Appropriate signal generator on a budget

[Noidzoid]

What about an old HP boat anchor?

3325A units go for a good price here all the time for example.

Nice, but not cheap here 

[Noidzoid]

This is the inside of a TTi TG210 with the LCD 

I see from pictures on the internet that the TG210 was available with and without the LCD display although I didn't notice any difference in the model name, am I missing something (quite likely)?
I assume having the screen version is an advantage but how much and why?

Also, is the TG315 similar in the way it is put together and repairable as the other TTI machines already mentioned in this thread?

[bd139]

They're all based on a similar design. It roughly goes:

TG2xx = 2MHz series
TG3xx = 3MHz series (this replaced the TG2xx)
TGxx5 = +display
TGx2x = +sweep
TGx3x = +modulation

Ergo TG315 is 3MHz + display

There is no service manual for the TG300 series AFAIK and the thing is likely surface mount as all devices they ship in that chassis seem to be now.

There's a tear down of a TF930 here which is same chassis and era to illustrate their design changes: https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg1373109/

TBH most of the TTi stuff never breaks though. I've never had a bad item other than some of their very early Thandar branded power supplies but they complete reengineered them since.

[Noidzoid]

Regarding the little screen vs no little screen. Is it a big disadvantage not having one?

[bd139]

The ones with screens allow you to set accurate frequency, amplitude and offset. That certainly is an advantage. Big vs small depends what’s on it. Big one shows two parameters at once.

[nctnico]

Regarding the little screen vs no little screen. Is it a big disadvantage not having one?

Yes. I have an RC based function generator like the TTI one and a Feeltech FY3200 generator. Actually I'm not sure whether I even have the RC based function generator or that I have thrown it away. The FY3200 generator OTOH is in the stack with equipment I use regulary. To me the FY6900 seems to be even more convenient to use because it has a graphical display.

[Noidzoid]

The ones with screens allow you to set accurate frequency, amplitude and offset. That certainly is an advantage. Big vs small depends what’s on it. Big one shows two parameters at once.

So, if using a generator with no screen/readout, does this mean that a separate frequency counter would have to be used to generate a frequency accurately?

[bd139]

Yes but the dial is good within 3-5% usually and that’s mostly good enough unless you’re doing RF or analogue synthesis or digital clocking. If I’m designing band pass filters for example when I measure the resulting circuit I will peak the output of the filter by sweeping it with the function generator control until the amplifier output peaks on my scope. Then it’s advantageous to have a counter connected to the sync port in the generator to work out the frequency.

To note though it’s generally better to have two separate instruments for this as the standalone counters are way more sensitive and have more useful features. I have separate HP 5316A and 5334B counters.

Edit: another vote against encoders here: they’re horrid for sweeping things (and the sweep function is awful for finding peaks etc being suited to plotting trends)

[Kleinstein]

The cheap RC type generators may need an external counter (could be the scope) to get an accurate frequency reading. It may still drift quite a bit even if there is a digital reading (and still set the frequency via pot). How accurate the analog scale is, depends, but often it's more like +-5 or 10%, with switches for the decade and a pot inside the decade.

There is still one point where an analog generator may be better than the cheap modern DDS type ones: this is the triangle waveform, especially if use in a kind of differentiating circuit. The DDS type triangle is usually just some stair steps - sometimes visible in the cheap (e.g. < $60) ones.
The user interface also depends on the use - sometimes adjustment with a pot is more suitable than digital adjustment.

There may be a few other point's that an old analog generator may offer and some cheap DDS one miss, like the option to use it as an VCO, do sweeps (wobble) , maybe more powerful output or parallel sine and square outputs.
Generally even the simple DDS Generators are not that bad and can do most things better. Especially the frequency is more stable and accurate.

[Berni]

Well with encoders its depends on how good the encoder implementation is. There is a huge amount of variability from barely usable to amazing.

A example of good encoder implementation are the low end Agilent/Keysight scopes. The excellent velocity control lets you slowly tweak it in fine steps or quickly flicking it across half its range. Some old boatnahcors also have pretty nice optical encoder knobs, but the encoders on a lot of the modern lower cost gear are indeed really bad.

But when working with filters and similar i like to use frequency sweeps from a signal generator. If you can trigger your scope on the sweep start and tune your scope settings so that the sweep fills the screen you essentially get a poor mans network analyzer. The scope screen now shows amplitude versus frequency and you can pan and zoom around it by tweaking the signal generator controls for the sweep start and sweep width. This is the one reason why i miss my old scopes having a built in signal gen as i really like using this trick on the MSOX3000 at work.

[bd139]

Yeah the ones in the Rigol units are total shit. I’ve got a high end Bourns optical encoder in my radio. That thing is pretty excellent. But they are £68 a go.

I use my DG1022Z and DS1054Z to do filter sweeps for a long time. But honestly I usually just want to know when it’s 3dB down and 20dB down etc and that’s easier to find by manual sweeping after you’ve referenced the thing to the insertion loss in the pass band.

[Kosmic]

Seriously I'm not sure why someone would recommend or buy Feeltech / Feelelec products. There's a thread on the forum full of peoples complaining about their units. It's not necessarily cheap and everything they have been making is super suspect.

https://www.eevblog.com/forum/buysellwanted/re-feelelec-new-arrival-fy-6900-signal-generator/

Also I'm not sure why but they have been banned from this forum …

[nctnico]

Seriously I'm not sure why someone would recommend or buy Feeltech / Feelelec products. There's a thread on the forum full of peoples complaining about their units. It's not necessarily cheap and everything they have been making is super suspect.

The reason is simple: the price is unbeatable where it comes to value for money. Just set the China bashing and boat-anchor blues aside (*).  Sure some Feeltech models have more problems than the others but AFAIK the older FY3200 and the FY6900 just work. The forum has plenty of detailed information so it is clear what to expect from each model. The FY3200 needs a grounded inlet and a wire to connect 0V to ground and the FY6900 could do with a thicker ground wire but the wire used is not outright unsafe. However some people make minor problems much larger than they are and turn these generators into projects of their own. That is their right but don't go around saying it is a bad buy. I'd take a Feeltech any time over an old RC function generator or an old HP unit with their own set of problems and a loud fan (been there, done that). If you want to go a step up then you'd need to look at Siglent's SDG2000 series for example but then you end up in US $500 territory.

* Some people just seem to be hung up on build quality from the old days but forget that old equipment does get affected by time and safety and built standards have not always been what they are today. I also fall into that trap every once in a while. I've had various bits of HP gear through my hands in which I could pull the mains wires straight from the solder joints on the circuit boards. Talking about an accident waiting to happen... Or look at the original shoddy mains wiring of the Dynaload DC load I bought nearly 2 years ago: https://www.eevblog.com/forum/testgear/dynaload-dlf-100-100-1500-(100v-100a-1500w-dc-load)-teardown-repair/msg1381740/#msg1381740

The bottom line is: there are some great pieces of cheap Chinese gear out there which offer excellent value for money. Don't dismiss those off-the-bat with less than solid arguments. I have a few and they serve me well.