TMS 2532 EPROM adapter: one byte every 50 ms…..

2015/08/10 Simon 2 Comments

EPROM progammers seem like a thing of the past, still, they are very popular for test equipment repair, arcade games, and all kinds of other occasions where small amounts of data need to be stored in a bulky, fancy package.
Such programmers, mostly copies of the “Willem” design, are widely available, Made in China, and generally, these work pretty well. Well, as luck would have it, most of the ancient pieces of equipment use 2532 EPROMs, and just this kind is not supported by the common programmers, which support the 2732….. same capacity, different pin layout.

To adapt the 2532/2532A (these only differ by their programming voltage, 25 V vs. 21 V – make sure the set it correctly) to the common 2732 programmers, the only thing you need is a small adapter, with a most complicated schematic (the only pins that change are 18, 20 and 21). Most of these EPROMs require programming pulse widths of about 50 ms, but often program OK with just 10 ms, or less.

Noise Meters and Noise Figures

TWS-N15 Noise Source: noise generating elements

2015/07/26 Simon Leave a comment

Some trials with various low-cost noise generating circuit elements:

(1) Zener diodes
(2) Transistors B-E junctions in break-down mode
(3) Noise diodes – these are not being considered, not low cost.

For (1), a BZV55-12 diode was used, directly soldered on the traces of the noise source circuit described earlier.
For (2), as a first try, a BC238B transistor was used (with legs cut to very short length). Sure, I will try some RF transistors, but these are all back in the main workshop in Germany and will come over in a couple of weeks.

The output, measured with a HP 8970A noise figure meter and some GPIB software to do this efficiently, it shows quite interesting behavior.

For the Zener diode, there is appreciable 1/f (pink) noise at <30 MHz, but the output is pretty much flat at higher frequencies. The transistor, well, it is working fine at lower frequencies, at 10 mA bias, the noise is flat-white up to about 300 MHz. But not enough noise at higher frequencies - maybe just not the right part for this purpose. These are just a few of the components tested, stay tuned.

Noise Meters and Noise Figures

TWS-N15 General Purpose Noise Source: some progress on the design, and some tests

2015/07/12 Simon Leave a comment

Many design of amateur noise sources have been published, they all have there benefits and shortcomings, but it is mostly the lack of a calibrated test source that makes it difficult for the hobbyist to employ a cheap, home-made noise source for the ever-so-critical noise figure measurements of the amplifiers and mixers he may build.
Having recently acquired a good calibrated source, HP 346B, I have decided to make available a noise source design and build so many, and calibrate them, in order to make calibrated sources, up to, say 1.5 or 2 GHz, available for everyone at a really low price. Thinking about USD 45 per piece which should be fine for everyone dealing with such measurements.
Requirements are pretty simple, it should be a ‘low-frequency’ replacement of the HP 346B, about 15 dB ENR output, flatness, preferably, within 0.5 dB, starting from 10 MHz. It should also have high output return loss (low SWR), which can’t change significantly from on to off state. Last but not least, powered by the ubiquitous 28 VDC noise source drive signal common to most noise figure analyzers.

The bill of materials, combined with the desired target price, won’t allow the use of a custom-made noise diode. But this is not really a disadvantage for the intended frequency range and purpose.

Three main tasks will have to be solved, to get this thing (called, the TWS-N15 Noise Source) to work:

(1) First and foremost, we need a noise generator circuit; these require a bias current, typically 5-15 mA.

(2) We need a temperature-compensated current source; currently experimenting with discrete Zener and TL431 based circuits. Current should not vary significantly, if input voltage is changing from, say, 27.5 to 28.5 VDC.

(3) Mechanical package. This is quite important, because the noise source needs to be well shielded, and put in a sturdy case – these sources tend to float around labs, and are often dropped, or dragged down from the bench by the heavy cables attached. Output connector will be SMA, because I have a large supply of really nice quality SMA print connectors.

The draft schematic (current source not shown, cirucit works, but still need better characterization, and possibly, some improvement). Note that the output attenuator will set the ENR level. Might need to adjust this a bit; for the time being, anything from 10 to 15 dB ENR will be fine.

This is the small cirucit, build on a 0.6 mm FR4 board. Traces were simply carved out with a knive…..

Here a few plots from the VNA characterization. Not bad for a start. Input return loss is at least 15 dB. This will still be improved. Using 0603 SMD resistors for the critical section.

ON and OFF traces are shown – virtually, no effect on the return loss.

Some tests of the noise output, really much better than I thought. Bias current has some impact on flatness; low frequency end is determined by the first capacitor (between diode and attenuator). This will need some further tweaking to get it as flat as possible, but no rocket science.
To measure the noise output flatness and level quickly, there is no also an automated test rig here, which measures bias current and on-off noise figure differences.

Next steps… will need to decide if the 0.6 mm board is the best option (these boards allow rather narrow 50 Ohm traces; most of them, I machine using a router mill – no etched traces), or if a commercially made board of regular dimensions would be the better option. Cost ist not really a concern, because the noise source only needs little space. Stay tuned.

Various

HP 8565A Spectrum Analyzer: a ‘new’ CRT for a trusty unit

2015/07/12 Simon Leave a comment

Not a very major repair, but certainly, noteworthy. I have a 8565A here on the bench, and actually use it quite a lot, along with the 8569B, because it saves you a lot of time not to have to wonder about all the buttons and switches of more sophisticated analyzers. Also, for its coverage (up to 22 GHz with no external mixers), it is rather affordable, and should it suffer from accidental abuse, which can always happen on a test bench with so many cables, it is rather easy to fix because of parts units being available, and because of its discrete construction. Needless to mention, full schematics are available from the HP service manuals.
The only downside of the unit, the CRT – it is working just fine, for all practical purposes, but has some ‘slow’ sections in the variable persistance and storage modes. These show up as green spots in the baseline region. Over time, you can make them disappear, but it takes multiple erase cycles, quite a tedious procedure. For the most part, I just did not care about these spots.

Fortunately enough, I was able to get hold of a spare 5083-4471 CRT, which has been sitting in the storage room for quite a while. Condition was said to be ‘essentially new’ but never checked.

Last week, finally decided to give it a try, risking to have to install the old CRT again, in case the new one doesn’t turn out to be so new.

You be the judge…. conventional mode

… stored display …

… variable persistence mode …

…. good as new.

Various

Clothes dryer repair: AKO 742336 control unit type EDR0692XAX

2015/07/08 Simon 27 Comments

Repairs of household appliances aren’t generally my field of expertise, but in some cases, it can be a very rewarding activity. Some particular models of clothes dryers (“AEG”, “Whirlpool”) common in Europe use a control board, and this is not designed up to standard. The design flaw, it renders the machine inoperative in the very sense, you can’t switch it on, and it doesn’t show anything on the display. Typically, this occurs after roughly 3 years of service….

This is the control unit:

After a quick inspection, it is fully clear that the defect rests with the control board, model EDR0692XAX. Easy fix, just get a spare! Well, easy, but outrageously expensive.

The defect, it is related to a DC switch mode regulator converting mains voltage down to some useful voltage to run the controller. This is a step-down converter, NOT mains insulated!

Two dead parts were found, the LNK304 switch mode converter circuit, and a 47 Ohms resistor.

The LNK304GN is easily found, and replaced. The resistor: WATCH OUT! This is a fusible resistor, NEVER replace with just a common resistor – it will potentially set your house on fire, when the next switch mode failure happens.
The 47 Ohm resistor, it’s a 3 Watt resistor, and the ULW3 series, available from all major suppliers, should be a good replacement.

This is the failure charcteristics of the ULW3 resistors – it will go open circuit if overloaded, without release of any flames or particles. It a hybrid, partly fuse, partly resistor.

R820T/RTL2832U USB SDR: Various hacks and measurements

USB RTL SDR 28.8 MHz Reference: VCO design established

2015/06/07 Simon 1 Comment

A quick update on an earlier post, USB RTL SDR 28.8 MHz Reference: VCXO, development of a low-noise 28.8 MHz is now complete. A BB159 varicap has been selected for the voltage tuning control, and it works nicely, even within a 10 V tuning range. This is a UHF varicap diode, C_28V of about 2.1 pF, 9:1 ratio.

The updated schematic – the test setup still shown here still uses a few through-hole parts, put most of the RF caps are SMD 0805. J310 J-FETs are used, both for the oscillator, and the amplifier – mainly because of their low cost, and they are widely available.

This is the test setup – test signal provided by a 8904A, and frequency measured by a 5372A Time and Frequency Analyzer, 4 s gate time.

That’s the tuning curve, it happened to be at 28.800000 MHz, for about 5.5 Volt, nicely centered within the tuning range. No need to worry about the deviation from linear slope, the PLL will have a very long time constant, and the non-linearity of the tuning curve won’t have any impact on the VCO performance.

A nice additional feature – this VCO circuit works with the default 28.8 MHz crystal (which is actually no so bad, it is quite stable over temperature, at least the samples I have tested here, taken from cheap USB RTL SDR sticks). +-700 Hz range, +-25 ppm, should be pretty much sufficient to keep the VCO locked over a wide range of temperatures. If not (for other 28.8 MHz that might be around out there), two of the varicaps can be used in parallel, and the C* capacitor adjusted a bit; pullability of the xtal is pretty good, +-1.8 kHz is easily possible. It is best not to use a trimmer cap, but to solder-in suitable capacitors, to keep noise down, and stability up.

Noise Meters and Noise Figures

HP (Agilent Keysight) 346B Noise Source: finally, a calibrated ENR standard, and a temperature compensated current source

2015/06/06 Simon 1 Comment

Today, a rather ordinary envelope arrived, still it feels a bit like xmas, because of the contents….

…. a HP (Agilent Keysight) 346B Noise source, with nominal 15 dB ENR. I have long been looking for one, at a reasonable price, and finally scored this unit on xbay.

The calibration sticker shows good flatness, especially, in the 0.01-1 GHz region, which I need most, it is perfectly flat.

Prior to having it re-calibrated, a good opportunity to look inside. There are two sections: the current source, and the RF noise source assembly (which is hermetically sealed, and you better don’t touch!).

These are some close-ups of the 00346-60001 power supply and current regulator board.

The current regulator inside of the 346B has always been a big mystery to me, because no schematic has been published by HP, in any of the service manuals. How it works, check out the schematic. The incomming 28 V (which is provided by the noise figure meter) is converted to a square wave, about 7-8 kHz, using a LM311H comparator. This is then converted to a negative voltage, about -20 V, absolute value varies a bit with loading condition.
The negative voltage is then used to sink current from the noise source assembly. The current setting of my unit is about 18.7 mA, programmed by the “10 Ohm” resistor.
Why the negative voltage? To simplify the design of the noise diode.

Why did HP use a 5V6 Zener for the current reference, well, this is fairly obvious, when looking at the datasheet of such diodes.

Around 5.6 V, the temperature coefficient virtually vanishes (this is why such voltages are also used for voltage reference circuits). The other Zener diode, unfortunately, I was not able to identify. It has 24 V drop, fair enough, any regular Zener should to the job to keep the base bias of the output constant.

For a quick burn-in, the source has now been connected to a 8970A Noise Figure Meter, and output appears to be very steady, less then 0.1 dB drift over a few hours. More noise measurements and calibration tasks to come, let me know if you need any noise sources measured, might be able to help.

Attenuator calibrator (objective: a really precise and accurate apparatus)

Latching Coax Relais Driver: useful for all kinds of HP/Agilent/Keysight attenuators and switches

2015/05/31 Simon Leave a comment

Driving a latching relais doesn’t sound all that complicated, and it isn’t, still, some thought is needed to get it working properly. This is what the circuit should do

(1) Accept one 5 V TTL input signal, LO signal will result in the relais switched to the rest position, HI signal to the activited position (“dash” position), the switching signals are called A and A’, for relais A.

(2) There should be an output-enable signal for all relais, to be able to de-energize the relais, because otherwise, the circuit can suffer if the relais is disconnected while powered; these latching relais only need a few 10s of Milliseconds to switch, power will be turned off, by the ATmega32L, 1 sec or so, after each switching event, just to avoid any unintentional short circuit or spike, and the positive supply line will carry a fuse.

(3) The circuit should be able to handle any common relais voltage, 5, 12, 15, 18, 24 and 28 V. The relais I am using here are 24 V rated, but work fine at 18-20 V, and up to 28 V.

(4) It must be avoided, at all cost that both the A and A’ signals are active at the same time. This can cause nasty relais oscillation, and damage/wear of the expensive relais. We don’t want to rely on software control here, because things can go wrong, during startup, program freeze, and so on.

The circuit is almost self-explanatory. The LS04 generates the complementary control signals, from the digital input. The LS373 is configured as a transparent latch, in fact, the latch function is not used, but the output control function is. If the OC input goes LO (and thus, the neg_OC high), the outputs of the LS373 will tri-state High-Z.

The output driver, a Toshiba ULN2803APG is used. These are very reliable circuits, Darlington transistor arrays with build-in diodes.

Make sure to put a good quality capacitor close to the COM pin, the return path for the snubber diodes, otherwise, the inductance of the traces will deteriorate the action of the diodes. Actually, the HP coax relais have build-in diodes, so I don’t expect and issues with voltage spikes here.

Note that the inputs of the ULN2803 have adequate resistors to ensure LO state when connected to a High-Z output; if other transistor arrays are used, the circuit might need some ~10 kOhm pull-down resistors to ensure noise immunity and defined signal levels.
The 15 kOhm input resistors serve the same purpose, they keep the relais de-energized if no logic input is connected.

This is the little board, with all space well used. Sure the logic could build using more modern devices, and I would definitely do so for a commercial device, or anything build in series, but LS logic is still popular, and it is cheap, at hand, and reliable.

That’s the setup, with the two 8673B transfer switches, and a 0.3 Hz test signal fed to the digital inputs by the brown wire shown above (removed for the picture below).

The signal at one of the contacts, 24 V drive level, 1 V per vertical DIV, 10 ms per horizontal DIV. No spikes, high voltages, or similar undesirable features are present.

After about 2000 switching events, two events per 3.3 seconds, everything is still working well, and all circuits, in particular, the ULN2803 stays cool.
As I said, not a very complex circuit, but may be useful for other purposes, and is a very cost-effective, reliable solution.

Attenuator calibrator (objective: a really precise and accurate apparatus)

Tripple PLL Controller, for Micro-Tel SG-811/1295/1295: converting a ratsnest to a shiny box

2015/05/31 Simon Leave a comment

Comming back to an earlier project, the frequency stabilizers/PLL controls for the Micro-Tel 1295 receiver (2 pcs, one for through, and one for reflected power), and the Micro-Tel SG-811 generator (0.01-18 GHz).
The setup has been working well, but it is an awful mess of cables, as a result of the development process.

Now is a good time to finalize the circuit, and to put it into a nice case.

This is the front panel – the back panel has numerous BNC connectors, for the “PLL Phase Lock” voltage, and the “Frequency Control”, i.e., coarse tune voltage. The latter voltages, 3x 0-10 Volts, are generated by a DAC board, which is now ready and tested. Not a thing of beauty, but it works, and no reason to assemble another one just to clean things up a bit.

The circuit is reasonably straightforward, a 2.5 V precision reference is used, and three MAX541 16 bit DACs, followed by OP284 amplifier to convert the signal to the 0-10 V range.
The MAX541, it’s a really great part, full 16 bits, +-1 bit integral nonlinearity, and very stable over temperature and time. Highly recommended for any precision application.
One of the channels has an additional TLC2201 opamp, which is there more for historic reasons than for anything else.

The PLLs use three ADF41020 18 GHz chips, following the approach discussed earlier. This will give 100 kHz frequency resolution, which is more than sufficient for the intended purpose of measuring gain/attenuation and SWR over the full range of microwave frequencies up to 18 GHz, or 40 GHz, if no SWR measurement is required.

The 10 MHz reference circuit has also been completed, and is working well, converting a 10 MHz input signal (of more or less arbitray shape and amplitude) to 3x 10 MHz REF signals for the ADF41020, and two 5 MHz outputs, for the 1295 receivers, just in case I need to work with external downconversion-the 5 MHz signal is only affecting the 0.01-2 GHz range of frequencies. Well, why not having everything phase locked, if we can.

The 10 MHz circuit has been modified slighly, to accept 1 kOhm impedance 10 MHz input signals, which are rather common for instrumentation purposes. Some caps and protection circuitry has been added, output levels are just about 0 dBm. No need to go to stronger signals, it will only cause spurious response, and other trouble, because shielding inside of the PLL case won’t be very strong.

Some remaining work, before we can call this project complete:

(1) A power supply regulator, +5, +3, +3 (Vp low noise), +15, +20 supply has been build, but need to be mounted to the case, for heat sinking. This will need to wait for a few weeks, need to wait for some travel to Germany coming up, where the metal working machinery resides.

(2) Digital interface and cables for band control of the SG-811, and the two 1295s are complete, just need to be mounted and tested.

(3) Relais control module needs to be designed and build – there are two 18 GHz transfer switches (one is needed for basic functionality, a second one for the various unexpected test configurations). The transfer switches are HP 8763B, see earlier post. These are wonderfully precise and repeatable, albeit, list price is about USD 1k, each.

(4) Need to route the two serial signals (dB reading, signal strength) from the Micro-Tel 1295 to the ATMega32L, which only one USART input – no problem, because this is all TTL-level USART signals, but need to get a multiplexer/a few NAND gates to set this up. Currently, only one 1295 can be recorded at a time, which means, either gain or SWR measurement.

(5) Sure, the software, both firmware and instrument control software will need to be refined and consolidated. All PLL calculations and adjustments are done within the ATMega32L, still there is a need for a more convenient user interface than just command line.

… to be continued!

Noise Meters and Noise Figures

HP (Agilent Keysight) 8970A Noise Figure Meter: a makeshift noise source, and some test

2015/05/24 Simon Leave a comment

With the 8970A back working, what would be the first thing to do with it – well, let’s measure some gains and noise figures. Unfortunately, the 8970A alone won’t be sufficient, because it uses a small, external noise source unit, commonly refered to as a 346A, B (or C model, if you need noise up to 26.5 GHz). These sources are still widely used, although Keysight has introduced a new series, the N4000 series, but still the 346 models are very common, and available – this product has been around for 30+ years, not bad. The only downside – most of them seem to get lost or damaged, so they are rare on the second hand market, at least, if you don’t want to pay more then USD 0.5k for a used, out of cal, and scratched item, for a device that sells for USD 2.5k brand new.

Key characteristics of a noise source for noise figure measurements, and related tasks:

(1) The connector, preferably, get a 3.5 mm APC, then you can add a connector saver, and most of the small devices being characterized are SMA or 3.5 mm design; sure, have a few adapters at hand, or a SMA to N cable. A noise source with N connector is more sturdy, but also these connectors wear out, and aren’t all that hand except for directly connecting the noise source to the analyzer, which is not often done. Typically, the device-under-test (DUT) is connected with some short test cables anyway, and for calibration, you just remove the DUT, rather than all the cables.

(2) Flatness. The noise output needs to be so-called white noise, absolutely flat with frequency.

(3) Related to flatness, very low SWR. The various common DUTs, amplifier, mixers tend to have not too good SWR, so at least the noise source needs to have low SWR, otherwise, measurement errors will be enormous. Also, the SWR needs to be close, or the same, irrespective of the on or off state of the noise source.

(4) Well-known absolute noise power, measured in ENR, which is noise above a 290 K floor, -174 dBm/Hz (a 1 Hz bandwidth power density). 290 K is the Kelvin temperature of an average antenna on the surface of an average place on earth. Well, where are these average places that are at these constant 290 K…

(5) The driver input, commonly, a BNC connector that is driven by a 28 V DC signal. Most sources adopt this style of input.

This is one of these desirable items, in the typical used condition. Very similar device are available from Anritsu, NoiseCom, and others. The 346B has 15 ENR output, which is a good amount for general purpose application, maybe a bit too much for certain GaAs preamps, or other low level low noise applications; then you can just add a good (really low SWR) 10 dB attenuator.

…unfortunatly, I currently don’t own any of these extremely broad-band calibrated and well-working sources, and need to deal with less fancy apparatus, but let’s at least investigate what it is all about.

The block diagram (taken from the April 1983 issue, of the HP Journal, http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1983-04.pdf, shows the internal construction, still looking for a schematic of the current source, it seems to convert the positive 28 V signal, to a negative current, looking at the polarity of the noise diode. Maybe more about this later; to get proper accuracy and repeatability, it is a must to have a very constant bias current supply, on the order of 8 to 10 mA. It should provide a low noise DC current, without any large buffer caps, because the 8970A will switch it on and off periodically, to do the actual noise figure measurement. But there plenty of circuits around to accomplish this.

Most interesting, the matching network. Noise diodes have about 15-30 Ohms impedance, so this all makes sense. The strange stub is one of the secrets (the major secret) that ensures the 18 GHz flat output. The 6 dB attenuator improves the output SWR and SWR change from on to off condition. In fact, it is a good idea for any noise source design to have a high quality attenuator at its output, with at least 6 dB, or a bit more.

To replicate the 346B design, or at least a similar design that is good to a few GHz will remain a venture for future cold winters (good designs have been published by others but they all appear to lack flatness, and some use pretty costly noise diodes, and all need calibration that is not easily achieved unless you have access to a calibrated source).

For work demanding less accuracy, many design are pretty suitable to get reasonably flat noise of the desired power, in the 10s to 100s of MHz range.
This is one of the circuits that I have successfully employed.

It uses the breakdown of the emitter-base diode, according to the datasheet, about 5 to 6 Volts for any common NPN transistor (minimum values, actual breakdown might not occur up to 8-10 Volts). The noise source currently in use has a BC238B transistor, because it was the first one to grabbed from the junk box. Others will work as well, including BC107, BC548, 2N2222, 2N2904, and so on. The latter two appear to have a higher breakdown voltage. Obiously, there is no bias current regulator, and the 5k6 resistor will need to be adjusted to get the right level and flatness of noise in the desired range of frequencies. Sure, better results can result from a RF transistor like the BFR93, or other 4 GHz, or even 22 GHz type transistors – will give it a try back home in Germany because it really only makes sense in a proper RF setup, and on a small test board.

A quick test, to determine the gain and noise figure of a 6 dB attenuator. Attenuators have negative gain, equal to their attenuation value, and increase the noise figure of a system by the same magnitude.

For the time being, let’s call it close enough. With the simple noise source, calibration works perfectly fine from well below 100 MHz, to above 1 GHz, making it suitable for various general purpose application.

SimonsDialogs

TMS 2532 EPROM adapter: one byte every 50 ms…..

TWS-N15 Noise Source: noise generating elements

TWS-N15 General Purpose Noise Source: some progress on the design, and some tests

HP 8565A Spectrum Analyzer: a ‘new’ CRT for a trusty unit

Clothes dryer repair: AKO 742336 control unit type EDR0692XAX

USB RTL SDR 28.8 MHz Reference: VCO design established

HP (Agilent Keysight) 346B Noise Source: finally, a calibrated ENR standard, and a temperature compensated current source

Latching Coax Relais Driver: useful for all kinds of HP/Agilent/Keysight attenuators and switches

Tripple PLL Controller, for Micro-Tel SG-811/1295/1295: converting a ratsnest to a shiny box

HP (Agilent Keysight) 8970A Noise Figure Meter: a makeshift noise source, and some test

SimonsDialogs – A wild collection of random thoughts, observations and learnings. Presented by Simon.