Well my scope has FFT under math functions that allows to operate like a spectrum analyzer just not as precise and high resolution as the real deal!Once again a 20 Mhz scope will work just fine on 27 Mhz and higher frequencies.
The 20 Mhz refers to BANDWIDTH not the maximum usable frequency.
It is more akin to a low resolution camera VS a high definition 4D Video camera.
What you would not see is something you would need a spectrum analyzer to identify.
You just end up spending more money for bandwidth and not really getting the benefit.
Mine is the OS-2 version of this scope and it is even older than the one pictured.
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LOL LOOK AT THE SCOPE. Especially when he says it looks good
- Thread starter Low_Boy
- Start date
I have a Nicolet digital scope that does the same thing but I still use a frequency counter.
And I cannot rely on Frequency counter and Oscilloscopes alone - just part of a triad.
The Third part is a monitor radio of known reference - that is the final test for the customer to hear their results.
And even that is relative, they - the customers, have the final say.
Good thread, thanks!
The Third part is a monitor radio of known reference - that is the final test for the customer to hear their results.
And even that is relative, they - the customers, have the final say.
Good thread, thanks!
Maybe for the negative Peaks but watch how the positive Peaks can't be measured accurately @300% modulation with the 20mhz bandwidth button pushed in.
I call that the "ZOOM" feature - it let's you narrow down and see the RF.
But again, if you have bleed or lower audio-frequency artifacts - like the NPC mods I've seen done - the RF wave looks like it should - but the "boxcar" effect comes from the saturation effects at the nearly DC level - far down the spectrum to the baseline. Aka = Hz and kHz versus MHz...
:+> Andy <+:
Did he say RG58 is limited to 30mhz? OooooKayyy! We have been using "High-Quality RG58" at much higher freq. for many years and it certainly is more than cool to use for bench equipment at low frequencies and on the bench 1 to 6-foot runs have virtually no loss that would cause issues for what he is doing LMR 195 Is usable to 1.5 ghz and beyond is there loss at those freq. you bet but even 1.5ghz at a 100ft it's only 14.5db. The real problem is always going to be the quality of the coax and there is some real junk out there that will give you issues at any frequency.
Although 'the customer is always right'; we both know differently. How many times has a trucker came from a CB shop, first hearing his radio on a monitor radio, and then another trucker tell him 'it sounds distorted and nasty' when he hits the road with it? I don't know; but I do know I hear those radios myself, and I know some are nasty.
A local guy I work on radios for has expectations that I will not do and do not agree with. I finally got him to see things my way after I showed him a before/after scope display. He got the picture that 'max smoke no matter the means' isn't really a good idea. All of his radios now sound xlnt on AM as well as SSB - now. Yes, I put the limiter back in and peaked the TX coils. Turned a lot of heads in the area; now they all want it that same way for their radios as well.
Sometimes the customer needs to be schooled a little bit . . .
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I put a UHF ground plane on the roof decades ago, to access a repeater a friend had put on the air. The only coax I had on hand that was long enough was RG58. Had a hard time hitting his machine, since it wasn't elevated all that well. The Bird showed 8 Watts coming out of the radio. Took the meter up to the roof and inserted it at the base of the antenna. Showed about 6/10 of a Watt.
It did work, technically. But not well enough. A short piece of coax won't attenuate frequencies that are higher than it's meant to carry. Not enough to matter.
But the power rating also falls as you push beyond 30 or 100 MHz.
All coax has some attenuation. The real question to ask is how much attenuation you can tolerate.
73
It did work, technically. But not well enough. A short piece of coax won't attenuate frequencies that are higher than it's meant to carry. Not enough to matter.
But the power rating also falls as you push beyond 30 or 100 MHz.
All coax has some attenuation. The real question to ask is how much attenuation you can tolerate.
73
Yes but I have tested this up to including 100+ mhz and the loss with good coax is not even worth talking about. Now maybe when you get up to 400-500 mhz range it's and issue but a 0.3db loss at 50ft is pretty acceptable in my world. I thought this would be interesting for others on here so I grabbed some junk coax I have here about 48 ft or so and the images below show the relative loss at 3 frequencies. I tested many 12 foot jumpers as well and all showed 0.0db loss so on the bench it's more than ok. All I was responding to was the turkey making a video claiming rg58 was not acceptable for bench work? I tested the MFJ That was recently fully aligned against the spectrum analyzer with tracking gen and marker table setup and MFJ passed with or was at least real close so Im fairly confident its pretty accurate just in case anyone was wondering.
The accuracy of the readings still depends on calibration and the skill of the operator.
I watched the entire video and nothing was proved or disproved on the bandwidth of the scopes. While I have spent crazy amounts of money on test equipment for daily use and doing alignments I use my scope that I have had since 1995 and it is a 20 MHz Band Width. When you are just looking for a low power peak or dip 20 is more than good.
If your scope is clipping the top readjust your scope. And who really is worried about the symmetry of top vs bottom peaks. No CB'er I have met. If you are getting 300% and it looks good and sounds good what the hey?
Even I don't get that anal retentive.
I watched the entire video and nothing was proved or disproved on the bandwidth of the scopes. While I have spent crazy amounts of money on test equipment for daily use and doing alignments I use my scope that I have had since 1995 and it is a 20 MHz Band Width. When you are just looking for a low power peak or dip 20 is more than good.
If your scope is clipping the top readjust your scope. And who really is worried about the symmetry of top vs bottom peaks. No CB'er I have met. If you are getting 300% and it looks good and sounds good what the hey?
Even I don't get that anal retentive.
Without perfect symmetry, the measurement of the positive peaks will always be wrong. That being said, any adjustment made based upon incorrect measurements will also be wrong.
No body that is a technician would ever make an adjustment worrying about 300% modulation. All alignment procedures I have ever seen always specify 95% modulation or less. Worrying about how symmetrical the asymmetrical modulation is tells me you are looking for something else and I won't bite. 20 MHz for most people is good enough. Was that video from the guy that is ridiculed all of the time?
a·sym·met·ri·cal
[ˌāsəˈmetrək(ə)l]
ADJECTIVE
a·sym·met·ri·cal
[ˌāsəˈmetrək(ə)l]
ADJECTIVE
- having parts which fail to correspond to one another in shape, size, or arrangement; lacking symmetry.
"the church has an asymmetrical plan with an aisle only on one side"
synonyms: lopsided · unsymmetrical · crooked · uneven · unbalanced · off-balance · off-center · to one side · awry · askew · skew · skewed · squint · tilted · tilting ·
irregular · unequal · differing · dissimilar · unlike · unalike · unidentical · unbalanced · lopsided · awry · askew · crooked · asymmetrical
IF you want a good example of Asymmetry, go grab a "Barry Manilow" (or any 70's LP) album from the Record Player days - record it into a MP3 editor, just record, nothing fancy.
Then compare that recording to say, Rachel Platten - and her voice digitized - synthetized - and review that transferred over to an MP3...
Review - zoom in on their waveforms - note that the sampling rate is the equalizer in the effort to capture the signal from analog world into the digital realm. Analog seems "low-level" compared to the later compression techniques used for voice and music - its' why you look for AAD not ADD or DDD when it comes to Moody Blues Greatest Hits - because you want the ORIGINAL preserved as much as possible - not the remanufactured stuff else grab the turntable and do it yourself.
Dynamics are favored in Asymmetrical - but you lose the fidelity. The effects are reciprocal too. You lose bandwidth but obtain punch, you lose fidelity of inflection but gain voice at the cost of dynamics in compression - but you have voice intelligence (or at least the intelligible part). Fidelity is lost in the narrowed bandwidth but you gain voice in the noise.
RIAA had Analog - Equalization emphasis and De-emphasis - while CD's were/are just plain hammered...
Asymmetry has it's place. Just the various techniques used are not the best with fidelity, or dynamic range or distortion - al 3 are sacrificed in one form or another when it Asymmetry, is used either in compression or expansion...
:+> Andy <+:
Then compare that recording to say, Rachel Platten - and her voice digitized - synthetized - and review that transferred over to an MP3...
Review - zoom in on their waveforms - note that the sampling rate is the equalizer in the effort to capture the signal from analog world into the digital realm. Analog seems "low-level" compared to the later compression techniques used for voice and music - its' why you look for AAD not ADD or DDD when it comes to Moody Blues Greatest Hits - because you want the ORIGINAL preserved as much as possible - not the remanufactured stuff else grab the turntable and do it yourself.
Dynamics are favored in Asymmetrical - but you lose the fidelity. The effects are reciprocal too. You lose bandwidth but obtain punch, you lose fidelity of inflection but gain voice at the cost of dynamics in compression - but you have voice intelligence (or at least the intelligible part). Fidelity is lost in the narrowed bandwidth but you gain voice in the noise.
RIAA had Analog - Equalization emphasis and De-emphasis - while CD's were/are just plain hammered...
Asymmetry has it's place. Just the various techniques used are not the best with fidelity, or dynamic range or distortion - al 3 are sacrificed in one form or another when it Asymmetry, is used either in compression or expansion...
:+> Andy <+:
It was done to prove a point. 20 megahertz is totally useless for precise measurements if you take people's money and do this stuff for a living as the video clearly states. It might be okay for imprecise hobbyist measurements.
I'd have a hard time taking anyone seriously that says precise measurements aren't necessary, so I find it amusing when those people ridicule someone who says precise measurements of a 27mhz signal cannot be taken with a 20mhz scope.
Perhaps distortion of the waveform might have been more accurate terminology than symmetry of the waveform. Asymmetry can mean different things depending on how you look at it. A lopsided waveform that leans to the left could be construed as asymmetrical even if the positive and negative peaks are identical in amplitude. (Distortion)
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I don't tune perfectly good radios and advise against modifying the FCC Approved design. The 20 MHz scope is just fine for technician level repair work and normal alignments. I have had to re tune radios that had the super whack pack modifications and alignments and I checked my results on two calibrated spectrum analyzers and the radio was well with in the specifications. Checked over the air and got good comments on the sound quality. The shop that did the wack pack has 200 MHz scopes, I guess they did not know how to use them.
The one variable here is the skill of the operators. You can't compensate the lack of skill with fancier tools. I used my 20MHz scope and the radio performed better than the alignment with the 200 MHz scope.
a·sym·met·ri·cal
[ˌāsəˈmetrək(ə)l]
ADJECTIVE
The one variable here is the skill of the operators. You can't compensate the lack of skill with fancier tools. I used my 20MHz scope and the radio performed better than the alignment with the 200 MHz scope.
a·sym·met·ri·cal
[ˌāsəˈmetrək(ə)l]
ADJECTIVE
- having parts which fail to correspond to one another in shape, size, or arrangement; lacking symmetry.
"the church has an asymmetrical plan with an aisle only on one side"
synonyms: lopsided · unsymmetrical · crooked · uneven · unbalanced · off-balance · off-center · to one side · awry · askew · skew · skewed · squint · tilted · tilting ·
irregular · unequal · differing · dissimilar · unlike · unalike · unidentical · unbalanced · lopsided · awry · askew · crooked · asymmetrical