Test Equipment: Oscillocopes

[Brian516]

A quick update on the status of the GR 1330-A to O-scope testing vid:

Acc to USPS tracking, my Digikey order with my fuses SHOULD be here tomorrow, so I am hoping that I will be able to start using the Oscillator at some point tomorrow and make an initial vid.   
I say "SHOULD" because we have received around a foot of heavy snow here,  and almost all of the roads are completely iced over with a thick later, so I'm keeping my fingers crossed that the trucks don't get delayed. As of now, according to their website, everything is on schedule. 

Also, an off-topic comment:  I have decided that my first REAL project (non ###### related) is going to be a crystal radio set with as many tunable components as I can make it (within reason).  I have been studying up on how it's done, expected results per build specs, etc and feel confident that it's definitely within my skill set to do. The thread I have been reading/re-reading specific posts: http://www.overunity.com/15538/crystal-radio-the-first-real-free-energy-device/
This should be a great starting project for the Scope/Oscillator that I am currently learning to use.

Brian

[Brian516]

Hey there everyone,

My fuses FINALLY arrived, and my GR Oscillator seems to be working great!  I have made a video while running thru a number of the various settings of the Oscillator. It's fairly long, especially since I didn't run any tests at all with it before making the vid.  I apologize for the lighting (again), as I haven't managed to get a good setup in place with my mini-lab just yet.  (Any suggestions for the type of lights I should install in my 3-lamp ceiling track light for this would be appreciated.)

https://www.youtube.com/watch?v=EPR4aRoIVPE

I still don't yet have the proper adapters for the Oscillator just yet, but hopefully will soon.  I ordered some Hantek HT30-A cables and mini grabber attachments so far.  Right now, on hand I have (2) T's, (4) F-F 75ohm adapters. I also have several compression BNC fittings and 75ohm RG6 coax that I can make some patch cables with. (I need to dig up some of my NOS RG-58 50ohm. - I'll order some higher quality ones once I have most of the other necessary fittings I need, or if I run across a cant-pass-up deal on some).
As for a list of fittings  I still need to get: GR874 to BNC; 50ohm Terminators; BNC to Phono; 50ohm F to F; 50ohm M to M; BNC to SO-239/PL259; and good patch cables.

TK - is there anything I am missing in that list that you think I should get?  What is your opinion on the broken panel mount GR874 fitting for RF on the Oscillator? Does it look like it may cause me issues, or should my connection strength still be OK for the time being? 
I am taking my time building my variable capacitors (I'll probably still just order a couple from that site that was suggested in that thread), so I'll likely just build the Variometer that you made and use some fixed capacitors for now. Other than that project, what do you suggest I do for a good project to enhance my learning experience with the oscillator and/or scope?

Brian

[TinselKoala]

@Brian: Congratulations on getting the GenRad oscillator up and running!

Some comments:

Determining frequency: Millisecond or ms is 0.001 second. Microsecond (Greek letter "mu" which looks like a "u") is 0.001 ms or 0.000001 second. Nanosecond (ns) is 0.001 us. (I always remember "nanosecond" because "nan" sounds like "nine" : 0.000000001 second (nine decimal places)).  And frequency is 1/period, and period is 1/frequency. So if your timebase is set to 1 ms/div (0.001 sec/div), then the middle 8 divisions of the graticule indicate 8 ms (0.008 seconds) of time, and if you have, say, 12 complete cycles in that time, your frequency is 12/0.008 or 1500 cycles per second, ie 1500 Hz. I use the middle 8 graticule divisions because this is where the sweep will be most accurate wrt the actual knob setting. ("var" in the cal detent of course).  The 1000 Hz setting of the audio output looked right on, it was putting every peak exactly on a graticule line when you had the timebase set to 1 ms (0.001 sec) per division.

The broken GR connector: the determining factor here will be to see if it still mates properly with another GR connector, like when you get your GR-BNC adaptor. It probably will but I can't tell from the video whether the damage is severe enough to prevent proper connection. Somebody probably twisted when they should have pulled, or something like that. If it doesn't mate properly with another GR connector then you have a couple of options. You _might_ be able to find a replacement bulkhead-mount GR connector for replacement -- this will preserve the authenticity and collectability of the unit. Or you could remove the connector and replace it with a panel-mount BNC connector and a bit of aluminum sheet to fill the gap. This might be the cheapest way to go but it might offend the true General Radio aficionados.

The modulation: Hmmm.... when you were connected to the "Audio" output jack it looked like you were seeing the RF superimposed on the audio modulation signal. I kept wanting you to turn the timebase down to 1ms/div so you could see the audio. The scope was triggering on the audio rather than the RF within the audio. Once you changed to the RF output jack it looked more normal to me. It looks like the oscillator and scope are both working perfectly. The sine wave is a little distorted but not too bad.

Nice work! I'm glad to see that nice old oscillator working properly.I don't have any specific suggestions at the moment but if I can think of any I'll let you know. Cheers!

[Brian516]

@Brian: Congratulations on getting the GenRad oscillator up and running!

Some comments:

Determining frequency: Millisecond or ms is 0.001 second. Microsecond (Greek letter "mu" which looks like a "u") is 0.001 ms or 0.000001 second. Nanosecond (ns) is 0.001 us. (I always remember "nanosecond" because "nan" sounds like "nine" : 0.000000001 second (nine decimal places)).  And frequency is 1/period, and period is 1/frequency. So if your timebase is set to 1 ms/div (0.001 sec/div), then the middle 8 divisions of the graticule indicate 8 ms (0.008 seconds) of time, and if you have, say, 12 complete cycles in that time, your frequency is 12/0.008 or 1500 cycles per second, ie 1500 Hz. I use the middle 8 graticule divisions because this is where the sweep will be most accurate wrt the actual knob setting. ("var" in the cal detent of course).  The 1000 Hz setting of the audio output looked right on, it was putting every peak exactly on a graticule line when you had the timebase set to 1 ms (0.001 sec) per division.

The broken GR connector: the determining factor here will be to see if it still mates properly with another GR connector, like when you get your GR-BNC adaptor. It probably will but I can't tell from the video whether the damage is severe enough to prevent proper connection. Somebody probably twisted when they should have pulled, or something like that. If it doesn't mate properly with another GR connector then you have a couple of options. You _might_ be able to find a replacement bulkhead-mount GR connector for replacement -- this will preserve the authenticity and collectability of the unit. Or you could remove the connector and replace it with a panel-mount BNC connector and a bit of aluminum sheet to fill the gap. This might be the cheapest way to go but it might offend the true General Radio aficionados.

The modulation: Hmmm.... when you were connected to the "Audio" output jack it looked like you were seeing the RF superimposed on the audio modulation signal. I kept wanting you to turn the timebase down to 1ms/div so you could see the audio. The scope was triggering on the audio rather than the RF within the audio. Once you changed to the RF output jack it looked more normal to me. It looks like the oscillator and scope are both working perfectly. The sine wave is a little distorted but not too bad.

Nice work! I'm glad to see that nice old oscillator working properly.I don't have any specific suggestions at the moment but if I can think of any I'll let you know. Cheers!

TK,

Thank you, I have been wondering how exactly to calculate frequency from traces. I knew generally how it was done from your videos, I just didn't know the exact numbers and specific method. I copied/pasted that section to Word, enlarged text, and am printing it off so I can reference it every time until it's memorized.

The GR connector: hopefully it does mate well with another 874 with the two broken prongs. Unfortunately, instead of the broken prongs being opposite each other, they are one of each vert and horiz. The bottom and right prongs are broken off all the way in to the plastic backing piece. At some point, even if it is operable, I would like to replace it anyway, but hopefully I can do it some other time when I am more comfortable disassembling it to get to the connections properly.  If it does cause issues with another GR fitting, what about soldering directly to the remaining tabs with a short, thick lead and going to a panel mount BNC for the time being (until I obtain a proper replacement 874)? Or do you think that may cause various issues such as excessive leakage RF at higher frequencies?

The MOD: I will make another video and connect to the audio jack with RF output, leaving the scope on 1ms/div and see what we get.  What do you think may be causing the distortion? the cheap probe, lack of proper connections and termination, or something else?  I ordered some terminators along with BNC-Phono, and some realllllly good long minigrabbers I found for a great deal from Vetco.net.   If you haven't found that site quite yet, please take a look and let me know what you think of their goods and if they appear to be of good quality, or of cheap Chinese manufacturing origins.  Of course the best way to find out will be when I receive my goods in the mail, but I found the exact grabbers on ebay that someone was selling for about $9 each, when they are only $2.69ea there. Here's a link to the grabbers I scooped:  http://www.vetco.net/catalog/product_info.php?cPath=41_438&products_id=6944

Do you think I did the right thing by waiting until I had the proper fuses before operating it?  I feel like I left you waiting for a demo far too long, and possibly made you think that I'm not really interested in learning how to use the scope and my equipment. I assure you that is not the case!  I may get a little too excited at times and get a bit ahead of myself (like I did with building my own var-air-caps, which are a big PITA - but I'm not giving up on!!) and then calm down and come back to full reality later, but when I decide to start something I always follow thru.  I just wanted to clear that up, since I kind of got the feeling that you thought you had possibly wasted some of your time instructing me.  I really do appreciate the guidance, and any way I can get you back for the help, I will, so just ask anytime and if it's something I'm capable of or something I have, I'll happily assist or send it your way.  Currently my main expertise relating to what's done in this field is designing and building mechanical related things, and woodworking.

Anyway, in your opinion, above what frequency should I need to be using a termination setup to get proper output signal/measurements?  Do you think that 75ohm coax is worth making any patch cables out of, or do you think I should just wait until I find my RG-58? I may just go to the store and buy a 25 or 50 foot RG-58 cable and chop it up so I have some patch cables for now til I get some better ones.  I don't like spending money on low-mid quality goods like that, so I'd like to wait until I find a good deal on and can afford to get a set of high quality patch cables. Kind of like I did with my T's - I got a pair of new Amphenol's for 3 bucks. Those are fairly decent, right? If not, I only spent 3 bucks anyway, haha. 

Saludos!

[MarkE]

Frequency is just the inverse of time period.  You can find the time period by counting off the number of divisions a complete cycle takes and multiplying that by the time period per division.  Divide that into one second and you have the frequency.  A scope sweeping at 5us per division and 10 divisions across the screen takes 50us for one pass.  A waveform that is exactly one cycle per screen is:  1/50us/cycle or 20k cycles per second.  If two cycles complete each screen then the frequency is 40kHz.  If five cycles complete, then it is 100kHz, and so on.  If one waveform fills 3.5 divisions, thent he frequency is: 1/(3.5*5us)/cycle or 57kHz.

For decent coax and sinewaves:  20MHz*meters will be OK.  IE if you have a 10MHz signal a 2 meter unterminated coax won't cause much distortion from the reflections.  For squarewaves, 0.4ns/cm = 1ns/inch rise or fall times will be reasonably clean.  Modern logic like DDR3 has rise and fall times down to around 50ps - 70ps which demands termination in almost all applications.  Stuff like common CMOS logic is much slower and can go a couple to several inches without termination cleanly.