Johnny B Good, is it possible to calibrate FY6600 for real amplitude voltage?
I mean is it possible to calibrate it in such way, so I can set 1 Vpp, connect 50 Ohm load on the output and get real 1 Vpp. This is expected behavior and it is too complicated to convert voltage into some strange "Chinese volts" which is twice higher than standard volts.
I'm glad you asked me that question, radiolistener.
It gives me an excuse (and the opportunity to attach higher resolution movie files of the previous 'scope traces) to explain why this lack of accounting for high impedance versus matched impedance voltage levels when setting the output level is not the heinous crime many posters to this thread seem to think it is.
I guess the Chinese didn't want to add that particular 'Bell' to the "Bells and Whistles" list. Not only that, they may have wanted to avoid any possible insult to our intelligence by suggesting that us 'westerners' aren't even in possession of the most rudimentary of mathematical skills (i.e. being unable to handle simple multiplication and division by two and optionally 1.4141414)
This halving of the output voltage when driving a correctly terminated cable (or just a terminating dummy load directly) from a generator with an output impedance matching said cable and dummy load, is expected behaviour. If you observe unexpected behaviour such as no to very little volt drop or much more than the expected 6.02dB drop, you know something is wrong when driving a circuit that supposedly has an impedance of 50R.
Indeed, when it comes to having the generator output impedance match the load, it doesn't have to - the key thing being that the terminating impedance matches that of the connecting cable (transmission line). For instance you can use a generator with an impedance of 75 ohm to drive a 50 ohm line, allowing for the additional 1.94dB drop (a 60% drop versus the matched case of a 50% drop).
In any case, the operator usually has to press a button to tell the signal generator that it should scale the p-p voltage setting to match the operating mode (matched or high impedance loading). The fancy and more expensive signal generators may well offer such a feature. Considering your question, they probably do and possibly by monitoring the current versus voltage output to calculate the actual impedance it is connected to so as to leave the operator a hand free to scratch their balls.
Personally speaking, I'm rather glad that the Chinese designers of cheap affordable T&M kit have avoided this insult to the intelligence of their hobbyist target market demographic by not adding such unnecessary "Bells and Whistles" which would detract from the budget allowed for offering the best possible performance at such a low price point. There's only so much money to go round and I'd rather it was all spent on the core features of my signal generator rather than diluted by such "inessentials".
In this case, the voltage setting is based on the unloaded condition, leaving the operator to expect half this voltage if and when driving a matched load. This characteristic of your 'basic' signal generator is a very useful diagnostic aid in the hands of anyone familiar with basic transmission line theory, in particular the bit that says maximum power transfer between the generator and its load occurs when their impedances match each other as well as any transmission line linking the two.
Calibrating the voltage setting for the unloaded condition is the most logical choice (it's very easy to check this well defined unloaded voltage output). It's also useful that it's calibrated this way since anyone working with audio frequency gear outside of communications equipment maintenance or design, will generally be driving high impedance loads, making the voltage setting immediately useful without the complication of having to divide by two or subtract 6dB.
In answer to your question... what was it again? Oh yes, the business of the unloaded voltage being a "Chinese Thing"(tm) and the possibility of having the voltage setting expressed as that which a matched load would produce (i.e. display 1Vpp instead of 2Vpp to account for the loading effect of a termination matching the output impedance of the generator).
The answer in the case of these Feeltech generators is no (at least for the moment - if development of an OSS front panel firmware package ever resumes (seems rather unlikely though) you may well get the opportunity to add this feature to your "Wish List").
However, in the case of other more expensive T&M kit there's nothing to stop designers from implementing the additional complexity to achieve this, and to varying degrees of sophistication, ranging from a simple press button to toggle between the two basic calibrations which match the two reference impedance conditions of either a matched or open circuit (Hi Z) loading (a feature that could trivially be added to these cheap Feeltech generators), to a more sophisticated monitoring of both output voltage and current to not only compensate for the loading but also to calculate the impedance of the attached load for display to the operator (only stopping short of wiping said operator's arse, of course!
).
Anyway, that's my view of the matter. You're free to accept or reject this viewpoint; I don't really care, I've said my piece on the subject.
I've (hopefully this time!) attached higher definition movie files of the traces I posted in my previous two postings mainly to reduce the pain of having to watch the effect at such an execrable resolution of just 320x240. Please enjoy!
JBG