Tabor 8025 Arbitrary Waveform Generator

[pigrew]

I recently purchased a Tabor 8025 waveform generator (~US$120 from eBay), designed circa 2000. It is in quite good condition (only issue is failing batteries), and the outputs are all within spec.

This model has a <=100 MS/s clock, generates output sine waves at up to 50 MHz, has 1 M-word of RAM, switchable 25 and 50 MHz filters, segmented ARBs, GPIB control, 10 MHz reference input, and a 4X20 character LCD.

The only disadvantage I've discovered of this generator is that its internal waveform cannot be used as an AM source. So, a second generator would be required to have an AM modulated output. On the plus side, the AM input has a bandwidth of 500 kHz (quite high).

I believe that this model was also sold as a LeCroy LW110. While mine is the base model, a 2 channel version was also sold (Tabor 8026/LeCroy LW120), and a 4M-word RAM version. It may also be related to the Tabor 3361 (which is also the Fluke/WaveTek/Datron 301 or 302).

This generator has a couple unique features that are not available on other generators that I've used. The most interesting is that the sample clock has a variable rate. This allows pulses of nearly any length to be created (at any length >= 10ns). Other instruments I've used have some large step size for their pulse width resolution. The output rise/fall time is about 4.5ns (approx 75 MHz output bandwidth) as measured with a 200 MHz oscilloscope. This unit also supports segmented ARBs, where multiple pattern segments can be programmed, and then played in some order. This allows repetitive signals to be created which are much longer than the 1 M-word memory would normally allow.

There is an auxiliary sampleclock output at the back of the unit, which is a fairly clean sine wave (I don't have equipment to analyze it), at up to 100 MHz (the maximum sample clock rate) but its amplitude cannot be adjusted. The standard output can generate a 50 MHz sine wave, though by default it is very distorted. The distortion is because the unit disables its filters when outputting between 40 and 50 MHz. A much cleaner signal can be created by outputting a square wave, and enabling the 50 MHz filter, although the output amplitude will be reduced.

The unit has two PCBs (front panel + main board), and a NEMIC-Lambda power supply module. There is a small case fan, which is somewhat loud. The main board contains a processor, 10 MHz reference, 1.5625 MHz clock (CPU clock???), a pair of NiCd batteries (which power the SRAM during shutdown), six Altera MAX CPLDs (memory controllers, etc), an Analog Devices AD9767 dual-channel TxDAC, and filters.

It's tempting to try to upgrade the unit to be dual-channel.There is a jumper on the board to select between 1 and 2 channel, and also between the 1 and 4 M-word RAMs. But, without full schematics, it'd be very difficult to determine the component values for all of the passive elements of the filters (L and C values). Also, I don't know if my firmware even supports two channels. The ROM chip has a label marking it as a 8025 unit, so it may not be able to be easily modified to become an 8026.

Upgrading the RAM would be too expensive for its value (for me). It would involve populating 24 SRAM ICs, at about $3 each.

[pigrew]

Photos of the bottom of the board. (Sorry for the poor lighting and cell-phone camera quality)

[Dwaine]

Love the double A batteries

[pigrew]

Love the double A batteries

The manual states that the batteries' charge lasts "almost four days", and that it takes 16 hours to charge them fully. While the unit is unplugged (or powered off), the batteries are discharging. The battery backs up the waveform memory (but not the segment tables). The batteries also store the selected front-panel mode (and up to 10 saved states).

I was thinking that perhaps the battery would power the SRAM, but I think not. Each SRAM uses about 75 mW in shutdown, a few watts for the 4M-word memory model. Instead, I'm imagining that DRAM may be used for the battery-backed data.

I do not see myself even bothering to replace the batteries since they'll just discharge within a few days. I just hope that they won't leak.

It has no calibration RAM/flash. All of the calibration is done by adjusting potentiometers.

The build is rather nice, actually, in that both the top and the bottom of the case can be removed, allowing access to both sides of the main board with minimal disassembly (four screws for the top and four for the bottom).The fan's intake is in the back. Its outlet in on the bottom towards the front. It seems that the fan forces the airflow to go over the PSU, and also through the slit between the main board and the display board...

[Dwaine]

At least the batteries are easy to replace if you wanted.  Not like some other older equipment that you have large effort.

[bitseeker]

Thanks for the pics. I haven't seen too many Tabor devices here. Tabor has done OEM for many other brands (Fluke, Keithley, WaveTek, etc.) and can be had at good prices since the name often isn't recognized.

I have an 8551 (analog function gen). It also has pots for calibration and fairly loud fan that runs at 100% all the time.

The NiCd batteries could leak eventually, so keep an eye on them.

[pigrew]

I have an 8551 (analog function gen). It also has pots for calibration and fairly loud fan that runs at 100% all the time.

That 8551 looks amazingly analog. I'd guess its design is decades old.

The NiCd batteries could leak eventually, so keep an eye on them.

I've been thinking about just removing the batteries. I'll definitely keep an eye on them. I'd bet that they've been in a discharged state for most of the generator's life.

I'm still thinking about trying to "upgrade" this model to have a second channel.  Tabor released the 8551's schematics on their website, but no such luck for the 8025.

[bitseeker]

That 8551 looks amazing analog. I'd guess its design is decades old.

Yeah, it's been around a while. They appear on eBay with Fluke and Wavetek branding and still sell for $200-300.

I've been thinking about just removing the batteries. I'll definitely keep an eye on them. I'd bet that they've been in a discharged state for most of the generator's life.

If you don't plan to replace them, taking them out is probably a good idea. I have a power supply that used a NiCd for storing configuration data. It leaked at some point in its life, so it can happen.

I'm still thinking about trying to "upgrade" this model to have a second channel.  Tabor released the 8551's schematics on their website, but no such luck for the 8025.

Sounds like a fun project. I wonder if anyone else here has an 8025 and might join you on the investigation.

[raptor1956]

Boy I don't like batteries mounted to PCB's -- too much chance they leak and there goes the whole thing.  There's more than a few devices, even some quite pricey ones, where the main failure mode was leaky batteries. 


Brian