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I guess my next question would be: is that horrible 40mV p2p signal coming out of the MARKER OUT "normal" in 1ns mode? Yuck.

I can see how mitigating coupling through the contacts of K450 could be challenging. But does this indicate any issues with Q460, CR468, or any other associated components and wiring? It seems that Q460 should be pulling MARKER OUT up.

I guess my next question would be: is that horrible 40mV p2p signal coming out of the MARKER OUT "normal" in 1ns mode? Yuck.

I can see how mitigating coupling through the contacts of K450 could be challenging. But does this indicate any issues with Q460, CR468, or any other associated components and wiring? It seems that Q460 should be pulling MARKER OUT up.

I have to ask how you handle the transition from coax to the Xmas lights? And how you interpret the results.

A picture of two may be worth a 1000 words.
D.

-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Glydeck via groups.io
Sent: 02 December 2021 05:23
To: [email protected]
Subject: Re: [TekScopes] 1502 TDR RECORD functions

Good question. I don’t think it matters. An interruption in the transmission line does not care if it’s a LED or a bulb. I’m so trying this on some recalcitrant light strings.

Glydeck KD6NEW

On Dec 1, 2021, at 6:32 PM, Paul Amaranth <paul@...> wrote:

?Was that incandescant or LED lights?

I have an entire bin full of LED strings that are dead and that might
be worth a try.

Paul

On Wed, Dec 01, 2021 at 01:51:54PM -0800, fiftythreebuick wrote:
Tom, the 1502 is one of the most useful instruments around!

I just finished finding the fault in a long string of Christmas lights with mine! :-) Definitely something essential to have around...

Tom

--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix/Linux - We don't do windows

On Thu, Dec 2, 2021 at 10:56 AM, Harvey White wrote:

Couple things on USB that might help.

You can easily buy a TTL to USB converter.? Takes TTL level (as from
uart/usart) signals, either 3.3 or 5.0 volts, and translates them to a
USB signal.? That USB signal, when plugged into a PC, enumerates as a
serial port.? You set the baudrate at the terminal to match the TTL
baudrate.

In a number of microprocessor boards (my experience is with the ST-MICRO
boards), the USB chip on the board used for programming also has a
virtual terminal function (at the same time as debugging).? The USB chip
is hardwired to a USART output on the processor.? If you don't use those
pins for something else, and don't disconnect them, you can initialize
that particular USART on the processor and use it to communicate through
the debugging cable.? Your debugging system runs an instance of a
terminal program.

In addition, if you enable the fprint functions in your system and
direct them to the USB usart channel, you can get ongoing outputs from
the processor to the computer for monitoring a process.? You could also
use the console in and out functions, but those may need to be
redirected in your program.

Really easier than you might think.

As to emulating a true HID device, I haven't tried that, haven't needed
to, but I suspect with the right drivers, emulating an HID device
(mouse, etc) might be easy enough.

Harvey


On 12/2/2021 12:07 PM, Chris Wilkson via groups.io wrote:

This is fantastic work, Holger!

I have a disembodied P7001 that I keep meaning to add to a 7704 so I can

play with it. Or, finally accept that I will never get to it and pass the
p7001 to a new owner.

Your project tilts my internal debate toward "keep it". :)

Quick question on Teensy: Can it be configured as a USB HID host?
I have many homebrew projects that would benefit from a USB keyboard-to-TTL

converter but I'm honestly intimidated by USB complexity so I haven't done
much research on USB hosts.

Hi Harvey,

My need is actually in the other direction. There is no PC involved anywhere.

There are a million ways to connect a random electronics project to a PC through USB, typically using an FTDI IC with a virtual com port in Windows. Which is the way you described. Or using a development board from an MCU manufacturer or something in the Arduino ecosystem. But cursory searches turn up little info on preexisting solutions for connecting commercial USB devices (keyboard, mouse, usb stick, whatever) to a random electronics project.

Here's an example of what I want to do. I have a working USB keyboard (standard COTS device) that I want to interface to a vintage CPU. Say a 6502 for example. Or even to a discrete TTL design. So I need a USB *host* that can talk to the keyboard and spit out raw data on the other side in serial or preferably parallel format. I went down the PS2 -> TTL route years and years ago. It was fairly trivial. But USB host implementation is a whole different animal.

Best,
Chris

Why does switching 2ns/1ns push buttons change the 2ns output at all!? Given
the schematic for the 10ns Amplifier input U450C.

Hi all,

I've been working on rehabbing a TG501. After replacing the shorted Tantalum filter caps on the 15v supply the device has operated pretty well. I've been learning the operation, circuits, and tuning of it without too much difficulty. I've gotten the timing marks synced with a Leo Bodnar GPSDO and, despite not having the OPT1 1MHz oscillator, can achieve a very stable output. That is, almost no drift relative to the GPSDO at 1MHz over long periods of time. Nice output levels too.

A remaining issue I'm having leads me to wonder how the 1ns and 2ns circuits are intended to work. First, I understand 1ns is pretty fast for the equipment I have on hand, but I do have a 7934 with 7B92A time base, and 7A29 vertical amplifiers. It's all in less than ideal condition, but functioning well enough for me to observe the 1ns sine wave. Albeit at a weak level. Is this the 7934 BW limit, or the TG501? Undetermined yet.

But the 2ns output is plenty strong - up to 1.5v p2p. Adjustment of C515 between 1ns and 2ns levels has me turning it down to about 800mv p2p. But still I cannot get anything more than about 40mv p2p on the 1ns output (see above - is it the BW limit of the 7934, or the TG501?).

In working on these outputs I've had them both on the 7934 through both the left and right vertical slots, both going through 7A29s. Switching between the 1ns and 2ns push buttons results in both outputs present (2ns on MARKER OUT, 1ns on 1NS ONLY), but when in 1ns mode the 2ns output drops from 800mv p2p (or whatever I've set it to) to about 40mv p2p. The 1ns sine wave output remains fairly consistent at about 40mv p2p. It looks pretty good - a good sine wave, and the level does change a few mV between 1ns and 2ns settings. The 2ns waveform however, goes from looking beautiful in 2ns mode to ugly (not a clean sine waveform) in 1ns mode.

I'm trying to understand how this is happening. Studying the A2 Multiplier Board schematic <4>, I don't see what the 1ns/2ns push buttons even do to affect the 1ns/2ns circuit operation. It looks like these push buttons are tied together at the input of NOR gate U450C. That having either pushed in enables this gate to pass the 100MHz oscillator into the 10ns Amplifier of Q484/Q486. And it also looks like these push buttons both operate/enable K450, and should result in both 2ns and 1ns outputs to be at their respective output BNCs: MARKER OUT and 1NS ONLY. How is selecting 1ns causing the MARKER OUT output to drop?

I'm suspicious of CR515, but given I don't even see how the 10ns Amplifier output should change at all, that seems to be ignorant grasping. Is there something about the input to U450C I'm not understanding? It seems the 1ns and 2ns outputs should always be present, and the 1ns and 2ns push buttons seem redundant - there should just be one button and both outputs?

I'm perfectly comfortable recognizing the 1ns output level to be BW limited by my setup. It makes tuning C515 guesswork, but I can live with that. If I can't even discern the 1ns output reliably with the equipment I have, I don't actually have much (any?) need for it. But it bothers me that that 2ns is so adversely affected. And that I can't understand why the circuit behaves this way. So any insights are greatly appreciated.

Thanks,
Dave

This is fantastic work, Holger!

I have a disembodied P7001 that I keep meaning to add to a 7704 so I can play with it. Or, finally accept that I will never get to it and pass the p7001 to a new owner.
Your project tilts my internal debate toward "keep it". :)

Quick question on Teensy: Can it be configured as a USB HID host?
I have many homebrew projects that would benefit from a USB keyboard-to-TTL converter but I'm honestly intimidated by USB complexity so I haven't done much research on USB hosts.