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| FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator |
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| beanflying:
From memory mine was always always about 30+ Hz high at 10Meg against my GPSDO and I think early on in the thread there is some mods done on the time base if you look for them with different TCXO's fitted. What all of this shows is that they were chasing the bottom line against 'their' competitor in JDS instead of focusing on being best in class. What they failed to see is there is a huge gap to anything better they could have played in. Better Power Supply More accurate Time base Better Op-amps and trimming in the factory Upgradable Firmware Maybe $20-30 retail needed to get it done right? Compared to most likely hundreds of hours of 'fun', speculation and tinkering by us all. Still great bang for your $ :) |
| Zenith:
--- Quote from: beanflying on February 16, 2019, 01:07:48 am ---What all of this shows is that they were chasing the bottom line against 'their' competitor in JDS instead of focusing on being best in class. What they failed to see is there is a huge gap to anything better they could have played in. Better Power Supply More accurate Time base Better Op-amps and trimming in the factory Upgradable Firmware Maybe $20-30 retail needed to get it done right? --- End quote --- Yeah. Conspiracies exist, and a few conspiracy theories have been proven true, but I think the cock up theory usually wins out over the conspiracy theory. So thinking about the history of the instrument business, I don't see JBG's view of the hierarchy ringing true. Look you lot are educational and skint hobbyist, see? A nice little function generator you've got here. Too nice. You're getting above yourselves. So we'll have a crappy 85 Ohm pad in here. Your choice of op amps is unfortunate, and could prove unhealthy. Change it. As for that TXCO and the option for an OCXO and an external reference, err, no. Now if you can't see the logic of these design improvements we have associates who will explain them more clearly. They are persuasive if not altogether civiliised. This is a cock up. --- Quote from: beanflying on February 16, 2019, 01:07:48 am ---Compared to most likely hundreds of hours of 'fun', speculation and tinkering by us all. Still great bang for your $ :) --- End quote --- Better value than going to the pictures. |
| Johnny B Good:
@Zenith Specifications are an important marketing tool, especially in such a competitive market as this where the feature set can be overwhelmingly complex with modern DSO and MSO kit so 'Specmanship' is going to be inevitable. My first experience of the Siglent going into a fugue was a little disconcerting at first but bearing in mind all the microprocessor control and digital processing used in a modern DSO, I instinctively applied the 'switch it off then on again' technique the first two or three times this happened before it occurred to me to try the 'Default' and 'Auto setup' (amongst other) buttons to avoid the protracted power cycling method which provided reassurance that these episodes were more a case of 'Operator Error' than any indication of something more serious. These buttons are obviously provided to back out of any conflicted settings that may have been applied by operator abuse. I had hoped to be able to discern the model number of the Marconi signal generator from the photos, forgetting I still had the camera set to the 640 by 480 setting from a previous photo shoot to minimise the risk of going over the 2MB attachment upload limit when posting images of the u-blox GPS module to [urlhttps://www.eevblog.com/forum/projects/ublox-neo-m8n-gps-navigation-signal-amplify-module-for-arduino-rasppery-pi/][/url] Hopefully, that link hasn't been mangled too badly (if at all - I'm not quite sure how you're meant to use the "Insert Hyperlink" button in the compose a reply window). It looks ok here so that will take you to a thread I started some 2 1/2 weeks ago trying to get some advice and opinions over its suitability as the basis for a homebrewed GPSDO. I think I must have bought the sig genny at an amateur radio rally some thirty years ago. The scope was an earlier purchase from a local government surplus shop afaicr some time around 1972/73 to let me record oscillographs of test waveforms of a 200W per channel (RMS per 4 ohm loads) PA amp I'd been commissioned to design and build by a friend who played in a local band. The need to photograph the CRT display led me into the amateur photography hobby, something I'd previously never had any interest in. It's surprising how one thing leads to another. :) Anyway, the one of each item, 'scope and signal genny, was all I needed and could afford so I neatly avoided accumulating any more 'boat anchors'. Your frequency calibration checks of the FY6800 appear, on the face of it, to be fairly respectable considering how Feeltech cheaped out on the XO chip. You'd expect OCXO s to be pretty stable even if they're in need of recalibration after twenty years. Mind you, if they've not been used very often, they might not be all that far off frequency even twenty years later. The hardware frequency counters built into these Siglent 'scopes aren't remarkably accurate. Mine, after 8 or more hours of warm up was adrift by about 4.33ppm (it read high on frequency to the tune of 130Hz on a 30MHz signal afaicr). Not very impressive at all imo but, as you've observed, more a courtesy feature to get a ball park figure. Your own thoughts on what's going on at Feeltech are possibly closer to the truth of the matter. The cynic in me tends to nurture conspiracy theories since I prefer to look for less chaotic reasons for such otherwise inexplicable behaviour. Whatever is going on, they're certainly not doing themselves any favours, more's the pity. There's no doubt that the Feeltech generators, as cheap as they are, are in a totally different league to even modestly vintage test gear that wasn't made by Hewlet Packard. If the generators you saw in Lidl last year were either the very retro styled PGI 1200 A1 (still surprisingly carrying their original £129.95 price tag of the previous year) or the more suitcasey styled PGi 1200 B2 at just £99.95, they're both 4 stroke powered in spite of the A1's rather retro two stroke styling with its top mounted gravity feed fuel tank and open frame with plastic panels slung around the sides to disguise its open framed nature. It's rather surprising that an earlier version of the B2 model should be placed on sale about a month after the B2s had been on sale with a 30 quid higher price tag. Hopefully, the B2 models will reappear again come the Spring and I'll be able to pick myself a couple of donor machines to resolve the irritatingly low overload trip point on my current acquisition. My interest is in their use as an alternative to investing several hundred quid in SLA battery packs just to extend the autonomy of my APC SmartUPS2000 an extra 6 to 8 hours. Basically, it's a backup to the UPS. As an autonomy extender, it's a far less expensive option to installing a bigger battery pack which, at the end of the day, is just an expensive consumable. With only a 1KW rating (30 seconds surge rating of 1200W), it's a little on the marginal side but the 2KW rated Workzone inverter gensets that Aldi had on sale about a month or so after I'd acquired the Parkside unit proved to be total shite, to put it mildly (and I should know since, optimist that I am, I tried three of these before giving them up as a lost cause). Compared to the Workzone units, the Parkside ones are inverter genset perfection, not the slightest hint of engine revs dropping on application of full load in the eco idle setting, unlike the Workzone units which threatened to completely stall out when subjected to full load from the half loaded state. AFAICR, the Workzone units were permanently in eco-mode with no option for 'normal mode' so there was no way to mitigate the problem like there was with the Parkside units to reduce the risk of a stall whilst they were warming up from stone cold (the only time I managed to stall a Parkside unit was switching straight to eco-mode after startup followed immediately with the application of full load - restarting it and giving it a couple of minutes to warm up solved the problem). Take it from me, those little Parkside PGi1200 B2 suitcase gensets are well worth the money, even if they hike the price up to that of its predecessor. The Aldi Workzone units otoh, aren't worth touching with a ten foot bargepole so take note. I hear what you're saying about the effects of prolonged damp on electronic kit, particularly when bias voltages of two or three hundred volts are involved. As it happens, I do have a small 180VA Variac but it's a a panel mount unit and I don't have a suitable box to mount it in. Also, I'm not sure whether a 180VA rated unit would be up to the demands of an ancient scope or even the Marconi sig genny but I guess it might be able to cope with the overload for the few minutes it would take to bring the voltage up slowly enough for the electrolytics to reform. Otoh, I might just say "Bugger it! I'll just switch them on and take my chances.". If either or both go bang, then so be it. That'll just be a boat anchor or two less to clutter up my storage space. They're so ancient that at best they'll simply be electronic curios to admire for their sheer chutzpa at even pretending to be test gear. Life's just too short to be trying to repair such ancient kit of limited utility, hence the fatalistic attitude to the problem. Apologies if that sounds a little cavalier but that's just the way things are right now. JBG |
| Noy:
So today i put the THS3491 into the generator and put a new proper heatsink pad below the Heaspreader. Now i can get 22 Vpp with 20 MHz sine. But i get now an overshoot with square wave If i go above 500mV Independent of high impedance or 50 Ohm termination... |
| Johnny B Good:
--- Quote from: Noy on February 16, 2019, 02:18:08 pm ---So today i put the THS3491 into the generator and put a new proper heatsink pad below the Heaspreader. Now i can get 22 Vpp with 20 MHz sine. But i get now an overshoot with square wave If i go above 500mV Independent of high impedance or 50 Ohm termination... --- End quote --- Remind me please, Noy. Is this the FY6600 or the FY6800? I've lost track of who has what. :-// Also, can you provide some details about the 'scope and the way you've got it connected up to the generator. If you can post a screenshot or two of the relevant traces, that'll help us to work out what's actually happening. I'm a little puzzled as to why you're getting 22v p-p. This is 10% above the 20v p-p limit of the generator's amplitude range which begs the question as to whether this is a calibration issue or a voltage magnification effect due to the use of a few metres of unterminated 50 ohm BNC patch cable. Out of curiosity, I repeated your tests using the half metre BNC patch lead that was supplied with my FY6600. I wanted to verify whether the square wave was limited to a 5 or 10 volt p-p level or not at 20MHz and lower frequencies since, if it had been (it isn't - the 5v p-p limit only kicks in for frequencies above 20MHz), that would have excluded the THS opamp from the circuit (that only gets switched into circuit for p-p settings above the 5 volt mark). That reads like you've installed just the one THS3491 (U21 and U22 showing the THS3001 locations) and left the original THS3002i chip (U5A and U5B) in place. The reason why I'm querying this is because the reverse engineered circuit so kindly provided by ebel0410 last year (which he uploaded to the Github repository) implies the simultaneous presence of the original dual opamp along with the additional single opamps. That's a little confusing to say the least although most would realise that it's either just one or the other arrangement (just the original 3002i in the U5A/U5B locations with the U21/22 left empty or else the original 3002i removed with either 3001, 3095 or 3491 ICs fitted in the U21/22 locations. Hopefully, what you actually meant was that you'd removed the original THS3002i chip and fitted a pair of THS3491 chips into the vacant U21/22 locations. Assuming this to be the case, one possibility for the overshoot could be the need to tie the Vref pins to a voltage 5 volts or lower than the V+ rail voltage, typically either to ground or else the V- rail. Provided this is the case, the /PD pin can be left to float as with the earlier 3495 chips. The easiest way to meet this requirement, is simply to strap pins 1 and 4 together (the data sheet insists that the Vref pin (pin 1) should not be allowed to float). I've attached some screen shots for you to compare with yours. The first two are from the end of last year just after I'd upgraded the opamp. The second pair were done just now, using the half metre of supplied BNC patch cable, without termination (the terminated traces looked virtually the same only, of course, at half the p-p voltage). JBG |
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