Category Archives: Electronics

Electronics

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

Micro-Tel MSR-902C

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).

SimonsDialogs

Category Archives: Electronics

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

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

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