Wavetek 75 Arg gen ... limited to 1 kHz ? - Page 1
Forum section: electronics / testgear

author: Vince
author_rank: Super Contributor
timestamp: July 30, 2017, 12:39:24 am
content: Hi all,Currently I am using an old '70s analog Philips function generator. Frequency and amplitude stability has never been it's thing. Sure, cleaning the pots and replacing a few 40 year old electrolytic caps, helped tremendously... but still.So, I fancied an arg gen to fix this problem, as well as enjoying all the features of an Arb Gen in general. Can't afford the one I would like, not before some time. Not that easy here in France to find good test gear, never mind at reasonable prices, so when I came across that ad for a Wavetek 75 arb gen for only 60 Euros (similar cost to my old analog unit !!! ), which even came with a thick original printed service manual, I just couldn't resist ! Of course before contacting the seller, I had a quick look at the specs online... said 2MHz, was fine by me ! Sure for that price I didn't expect a 10+ MHz thing, but 2MHz was still twice faster than my old analog unit, so what's not to like. It would make a great stepping stone toward a faster and more modern arg gen when I get the money.Was all fine... until I played with it and... what's going on... I can't make it go higher than 990+ HERTZ ?! WHAT ?!I thought well maybe it's just defective, that would make for an interesting repair thread... then I looked at the manual more closely... it's indeed a 2MHz unit but ... there is a BUT : 2MHZ SAMPLING frequency ! So since the waveforms are 2048 points long, at 2MHz that makes for a signal frequency of slightly less than one kilo hertz... so my unit is not defective at all... it's meant to be this way.That said, I played with it and I love it very much, so versatile, these little things are incredible. Compact but no less than 11 BNC connectors to play with (6 front + 5 at the back), it's featureful ! You can even them put them in series or parallel.. in case you have several of them.. .who would.So, after using it, I am sold on arg gen in general, I will definitely buy that popular HP unit when I get the money.What I don't understand is... why would one want an arb gen limited purposefully to not even 1 kHz ?? It doesn't even cover the audio range, and I guess a 10+ MHz arb gen can cover that audio range just fine anyway ?So... I don't understand. Is there some niche, highly specialized market, that I never heard of, for this type of instrument ? Seismology studies maybe ? Even then, I read seismic waves are usually of the order of 20Hz, that's quite a "high" frequency for this unit which goes down to a few micro-Hertz....I intend to keep this Wavetek 75 anyway, because I find it cool, somehow.. it's just that I don't know what on earth I could do with it...Now I am hardly into super fast modern high-tech digital stuff, not my cup of tea, but still, 1 kHz max, that "hurts" !If someone could teach me about the reason for this type of ultra, ultra, ultra low frequency arg gen to even exist, I think I might learn something interesting...

author: MK14
author_rank: Super Contributor
timestamp: July 30, 2017, 01:03:52 am
content: It appears to have a maximum of 1 MHz, not 1 KHz.Have you tried reducing the number of points used ?If not, then you would be limited to 1 KHz, because the 2,000+ points at 2 MHz, would give a max of 1 KHz.Less points = higher possible maximum output frequencyAt 1 MHz, it needs to be set to 2 points for the waveform, hence 2 MHz / 2 = 1 MHz. Which is what the spec sheet, seems to be saying.But I've never used a Wavetek 75, so could easily be mistaken.It seems to be intended for relatively low frequency things, such as motors/solenoids and stuff. Which turn/move at relatively low frequencies.

author: Vince
author_rank: Super Contributor
timestamp: July 30, 2017, 01:44:34 am
content: Been playing a bit more with it. Yes you can indeed go up to 1Mhz if you use 2 points sample, but then how pretty a sine wave would be if you described it with just 2 points !Okay, so let's say I reduce the sample size to 1K point instead of two... that will take me 2kHz, still ridiculous. An dthen I woul dhave to actually program that wave form into the thing, no trivial task.Actually it's even worse than I thought : thisthing is not even a "function" generator... not that it claims to be, now I look at it !I mean when it pretend that it can do ramp/sine/square etc... it's not even true !In a "normal" function gen, you get al the usuzal waveforms pre-programmed, which you can select at the touch of a button at will, and then you have on top of that, some memory to store your own custom waveforms. Well this generator doens't work like this : you don't have any pre-programmed wave forms ! When it says it has 4 slots available... it's not 4 slots ON TOP OF the existing/usual waveforms.. no, it's 4 slot, IN ALL ! So if you want a ramp, you have first to program the ramp into one of the 4 memort slots, and then only can you get it at the output. What a pain.So in short.... I was completely mistaken : this device is NOT AT ALL a function generator for an electronics lab ! It's a specialized bit of kit, but not meant for general purpose use in an electronics lab.So in short, it's a pain to use and super low frequency... so clearly it will sit on my shelves sadly ! I was all set to upgrade it with a backlit LCD which I actually already have bought, and meant to replace the bunch of defective electrolytic on the synthesizer board... but why bother if I am not going to use it for anything !So it will not stay on the bench, no point...Still, was fun studying its service manual, study the schematics and theory of operation, to learn the basics of a synthesized generator, was educational.Will keep it.. just not USE it, hum hum... might come handy one day you never know, but right now noooo....

author: Vince
author_rank: Super Contributor
timestamp: July 30, 2017, 01:58:23 am
content: OK, getting worse :after a few hours playing with it... the output signal is gone, no way to get any signal out of the thing any more. I am done with this thing....

author: MK14
author_rank: Super Contributor
timestamp: July 30, 2017, 02:04:14 am
content: It lets you do things, which would be highly impracticable, with standard function or pulse generators. For complicated electronics/software test and development.But if what you really wanted was a function generator, then (trying to put on my pleasant, smiley face), that is really what you needed to buy.When I buy things. I try to be as careful as possible, to make sure it is the right decision. But I don't always get it right.Yes the 1 MHz, at 2 points was just me explaining what it can do. Not necessarily giving you nicely controlled waveforms at that frequency.You are not asking my advise, so I won't give it.I lied, I'd suggest you seriously consider selling it or something, and using the money and shelf space, towards something much more useful for yourself. Otherwise you could end up with half your shelf space filled up with stuff you can't/won't ever use. Which will probably bite you back one day.

author: Vince
author_rank: Super Contributor
timestamp: July 30, 2017, 02:14:22 am
content: Yeah my bad... I should never have bought it in the first place, I fully agree !It's just that I assumed it was a general purpose function gen, sounded like a decent assumption for something that's called "arb gen"....Still, it was very cheap so I figured I had not much to lose. Ha dit been more expensive yes, for sure I would not have taken it so lightlyAs for selling it, it's worthless. It would take me 10 years to find someone to buy it, and even then it wold probably be a mislead punter like I was !No, I will just keep it. It's still an interesting piece, doesn't take much space on the shelves... and worse case scenario, I could salvage parts from it ! .... would break my heart though.