Category Archives: Electronics

Electronics

Micro-Tel MSR-902C Microwave Surveillance Receiver: a very intriguing, 60 pound briefcase

2016/05/06 Simon Leave a comment

A few days a ago, a most intriguing briefcase arrived, brown color, looking like the late 70s… Samsonite. It is heavy! Really heavy!!

Inside – a fully equipped MSR-902C receiver, including all cables (which are rare, and extemely expensive to fabricate, because they use special military connectors). This receiver can more or less receive any signal, down to very low levels, and comes in 3 modules, the actual receiver, a 1-18 GHz tuner, and a 18-26 GHz tuner. Other tuners and harmonic mixers were also available from Micro-Tel, but most likely, not many of these have ever been sold.

A brief description of the MSR-902, which is very close to the 902C:

Unfortunately, there is very little literature or even manuals on the MSR-902C, no instructions, no schematic – fortunately, is shares some circuits with the MSR-904A, and 1295 Micro-Tel receiver, and it is an all-discrete construction, with a lot of wires and circuit boards, so it is repairable, even without schematic (just taking 10x longer….). Should you have a manual, or any other related documentation for the MSR-902C,

Inside of the main receiver (the tuners have not yet been touched), a most amazing combination of wires, switches, boards, and so on. All hand-soldered in Maryland, USA.

It is a marvel of engineering, but, currently, not in working order. It blows the fuse, as soon as it is connected to mains power. Something wrong with the power supply. After removing a cup full of screws, here it is.

Strongly shielded by a thin magnetic shield, all nicely machined and assembled. Now all has to come apart for repair.

The internals of the power supply, a good number of boards and parts. The power supply can either work from AC mains, or from 12 VDC. The 12 VDC section appears to be find.

After some tests, found the first suspect item, a full short on one of the MJ12002 transistor that drive the primary of the switchmode power supply converter.

It a quite old-fashined part, but could still find 3 pieces, USD 5 each. Not cheap, but OK.

Once the transistor had been removed, time for some checks of the drive circuit. This circuit is based on an MC3420 switchmode controller.

As you can see, the switch mode regulator is working, just no drive transistors around that could actually drive the transformer. But will be only a matter of days.

For those interested, here are the specifications (of the very closely related MSR-902).

More to come – stay tuned!

Various

HP 11683A Range Calibrator: no power meter calibration without it

2016/04/17 Simon 4 Comments

With all the various HP power meters for repair, it would be really handy to have a range calibrator, HP Agilent Keysight 11683A. These have been around for 40+ years – any still not easy to find at any reasonble price – even used and non-calibrated units may be as much as 500 to 1000 USD. You can still buy it new:

The internals, check out the picture provided by Keysight – there is a modified 8481a power head (using the same FET chopper assembly), a range switch using high quality 140 series Micro-Ohm non-inductive wire-wound resistors (0.1%, +-10 ppm temperature coefficient).

Note that the schematic shows the H01 option – which allows an external DC connection, from a calibrated DC source. This is much preferred over the build-in power supply and resistive divider (which has known issues at low output voltages). The design of the 11683a also has some ground loop issues, better to just leave it disconnected from mains, and supply the DC voltage from a known-good source.

These issues are known to the experts of the field, see, e.g., this comment from the Keysight EPM-P power meter manual.

Now, a very complicated issues with the range calibrator – it’s output isn’t strictly linear over the dB range, because the power meters have a shaping circuit, to compensate for the somewhat high output of the 8481A and similar sensors, above about 5 dBm of input power. Accordingly, the sensitivity is reduced for this range.

Furthermore, the 11683a has ranges labelled in mW, e.g., 3 mW, but the output actually is calibrated in 5 dB steps…. so the output power is more like 3.16 mW, etc.
To figure this all out, a thorough calculation has been done, considering the FET input impedance, the resistive network, and the range switch.

At the 10 mW and 100 mW ranges, calibrations applied in the 11683A (and the 43x series power meters) were determined to be different from the newer EPM-P meters – quite surprising. The reason for this difference of the older meters, to the new EPM-P meters is rather hard to guess, but thanks to a kind engineer at Keysight, we now know: the EPM-P meter reacts differently to the 11683A (because it measures in virtually one range), in contrast to the 43x series meters that have several ranges. So, there is no difference in the actual power meter calibration, it is just a difference needed when considering using the 11683A for either 43x or EPM-P meters, because of the different response to the level calibration, but not actually different response to the power head when measuring actual RF power.

This table has the voltages that should be provided to the calibrator, depending what you want to do – (1) calibrate a EPM-P meter, (2) calibrate a meter “simulating” the acutal 11638A range switch voltages, (3) calibrate an old 43x power meter, with corresponding scaling factors for 10 mW and 100 mW ranges.

A quick scheme of the 11683A power supply, and the clear-written resistor values, which are not so clearly seen in some of the schematic copies.

Now, how to get a 11683A range calibrator at reasonable cost? Turns out, you can build your own from one of the many defective 8481A that are around in most labs, and on xbay. Well, in fact, most “working” powerheads sold only for below USD 100 are dead anyway… but this is different story. These powerheads hardly ever have any issue with the copper and FET boards, but in most cases, the thermistor is dead, blown by too much input power.

The modification – a wire has to be added to connect signal and guard ground (brown wire), and a 196 ohms resistor soldered over the FET input (I used a 220 ohm resistor for the test, but will replace one 196 ohm on hand). Also, you need to add a 196k resistor to the input, according to the 11638A schematic (this can be assembled from some other resistors, if no 196k in stock).

Make sure not to bend the wires – this can affect the FET chopper balance (see 8481A or 11683A service manual to re-adjust if needed).

The input is currently still arranged with open wires, but I will fit a 1n feedthrough cap soon – will modify the original N-connector (the golden part holding it). But this will need to be done back at the main workshop in Germany – need to use a lathe for it.

Some test results will follow soon – but so far, everything is working just fine.

Various

HP 11708A 30 dB Reference Attenuator: less than 0.0005 dB drift per year?

2016/04/07 Simon Leave a comment

One of the products that have been in the HP/Agilent/Keysight catalog for 3 or 4 decades, or more, the 11708A reference attenuator. Specified at +-0.05 dB, it is a remarkably simple device – it just provides 1:1000 attenuation, chiefly, 30 dB. It’s main application is the calibration of 8484A power sensors, from a 1 mW source – the 8484A needs a 1 µW reference level.

Unfortunately, it doesn’t come cheap, when ordered from Keysight today, at least for a hobbyist’s budget. So I got mine used, aged (30 years?), and at a minor fraction of the cost.

Before using it for a considerable number of power measurements, it is a good idea to confirm it’s performance. Measuring attenuation to +-0.05 or better is no easy tasks, but fortunately enough, a tractable one, with a 8642A signal generator, and a Micro-Tel 1295 precision attenuation measurement receiver. The Micro-Tel is specified to +-0.02 dB, plus +-0.02 dB for each 10 dB, say, +-0.08 dB. Actual performance, of a well-calibrated and well-heated-up unit is considerably better, but only in combination of other high quality components, like, a stable source (the 8642A has virtually no measurable drift), and, good test cables (using Suhner Sucoflex).

The Micro-Tel 1295 employs IF substitution to determine attenuation, and the IF attenuator works in 10 dB steps. Therefore, for best accuracy, the tests should be done at various power levels, to use various combinations of x0 dB segments, of the IF attenuator.

The results, quite remarkable!

One thing to consider for the test – the input and output matching losses. Neiter the source nor the cable/receiver are perfect 50 Ohm terminations – but the 6 dB pads will ensure only very minor losses. Obviously, you need to use high quality pads here, specified to small return loss, 18 GHz parts preferred.

First step – reference measurement is taken without the attenuator-under-test:

Second step – actual measurement is taken with the attenuator-under-test installed between the two 6 dB pads:

Before the start – best to check reproducibility and repeatability. With good cables and hardware, +-0.005 to +0.01 is achievable with the current setup.

Well, let’s say, chances are that the 11708A is +-0.02 off its nominal value, most likely, it didn’t drift at all over the last 30 years.

Precision Timing

TIC4 Time Interval Counter: 64 bit timestamps – 100 ns resolution

2016/04/05 Simon 1 Comment

A time interval counter – this little device, based on an Atmel AVR ATMega32L assigns 64 bit time-stamps to events (event being a rising edge on INT1 interrupt), based on a 10 MHz OCXO, a Trimble 65256 10 MHz double oven oscillator. So, 100 ns resolution. The main purpose: precise monitoring of pendulum clocks – in combination with a temperature-air pressure-real time clock data logger.

Why TIC4 – well, there are several other (earlier designs), some with better resultion by interpolation (via a clock synchronizer and interpolation circuit). But for the given purpose, there is no need for any more than a few microseconds of resolution, because it is really hard to detect the zero-crossing of a mechnical pendulum to any better resolution.

For test purposes, I had the circuit running on a 16 MHz clock, with ordinary (not very precise or phase locked) 20 Hz, and 2 Hz signals at the input – running overnight to check for any glitches.

The Allen deviation plots show that for single events, the timing accuracy is about 150-200 ns, close to what is theoretically possible for a 16 MHz clock.

The AVR program code, it looks simple, but believe me, it isn’t. There are quite a few pitfalls, because for any timing of the interrupt, there needs to be a precise time-stamp generated, and transmitted to the host. Maximum time stamp rate is 100 Hz nominal (1 timestamp every 10 ms), but will work up to about 150 Hz, without missing any events. Timestamps are transmitted with every 16 bit timer overflow, chiefly, every about 6.6 ms (65535 x 100ns). Each timestamp and control info is 120 bit long (12 bytes, 8N1 protocol, 57600 baud) – 2.1 ms.

tic4.c AVR code

For test purposes, the serial data is sent to a PC, via a MAX3232 TTL to RS232 converter. Alavar is used to process the information into Allan deviation plots.
Test showed absolutely no glitch in about 1.3 million events – fair enough!

More details to follow.

Various

A13 30 MHz Reference Oscillator: a reasonably quiet oscillator, and a noise cable

2016/02/08 Simon Leave a comment

A nice little oscillator assembly came my way, supposed to generate about 17 dBm at 30 MHz. Nothing special at first glance, but after checking out its internals, it appeared to be worth a more careful look.

A hand-made box, and even more labor intensive assembly work inside. All build by point-to-point wiring, using only the best components available, glass trimmer caps, filters, mica caps – most of these parts are still available today – about 100 USD bom, at least.

After a bit of reverse engineering, here the schematic, a modified Colpitts oscillator. Note: base resistor of 2N5109 is 150 Ohms.

To measure phase noise, connected it to my HP 3585A spectrum analyzer (this is really a great piece of equipment, a bit heavy, but still best of class noise performance and holding this title for the last 35 years….). Connected the oscillator via a 6 dB attenuator, to provide a clean load to the output, rather than dealing with the imperfections of cables, adapters, and the analyzer input.

Quite shocking, all this noise. The green trace shows the analyzer noise floor. Check, and re-check, still a lot of noise. Too much to be true. After 3 hours of tests, found the issue: a defective BNC cable. Center connector was fine, but both shields were non-connected.

A bit more examination of these cable shows their lousy construction. Not bad for 2 dollars a piece, but you get what you pay for…. the shield is not even reaching to the plug – there is a 5 mm gap from the screen end, to the actual plug. So even if all would have been connected fine, the would still be a lot of leaking, from inside out, and outside in.

Notice the BNC plugs – these have a somewhat uncommon construction, the dielectric is covered at the front… not quite according to BNC standard.

Clearly visible, the cold solder joint…. Turns out, both ends were open-circuit at the shield.

Finally, using a good quality BNC cable (also, using LMR-195 double-screened cable). Looking much better. Noise is down -115 dBc at 10 kHz from carrier. It’s good, but not great. I think one could do better, especially, considering all the pricy parts, and high-quality construction. A good target for a Colpitts osciallator would be better than -130 dBc, at 10 kHz separation.

Note the pink trace – this is the bad cable, terminated with a 50 Ohm resistor (with the shield broken at both sides, it is actually a 1 meter wire antenna, with an open-circuit 50 ohm resistor at the end).

Various

440 MHz ISM Band Amplifier: a few extra milliwatts….

2016/01/10 Simon Leave a comment

There are quite a few devices that use the ISM (industrial-scientific-medical) band at around 440 MHz to transmit information, like, remote thermometers, or to control some installations, like, garage doors, or for personal communications, like, LPD radios, or cordless headphones. Another general term for these devices is SRD – short range devices, and the short range is ensured by a typical maximum power of 10 mW, chiefly, 10 dBm.

In some cases, it may be desirable to boost the output a bit, especially, if you are out in the woods, or for some experimentation of various kind. Be aware, depending on your country of residence, there may be limits to the allowable power of SRD units, make sure you know the rules!

Various MMIC gain blocks exist to provide amplification and output power, but why not go for a discrete transistor solution, using a BFG541 (or BFG591) device. These 9 GHz/7 GHz transistors are SOT223 devices, very robust and easy to work with, and they are pretty low cost, less than 0.5 USD a piece. All the other parts needed are just sub-1-cent capacitors and inductors, except, maybe, for the electrolytic cap.
The small inductors and capacitors at the input/output improve the input/output match (to 50 Ohm impedance), and provide some low-pass filtering (about 800 MHz).

The test circuit on a piece of perf board (adhesive copper tape used for the back plane). Note that this test circuit still has variable capacitors that were replaced by fixed caps in the final design. Also the bias voltage trimmer can be replaced by fixed resistors, it was just added here for convenience of bias current adjustement during test.

The gain measurements were done at +7 dBm input power. To get accurate results and to avoid overload of the VNA input, a 6 dB attenuator was attached to the output (with 2 Watts load capability), followed by a test cable, and with a 20 dB attenuator, directly at the VNA input. This gave about 26 dB (plus minor cable losses) of attenuation, or about -5 to 0 dBm at the VNA input, which is good. The gain offset introduced by the attenuators was removed by recording a reference trace and subtraction from the measured gain trace.

As you can see, well above 15 dB gain, and all reasonably flat (note that this is not the true gain, but the limiting characteristics; gain, at lower input power, is larger). We don’t want too much gain above 800 MHz, otherwise, amplification of harmonics and spurious signals comming from the SRD output (which typically is not filtered very well) could interfere with other communications.

Here a few plots of the output power, at various input levels.

To get about 200 mW output power, about 5 mW (7 dBm) are enough, at 440 MHz, even less, at lower frequencies (in case you need to amplify other signals). 200 mW should be plenty for all practical applications related to SRD or ISM personal devices.

Various

Vintage IC Stock: listing

2015/12/31 Simon Leave a comment

For all folks that are into repair of vintage gear, here is another list (earlier list: Vintage Transistors) of circuits that I have in stock.

There are many more in stock, but these below have been listed and are stored in a way that I can find them easily… Primarily, these are for my private shop&repairs, but if you are in desperate need for one of these goodies, just shoot me a line (I may ask for a fee to cover my expenses&time).
Note that I don’t keep exact stock lists – some of the parts may become unavailable over time. Listings of more outdated ICs – will be added soon.

Location Part Count

K-T01 LA7212 – 1 Pcs
K-T01 M58653P – 1 Pcs
K-T01 LM3915N – 2 Pcs
K-T01 TD62103P – 1 Pcs
K-T01 NE5534AN – 1 Pcs
K-T01 LC24085P – 1 Pcs
K-T01 LC74084P – 1 Pcs
K-T01 UAA170 – 1 Pcs
K-T01 TBA120 – 1 Pcs
K-T01 TBA120S – 1 Pcs
K-T01 SAB2022P – 1 Pcs
K-T01 SAB1046P – 1 Pcs
K-T01 SAJ110 – 1 Pcs
K-T01 TDA2721 – 1 Pcs
K-T01 WD1100V-12 – 1 Pcs
K-T01 TDA2710/1 – 1 Pcs
K-T01 TDA2730 – 1 Pcs
K-T01 TDA3780 – 1 Pcs
K-T01 TDA2560/3 – 1 Pcs
K-T01 TDA1054M – 1 Pcs
K-T01 SAB1009B – 1 Pcs
K-T01 TAA611 – 3 Pcs
K-T01 CA3081 – 4 Pcs

K-T02 Z85C3008PSC – 1 Pcs
K-T02 SN76477N – 1 Pcs
K-T02 4N33 – 3 Pcs
K-T02 TDA2151 – 1 Pcs
K-T02 TDA2160 – 1 Pcs
K-T02 KM6264AL-10 – 1 Pcs
K-T02 MM74C906N – 1 Pcs
K-T02 SN7493AN – 1 Pcs
K-T02 ICM7049AIPA – 2 Pcs
K-T02 SN16913G – 1 Pcs
K-T02 MAX690A – 1 Pcs
K-T02 TL7705ACP – 1 Pcs
K-T02 TDA2320A – 1 Pcs
K-T02 SAJ110 – 1 Pcs
K-T02 TDA1950 – 1 Pcs
K-T02 HM4334P-4 – 1 Pcs
K-T02 TDB0556A – 3 Pcs
K-T02 SN76660N – 3 Pcs
K-T02 TC5508P-1 – 12 Pcs
K-T02 UA733CN – 2 Pcs
K-T02 TAA710 – 3 Pcs
K-T02 TDA3562A – 1 Pcs
K-T02 CA3083 – 1 Pcs
K-T02 ULN2111A – 1 Pcs
K-T02 SAA1027 – 1 Pcs
K-T02 TDA2790 – 1 Pcs
K-T02 TDA2740 – 1 Pcs
K-T02 TDA1170S – 1 Pcs
K-T02 TDA3770 – 1 Pcs
K-T02 TDA4942 – 1 Pcs
K-T02 TBA440C – 1 Pcs
K-T02 TDA1940 – 2 Pcs
K-T02 TDA2591 – 1 Pcs
K-T02 TDA2730 – 1 Pcs
K-T02 TAA630S – 1 Pcs
K-T02 TDA1180P – 1 Pcs
K-T02 TA7630P – 1 Pcs
K-T02 MC14584BCP – 1 Pcs
K-T02 709CJ – 1 Pcs
K-T02 MC1307P – 1 Pcs
K-T02 WIC7015 – 1 Pcs
K-T02 V4001D – 1 Pcs
K-T02 MC14503B – 1 Pcs
K-T02 TDA2140 – 1 Pcs
K-T02 M3-7603-5 – 1 Pcs
K-T02 N82S25 – 1 Pcs
K-T02 N8T10B – 1 Pcs
K-T02 L6506 – 1 Pcs
K-T02 TCA830S – 2 Pcs
K-T02 TAA930 – 1 Pcs
K-T02 TDA2522 – 1 Pcs
K-T02 TDA2532 – 1 Pcs
K-T02 SN76001ANQ – 1 Pcs
K-T02 TDA7250 – 2 Pcs
K-T02 WD1100V-03 – 1 Pcs
K-T02 R5620 – 1 Pcs
K-T02 WIC6020 – 2 Pcs
K-T02 LM339N – 1 Pcs
K-T02 DS8836N – 2 Pcs
K-T02 A10N – 1 Pcs
K-T02 TA7171P – 1 Pcs
K-T02 9602PC – 1 Pcs

Various

IBM Thinkcentre M50 P4 3 GHz: electrolytic capacitor repair

2015/12/30 Simon Leave a comment

One of my computers, a trusty IBM Thinkcentre Desktop, decided to fail on me. Symptoms – sometime it starts up normal, sometimes it doesn’t. Already hangs at the boot screen. Smells like a hardware issue, and in fact, it is a hardware issue – with some electrolytic caps (note the brown substance leaking out from the top vents; fortunately enough, no damage to the board).

Electrolytic cap failure are a very common feature of modern consumer electronics, the remarkable thing here: only some of the caps failed – 1500 µF, 10 V, and 1000 µF, 10 V. Maybe these see particular load, or they are from a batch that wasn’t all that good. All were high quality Nichicon brand, 105°C, HM series, specially designed for PC motherboards, low impendace, etc.

Board with new caps installed…

All caps were replaced by 1000 µF, 25 V – these were the only caps I had available with the given footprint and capacity range; 100 n X7R multi-layer caps were added (solder side), hopefully, to prolong the lifespan of the electrolytic caps.

These are the culprits… a last look before they go into the bin. Board is working good as new. Let’s see how long the repair will last.

Various

EMI Sniffer/Checker

2015/12/30 Simon Leave a comment

Many designs have been published in the past for various EMI probes. All have there merrits for particular applications. Here, a very handy small probe, especially suited to check enclosures of switch mode power supplies and similar circuits for EMI leaks. The probe has particular advantages for localizing the actual leakage spots, because it only captures fields in its close proximity, unlike many other EMI test probes.

The setup is very low-cost, using the venerable LM386 amplifier to directly drive a small speaker. Gain is set to 200, 46 dB. Sure, you can also hook this up to an oscilloscope, or to the line-in of a soundcard for waveform/spectrum analysis.

A 9 V battery is used to power the thing.

The sense coil – a small ferrite rod, with a coil of about 150 turns, small-diameter copper wire.

To protect the coil, seal it with some heat shrink tubing.

Happy EMI sensing!

Various

Ultrasonic Pest Chaser: final design

2015/12/30 Simon 2 Comments

Following up on an earlier post, , design is now complete and a test unit has been completed.

First, a nesting box was made using 9 mm birch plywood. This can be varnished, to any color you like, and is in itself very much weather resistant. All edges and gaps were sealed with hot glue. For added stability, the bottom plate is inserted into a grove of the side and front panels.

The driver was upgraded a bit, from the earlier version, by using a IRFP460 MOSFET. This is a very sturdy part, and will most likely not fail even under some severe operation conditions. It it can also be mounted to the heatsink in an insulated fashion, without any special washers, etc. – this is the main reason for selecting it.

The speakers are 2x KEMO L010,

and 2x PTI-1010; one of the PTI-1010 has its horn cut-off; both were fit with two layers of wrap foil to protect the membrane (PTI-1010 has a paper membrane, whereas the L010 has a plastic membrane).

One key component of the setup, an inductor, in parallel with the speakers. This converts the capacitive load of the piezos to a much more well-behaved load, resonance frequency of the setup is a few kHz. The coil needs to be capable to handle currents of 1 Amp easily, otherwise, it will heat up and may even fail. The one used here may be a bit oversized but it was on hand and still has acceptable size and dimensions.

Three of the 4 speakers are mounted in Schedule 40 1.5″ PVC pipe (this pipe is common in the US and dimensions match well the dimensions of the speakers; you can use other types of plastic pipe as well).

The holes in the wood panels are precision machined, for a snug fit with the pipes. Hot glue is used to seal it all together and to firmly lock everything in place.

Typical waveform during a test run, driving at somewhat above 12 VDC to test system durability… gate drive (yellow) and source-drain voltage (blue).

Final testing…

Operated from a 12 Volts DC supply, the final tests show that the output voltage is pretty much in line with the allowable voltages for a series connection of two L010 speakers, and flat over the frequency band of interest.

SimonsDialogs

Category Archives: Electronics

Micro-Tel MSR-902C Microwave Surveillance Receiver: a very intriguing, 60 pound briefcase

HP 11683A Range Calibrator: no power meter calibration without it

HP 11708A 30 dB Reference Attenuator: less than 0.0005 dB drift per year?

TIC4 Time Interval Counter: 64 bit timestamps – 100 ns resolution

A13 30 MHz Reference Oscillator: a reasonably quiet oscillator, and a noise cable

440 MHz ISM Band Amplifier: a few extra milliwatts….

Vintage IC Stock: listing

IBM Thinkcentre M50 P4 3 GHz: electrolytic capacitor repair

EMI Sniffer/Checker

Ultrasonic Pest Chaser: final design

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