Test Equipment Anonymous

This is a Philips pulse generator from the late 1970s. No GPIB, so I shouldn't have bought it really, but it's very compact relative to the HP 8007B that I bought earlier this year.
I was expecting this to be a repair for the £15 price, but it works, albeit with the expected slightly scratchy vernier variable resistors.
The innards scream Philips at you in a way that no manufacturer does today, the boards are also quite aesthetically pleasing.



There's a big amplifier stuck on one end of the pictured board, it contains many BFW16As and 2N5160s. It also runs them in parallel with the "sharing" resistors on the base. A real brute force approach. The back panel is a custom power supply regulator heatsink and rather nice, it's even Philips blue.

I recall discussing this just after you bought it. I couldn't quite see what this thing could do that a modern DDS function generator couldn't do better. Maybe not with GPIB, but USB is now the scene. This has neither.

On mature reflection, it was a blow beneath the belt and unworthy. People who live in glass houses shouldn't throw stones.

It was only £15 and I'm sure it's given that much in pleasurable diversion already.

Variable rise/fall time?

Pulse width remains constant as period is changed?

Double pulses?

Nothing that an AWG couldn't manage.

Having said that, I've never found a USP for generic pulse generators. Back in my first job one of the early things I did was to make a weird specialised pulse generator for a specific piece of equipment I was building. I've repeated that concept many times since.

tggzzz wrote: ↑Tue Aug 26, 2025 9:32 pm ...............
Nothing that an AWG couldn't manage.

Exactly.

Back in their day they were the ducks nuts and I used to borrow a buddy's 100 MHz PM5771 for checking the CRO's I fixed back then and flicked.
These days most of the SDG models can do as much and lots more.

Some links:
https://www.sglabs.it/public/Philips__PM5712.pdf
https://www.eevblog.com/forum/testgear/ ... genarator/
https://elektrotanya.com/philips_pm5771 ... nload.html

tautech wrote: ↑Tue Aug 26, 2025 9:39 pm These days most of the SDG models can do as much and lots more.

You wicked salesman you. These things have a savage grandeur entire unto itself. Well sort of. But for £15, it's a bit of fun.

tautech wrote: ↑Tue Aug 26, 2025 9:39 pm

tggzzz wrote: ↑Tue Aug 26, 2025 9:32 pm ...............
Nothing that an AWG couldn't manage.

Exactly.

Back in their day they were the ducks nuts and I used to borrow a buddy's 100 MHz PM5771 for checking the CRO's I fixed back then and flicked.
These days most of the SDG models can do as much and lots more.

Some links:
https://www.sglabs.it/public/Philips__PM5712.pdf
https://www.eevblog.com/forum/testgear/ ... genarator/
https://elektrotanya.com/philips_pm5771 ... nload.html

AWGs are useful for analogue signals, of which digital signals are a subset.

For many modern purposes a dual AWG is necessary, to generate I and Q baseband signals.

Beyond that, a digital pattern generator is much more useful for digital systems with clocks, enables/selects as well as data.

Zenith wrote: ↑Tue Aug 26, 2025 9:52 pm

tautech wrote: ↑Tue Aug 26, 2025 9:39 pm These days most of the SDG models can do as much and lots more.

You wicked salesman you. These things have a savage grandeur entire unto itself. Well sort of. But for £15, it's a bit of fun.

And more that that, for simple signals.

Zenith wrote: ↑Tue Aug 26, 2025 9:52 pm

tautech wrote: ↑Tue Aug 26, 2025 9:39 pm These days most of the SDG models can do as much and lots more.

You wicked salesman you. These things have a savage grandeur entire unto itself. Well sort of. But for £15, it's a bit of fun.

100%

These Philips units do provide double pulses which is what's required for a time mark generator but an AWG can do the same with both pulse width and frequency configurable and with multiple channels to can take this much further with n# of pulses triggered by settings on the other channel.
Needless to say again, these Phillips units were the ducks nuts decades ago.

AWGs don't appeal, even though I do have a couple of instruments that implement a very early form of it - the "join the dots" approach used in HP's 3325B modulation generator (that most people with a 3325B probably never use) and 3314A (which uses the feature to achieve polyphony with a single output channel in its Easter egg and again, I can't see many real users ever using it except with automation).
I did build my own AWGs back in the very early 90s, but only ever programmed them with basic functions and the reason I made them was to generate sine waves with very precise phase matching. Recently I was thinking about building one based on old PC cache RAM chips and video DACs, might even try to add a flash ADC so it can digitise waveforms too. Not sure if I've got enough fast logic lying around to do it… yet.

I don't recall seeing step-free transition adjustments on any of the inexpensive DDS generators and I'm ignorant of the time resolution of these things - presumably with DDS it should be possible to have the same near infinite resolution that does come in very handy for spotting unwanted lumps and bumps in high speed switching circuits. It was switching to the digitally controlled 8112A after using HP pulse generators from the dawn of the transistor age that made me realise the importance of being able to manually sweep the parameters smoothly.
For a timebase applicable to the PRF only, I generally drive these knobby pulse generators with my 3325A which gives more than ample resolution and a continuous phase sweep, all locked to the same reference as my counters, rf generators and analysers. It would be nice to lock the pulse times to that reference and I've thought about seeking out a 5359A time synthesizer for that but it's not knobby enough - I think it'd only be useful for automated testing.

Yup 16bit AWG's are common now and produce somewhat cleaner waveforms than earlier stuff but only to 500 MHz where anything beyond that gets stupid expensive.

SDG1000X was the goto in cheaper stuff with a fast 4ns edge but only 14bit and 60 MHz tops.
Now a Plus version is available with a 25 MHz version and 16bit with 1GSa/s but not the fast edge of its predecessor but still hackable to 60 MHz.

Just 10yrs back we didn't have such cheap and capable choices.

Some modern scopes, including a few Siglent models, have a built-in AWG as an option. They are not the last word in AWGs, but they are good enough for most things and save bench room.

tggzzz wrote: ↑Tue Aug 26, 2025 9:32 pm Having said that, I've never found a USP for generic pulse generators. Back in my first job one of the early things I did was to make a weird specialised pulse generator for a specific piece of equipment I was building. I've repeated that concept many times since.

Back in the day I had to investigate a strange problem on a SCSI bus which needed a specific pulse train to trigger it. I borrowed a huge 19" rack mounting HP sig gen with an arb facility, and that could generate the pulse train. It seemed limited at the time and had a very small memory. I can't recall the model number. I suppose a pulse generator could have done it, but there wasn't one around.

These days, for a one-off like that and not too demanding, a µcontroller, such as an Arduino would do, but capable AWGs with software to create custom waveforms, are not expensive.

Zenith wrote: ↑Wed Aug 27, 2025 9:26 am Some modern scopes, including a few Siglent models, have a built-in AWG as an option. They are not the last word in AWGs, but they are good enough for most things and save bench room.

Yup and owned a good few of them at one time or another but don't care much for the limited drive and mediocre feature set compared to a 2ch standalone AWG.

Over the years my hobby now business has funded a good array of instruments from profits but knowing when to stop is the hard part especially when every new to the market product gets offered to you as a demo unit at some stupid cheap price....still, I treat myself to something flashy every year or 2.

Arriving soon is a new to market active (scope powered) HV differential probe which I'm looking forward to having something like this that is proper plug and play instead of farting around to set it up.

Almost all DDS devices are not useful as general purpose digital pulse generators, of course. They can be used to produce a 50% duty cycle square wave by connecting a comparator to the DDS filtered output.

But DDSs can be extraordinarily versatile. About 1990 HP made one that was classed as a munition. I know because I went through the paperwork to import an HP8791 FASS (frequency agile system simulator). From the T&M catalogue:

High-Precision Signals for EW, Radar, and Advanced Communications
The HP 8791 family of Frequency Agile Signal Simulators (FASS) generate the complex yet realistic test signals needed for today’s sophisticated signal simulation and system test. Whether you’re simulating advanced EW threats, radar target returns, satellite transponder traffic, or cellular radio’s multiple-signal environments, FASS combines powerful modulation capability with digitally-generated signal precision. The 40 MHz instantaneous modulation bandwidth can be switched anywhere across the 0.05 to 18 GHz coverage of Model 21 (3 GHz for Model 11) in 100nanoseconds to generate spread spectrum formats, radar chirps, video, pseudo-noise, multiple carriers, QAM and FSK.
...
Electronic Warfare
FASS is ideal for simulating advanced threats with intrapulse modulation, PRI stagger, frequency agility and antenna scan modulation. Being fully synthesized, FASS is especially well suited for pulse Doppler radar simulation.

Communications
FASS can produce a variety of sophisticated signals for testing satellite, terrestrial, and mobile communications systems and components. In parametric testing, FASS’s high clock rate, frequency agility and digital precision can significantly shorten test times for tests like NPR, group
delay and gain flatness. More importantly, FASS can simulate actual link traffic and signal environments, increasing accuracy and realism while eliminating the need for time-consuming and costly field testing. Link FASS with your computer simulation software to generate production test signals identical to the test vectors used in your design simulations. Add signal impairments and propagation effects to evaluate system operating margins. Complex signals like TDMA and CDMA are easily generated using FASS dynamic sequencing.

Radar
FASS can simulate target returns for testing and calibrating radar receivers. FASS can also be used as a major subsystem for instrumentation radars, serving as a complex waveform exciter or a frequency agile STALO for coherent systems.

Reportedly it could communicate with military aircraft

Naturally it came with its own DSL: the Waveform Generation Language.

I suspect it is still supported by Keysight. Searching for "keysight 8791 fass" leads to the catalogue pages
https://keysight-docs.s3-us-west-2.amaz ... +Sheet.pdf (which I thought worth skimming)
That refers to HP 8791 Model 21 Frequency Agile Signal Simulator (E2505A). Keysight marks the E2500B as obsolete, and suggests an alternative.

I've got two AWGs (three including the one built in to the scope). One is an el-cheapo FeelTech FY6900, which I used for a few years. These had a number of problems, gone into in a very lengthy thread at the other place. Feelech weren't quick to pick up on these. The software they supplied with them was truly dreadful. It was a remarkable product - for the money.

The other one is a Siglent SDG 2042X (now upgraded), which is a much better unit. I find I use it all the time. I almost wish I'd splashed out and bought its big brother. It produces a pretty good sine wave. 0.075% THD over the audio range. The sine wave goes up to 120MHz, and the output level down to 1mV ptp. It sweeps and provides a trigger. The rise time is 9 ns and it's frequency standard is rated at 1ppm. It also includes a 200MHz frequency counter. I sometimes find it's a convenient and surprisingly good low voltage source.

Not in the same league as a proper ultra-low distortion audio oscillator but good enough for most things. Not to be compared with a proper RF signal gnerator with fanatical screening and an attenuator going down to µV levels. Not to be compared with a purpose built frequency counter, and anyway, the digital scopes have a frequency readout which is close enough for most things. etc, etc.

However, it's a very good Jack of All Trades, which analogue function generators were. It's a lot more versatile and capable than analogue function generators.

I haven't really looked at the AWG on the scope. It produces a 50 MHz sine and it looks OK. I wouldn't expect an extra put there because it was cheap and easy to do, to compare with a dedicated unit. It's supposed to integrate with the scope to produce Bode plots.

I don't have the problem of having to generate digital pulses, of particular duration and frequency in a very versatile way, often enough to investigate a dedicated piece of gear to do it. I can see that back in the day, developing Z80 systems, a PM5715 may have been the very thing.

Zenith wrote: ↑Wed Aug 27, 2025 11:43 am I don't have the problem of having to generate digital pulses, of particular duration and frequency in a very versatile way, often enough to investigate a dedicated piece of gear to do it. I can see that back in the day, developing Z80 systems, a PM5715 may have been the very thing.

Nowadays a good litmus test is I2C or one of the other 3/4-wire onboard comms channels.

For that I'd use either a pattern generator (e.g. my Analog Discovery) or a BusPirate type thingy.