Products > Test Equipment
FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
Zenith:
It didn't work at first. Then I remembered my FY6800 does not power up with factory defaults, so I set it to do that and it's as you describe, apart from being an 8mV offset on the DVM and I recall a 9mV offset on the scope. The rest of it is exactly as you said. However, there isn't the noise superimposed on the offset as I saw before. Firmware is V 1.7.1. An offset which can appear depending which settings the system boots with? It has to be a firmware bug.
If I remember correctly, nothing but power cycling got rid of the 13mV noisy offset, so it could be two different fw problems.
Johnny B Good:
To Zenith
I chose the 1202 since, for my immediate needs, it seemed the "Best Bang for my Buck" option. The 1204 was just 30 quid shy of double the price at 700 quid and a 4 channel 'scope was one luxury I could happily forego for my immediate needs. If I needed a better 'scope in a year or three's time, I'd probably be considering something much better than the 1204 anyway.
I ran into the "'scope gets all confused issue" too. The first few times, I just switched it off and back on again (windows PC syndrome - usually my customers', rarely my own win2k setup) before I noticed the big blue "Auto Setup" button. :-[ Strangely, "confusion" doesn't seem to happen quite so often these days. TBH, I'm not sure whether or not I've tried the default button. Possibly I have but hitting the blue button usually sorts things out.
All manuals, as a rule. could be better written but with something as complex and fully featured as a DSO, it's no easy task for the author to get a nice balance between simple and complex. As technical manuals go, the Siglent one isn't so bad. I've seen far worse with other (even less complex) kit.
As for my own "Boat Anchors", they're both languishing in my basement workshop come radio shack. The scope, as you can see from the attached photos, is parked on a currently inaccessible shelf (I can't even gain enough access to unclip the cover to reveal the CRT face and controls, let alone haul it out to look for a make/model name plate).
AFAICR, it's a 5MHz BW 'scope, possibly even dual beam - it's been more than a decade since it was last used). The Marconi signal generator has probably not been used in over two decades (but at least it's more accessible) so these recent T&M kit purchases have been a very welcome upgrade on what may well be non functional kit, never mind an upgrade specifications wise (apart from the 310MHz top end of the Marconi sig genny - assuming it could still stretch itself to such a giddy frequency limit).
Whilst the FY66/6800 generators are, in many ways, a vast improvement over older kit that's even younger than those boat anchors of mine, I rather think you'll find the frequency stability rather leaves a lot to be desired. Before I turfed out the rather cheap 'n' nasty commodity CD player 50MHz reference oscillator chip it had been cursed with, I tested several of my stock of standard DIL packaged oscillator modules recovered from various scrapped electronic kit over the past three decades (mostly PC boards), comparing their frequencies against the FY6600 using the siglent 'scope.
Trying to get the 6600 to match frequency was like chasing "Wil 'o' the Wisp". When I did manage to get a meaningful display, it only took a gentle breath (literally!) of wind on the Oscillator under test to send the waveform racing ahead/behind, neatly demonstrating just just how precise you had to be to match them up.
When I repeated this exercise after the TCXO upgrade, there was far less chasing "Wil 'o' the Wisp" and the effects of small temperature changes on my oscillators under test were far more predictable and stable. Now that I've gotten hold of a u-Blox M8N Arduino/RasPi GPS module to generate a 10MHz reference directly from its PPS pin, I can see that the TCXO stays within 20 ppb from cold startup to a nice toasty room temperature of around 23 deg C and settles to within 10 ppb of frequency ( it's currently just over 7.5ppb in error at 22 deg C at 0100 hours UTC).
No doubt the fact that the TCXO module is in the direct firing line of the small cooling fan to hold it to within two or three degrees of room temperature (instead of running at 50 deg C like the original oscillator chip did) contributes to its rapid "warm up" since it doesn't have to do very much warming up to reach thermal equilibrium. Even so, there is still the issue of 'self heating effect' to account for but this is negligible compared to what the original oscillator chip was subjected to by being within 1cm of a 70 deg C heat source (the three analogue voltage regulators or "Stooges" as they might best be named in this joke of a main board layout).
I tend to leave the signal generator running 24/7 (it only consumes 8 watts at its current settings) and for the past three "mornings", my initial frequency check has shown it unaccountably running within 0.5 ppb of the GPS reference. However, within minutes of taking stopwatch timings, it will start to drift off, typically showing all the signs of passing through the exact frequency of 30,000,000.000Hz (I'm monitoring the third harmonic) before it drifts to an initial offset some ten to fifteen minutes later of around 4 to 5 ppb where it will then very slowly drift by another 3 to 5 ppb over the rest of the day.
This 'morning behaviour' is a little 'spooky' since it implies it can sense my mere presence in the room. My best guess is that it's not so much my presence as the effect of powering up the adjacent TS140S HF rig and the 10A 13.8v psu made up from a couple of 40 year old 5v smpsus strapped together in series and maladjusted to 6.9v each. The HF rig consumes 14W in Rx mode with the PSU raising the 'from the mains socket' load to 25 to 30 watts. It seems unlikely to be convective heat polluting the fan intake and I can't see the slightly increased loading on the long but heavy duty mains extension cable having any effect on the FY6600's smpsu voltages sufficient to upset the 3.3v regulator on the oscillator board so my best guess is that it must be responding to infra red energy from the 13.8v PSU and the HF rig (not forgetting my own small contribution, assuming this IR hypothesis has any validity).
I can now see the motive behind adapting these generators to utilise an external GPSDO 10MHz reference. A 0.1ppm TCXO whilst undoubtedly a vast improvement over the commodity XO chip, is still some three or four orders of magnitude short of GPSDO perfection. Anyone motivated enough to put Feeltech's 'wrongdoings' to rights is going to find the challenge to achieve the best possible frequency accuracy and stability irresistible.
Until I got my hands on the u-Blox module and active antenna, I was still thinking that Arthur Dent's posting a year or so back regarding his replacement of the XO chip with a 10MHz OCXO and a low jitter PLL chip to mulitply it up to 50MHz, along with a change over switch and external BNC socket to plug an external 10MHz reference source into the FY6600 was a little OTT to say the least.
I can see his point and I'm now sorry I didn't use an easier to obtain 10MHz TCXO to use with a PLL chip rather than aim for a 'drop in replacement' 50MHz TCXO. Never mind, I daresay I'll be able add the PLL chip and automate the changeover on sensing the presence of a valid 10MHz reference on the external reference socket to minimise the switching glitch between local and external references. I suspect any nasty glitching on the 50MHz clock signal might crash the main board so this might be more complicated to achieve, especially in the event of loss of the external reference, whether by unplugging it or just simply due to a loss of the feed for any other reason.
Anyhow, that's a new adventure for my own satisfaction. Returning to the business of the 85 ohm attenuator pad still being present on the FY6800 main board, that does rather suggest a deliberate action on Feeltech's part since they've had ample opportunity to put this particular "Skoolboy Howler" well and truly behind them with the new iteration of the main board.
Either they're still leaving temptation to tinker so as to minimise after sales service costs (voided warranties) or else are bowing to pressure from the likes of Rigol and Siglent to retain such annoying defects so as not to seriously dent their own sales, otherwise I can't see how they could have missed the opportunity to correct this error with the reworked board designs. They must have become aware of the problem straight from day one since they've obviously applied a fix in the firmware - admittedly one that could only be effective in the Hi Z condition they elected to correct for.
It's not a fatal flaw so much as an egregious annoyance. You can get round the issue of generating sub 500mV signals by never going below the 500mV setting and using an external 20dB 50 ohm pad instead. Aside from such limitations and seemingly deliberately included annoyances, these Feeltech products are otherwise excellent value for money test gear.
Sure, the penny pinching effects are there but I don't think all of the deficiencies are down to random penny pinching alone. A lot of it seems to be down to 'defective by design' since not all defects are the result of saving a penny or two. That 85 ohm pad cost them just the same to implement as a proper 50 ohm pad would have.
When it comes to accessories like 'scope probe leads and welding cables, it is just a matter of 'penny pinching'. The decisions taken by manufacturers are rather dependant on what their customers' needs are. For a budget item where expectations are low, the manufacturers see a chance to bundle cheap but serviceable accessories to provide 'instant gratification'. With high end kit, the manufacturers will often take the view that it's better to let their customer decide what to spend on their own accessories which may be nothing at all if they already own high quality accessories to begin with rather than spend a small fortune supplying accessories of a quality that matches that of the product which their customers may not need or even wish to use.
Regarding the lack of a coarse voltage offset adjustment, I think you'll find it in the form of a rate control where it jumps in bigger increments if you twist the control fast enough. However, it tends to result in overshooting the mark. I guess familiarity from lots of practice in its use helps mitigate this problem. :)
I guess a firmware update might tame this "All or Nothing" effect of the rate control. Unlike the volts per division setting control where the push action toggles between coarse and fine, the push action on the offset adjustment is used to reset back to zero offset, leaving rate control as the only convenient alternative way to increase the step size of the increments. Short of adding a separate push button or adding it as "pull" action on these knobs, there's really no easy solution. Although it is a little hit and miss, I don't find this is that much of a problem.
As for the staggeringly high digit count on the FY66/6800 frequency setting (14 digits worth! And all of them valid), not even the best frequency reference standards (Rubidium or GPSDO) can match that amount of resolution. They might all be valid but even with the best available atomic clock derived laboratory frequency reference, the last digit or two will be meaningless or, at best, only meaningful for frequency settings lower than 1MHz.
You can take some comfort from the fact that a lack of digits won't limit its ultimate frequency setting precision, not even when fed from a Rubidium or GPSDO reference clock. The fact that its original XO chip makes a complete mockery of the nine least significant digits in the display is neither here nor there. Once you're familiar with your test gear's limitations, such 'anomalies' cease to be an issue. However, in this case, the desire to upgrade the XO to a decent TCXO or OCXO (with or without an external atomic frequency standard clock drive option) can become an irresistible challenge. :-\
Regarding the various mods to the FY6600, most of the more interesting ones started to appear around page 8 of this 73 page forum. I've already mentioned most of them in recent posts in the last three pages or so but if you're interested, it's well worth a skim through the early pages to pick them up. Be warned though, you could land up spending a solid couple of evening's worth trying to plough through them all. Obviously, you can skip the discussions and progress reports on fixing the firmware issues that sadly afflicted some of the early adopters stuck with bricked firmware (versions 3.0 AFAICR). :( >:(
Mention of the 3 quid radio and the Lidl astronomical telescope modding exercises, that reminds me of my own, paused project to add an electric starter function to the Parkside PGI 1200 B2 inverter generator which Lidl were selling last April and May for just £99.95. I bought one, returned as faulty for an exchange for one that also had a fault and landed up with a refund since they had no others in stock to exchange.
Frustratingly, I'd discovered by then that both faults were the result of handling 'damage' from the endless motorway road trips they were routinely being subjected to whilst being shunted from store to store or central depot because the shop floor also had to double as the shops' stock rooms and each new "This Week's specials" which had to have space cleared to display them, they'd be shipped out of the store.
These 'stock faults' (quite aptly named in this case) were quite trivial to fix since it was either a stuck oil level float or else a dislodged connector on the inverter module both of which could readily be fixed. About a week after that episode, I tried a less likely Lidl shop in the unlikely hope that they'd also received a delivery of these excellent little generators and very much to my astonishment, they had three in stock.
I picked the two with the least scuffed boxes to take to the checkout. I just wanted to do any returns wholesale rather than piecemeal one at a time. As it happened, both proved fault free so I had to choose which one to return to the store for a full refund. Unfortunately, I hadn't thought to verify the 1KW overload limit settings and I landed up with the one that regarded 980W as the trip point instead of the expected 1030 or 1050 watt setting (whether the one I returned did have a higher set point remains an unknown).
Unfortunately, unlike every other inverter module I've ever seen pictures or videos of, these Parkside ones don't have any of the otherwise ubiquitous trim pots to adjust such niceties as overload current trip points and voltage settings - not one single trim pot! I guess the adjustments are flashed into the controller's firmware, never to be accessed with something as simple as a trimtool. >:(
Never mind, when these come back into stock again, as they must, I'll snag a couple more to use as donors to replace the ungenerously set unit in mine, assuming at least one is more generously configured with regard to the overload trip point. If both are good in this respect, I'll keep one and return the donor machine for another full refund. At just £99.95 each, it's worth keeping an extra one just as a spare.
Anyway, after struggling with the recoil starter to get it up and running on account the fuelling system not being the simple gravity feed type where you can use a float tickler to flood the carb to ease starting but one relying on an engine vacuum driven fuel pump which after running the float bowl dry to prevent it gumming up means you have to crank it several times to prime the carb float bowl, I considered how I might be able to add some sort of electric starter to it. There was no easy way to add a conventional starter motor and since the inverter module blocked access to the end of the crankshaft where the common trick of using a cordless electric drill with a suitable socket spanner to engage the retaining bolt so as to spin it up, I started to think 'outside the box' when I realised that the 6 or 7 pole pair three phase permanent magnet 380v alternator was nothing more than a BLDC motor in disguise simply waiting to be turned into a starter motor by a genius like myself. ;D
I have to say, I've managed to get as far as testing with a 60v rated BLDC scooter motor controller and 48 volt's worth of battery, proving the concept. Unfortunately, sensorless control option just doesn't cut it with such mechanical loadings. I could get it to spin up with the spark plug removed just fine but even just blocking the spark plug hole with a finger tip was all that was needed to confuse the sensorless control algorithm and stall it.
However, fitting an angular position sensor to the end of the crankshaft will overcome that problem once I finally get around to figuring out the pole pair count so I can order a unit programmed to emulate a hall sensor drive signal more accurately than even the best conventionally hall sensored BLDC motors can achieve. The project is paused because I'm waiting for another Round Tuit. Besides which, I'm still busy fettling the test gear needed to test and configure my electric start system.
Harking back to Andreax1985's problem with the offset voltages he's seeing, I suspect it's probably more to do with thermocouple effects or galvanic corrosion within the hard mains earth loop between the 'scope and generator grounds. Compared to such a low impedance ground loop circuit, the scope lead's shielding resistance and that of the crocodile clip contact resistance is far too high to shunt such low impedance voltage sources effectively. If he can bring himself to disconnect the safety earth and cross bond any of the FY6800's BNC grounds to his scope, he may well find a significant reduction in this offset voltage. This was one of the reasons why I used an 11K resistor in series with the signal ground and the mains protective earth on the C6 socket (although, to be fair, I hadn't considered DC offsets, just ac induction voltages).
Regarding the photos. Apologies for the low resolution but I'd forgotten about the 640 by 480 setting from when I hadn't wanted to exceed the 2MB limit in a previous posting. Also the two offset angle views of the Marconi signal generator were required to avoid reflection from the on camera flash burning the image out.
The scope shot is the best I could do on account of the foreground clutter as shown in the next image (the scope is at the top in that picture). I thought the Min/Max thermometer would give you some idea of the storage environmental conditions. Whether any of this kit is still serviceable after spending some three decades in my basement remains an unanswered question although the remarkably good condition of my HF transceiver, which had spent just two decades there, does offer some hope.
JBG
Andreax1985:
I decided to float my scope (ok, I know it's not advisable, but considered the particular application I felt safe in doing so) in order to break possible ground loops. I can confirm that the residual dc offset was due to ground looping and now my readings are perfect. My device is working properly and I'm not going to return it.
Johnny B Good:
--- Quote from: Andreax1985 on February 15, 2019, 05:00:48 pm ---I decided to float my scope (ok, I know it's not advisable, but considered the particular application I felt safe in doing so) in order to break possible ground loops. I can confirm that the residual dc offset was due to ground looping and now my readings are perfect. My device is working properly and I'm not going to return it.
--- End quote ---
Excellent news! Thank you for that feedback. I'm so glad my 'educated guess' actually "nailed it" for you. ;D
Since you're planning on keeping hold of the generator, does that mean you're going to modify its earthing circuit with a 10K or so resistor to avoid the low impedance earth loop problem but still suppress the half live mains touch voltage issue (that so many of us here were bitterly complaining about with the FY6600) to a more acceptable half volt or less? The PSU is still essentially a class II double insulated type intended to be used without any need for a safety earth connection.
Looking at this, it seems Feeltech had a just, if flawed, reason not to encumber the FY6600 and its predecessors with a safety earth connection. The flaw being the penny pinching profit motive and the justness being the avoidance (more by accident than design) of this earth loop problem.
In responding to all the demands to eliminate the half live mains touch voltage issue, it seems they've created another issue by hard wiring the internal ground rail to the safety earth connection rather than choose the sensible compromise of a resistive connection to reduce the touch voltage to an acceptably low value without introducing a low impedance ground loop problem.
It would seem that FY6800 owners can add yet another modification to their "To Do List", adding a 10K or so resistor to the earth connection being the second of the earthing related mods with the first being to rejoin the cut off 0v rail wire in the ribbon cable linking the PSU to the main board to double up the 0v rail wires again as per the original FY6600 arrangement.
I do have to wonder at this demonstration of utter ineptitude on Feeltech's part. After all, a safety earth connection isn't actually required with the cheap commodity three rail class II smpsu board they're using so a 10K resistive link to avoid earth loop issues yet reduce the touch voltage from a high of 90 odd volts to an insignificant half volt wouldn't have been deemed inappropriate on the grounds of safety.
There's clearly three hierarchical levels within the T&M ecosystem with the likes of Keysight occupying the top slot, Siglent the middle and Feeltech the bottom and I can't help imagining conversations between Keysight and Siglent over the fine art of not treading on toes with Siglent then passing on this favour to their own underlings, Feeltech being one of them in this case. Such an imagined scenario offers a compelling rationalisation of the apparent "Shooting oneself in the foot" exercises that Feeltech seem to be so fixated on repeating at every opportunity that comes their way to improve their products for very little to zero out of pocket expense. The persistence of the 85 ohm pad into the FY6800 model being a prime example of such missed golden opportunities to correct the mistakes of earlier production runs.
Quite frankly, it's impossible to shake off the feeling that there's an element of design to the penny pinching practices at Feeltech since most of the resulting shortcomings are amenable to relatively easy fixes on the part of a reasonably skilled end user prepared to void the warranty.
If you include enough such warranty voiding enticements in your product, you may never have to deal with a single warranty return. This is a prospect made all the more likely by the rock bottom pricing and the one way export shipping subsidy adding the barriers of return shipping costs and delays to the headaches of collecting on a Chinese warranty. I do have to wonder whether anyone has ever managed to collect on Feeltech's warranty without being left out of pocket.
JBG
Zenith:
@ Johnny B Good,
I've always thought specsmanship crept into scope choices far too much, especially when a company is paying for them.
The scope has gone out to lunch problem caused some worry at first, What was going on? Would there be the hassle of sending it back? And so on. It seems to happen after using slow sweep speeds, but it's not a frequent thing and when it dawned that pressing the Auto button or the Default button clears its head, it's an occasional minor nuisance.
My Boat Anchors are something like 15 valve comms receivers, and a dozen valve scopes. There are also about 20 or 30 items of test equipment mainly from the 70s and 80s. I don't recognise that Marconi sig gen. I have a Marconi TF144 which I eventually started taking to bits and it's now in the garage. It was was one problem after another, dead meters, sealed and not easily fixed with similar meters, a dead double tetrode, which took ages to find a replacement for, and a host of other things. It really was a boat anchor. I have an HP8640A, which is excellent, apart from the silly plastic gears.
The FY6800 had been running for a day or so. I have a couple of Racal frequency counters with overnised crystals, which haven't been calibrated for probably 20 years and so probably wouldn't agree closely with a precision standard, but I'd bet are stable. I connected the FY6800 to one of the frequency counters and the scope, terminated. I set the FY6800 to a 10MHz sine at 2 volts. The frequency counter said 9.999923MHz , a couple of hours later, 9.999922MHz and ten minutes later, 9.999924MHz. A couple of hours after that it was reading 9.999917MHz. The scope said 9.99996/7MHz. I see the frequency measurement on the scope as a convenience more than anything else.
So an accuracy of maybe 100Hz in 10MHz setting and drifting through less than 10Hz in 10MHz over a few hours - this is assuming that the Racal wasn't drifting and isn't wildly out. I'd expect that from a decent quality, but not special crystal module in the FY6800. I'd say it's enough for most needs, but I'm inclined to get hold of a u-Blox M8N Arduino/RasPi GPS module you mention and do the frequency module upgrade. As you said previously, the FY6800 is likely to be aimed at the hobbyist.
What's behind some of the strange decisions in evolving the FY6800 from the FY6600 is open to all sorts of theories. Some bizarre culture in FeelTech. They got it working but it was all so skin of the teeth that they were frightened to modify anything too much. The lead engineer who came up with the design got another job, or left to form his own company, and they were left with no one who really knew what they were doing. One aspect I find odd is the PC software where some features don't appear to work at all. If you enter data in the wrong way in some fields, the program crashes and there's the almost unusable feature for drawing an arbitrary waveform. I get the impression that someone with no knowledge of, or enthusiasm for, software was presented with a PC with a VB system and told to write the software. They cobbled up something which could be described as the software, Feeltech had something they could include as the software, and whoever wrote it went back to their regular job with a sigh of relief. Of course, it could be as you say; they've generated a following and a lot of publicity for the product by its defects creating so much interest in retrofitted improvements.
OTOH, my TTI 5MHz function generator, calibrated according to the manual, has a very inaccurate scale and can only be set to 455KHz by using a frequency counter and gentle caressing the frequency control to get close to 455KHz. Half an hour later it can be at 457, half an hour after that, 454. I came across a Maplin catalogue from 2011/12. They had two function generators, both up to 3MHz. One was £145 and the other £205. I doubt either would bear comparison with the FY6800, for all its little faults.
I saw the generators in Lidl but I have no real need for one. Aren't they 2 stroke? My impression of Lidl and Aldi specials is that they are always interesting and sometimes remarkable for the price. I had a need for some 1 metre SDS drills a few years back. Wickes were £15 and upwards each. Aldi were selling three for a tenner. I thought we'd do the job with the Aldi drills, after which they'd be knackered, but we'd be a fiver in, so why not? As it was there was about five times as much work as we thought. We mainly used one drill and when we finished it was as good as when we started. It's a strange thing to find 1 metre SDS drills in a grocery store, but they do them quite often and they always seem to sell.
If you have equipment which has been kept in the damp for a time, it's very good idea to leave it in the airing cupboard, or somewhere similarly warm and dry, for at least a fortnight. Then it's worth reforming or replacing electrolytic caps and being generally cautious about powering it up. Bunging it on the mains can cause some unpleasant surprises.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version