Re: Time Domain Reflectometer (was Re: internet outages)
- Date: Mon, 24 Dec 2018 09:51:30 -0500
- From: Gene Heskett <gheskett@xxxxxxxxxxx>
- Subject: Re: Time Domain Reflectometer (was Re: internet outages)
On Monday 24 December 2018 08:57:27 Joe wrote:
> On Mon, 24 Dec 2018 08:09:11 -0500
> Gene Heskett <gheskett@xxxxxxxxxxx> wrote:
> > On Monday 24 December 2018 04:26:05 Joe wrote:
> > > There is normally a real Nyquist bandwidth quoted somewhere in the
> > > small print. I used to repair and calibrate Hitachi scopes for a
> > > while, until everyone stopped using them.
> > I wonder why, Joe. My V-1065 still works well enough to measure
> > frequency at a 1% accuracy, and its now pushing 35yo. In a pinch
> > I've looked at the output sample of an old analogue tv transmitter
> > to adjust the modulation depth when the monitor was bonkers, it was
> > actually usable at 180 mhz.
> I used to see about three or four of the 665/1065 series a week,
> mostly ten years old with mains switcher problems. Mostly routine
> fixing, after the initial pain of troubleshooting a mains switcher.
> Capacitors, mostly. Even the high-ripple ones will only run so long
> before they dry up.
> Then over about six months, it dropped off to nothing, and we never
> saw any more. I assume oscilloscope use had dropped off enough that
> people could just put a dead one in a cupboard wand say 'we'll get it
> fixed if we ever need it'. Fortunately, oscilloscopes were a minor
> sideline, so I didn't run out of work. The company still has a 1085,
> which I use occasionally. At home, I have a 35-yo Kikusui, and a
> temperamental Tek 465B of uncertain age, but older than that.
465B's were temperamental allright, and way the hell out of calibration
due to drifting R's on the custom made ceramic input attenuator, and tek
has had no service parts for that for nearly 40 years now, and wanted
nearly $400 for one then. Then they merged with GVG, and it all went to
hell. I needed the custom ceramic plate they made a video op-amp on in
about 1995 as we had bought KTLA's old 300-3A/B complete with a digital
effects unit. They had just one, $1500, as is, where is! I said nooooo,
I don't think so, and started looking in the chip books, finding a
single ended one from TI for just under $2. Should bought 2 sticks of
them, it was enough faster that it threw the color phase out more than
there was adjustments for. There was about 8 of them in each channel,
and 6 paths thru that switcher. I should have shotgunned them all, but
since the packaging was different, each one would have taken around an
hour to do neatly. And I was thinking of retireing by then so it never
got done. If I'd have done them all, the video bandwidth would have been
at least trippled. Way ahead of its time in what it could do, I think
that was close to GVG's last hurrah. But the controls were about shot
too. GVG had an accessory E-Disk so the tech directors could program
their own bag of tricks, gvg wanted 20 thou for it. But when we got the
first copy of that switcher from the Penny's production house in NYC, it
came with the edisk manual and the com protocol specs. I looked at that,
said I can do that on a trs-80 color computer, took an old coco2 and
added "the Forgitten Chip" to give it a hardware rs232, wrote the
utility in basic09, which ran on the after market *nix imitation, called
os9, and sold it and two disk drives to the tv station for $245. Later I
found out mine was 4x faster than theirs! Not to mention it gave the
operators english names for their bags of tricks. And because that gave
me a comm path into the switchers innards, I wrote some more utils that
could reach into its control logic and identify which logic chip had
died. Handier than bottled beer in the long haul.
Oh, and I lied about the year in a previous msg this morning, I was 16 so
that was 1950, and the scope was a Hickock 505.
Cheers, Gene Heskett
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>