April 2023

Tektronix 7104 – 1 GHz analog oscilloscope

I’m really happy of being a new owner of a Tektronix 7104 oscilloscope – one of the fastest analog oscilloscopes made by man.

Tektronix 7104
Tektronix 7104, 1 GHz analog oscilloscope
Last time I saw one of those on eBay, I was hesitating to buy it and it went away for dirt cheap. Anyways, I didn’t want to miss a chance this time. The unit is working and in a very good condition. The horizontal and vertical plug-ins delivered with the scope are meant for the full bandwidth of 1 GHz.

The Microchannel Plate CRT display is still in a good shape – no burn-ins except the typical wear-out areas (horizontal trace, annotation areas).

Measured rise time of Tektronix 7104 with Leo Bodnar pulse generator on a 7A29 single channel vertical amplifier plugin: approx. 300 ps
Sine wave at 1.0 GHz, approx. -13 dBm into 50 Ohm

Bandwidth test with Leo Bodnar pulser on one of the 7A29 plug-ins gave me a rise time of 300 ps with an estimated bandwidth of approx. 1.16 GHz. This is my fastest oscilloscope now. I’ll check the innards in a couple of weeks.

Voltnuts will hate this: Improve your DMM Resolution With One Simple Trick…

Measuring voltages accurately is a basic task for technicians, engineers and scientists. The voltages to be measured range from perhaps few picovolts to several megavolts – a dynamic range of 18 orders of magnitude! But every modern digital multimeter is kinda limited in resolution. The multimeter’s resolution can be stated in the number of digits it can resolve. A 6 digit multimeter can resolve six decimal places going from 0 to 9. In a decimal number system, this corresponds to \(10^6\) numbers or 1 million digitizing steps. Without going much into detail and exposing my limited knowledge on this matter, I’ll just link to Keysight’s Website where everything is well explained.

Older multimeter models such as the shown MeraTronik V543 can resolve only \(2 \cdot 10^4\) numbers in the selected measurement range (e. g. ±1 V = 2 V full scale:  \(2~V/2 \cdot 10^4 \rightarrow 100~µV\) resolution).

MeraTronik Type V543 (PRL T-189), 4.5 digit multimeter with Nixie tube display

One of the best and most accurate digital multimeters in present time – the HP 3458A – has “only” a resolution of 8.5 digits, which hasn’t improved for about 35 years.

HP/Agilent/Keysight 3458A 8.5 digit multimeter

The so-called “Voltnuts” (crazy electro-fanatics) buy those HP multimeters on a second hand market for $3k to $7k. This surely is crazy and overpriced and in my opinion just not worth it. How about buying a couple of cheaper 6.5 digit multimeters (e. g. HP 34401A for about $200 to $400) and combining them in a serial configuration? I’ve achieved a total of 19.5 digit resolution this way*. I was able to display 10 volts up to 18 decimal places, e. g. attovolts resolution and saved a lot of money.

Two HP/Agilent/Keysight 34401A 6.5 digit multimeters in an unusual configuration showing exactly 10 Volts on April 1st…

*If you don’t believe this nonsense, it’s fine. I can live with that. It’s April Fools’ day anyway 😉