Testing Tektronix 465B: Where is 100MHz? - Page 1
Forum section: electronics / beginners

author: nadona
author_rank: Regular Contributor
timestamp: December 07, 2012, 03:34:07 am
content: Hi all,My Tektronix 465B has finally arrived today!I'm testing its basic functions but as a newbie, all I can think of is checking the signals from my function generator. It has 2MHz maximum for the sine wave and square wave. And 1MHz max for the triangle wave. The scope also displays fine.For each wave, I checked by 10 multiples (example): 1KHz, 10KHz, 100KHz to the max.How do I check for 10MHz, 50MHz, 100MHz. Where can I find these frequencies? Inside my PC? Can you think of any electronics at home that would have like 100MHz? Or can I generate one with my function generator, like by using a 555?Thanks in advance!

author: nadona
author_rank: Regular Contributor
timestamp: December 07, 2012, 07:47:12 am
content: I just came to think about Arduino crystal, which has 16Mhz. So I soldered two leads to the crystal and my scope shows a beautiful 16MHz sine wave.And now, where's a 15Mhz, 100MHz?

author: amyk
author_rank: Super Contributor
timestamp: December 07, 2012, 07:52:52 am
content: Old (eary 90s) motherboards might have some clock generators in the 50-100MHz range. Not sure about the newer ones.

author: bitwelder
author_rank: Super Contributor
timestamp: December 07, 2012, 08:01:31 am
content: If you happen to have an FM transmitter (some MP3 players / mobile phones use it to help listen to music from a car radio), that is in the range 88-108 MHz.

author: nadona
author_rank: Regular Contributor
timestamp: December 07, 2012, 09:53:48 am
content: Thank you both. I didn't think about FM. Good suggestion.

author: w2aew
author_rank: Super Contributor
timestamp: December 07, 2012, 02:49:30 pm
content: Quote from: nadona on December 07, 2012, 07:47:12 amCan you program the Ardiuno to output a square wave on one of it's pins. Take a look at the rise-time, that'll give you an idea of the speed of the signal (or the scope). BW~=0.35/risetime

author: nadona
author_rank: Regular Contributor
timestamp: December 08, 2012, 04:27:38 am
content: Channel 1 doesn't work at 8MHz and 16MHz! No need to search for high band speed further.Another eBay junk repair project or ...

author: robrenz
author_rank: Super Contributor
timestamp: December 08, 2012, 04:58:57 am
content: With an analog scope if the scope was working before, always assumeyouhave something set up wrong. There are countless ways tonotget a signal displayed. Improper triggering is one of the best ways to get no trace. Vertical position is also a way to lose your signal off screen (beam finder helps here if you have it). Intensity has to get turned up as your sweep speed increases to display the same brightness. (probably your problem here). I am no beginner or expert and I still get situations where it takes me a while to get a signal displayed. All the versatility (lots of knobs and switch settings) makes for more ways to mess things up.

author: nadona
author_rank: Regular Contributor
timestamp: December 08, 2012, 06:50:44 am
content: robrenz:I'd like to make a clarification: Channel 1 has never worked at 8MHz or 16MHz. Sorry for the confusion.Here's what I also found:1) When channel 1 is used as the trigger source, both channels do not work.2) So Channel 1 cannot be used alone, only with channel 2.3) When channel 2 is used as the trigger source, while using both channels 1 and 2 to measure different signals, channel 1 does not work.Thanks

author: Unknown
author_rank: Unknown
timestamp: December 08, 2012, 11:51:04 am
content: Try using a square wave with a rise time of at most 35 ns. This requires 10 MHz bandwidth to be correctly displayed. Channel 1 should show a heavily distorted square wave. Square wave frequency doesn't really matter, something that channel 1 can display like 100 kHz or 1 MHz. If it requires repair, comparing the two channels will be a useful troubleshooting technique.

author: robrenz
author_rank: Super Contributor
timestamp: December 08, 2012, 01:20:01 pm
content: Quote from: nadona on December 08, 2012, 06:50:44 amSorry, you mentioned newbie so I thought that might help

author: nadona
author_rank: Regular Contributor
timestamp: December 09, 2012, 01:00:59 am
content: Even though I watched the w2aew's scope video twice while watching 465b market on eBay for the last two months, I went through the videos again thinking maybe I miss something.Maybe as robrenz said it can adjusting problem or it needs fixing. Or maybe cleaning the switches with some kind of cleaner?The following pictures show the the 3MHz waves from Instek SFG-1003, these pictures taken using channel 2 as the trigger source.1) There are something ghost like signal with sine wave.2) For square wave, ch1 starts with distorted signal and a few minutes later it looks same as channel 2As for trigger sources: 1) Channel 2 is OK. 2) After stabilizing the signal with Ch2, I flip to ch1 and they are scrambled. Intensity is a little bit less but still there. Trigger light keeps turning on. If I flip to Normal position, the signals disappear but with Normal I can do Ch 1 or ch 2 alone fine. With ch 1 as a source, I can't do neither ch1 or ch2.

author: T4P
author_rank: Super Contributor
timestamp: December 09, 2012, 04:22:57 am
content: It's the signal gen, they do that when you operate them at their peak frequency

author: robrenz
author_rank: Super Contributor
timestamp: December 09, 2012, 02:13:45 pm
content: What are yourexactconnections from the FG to each scope channel?

author: nadona
author_rank: Regular Contributor
timestamp: December 09, 2012, 11:27:17 pm
content: robrenz and T4P, thanks for your concern and time.Please keep in mind, English is not my first language.First of all this machine becomes stable if it is turned on over 12 hours. Now both channel works fine at certain specific trigger settings.Individually they can handle 16MHz sinewave out of Arduino crystal.T4P, yes, it disappears at FG's low frequency settings. I learned one thing about FG, thank you.Answer to robrenz; Original lead one side to main 50 ohm jack and the other side is connected with two 200MHz Scope probe.Another question, this is why I started this thread.This meter shows about 3 1/3 cycles of 16MHz waves at the minimum time setting. That means the scope cannot show just one cycle of 100MHz wave on the full screen. I thought the scopes' BW means they can show its maximum BW frequency's one cycle on full screen. I don't know where I got this BW definition from.My core.

author: w2aew
author_rank: Super Contributor
timestamp: December 10, 2012, 02:02:56 am
content: Quote from: nadona on December 09, 2012, 11:27:17 pmScope bandwidth is not rated by the nphorizontal time scale setting. It it rated by the bandwidth of the vertical channels. For the 465B, it is 100 MHz. This means that for a 100MHz signal, the amplitude shown on the screen will be 3dB (or less) lower than the true amplitude.The fastest sweep setting on the 465B can show you 2 full cycles at 100MHz. This is the 2ns/div setting. Adjust the TIME/DIV to 0.02us (20ns), and hit the X10 MAG switch below the CRT next to the calibrator loop.

author: nadona
author_rank: Regular Contributor
timestamp: December 10, 2012, 05:26:36 am
content: Thank you for enlightening me further. So "the high frequency cutoff is equal to the bandwidth?"

author: robrenz
author_rank: Super Contributor
timestamp: December 10, 2012, 12:01:51 pm
content: @ nadona,Please readthis threadabout termination connections of 50 ohm FG

author: w2aew
author_rank: Super Contributor
timestamp: December 10, 2012, 04:47:55 pm
content: Quote from: nadona on December 10, 2012, 05:26:36 amYes, but be careful of your interpretation of the word "cutoff". It does NOT mean that signals above this frequency can't be observed, it's just that their amplitude will continue to degrade as the frequency goes up. In the days of the analog scope, the roll off was often a simple single pole rolloff. However, with today's digital scopes, it is often steeper, due to DSP filtering, as well as Nyquist sampling limitations.

author: nadona
author_rank: Regular Contributor
timestamp: December 11, 2012, 12:33:23 am
content: @robrenzthank you for pointing to the thread. Very interesting and educational.@w2aewYour video helped me a lot to learn EE as well as the scope.I have to adjourn this thread.