Category Archives: Electronics

Electronics

Perfect time: upgrade to a Motorola M12+ receiver, and new GPS antenna

2016/09/13 Simon 1 Comment

For years, a Motorola UT+ GPS timing receiver has served me well as a frequency reference and source of accurate time (and location). While I primarily use a DCF77 locked 10 MHz OCXO, the GPS time is useful for various purposes, be it, to confirm that DCF77 is actually delivering the proper time.

One drawback of the Motorola UT+ is the rather large “sawtooth” error, which is caused by the quantization of the 1 pps signal derived from a 9.54 MHz clock. This results in a +-52 phase inaccuracy – which can be corrected, but only with further effort.

The later model, which is dated by now and available at low cost, the Motorola M12+, is much better in this respect, featuring a +-13 ns sawtooth, which is not a lot, and good enough for most purposes without any further corrections.

Below, some tests on an OCXO vs. GPS 1 pps pulses, for a OCXO under test (10 MHz, divided down to 100 kHz, and phase displayed in microseconds).

This is the small board, not a thing of beauty, but working. The only parts needed are +3.0 V and +5 V (actually using +4.4 V) voltage regulators: 3.0 V for the M12+, 4.4 V for the GPS antenna.
The 3.0 V also powders a MAX3232 TTL to RS232 converter.

Also procured a second-hand GPS timing antenna – this one has a nice radome, a quadrifilar helix element, and a 26 dB amplifier to compensate any cable losses. The cable, LMR-195, features N to SMA connectors, and a considerable of PVC tape was used to protect the N-connector from the elements. Still it would be better to use some special outdoor N connectors, but, sorry, don’t have.

A handy program to control the GPS – TAC32. Usual procedure is to carry out a location survey, which will take about 2-3 hours, and then continue in position hold/timing mode.

One drawback of my location – there is no way to get full 360 deg view, so reception is limited to the more southern satellites. But usually 6-8 satellites are in sight.

Still contemplating if it is worthwhile to put this in a larger box, together with a 10 MHz OCXO, and possibly a DS1023-50 delay line to implement a hardware sawtooth correction. Maybe a good project for winter time.

DCF77

DCF77 vs. GPS time comparison: not a lot of uncertainty…

2016/08/07 Simon 2 Comments

Some folks were asking about the accuracy of the DCF77 10 MHz standard described earlier, DCF77 10 MHz – which has an Piezo brand OCXO, steered by a long-time-constant PLL locked to the DCF77 77.5 kHz carrier.

But, how to assess the short and long term stability of such a ‘standard’ in practical terms? Well, short term accuracy – it will simply be that of the Piezo OCXO, and some noise injected by the power supply. Mid- and long term, the drift will be determined by the DCF77 master clock (which is dead accurate), and the propagation conditions of the long wave signal (which is by far worse).

With my location at Ludwigshafen, Germany, I’m reasonably close to the DCF77 transmitter – maybe 70 miles? So there is hope that the transmission induced effects are not all that bad.

To measure the mid and long term stability, see below two plots of the DCF77-locked phase of the Piezo OCXO, vs. the instantaneous phase of GPS, stable to 40 ns or better, and obtained from a Motorola M12+ timing receiver. Measurements were done by measuring the time interval from the GPS 1 PPS signal, to the rising edge of a 10 kHz signal – derived from the 10 MHz OCXO by a good divider (using a ADF41020 REF input – R divider routed to MUX output) by HP 5335A counter.

In short – DCF77 is tracking GPS extremely well, and the OCXO phase is stable to within a few 10 to 100 ns. In practical terms, 1 second of observation time would be well enough to calibrate any frequency standard to 1 ppm or better, by comparison with the DCF77 locked OCXO. In other words, the DCF77 locked OCXO instability appears to be dominated by the propagation of the DCF77 signal more then anything else.

Various

Switchable microwave filter – inside a HP 83732B

2016/08/03 Simon Leave a comment

Thanks to a kind friend, a few pictures of the 83732B (and 83711) internals. The 83732B is a pretty nice 20 GHz +10 dBm synthesizer, and still not cheap – about 5~10 kUSD for a good used unit.

Below, you can clearly see the set of bandpass filters, and the signal routed to one at a time, selected by appropriate bias conditions.

PLL

ADF41020 18 GHz PLL: universal divider and PLL board

2016/08/03 Simon Leave a comment

I cannot praise Analog Devices enough for the ingenious designs, and for providing parts like the ADF41020, a fully integrated 18 GHz PLL. This is actually part of a major design effort for a multi-channel frontend, here just a description of the small test board used to establish the general circuit layout and board design.

Probably interesting is also the hand-soldering of the LFCSP leadframe package, which is actually not as difficult as it seems. For soldering of the pad, there is a large via in the center, which does provide good heat-sinking and is easy to solder through the 1.2 mm board.

Above, the layout, below, 10 boards – 14 dollars and a few weeks later.

For soldering, best use 0.5 mm Ag-containing SMD solder, with Type 32 flux, which is halogen free resin flux.

To mount the LFCSP, first apply some solder to the chip pads, but not to the center/heat sink pad. Apply some flux to the board (which is already pre-tinned; use any good SMD flux pen). Then align with a good magnifier, using some Kapton tape to hold the chip in place – leave one side exposed. Then solder, in one stroke, using a medium hot soldering tip. Reflow another time – one side done. Remove the Kapton tape, and solder the remaining 3 sides. Then stick down the chip with Kapton tape again (to avoid any remote chance of movement, in case all the solder melts during the next step). Turn around the boards, and solder through the via, with a fine solder tip.

For a test, just apply a test signal to the input, and use the “MUX” output to check for any pulses. There we go:

These pulses aren’t quite long, so it is one of the few occasions where a scope more advanced than the 2215 Tektronix is really useful in the home shop… same pulses on a HP/Agilent/Keysight 54720A, 54713B plug-in, and 100 MHz 1:10 probe.

These fast risetime pulses, and the various prescalers, dividers and good input sensitivity make the ADF41020 quite useful for any PLL and frequency counting applications.

2 GHz in, 25 kHz out — confirmed.

About the input sensitivity: the ADF41020 is specified over a 4 to 18 GHz range – how about lower frequencies? A quick look at the input circuit shows a 3 pF capacitor – which equals a reactance of about 53 Ohms, at 1 GHz (i.e., the capacitor and termination resistor will cut the input power available to the buffer approximately in half).

… quite useful down to 1 GHz, no problem or instability at all. Also checked the the reproducibility, for 3 devices – not a lot of scatter.

Various

Major relocation, and numerous 230 V conversions…

2016/08/03 Simon Leave a comment

Long time no post, not because there is nothing happening here, more to the opposite. Relocated from the US, East Coast, back to Germany, including the US section of my electronics shop, 40+ pieces of heavy test gear. All made it over the sea just fine, in a 20′ container. Now, changing all the fuses and converting everything to 230 VAC mains voltage. I will spare you the details, just a few impressions for some trusty HP power supplies. These actually require some re-wiring, you have to break to circuit traces, and install a wire bridge.

Installing new plugs… wires properly protected.

Now just install a bridge between the middle solder points. Great that there are schematics and manuals, even for 50 year old devices!

…don’t forget to replace the fuse with one of the proper size for 230 VAC operation!

Various

YIG Oscillator/YTO Analyzer: linearity, output power, hysteresis

2016/06/19 Simon Leave a comment

With a good number of YIG oscillators (YTOs) around, time for a few tests. Rather than writing down all the numbers, a quick test setup, with two power supplies, an EIP 545A counter (with built-in power meter), an Agilent 66319D power supply (used as current source for the main tune and FM coils of the YTO), a 14.5 dB attenuator (just happens to be the value I had around) and a few cables.
When performing such test, make sure to put a 10 dB (or larger) attenuator of really good quality (low SWR) directly at the YTO output, without any adaptors or cables in between – some YTOs will show inaccuracies of not properly terminated in 50 Ohms.

This is a view of the setup:

One of the YTOs under test, a S081-0320 2 to 8 GHz Avantek part.

As you can see, the output frequency is pretty linear vs. main coil current.

The tests are carried out first with increasing coil current, then with decreasing coil current, and the hysteresis is calculated (difference of output frequency, when a approaching from higher vs. lower current).

One thing to watch out for are thermal effects, but let the YIG warm-up for 1 hour or so, with the main coil at half-range current. The effects aren’t all that big for the Avantek YTO discussed here, but you never now, for lower quality parts, other manufacturers, and so on.

Micro-Tel MSR-902C

Micro-Tel MSR-902C Microwave Surveillance Receiver: A3B5 and A3B6 analysis and repair

2016/05/21 Simon Leave a comment

Some progress with the MSR-902C, which is basically working, but not on all bands – see earlier post.
With no documentation on the MSR-902C available, except some data sheets, I first traced the band select signals – and they appear to be generated on the A3B5 board, which we may call, band control board. This board also converts the 0-4 V tuning voltage from the tune dial to a 0.5-9 V signal that corresponds to 1 to 18 GHz (0.5 V/GHz slope).

This is a top view of the A3B5 assembly. On the upper left, the tuning control voltage converter, left half, voltage comparators for the 1-18 GHz multi-band mode. These comparators assign the band number to the tuning voltage, when the 1-18 GHz range is used. It is disabled (even supply voltage cut) when the MSR-902C is in single-band mode (selected by band selector switch).

First observations – there are control LEDs that seem to indicate which band is currently active, but for some reason, they don’t light up on all bands. Very strange. Probed around the logic signals, and at least some signals are there, still no LED lighting up. Very suspicious. After some head-scratching, decided to probe the LEDs by supplying some external power, and poking around with a resistor. Turns out, some of the LEDs are dead. They just barely light up with 20 mA of current applied, and no sign of light at all at the current level supplied to them by the A3B5 assy.

After repair of the defective leads, you can clearly see the difference of the new LED, vs. the old LED – some of the old ones are still working, but not very bright any more, and I’m going to replace them all, once I have this back in the main workshop with a better supply of 3 mm red LEDs.

Another strange observation – two of the logic chips are rather hot. What is going on there? Furtunately, these are in sockets, a 7401, and a 7404, and a quick test revealed that one gate of each of these chips is sinking current, about 200 mA. So these need to be replaced.

Mugshots of the culprits so far….

Not sure if it is very clear, but here are the connector signals of the A3B5 assy, and the description of the adjustment pots. First adjust for appropriate tuning voltages, then adjust for proper band switching in multi-band mode, monitoring the LEDs.

The next thing, the A3B6 assy. No apparent defect, but still needed to find out what it does, and how to adjust. It appears to be the multi-band control assy, converting the 1-18 GHz full-range tuning voltages to tuning voltages for the individual bands, by applying offset and slope corrections. The offsets/slopes are selected by CMOS multiplexers as it is custom for most of the MSR series designs. The output tuning voltage is buffered, and forwarded to the other circuits.

Here, you can clearly see the order of the adjustment potentiometers. For adjustment, if may be best to first align A3B5, and then supply appropriate reference signals to the MSR-902C, or measure the LO frequency, and do the fine adjustment with the 1-18 GHz full range mode selected, and tuning through all the bands. The fine adjustments would need to be done both at the low end (for offset), and at the high end (for gain), for each band. No big deal, once you know which of the pots to turn.

Further repair will have to wait a bit, until a few spare 7401 have been received. But all is looking pretty good.

Micro-Tel MSR-902C

Micro-Tel MSR-902C Microwave Surveillance Receiver: power back on – first signs of (extraterrestrial?) life

2016/05/10 Simon Leave a comment

Today, a few spare MJ12002 transistors arrived. No time to lose, and put them into the power supply. Note that the new transistors are 1983 data code, whereas the Micro-Tel originals were 1988… fixing the power supply with old parts, but no reason to assume that these transistors have any issues with age. With such power supplies, I would always suggest to use a pair of transistors of the same manufacturer, rather than mixing up two very different devices. This is why both transistors were replaced, not just the defective part.

After this replacement, connected a 10 Ohms 25 Watts load resistor, and grounded the Interlock and ON/OFF lines. When powering up, the green AC ON light comes on, but not for too long. Look at the set of fuses sacrificed in the process:

Another set of tests – no issues found, all working fine. Something must be loading the power supply, and I can’t get any negative voltages out of it – but there must be at least one negative rail to provide -15 V to the various opamps in the receiver.

Not to long and the culprit was found – a shorted tantalum, a T310 series Kemet tantalum, directly at the – what turned out to be, -18 V output. Check out the date code. Why did Micro-Tel put a 1979, week 38 dated device, in such kind of expensive and specialized equipment (other parts suggest that this unit was made about 1989, at a price of about $40-50k – that’s about $70k in today’s dollars…).

Some tests show that there is a +18 V, -18 V, and a +12 V output. All are routed through feed-through capacitors. A fair bit of effort, and cost!

First test with the actual receiver connected –

– connected the 1-18 GHz tuner – a bit of a cable mess.

To test the basic functions, like, IF chain, detectors, etc, a 1.5 GHz test signal from a HP 8642B was routed to the tuner. And, to my greatest satisfaction, the MSR-902C is actually receiving!

1 kHz AM modulation…

… also tested the FM and AM detectors, both in sweep and fixed modes, the AFC, the IF gain, the marker – all working. Also the 8-12 GHz, and 12-18 GHz ranges, working fine. Clear signal down to -105 dBm input. So all working and pretty well tune.

Unfortunatly, this is not the case for the 2 to 8 GHz ranges – the frequency display is not showing a reasonable value – not sure what is going on here. Maybe something with the band logic, or the signal multiplexers (see the MSR-904A repair story – these instruments are notorious for defective CMOS multiplexers).

So far, so good – at least in some bands, we would receive satellites, or signals from other galaxies, given, there aren’t many strong sources out there, in space, and all the other solar systems, too far away!

Micro-Tel MSR-902C

Micro-Tel MSR-902C Microwave Surveillance Receiver: a metal box, microwave plumbing – 1 to 18 GHz tuner revealed

2016/05/08 Simon Leave a comment

With no manuals available, some investigations were carried out to better understand the workings of the MSR-902C microwave tuner, which has a 1 to 18 GHz range, good noise figure, fully-fundamental mixing with 3-stage preselection over the full band. IF output is 250 MHz, so the tuner can be combined with any resonable SDR or other modern receiver, as a down-converter, offering about 40~60 MHz bandwidth, and 60 to 70 dB image rejection, and huge capacity to deal with out-of-band overload signals.

This is the rough scheme, leaving out all ordinary electronics in the case, just the microwave parts (note that there is another SMA attenuator in the feed line of the splitter, coming from the 8-18 GHz YTO, not shown in the sketch).

Essentially, there are two inputs. One covering 1 to 12 GHz, and another one, covering 12 to 18 GHz. The 8 to 18 GHz YTO is used for both bands, and PIN switches are used throughout to route the signals.
The IF goes through a 300 MHz low-pass and a +13 dB monolithic amplifier.

Note that there are some different/earlier versions of the MSR-902 and maybe also MSR-902C which use a slightly different configuration, with a LO doubler. Maybe the could not get proper 8-18 GHz YTOs at the time, at any resonable cost, and had to resort to another topology (using a doubler) for this reason. However, I have never seen any of the earlier tuners, and can only report what I heared about them, with documentation on these units being almost completely absent.

For some of the key devices, see references below. Glad not to show list prices, as these would quickly add up to USD 10 or 20k, for all these microwave parts. Not to mention that these are all US made, most advanced and highest grade components of their kind. Datecodes are from the late 80s, mostly 1988, but still today, there aren’t much other options around to build a tuner of this kind. Maybe there just aren’t enough entities around that can afford such device nowadays, and software and digital signal processing certainly have contributed that todays devices can achieve perfect results even with less expensive, heavy, and energy-consuming parts. Still it is very instructive to study the design of this tuner. It even has a LO sample output, and with some effort, all the YTOs could be phase locked with relative ease (using GeSi dividers, etc).

qbh-101

anaren 42040

pin switch american microwave corp SW-2181-3

american microwave corp sw-218-2

Precision Timing

TIC4 Logger5 Clock Monitor (“TIC4LOG5”): update and test data

2016/05/08 Simon 1 Comment

A quick update on the clock monitor/time interval counter project, TIC4 Time Interval Counter. Main objective is to have a clock analyzer that will keep track of every tick of mechnical clocks and watches, in particular, of one of my precision pendulum clocks operated in Germany. These clocks are pretty accuarate, but are impacted by air pressure and temperature fluctuations. Ideally, rather than the air pressure, it would be great to measure the air density directly, but there aren’t any easy ways to do this (might be considered for a project later).

The TIC4, we have already discussed, it is based on an AVR Atmega32L, which eventually will be running of a 10 MHz OCXO ultra-stable clock, provided by a Trimble OCXO, more on this to come. For now, the circuits are running on ordinary crystal oscillators, fair enough.

The TIC4 circuit has now been combined with another Atmega32L, which I call the “controller”, aka “Logger5” here. Its only function is to wait for a TIC event to happen (timestamp received), and the the determine (room/clock) temperature, air pressure, and real time (from a real time clock, which is not very accurate, just for the purpose of keeping track of actual time and date, UTC time plus minus a few seconds, e.g, to correlate clock issues with events like earthquakes or sun storms…).

This setup represents the temporary “TIC4LOG5” wire rats nest, which will be put into a proper case once all has been tested thoroughly.

For the TIC4 and Logger5 Atmegas to work together, they need to run on the same serial baud rate. With the desire to run the logger at 16 MHz, and the TIC4 at 10 MHz, this leaves 38400 baud as a good compromise.

Some small console programs are used at the host PC to gather the data, and store them in files, about 4 Mbyte a day, for 1 s pendulum, or 40 for the 10 Hz clock under test now.
All has been designed for clocks up to about 10 Hz, but the circuit can work up to 100 Hz no problem, provided that the pressure measurement (which takes about 10-25 ms, depending on the resolution mode – selected the ultra high mode, 25 ms per sample).
A note on the BMP085 – this is a quite common part, and pretty ordinary to program and work with – typical accuracy is +-1 mbar, with max. 2.5 mbar specified. Typical noise is about 0.05 mbar, but can be significantly reduced with averaging (there aren’t any fast second-time-scale pressure changes anyway).

That’s how the console works away: recording RTC (in unix time seconds, counting the events, recording the timestamp, temperature and pressure). Two files are generated, one the has the full data, and a second one that only records to event numer (TIC events recorded- and reconstructed to actual clock ticks in case a few ticks are missed) and the absolute clock deviation (time gained or lost, in seconds). For those more familiar with electronics engineering, this time gained or lost is nothing else than the phase shift of the clock under test vs. the 10 MHz precision ultra-stable OCXO, measured in seconds.

For test purposes, and to get a lot of TIC events, a 10 Hz clock source is in use as the test clock. This will be replaced by a pendulum clock, or mechanical watch, eventually.

The boards and cables…

…and their output, one data package, 29 bytes, every 100 ms.

Some records of the last few days (pressure is as-measured, no corrections, location is Westfield, NJ, USA) – all working pretty well with no hick-ups or restarts so far!

Also the Allan Deviation looks ok, and plenty accurate to measure the drift of even the most precise pendulum clocks, or similar. From the temperature effect, it seems that the test clock is speeding up a bit, with increasing temperature, but overall the effects seems to be just some random drift. Hope you also notice that the workshop here is nicely thermostated at about 22.3+-1 degrees centigrade.

With the software now pretty much established, it is time to look at the precision clock source. Sure, it would be best to run this of a hydrogen maser or caesium clock, but all a bit too much for the given purpose, und consuming too much electricity. So I settled for a Trimble 65256 OCXO (oven controlled xtal oscillator), having a few of these on hand. They run at 12 V (note: which needs to be well stabilized, otherwise you will get a good amount of phase noise – not relevant for this application, but for others), consuming about 0.3 Amps, chiefly, 4 Watts.

The output of the Trimble is a sinewave, about 3.6 V p-p when terminated with a few kOhms (no need to terminate such osciallators in 50 Ohms). This signal can’t drive the Atmega32L directly, it needs to be properly squared up. This is acomplished by a 74HCU4, which also generates an auxilliary output 10 MHz signal, handy for other uses, and for alignment of the Trimble vs. a GPS or DCF77 frequency standard.
The OCXO may drift about 10e-8 per 10 years, 10e-10~10e-9 per day. This is 10 to 100 microseconds drift per day. Not sure about the Trimble units, but they seem pretty good based on past observations.

Everythings squared up properly, x axis is 10 ns per div. Well, this is close to to the limits of the 60 MHz BW scope used here.

Some data on the Trimble 65256 units – interestingly, they have a 2.6 V reference, but the VFC (variable frequency control) needs to be set to about 3.2 for this unit, to get exactly 10 MHz.

Here are some of the key source files, for those interested:

tic4 avrgcc tic4_10mhz_stable160423

logger5 avrgcc logger5_stable160430

console data logger log5_main_stable160501

USB control program log5usb_main_stable160430

tic5eval R script to make the daily plots

SimonsDialogs

Category Archives: Electronics

Perfect time: upgrade to a Motorola M12+ receiver, and new GPS antenna

DCF77 vs. GPS time comparison: not a lot of uncertainty…

Switchable microwave filter – inside a HP 83732B

ADF41020 18 GHz PLL: universal divider and PLL board

Major relocation, and numerous 230 V conversions…

YIG Oscillator/YTO Analyzer: linearity, output power, hysteresis

Micro-Tel MSR-902C Microwave Surveillance Receiver: A3B5 and A3B6 analysis and repair

Micro-Tel MSR-902C Microwave Surveillance Receiver: power back on – first signs of (extraterrestrial?) life

Micro-Tel MSR-902C Microwave Surveillance Receiver: a metal box, microwave plumbing – 1 to 18 GHz tuner revealed

TIC4 Logger5 Clock Monitor (“TIC4LOG5”): update and test data

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