tube scopes. So was wondering what would be good use for them.I have a guitar amp to repair in the shed, so one day, the scopes will come in handy, but they werent being used for the radio repairs and even building kit receivers.DMM and soldering iron were only tools being used a lot.Also wondering if oscilloscopes could be used for sniffing out the RF or oscillation from receivers or transmitters on repair or build.

author: bd139
author_rank: Super Contributor
timestamp: February 19, 2020, 10:59:43 am
content: If you're building from scratch they certainly have utility, particularly transmitters. You can use them for power and CW envelope measurement, two tone tests etc. However when building kits, particularly the K2 and QCX in my case which are half decent kits, I didn't need to use the scope once or a signal generator. The K2 didn't work first time due to a duff JFET and all the diagnostics for this were done with an RF probe, DMM and a bench supply. Turned out the primary oscillator wasn't running between two varactor voltages - no scope required to find that! The filter alignment was done entirely using a simple discrete transistor noise generator (about £1 of parts) and PC based sound card audio spectrum analyser (free)In priority order for me (highest first) the tools required are:1. Decent soldering iron2. DMM + RF probe3. Bench supply4. Frequency counter5. RF power meter6. Signal generator7. Scope

author: borjam
author_rank: Unknown
timestamp: February 19, 2020, 11:15:41 am
content: It can be useful to spot distortion (although the best tool for that is a spectrum analyzer) or to perform some adjustments such as SSB voice compression.And despite all the claims, digital oscilloscopes are also fine for this. Not just analogs!

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: February 19, 2020, 01:36:58 pm
content: Especially at 100MHz (maybe 200 MHz) or less scope can be quite valuable in evaluating anything that produces RF. You can see if the IF stages are working, you can see if oscillators are working. Anything much higher requires a more expensive scope and more expensive probes.At higher frequencies the spectrum analyzer is generally more practical. Until recently however, spectrum analyzers were much more expensive than scopes.A lot of newer spec analyzers do not work at low freq.Many scopes have a freq counter built in or you can calculate freq from the horizontal axis. A freq counter in a scope is very helpful.You can compare two signals as to their freq and amplitude. if the scope has two or more inputs as most do have. You can "follow" the RF in a radio and see where there is a problem. You can see if a filter is doing its job or if a mixer is mixing. an oscillator is oscillating or if a single transistor amp is amplifying.You can use it to tune the variable caps and transformers in a radio.If the scope has 50 ohm input you can use it as a power meter if you do the math using ohm's law for small power outputs.You can measure small DC voltages such as bias and you can measure TTL voltages and signals, it becomes a signal analyzer, modern scopes have multiple leads for uses like this. A spectrum analyzer will not do this.In the past scopes were used in X/Y mode without using time base and several interesting measurements could be made such as Lissajous patterns which give information on phase shift and other things.Old Scopes are particularly useful at audio frequencies.I think that scopes were the most affordable tool available in the past for evaluation of anything RF. Again, other things like spectrum analyzers were more expensive.This is not to diminish other peoples statements, I think a good multimeter is a very useful tool and I use several.The multimeter is the most useful and affordable piece of test equip.Recently I disassembled a HP VNA, A multimeter showed me the broken transistor and repair was successful.The list provided by bd139 is quite a good one.If you are going to use a scope you also need some good probes.I use a particularly rare scope, an HP 1980 that was sold in 1985 for maybe $15K I bought it for $50. (then had to fix it)Old scopes can be a real challenge to operate as you have to choose the proper time for X axis and proper range for Y voltage and then sometimes have to fiddle with triggering, modern scopes do all of this for you. However, learning to use these things can hopefully boost your understanding of electronics.Also if this is a Hobby, you are here to have some fun. Hook the scope up and test some low voltage stuff. Maybe like a big old transistor short wave radio.If you have one with a good display, hook it up to a signal and put it on the front porch for Halloween. It's really great if you connect an amplified mike to the input and show the audio on the tube. Or maybe some scary music like "Monster Mash"BIG PROBLEM: I have fixed many scopes with blown "front ends" This is not a horrible repair most of the time but is caused by putting too much power into the scope leads. Try to avoid doing this. I have (almost) never done this.Remember, if you get into using several scopes you risk mandatory membership in TEA!!!Wally

author: vinlove
author_rank: Frequent Contributor
timestamp: February 19, 2020, 06:48:48 pm
content: Great posts, thanks much appreciated.I now own 3x scopes, 1x DSO, and 2x vintage tube scope from 1950s. So, perhaps I am entitled to the membership for the TEA.There is another one on the way - a 1970s Marconi 20Mhz TF2204.I shall try using the scopes more often.

author: james_s
author_rank: Super Contributor
timestamp: February 19, 2020, 06:54:57 pm
content: I don't think I've ever used a scope to repair a radio. I've used them for testing small transmitters however in most cases a spectrum analyzer is the right tool for that job. I use my scope all the time, just not for radio work.

author: tggzzz
author_rank: Super Contributor
timestamp: February 19, 2020, 08:33:18 pm
content: Quote from: bd139 on February 19, 2020, 10:59:43 amPersonally I'd replace 4 and 5 with a spectrum analyser that can see the second of third harmonic of the carrier frequency.Apart from that, scopes are useful for the baseband waveforms.

author: bd139
author_rank: Super Contributor
timestamp: February 19, 2020, 08:48:40 pm
content: Most of the time you really don't have to worry about that and work on the assumption that it works absolutely fine due to the ubiquitous nature of well designed low pass filters.

author: vinlove
author_rank: Frequent Contributor
timestamp: February 19, 2020, 09:19:31 pm
content: Problem with the spectrum analyzers are, they have been pricey. But I read that there are now some DSOs equipped with spectrum analyzer in the unit and in good price, so will look out for that in the future.

author: bd139
author_rank: Super Contributor
timestamp: February 19, 2020, 09:23:47 pm
content: They are indeed. Reasonably good. Here's the output of my DS1054Z in FFT mode looking at mixer products:I didn't need to do that measurement though. I was just seeing if it could do that measurement

author: tggzzz
author_rank: Super Contributor
timestamp: February 19, 2020, 09:30:29 pm
content: Quote from: bd139 on February 19, 2020, 08:48:40 pmThat depends on the frequencies of interest and whether the local Radiocommunications Authority plod decides they want to see where you work when you apply for a licence to transmitWe had a nice friendly chat, and I added a stub filter to trap out the harmonics.I didn't mention the munitions he was sitting next to; that's another story.

author: DaJMasta
author_rank: Super Contributor
timestamp: February 19, 2020, 09:31:55 pm
content: They can be really good at spotting output amp/alc loop issues as you can see them adjusting quickly. Serial decoding with enough channels can be useful for internal digital communications, then the usual use for digital side troubleshooting. Not much use in the signal path, at least after upconversion (or before downconversion)..... unless you have a high bandwidth scope, and then you can just directly digitize things and get a bunch of useful info or direct demodulation from your signal.I've got an SA, so I don't really use a scope for FFT stuff, but especially if you've got a 10b or 12b ADC, they could be pretty sensitive/low noise for decent dynamic range.

author: tggzzz
author_rank: Super Contributor
timestamp: February 19, 2020, 09:35:51 pm
content: Quote from: bd139 on February 19, 2020, 09:23:47 pmThe devil is in the details; the first line of my .sig is relevant.High level unmodulated signals are easy. More difficult are low level signals, modulated signals, and looking at phase noise etc. Decent resolution fast ADCs are now available, for an arm and a leg.OTOH sometimes the FFT of an IF signal is exactly the right tool.Summary: it depends on what you are trying to measure.

author: bd139
author_rank: Super Contributor
timestamp: February 19, 2020, 09:38:25 pm
content: Well precisely. Those decent ADCs also seem to make up the front end of a lot of radios now. Not a lot to go wrong

author: tggzzz
author_rank: Super Contributor
timestamp: February 19, 2020, 10:17:43 pm
content: Quote from: bd139 on February 19, 2020, 09:38:25 pmSpoken like a true softie - hardware is easy, isn't itYes, but the test equipment needs to be better than the UUT!

author: vk6zgo
author_rank: Super Contributor
timestamp: February 20, 2020, 03:33:25 am
content: Quote from: Wallace Gasiewicz on February 19, 2020, 01:36:58 pmI agree, Wally.Scopes are very useful for general fault finding in just about any electronic device.I seldom start digging through a device with just a DMM, as with a 'scope, you can look at DC supplies, IF signal levels, audio output levels, local oscillators (for both the presence of, & level of the LO signal.)You can hang the 'scope across the AGC line when aligning a radio, or as a rough check whether a fault is in the stages before the detector, or after it.(If the AGC level peaks as the radio is tuned across the fequency of a known signal source, & there is still no audio O/P , you probably have a faulty audio stage)Some analog 'scopes have a vertical signal output which can be fed to a frequency counter or other instrument, with the 'scope becoming a high sensitivity buffer amp.

author: bd139
author_rank: Super Contributor
timestamp: February 20, 2020, 09:14:30 am
content: On AGC I had an interesting counter a while back. It was a Racal 9915. This had an AGC output on the back which you could connect to a DMM and get a DC reading of signal level. Neat feature that.Another scope eliminator!

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: February 20, 2020, 01:59:12 pm
content: VK6ZGO:My Tek 475 has such a vertical output on the second channel. Outputs whatever wave the scope sees. Quite useful since other scopes of that vintage used some of the input signal power for a counter. I think I had a Tek 465 with a freq counter that did this. That sort of arrangement decreases input to the scope part of the unit.My HP 1980 uses signal from the trigger for the internal optional freq counter. Interesting.People forget that scopes were quite a luxury and they are influenced by the newer equipment that enables them to get more information at a reasonable cost. (I think that is a good thing). Spectrum analyzers and VNAs were beyond financial reach for hobbyists.Currently, one can buy a working decent scope for maybe $100 or less. It is worth it as a learning experience, at least it was for me.A cheap volt ohm meter back in the last century was $20 which translates to probably $100 today.Wally KC9INK

author: GerryR
author_rank: Frequent Contributor
timestamp: February 20, 2020, 06:16:18 pm
content: I use my scope for calibrating my RF Signal generator and other equipment, so indirectly, I've used it for RF work. Many calibration procedures require the use of a scope. Actually, my scope is always on when I'm at my bench, no matter what I am probing.

author: David Hess
author_rank: Super Contributor
timestamp: February 21, 2020, 12:35:11 am
content: Even without RF capability, an oscilloscope is useful for quick and dirty testing of network response via impulse response measurement in any low frequency feedback circuit like audio amplifiers, regulators, etc.Quote from: Wallace Gasiewicz on February 20, 2020, 01:59:12 pmThe presence of a vertical output does not have to have any effect on signal levels. On the 475, the channel 2 vertical output comes from a duplicate of the trigger pick-off circuit which is integrated with the channel switch.QuoteSome or all of the Tektronix mainframe oscilloscopes work that way; the vertical output comes from the trigger circuit path instead of the vertical signal path which can be a little confusing in certain configurations where the vertical signal path and trigger circuit path are not processed identically.

author: vinlove
author_rank: Frequent Contributor
timestamp: February 21, 2020, 02:10:18 pm
content: Here is a good video on using your scope to monitor / check your transmitter / transmission.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 21, 2020, 02:27:37 pm
content: Quote from: Wallace Gasiewicz on February 20, 2020, 01:59:12 pmMany of us got their Oscilloscope experience from units at work, which had performance way in excess of anything we could have afforded.My first proper useable personal 'scope didn't come along till the early 1990s.(A 10MHz single channel BWD).I had a little philips 1940s/50s audio scope I bought for fun before then, but that was really just for the sake of having it as a collector's item!In Oz, back in the late 1950s, a Telequipment "Serviscope" cost as much as a reasonable secondhand car, & a Tektronix as much as a house!

author: vk4ffab
author_rank: Frequent Contributor
timestamp: February 22, 2020, 01:09:52 am
content: Quote from: vk6zgo on February 21, 2020, 02:27:37 pmAnd then dummies like me today have a scope, sig gen, vna, spec an and other assorted gear on their bench that cost fractions of the cost of that 10mhz scopeHow you been OM?

author: vk6zgo
author_rank: Super Contributor
timestamp: February 22, 2020, 03:44:43 pm
content: Quote from: vk4ffab on February 22, 2020, 01:09:52 amAs Electronics jobs have virtually disappeared, the opportunity to learn to use good test equipment has vanished with it.For many, the only way to learn the use of such devices now is to own them.Serendipitously, the technology to produce relatively cheap equipment with quite good performance has become available, so new players in the market have targeted the personal test equipment owner with affordable test instruments.

author: spongella
author_rank: Contributor
timestamp: April 05, 2020, 11:37:05 am
content: Excellent question. I use an o'scope mainly for radio repair and alignment if the service manual calls for one. For example, peaking a voltage when adjusting variable coils/caps/resistors in a radio.