The AM Forum

  Testing out a homebrew rig this morning; looking at RF envelopes with a sine at various audio frequencies into the mic jack. At a blazing 20khz, it looks superb, but way down in the basement at 50hz—wow!—that looks like monkey snot on my digital scope! Something wrong with the rig? Maybe I need to revisit my screen bypass cap and screen resistor?
  Just as a sanity check, I dust off my old Tek 465 (honestly, I'd forgotten I still had a 465). Imagine that! It looks perfect!
Yet another reminder that I should never give up all of my old analog scopes, of which I have a number.

I got my 465 about 30 years ago and never regretted it! Here's the reason: When I was a member of Unkle Sam's Canoe Club, we used them exclusively on systems below 100Mhz. They were slammed against bulheads, dropped down ladders, (that steps for you 'common folk' ;)), suffering nothing more than a broken handle. Also, they were built at a time whe Tektronix equipment was fairly easy to service. Wires were color-coded as were plugs and jacks. You always knew where pin 1 was on J101 ect! I thought about getting a digital job but then why mess with success?

I have a digital scope also. I've had it for about 6 months. I haven't run into any issues like Bill, yet but I do find myself going back to my old CRT scope as well on occasion mainly because of ease of use and familiarity. 

  Well, I do love my digital scope—it will do just about anything but make breakfast for me—but despite all those nifty tricks, I never forget that what I see on the screen is a microprocessor's interpretation of what's really happening. I can do an old-fashioned trapezoid display on it, but it's reduced to a bunch of little digi-dots.
  A few years back, the man in the corner office at my old workplace came around and told us that whatever analog scopes we had in the lab were to be heaved into the dumpster, because the company would no longer pay to have them calibrated yearly. I asked him if I could take mine home with me instead, and he agreed, so I brought home a Tektronix 2213 and a 2445A, both fine Tek scopes, but both sort of Toys-R-Us compared to the old 465 and its kin.
  My favorite Tek scope was an old 7623A "mainframe" storage scope, but it stopped working a few years ago. I couldn't bear to get rid of it, so it's stashed away in a bin waiting for the day when I'll get around to troubleshooting it.
  I've also got a Kikusui DSS-6520 analog storage scope, which is kind of an oddball. It works fine, but I've never been able to get the storage function to work.
  Amongst my current analog scopes, the old 465 is still my favorite. I've got the full service manual for it, and I plan to keep it going for as long as I can.

That's an awesome scope - one of my all-time favorites. Enjoy!

I was considering getting a digital scope some years ago just before I picked up my Tek 2232. I decided that any digital scope I could afford would probably disappoint me in some way or another.

I have a digital scope on the bench and its fun, displays frequency and things like that in addition to just being a scope, did have a lot of issues trying to look at AM Modulation envelopes until I was enlightened about how to use the external trigger when doing test.
The issue I have is SDR receivers and how they display spectrum, SDR receivers produce such a clean display of bandwidth limiting and two tone SSB signals that they are maybe twice as good as some of the spectrum analyzers that I have. My Agilent 8920 sucks on two tone test for SSB transmitters, have a very old HP-8568 that works well on doing two tone test and intermod on transmitters but a Flex somehow looks to outperform them all and somehow I just can’t square with this, maybe I am just too old or stupid to wrap my head around it?

  Here's a "Slinky" video—50hz to 12khz sine sweep—showing the RF envelope of my homebrew transmitter, using the same Tektronix 465. The trigger on that old 465 remained pretty stable across that frequency range.
  Note the amplitude remaining flat across that range, with no weird kinks or bends along the way. It does start to roll off just a bit between 13khz and 20khz, but only slightly. Most of us can't hear that high anyway. Looking forward to getting it on the air for the Rally.

The difference is frequency resolutions between the two displays. Your old swept-tuned spectrum analyzer probably has a resolution bandwidth in the 100s of Hz. Most SDRs displays are FFT-based and can have resolutions in the 10s of Hz.

I am completely sure, after these homilies, that I don't have to get up and add more preaching from the analog CRT scope pull-pit!  Preach it Brothers!

But most wierdnesses of digitizing scope image presentation is due to the setup/adjustment of the display timing.

Yeah, I thought it'd be cool to modernize and get one of these.   

(https://photos.smugmug.com/TEST-EQUIPMENT/SIGLENT/i-b34nZNB/0/NBGmcvDjFpnFsSvx7Vs7hrTsBjM6VgcmmNp2v8M2R/XL/P1010026-XL.jpg)

I was so impressed, that I sold it 30 days later.   

...and kept these.

(https://photos.smugmug.com/TEST-EQUIPMENT/SCOPES/Tek-454/i-5MqWL5W/0/MVFNqqcqvtNG3LRG73k9SmTBwRWDBPKqF28gJmFZ2/L/P2150006-L.jpg)

(https://photos.smugmug.com/TEST-EQUIPMENT/SCOPES/TEK-465/i-fXrMm57/0/KwDMBxFqm6S94snjXQvd5GM8H2Gwmbj9hDJGDTZ58/L/P2210047-L.jpg)

(https://photos.smugmug.com/TEST-EQUIPMENT/SCOPES/TEK-465/i-xHwWSnP/0/KHrhJkxqNgnrpB64r35KWKTw6PBPjqR65KpKdvqQX/L/P1010024-L.jpg)

(https://photos.smugmug.com/TEST-EQUIPMENT/SCOPES/TEK-2465/i-Km77KQn/0/Mskp5DjHMsbX9QGbjWTQ3v5bxn5D5gPd9k3HrDxQZ/L/P1120017-L.jpg)

  Wow...Tek 454! That is truly a classic. The scope I used in my first technician job was a 464 storage scope—very much like a 465 but with storage; using the old "mesh" or "dual phosphor" CRT. I suspect that replacement CRT's for those would be hard to find these days.
  The storage function is where the modern digi-scopes shine, but really, once you got the hang of setting the intensity and persistence on those old storage CRT's, you could catch some incredibly fleeting events on them. My old 7623A mainframe scope was great for that.
  I still like my digital scope, with all its nifty tricks like auto-tracking cursors and math functions, but for analog/linear stuff like looking at modulated RF envelopes and such, I'll still go for my analog scopes. I was so disappointed the first time I used my digital scope to do a trapezoid test, and got low resolution array of dots:

At one time it was a big deal for every AM Broadcaster to annually check there NRSC compliance that checks to be certain that you’re audio is limited to 10 KHz max. I use to do this with a spectrum analyzer and used a FCC mask of not exceeding 10 KHz on both sides of the carrier down to 25 DB below the peak carrier,  below 25 DB down the window to 35 DB down you were limited to 20 KHz each side of the carrier, from what I recall at around 50 DB down you can be as wide as 50 KHz. Was not uncommon to see the skirt of the modulation envelope widen below twenty five or thirty five DB and always assumed that was due to the rise time of the analyzer. Looking at the same signal on a Flex the skirts are way sharper and more pronounced then what you got with an analog analyzer. Got a HP ESA-1500 that I use for a bunch of stuff these days and figure its basically a SDR but still see a difference between looking at signals with that and a Flex, I sometimes wonder if the algorithms they use in the Flex lie to us? Or maybe the same deal with digital sampling scopes? Or maybe I am just too old accepting the modern technology?  I have a huge General Radio bridge that I use to find impedance and capacitance and cannot jive with those little cheap Chinese LCR meters that everyone loves. 

I have the opposite end.

An Advantest (Rhode & Schwartz I'm told / reference in its manual) 8 ghz spec an.

It does FFT for an scope display.  Haven't used it yet (discovered the entry in the manual after it was packed for the upcoming move) but I'm wondering what it's fft is going to look like lol.

Cool to have an 8ghz scope.

--Shane
WP2ASS / ex KD6VXI

I have a 475 with the DMM. My Dad brought it home from work. Its virtually new. It was a spare for the service techs but they never used it so the phone company was going to toss it.

I got the 2445 at my work. I think it was claimed to be intermittent and the calibration guys said they could no longer support it so our person in charge of equipment told me to sneak it out the backdoor and make it disappear.

The HP54610B I bought online.  It works ok but has a flaky vertical switch on channel 1.

My pair of Tektronix 7854 scopes with a large set of 7000 series plug ins will continue to meet my scope needs :)

Rodger WQ9E