Which signal generator?
 

I have just had 2 offers accepted upon first offer, for 2 different signal generators on ebay. I was obviously expecting a counter offer on them before making a decision to buy.

One is a Thurlby Tg230 and the other is an Agilent HP Keysight 3312A.

This leaves me with a problem, as I don't believe I need both of them (unless there are any over riding reasons for keeping both), so I'm looking for advice on which one to keep.

I would welcome any thoughts that people may have.

Many thanks

Steve

Re: Which signal generator?
 

1. What frequency range do you require?
2. What output level control do you need (Higher and lower levels)
3. Do you want synthesised (frequency locked) or a free running unit?
I don't know the individual units,but, you should be able to narrow it down greatly with those 3 criteria.
Also, you may need a sweep function for aligning filters etc.
HP gear would be favoured by me, but, I am set on test kit I like.

Re: Which signal generator?
 

First off, these things are usually referred to as function generators rather than signal generators.

Their oscillators make square waves and triangle waves primarily. They distort the triangle waves with diode-resistor networks to approximate sine shapes. The technique has been improved over the years, but their distortion is still orders of magnitude greater than a good audio signal generator.

They also aren't RF signal generators. The low-Q current-capacitor-comparator timed oscillators are not good for phase noise (or frequency stability) They lack output attenuators to take the signal down to the sensitivity thresholds of radio receivers.

What they are is jacks of all trades. You can do all sorts of modulation, sweeps and things like that. Some will let you simulate a pulse generator, though one with rather slow edges.
They are very versatile in the number of things they can do.

But if you want to work in audio, there are better options than a function generator
And if you want to work in RF, there are better options than a function generator.

Their natural home is on a general electronics bench. They're good for making sweeping waveforms, good fo education.

I do have a func gen, but I've never used it in anger. It comes out when I want to demonstrate different waveforms on a scope.

I last used one in anger as an audio source into a walloping great power amplifier to apply controlled sinewave noise on the 12/24v supply to some avionics gear to check that the gear wasn't perturbed by noisy supplies.

Sorry for being a bit of a downer.

David

Re: Which signal generator?
 

Hi All

To clarify

My original intention was to use a function generator to help with things like IF alignment in old radios (ie carrier wave with modulated output, etc). I am getting into restoring vintage radios and audio amplifiers.

Other than that, as a new comer to the hobby the main reason for buying one was the raft of recommendations on forums, blogs and videos that a function generator should be considered when setting up an electronics lab.

I found 2 on ebay that, from the limited info on specific generators, appeared to have good reviews within my budget, but now I have won them both I could do so with some more informed advice on which of the two may be the best one.

@radio wrangler: Dave, when you say better options for RF what do you recommend? And are what price bracket are those solutions in?

Thanks for the feedback, I love the community on this forum!

Re: Which signal generator?
 

Hi,
Yes they are both not really RF generator, nor low distorsion audio generateor but can help to align RF circuits, and with with audio, and also general purpose electronic. For my opinion, you need a frequency counter because both of them are not synthesized.

However TTI has a digital read out for frequency and amplitude and may be OK.

For the HP it is working up to 12MHz and has FM modulation, that is quite more better to work with radio that the TTI : you can work for 10.7MHz IF and FM demodulator. To use these kind of generator with radio and external 50ohms attenuator is usefull.

I Have an HP3312A because I like HP instruments....TTI seems to be a good equipement quite more modern...

Jean-Louis

Re: Which signal generator?
 

For radio fixing and alignment, most people use classic RF signal generators. Most of these will cover long wave RF up to 30MHz quite well, and may give harmonics up to 100MHz. Most are AM or CW with no FM. They'll do you for AM broadcast sets and shortwave receivers. What's missing is the VHF/FM band and frequency modulation, and the ability to sweep so you can set up bandpass tuned IFs (as opposed to simple peak-tuned ones)

I have a Marconi TF2008. Nineteen sixties/seventies vintage. It covers 9kHz to 510MHz, which is a bit excessive for broadcast/shortwave radio. It does AM and FM - and it can sweep so that you can use an oscilloscope to display filter shapes as you adjust wider IFs for FM sets - It's also good for tuning the bandpass filters in 'Wadley' type receivers (RA17 family)

Where it gets fiddly is in low frequencies, it may work down low, but the scale is a bit fast.

And it goes down to very low amplitudes. Don't undervalue this. It's useful to see if the RF or IF section you are aligning is sensitive enough. You can debug low gain faults. With a cruder sig gen without a good attenuator and good screening, everything seems to work!

So if you're interested in AM sets, then there are lots of old cheap sig gens on the market for pocket money prices. If you want to be able to handle FM sets, then you have to work a bit harder to find something with FM and higher frequency coverage.

A number of people have bought function generators to augment classic RF sig gens. They use them as an addition, to make sweep signals for bandpass alignment.

I too am rather fond of HP test gear, but I used to work there, designing it, so I might be a little bit biased...

David

Re: Which signal generator?
 

Out of the 2, I would choose the HP unit - if it is in good nick and working!
This is not based on owning or dismantling either !

Although the Thurlby unit is much newer, the typical build quality from this manufacturer is not in the same league as HP, but then, neither is the original price! My experience with Thurlby instruments is that it will not be reliable or robust while HP is typically the exact opposite! The switches on the HP unit may be the weak point ...

dc

Re: Which signal generator?
 

This model has a bank of multipole latching pushbutton switches, with various barred releases. Quite reliable. They're not the 'Bill West' clicker buttons.

David

Re: Which signal generator?
 

Thank you guys.

Looks like I will be keeping the HP then and on the lookout for a radio decent signal generator.

I have an old Altai TE-220 Audio generator, but nothing specific to radio frequencies, etc

Regards

Steve

Re: Which signal generator?
 

Here's an interesting thought.

What are members views on building this 150Mhz signal generator?

https://www.nutsvolts.com/magazine/a.../june2014_Reed

Would this just be an educational project, or would it be a valid piece of test equipment like the author suggests?

Re: Which signal generator?
 

Hi,

Seems to be an interesting home made signal generator. Based on the same MC1648 there is also some varations including sweeping function, always on N&V.

Jean-Louis

Re: Which signal generator?
 

Aaaargh! MC1648 alert!

The chip he's used as the oscillator is one I know well. It's ECL logic dating from the end of the sixties (ECL III to be precise) Over the years Morotola improved it dramatically in several stages. Later ones are capable of such high frequency operation that they will spuriously oscillate resonating the lengths of track to the intentional tank circuit.

These things need very very careful circuit layout and the tank right by their terminals.

Multiple tanks and a band switch is asking for trouble. Maybe the originator found a very early one, or hasn't noticed UHF parasitic oscillations?

1648s got used a lot in PLLs, where the loop counteracted their drift. In this open loop design, you'll find them somewhat more drifty than a single transistor oscillator. The tank is directly coupled into the transistors inside the 1648, normal oscillators have a degree of separation.

David

Re: Which signal generator?
 

I take it you're not a fan then ;D

I'll keep looking for a more appropriate solution :thumbsup:

Re: Which signal generator?
 

Ok, I may have an option of a working AVO CT378 for around £50.

Apparently working and in good condition

Am I getting warm or do I just need to get a bigger budget?

Re: Which signal generator?
 

You're in the right ball park. It'll do some of the things you might want to do, but not all. I don't thnk they all have FM.

David

Re: Which signal generator?
 

The little Marconi TF2016 is also worth considering. It covers 10kHz to 120MHz and does AM and FM and it has a proper ALC and >100dB step attenuator. The frequency scale is very crude so it really needs to be used with an external frequency counter and there is a connector at the back for a counter.

Prices for the TF2016 seem to be quite firm these days so you might have to pay £100 for one. This generator is quite small and light so easy to move around the bench or put away when not in use.

Re: Which signal generator?
 

I had a CT378A, nice signal generator, no good for receivers with AM/IF below 2MHz.

Lawrence.

Re: Which signal generator?
 

Nice one thank you!

There's a few on Ebay now so I'll take a look - they seem a better option to the CT378

Re: Which signal generator?
 

Is it also worth getting the TF2173 Synchroniser if possible for more stability, or would a frequency counter be enough (which I already have)?

Re: Which signal generator?
 

The total price starts to creep up a lot if you buy the synchroniser as well. If you want a synthesised/locked output then I think it would be better to pay a bit more and buy a Marconi 2022 sig gen. Prices for these vary a lot but scruffy examples sometimes turn up for under £200.

I've not used a 2016 but I do have a 10MHz - 520MHz Marconi TF2015 here and it is stable enough once it has been allowed 30-45 minutes to warm up. I'm not sure drift will be a problem with a 2016 unless you want to test radios with very narrow cw filters installed.

The low cost alternative is to buy something much older like a classic old Advance signal generator. These are fine for aligning LW/MW/SW radios and I would guess they cost somewhere between £20 and £60 depending on condition.

Re: Which signal generator?
 

As for maintenance on a TF2022, bear in mind that you can't swop boards around between different TF2022s.

Al. / Apr. 13.

Re: Which signal generator?
 

Yes I once had the pair of those Marconi Sign Gen + the Synchroniser unit, I had been given. But I donated to someone else, as already had / already too used to using some a bit more modern fully digital-entry/display synthesised ones I'd managed to get cheap from work sales.

And you may now be able to pickup Marconi 2018/2019 or even 2022 ones for a reasonable price, that are all fully-synthesised but quite old.
The classic 203x/204x models superseded these and were amongst the best, bust still probably a bit pricey - > £500 for a working one, although you may get one that needs fixing for less as many were scrapped when attenuators etc. played up due to silly repair prices (but DIY cleaning may often fix)
Marconi Instruments became IFR, Aeroflex then finally part of Cobham, who sadly closed all of this division down a few years ago so little support even for later models although there is a very active repair group with some ex-employees: https://groups.io/g/Marconi-Test-Instruments/

When fully-working, these will generally give you known very good performance.
In terms of much-newer models, the usual fairly-budget instrument makers like TTI, Rigol, Siglent etc. seem to now only do fairly high frequency RF signal generators, so quite a bit over £1k new. For a bit lower frequencies, they do some much more reasonably-priced Arbitrary / Function generators but these won't have the minimum output level / shielding required for this.
Digimess have a rather basic SG100 150MHz RF Sig Gen in Farnell etc. but it doesn't look like you could set frequency very accurate or output level very low. Their SG200 DDS looks much better but nearly £1k new, and probably difficult to get a cheap used one.

You can get MC1648 lots of cheap pre-built narrow range signal source module, that may overcome the potential issues with that Nuts&Volts project that doesn't even use proper PCB's.

Another option maybe Analog devices ADFxxxx PLL evaluation boards, but their minimum frequency can often be quite high.
Alternative there's quite a lot of Software Defined Radio units, that can also generate RF signals over a wide range.

These will mostly require a PC to control them, but can be made to do virtually anything regarding frequency / modulation that way - as well as many also being a receiver with spectrum display etc. e.g. The HackOneRF that isn't too bad new, but seem suspiciously cheap on:
https://www.banggood.com/Wholesale-S...r-c-11802.html

There is also a similar thing, that is fully-integrated with a controller:
https://coolcomponents.co.uk/product...enerator-combo
Unfortunately, the half priced version only starts at 24MHz:https://coolcomponents.co.uk/product...efff721c&_ss=r

And an RF output attenuator will be required to get much lower levels.

Re: Which signal generator?
 

Regarding the function generators choice, I have used quite a bit of TTI equipment - especially their bench PSU's that are amongst the most popular - and have generally been happy with most of this considering their relatively low cost. It does seem they are UK-based/designed and manufactured in the EU, and the company has effectively been around under slight name variances since the 1970's.
Being a much newer model than the HP one, it would probably be easier to get spares and may still be supported, whereas the as HP one is very old now, so could have much more wear on the controls / parts hard to obtain. Although there older models do have full service manual info easily available and will be much more solidly-built than more recent mainly plastic-cased ones, with even Tektronix making their very expensive 'scopes in China.

However, whilst the TTI one has a digital readout of Freq. / Amplitude & DC Offset, and a 1000:1 sweep range, the HP ones has much better modulation facilities including FM capability and a choice of modulating-waveforms plus a widely-variable internal modulating frequency rather than a single fixed one. As well as the RF going to a much higher frequency.
So the HP one likely to be of much wider use.

Re: Which signal generator?
 

I would definitely choose to keep the HP function generator but I'd recommend buying or making a DC block and a 20dB attenuator and keeping this on the output at all times that you use it with a receiver. I think those old function generators can output quite a large AC waveform into a 50 ohm load and this includes the ability to add a large DC offset. This could be enough to damage some receiver inputs or even some test equipment. For example it might be possible to fry the external modulation input of another sig gen with the HP function generator. It might also be possible to do the same with the Thurlby function generator.

I'd expect the HP generator to have better RF shielding than the Thurlby so this might be important for some tests.

When I bought my first test equipment many years ago I soon learned how important it is to have at least one classic RF signal generator that has very good accuracy in terms of amplitude and frequency. I've not counted how many sig gens and signal sources I have here today but I have quite a few!

Re: Which signal generator?
 

Well I've upper my budget and purchase a Marconi TF2008, it arrives at the weekend.

It looks in good nick but I won't know until I receive it.

I guess I'll have to open it up and check Caps, etc before powering it on an testing it.

Fingers crossed I got a good one!

Thanks for all the help and advice - I'll be keeping the HP function generator.

Does anyone have any BNC DC blockers spare?;D

Re: Which signal generator?
 

Commercial BNC DC-blocks don't seem too common - I can't recall seeing one, only inline through terminations and attenuators etc.
With N-types etc. DC-blocks being much more common, as were supplied with some Spectrum Analysers etc.

You could get small BNC Plug-to-socket boxes from RS, to add your own parts inside. But they are a bit bulky (and not that cheap).
Although could make something similar from a couple of back-to-back BNC sockets, with spacers in-between + a plug-to-plug adaptor.

Or if you can get one of those (RS etc) inline BNC attenuators, cheap, then most unscrew apart and just have some leaded resistors inside - which could be replaced with a capacitor.

Re: Which signal generator?
 

Good info :thumbsup:

I'll have a look for some inline DC blockers

Do you know if these are any good as attenuators?

https://www.ebay.co.uk/itm/Coax-TV-A...ondition=4%7C3

Re: Which signal generator?
 

The TF2008 has a spare output to drive a digital frequency counter, which you may find convenient. It also includes a reasonable audio signal generator as a source for modulation, so you can vary both the amount of modulation applied, and its frequency. There are also audio output terminals.

Without a counter you still have accurate markers from a crystal oscillator to check your tuning scale against. If you use the TF2008 as a sweeper with an oscilloscope, you can use the second channel of the scope to show marker pips to give you landmarks for frequency.

It's a full lab grade beastie and should do just about anything you want.

The tuning is clever, one range tunes upwards left to right , the next tunes upwards right to left, and so on. So if you're working close to the edge of one band, you don't keep having to wind the pointer from one end to the other. Cunning, huh!

That attenuator is a 75 Ohm one for TV systems and only goes down to 5MHz.

Proper 50 Ohm general purpose ones turn up at radio rallies. Mini-Circuits sell new ones, if you're feeling flush. Otherwise have a chat with Stewart of Reading and see if Wayne has anything in stock.

A straight fixed 20dB attenuator is three resistors in a box. A blocking capacitor is just that, in a box. Boxes with RF connectors seem to be rather expensive for what they are.

Junk stalls at amateur radio rallies are good areas to search.

David

Re: Which signal generator?
 

Yes, that's a 75R attenuator (and also has belling-lee 'TV' connectors, as well as not going down to DC for some reason)


I was thinking more like these ones: (RS-Pro are twice the price!)

https://uk.farnell.com/aim-cambridge...3db/dp/2357851

And may be able to pick up used / faulty ones, even cheaper to strip-apart.

Re: Which signal generator?
 

Thanks David!

Yes, looking forward to playing with when it arrives, and hoping to get to a few rallies later in the year when lockdown lifts. It will be good to interact more with the community face to face.

Where is the best place to find test leads, connection leads, connectors, etc?

Every piece of kit I have bought comes without any leads, do seller bin them or is there a magic black hole that swallows equipment leads? :shrug:

Re: Which signal generator?
 

Hi Steve,

The TF2008 seems to be a good RF generator with a quite wide frequency range from 10k to 512MHz. It providers AM,FM modulation, and also sweeping but with a limited frequency variation.
I have a HP8654B that it as also a good RF generator, but lower end limited at 10MHz.
For attenuator I recommend external rotary 10dB per step attenuator or switch attenuator 1,2,4,8,16,32. We cand find it used for a good price, or new Chinese model but I dont know quality. Yes a separate DC block is highly recommended.
How much for the TF2008?
Thanks

Jean-Louis

Re: Which signal generator?
 

With all my SG's I have some kind of adaptor/s permanently connected to the output socket. It avoids the possibility of the output socket getting damaged as a result of having a plug inserted into it hundreds of times. If the adaptor gets damaged it can easily be replaced.

Re: Which signal generator?
 

Thanks for the info.

The Unit was £245 and looks immaculate and came with the front cover with operating instructions on the back. lt still had tamper wax on the case screws and original tamper seals still in place inside - so I've left well alone for now.

After a cursory look over the 160mA fuse is blown so I've not plugged it in yet and could do with some advice on whether I should carry out further inspections or maintenance, or if I should just replace the fuse and turn it on through a dim bulb limiter and see what it does?

Re: Which signal generator?
 

Just replace the fuse.

Fuses die of old age and turn-on surges. The rated current is that which nominally takes 1000 hours to blow. Time/current is a curve, from milliseconds to years.

You might be lucky. If it pops the new fuse then investigation is needed. It's all semiconductor with regulated power rails and might not take kindly to dim bulb powering.

David

Re: Which signal generator?
 

Yes, you could use also a variac and increase line power slowly with current monitor. Some time psu electrolytic capacitor after a long time without use requires slow voltage rampup to renew.
Good luck


Jean-Louis

Re: Which signal generator?
 

There was a down convertor (11710B) for the HP 8654A/B and a synchronizer/counter (8655A). The 11710B can also be used with the 8640A/B.

David

Re: Which signal generator?
 

One of the problems with 'vintage' test-equipment is that you also need modern test-equipment to fix the vintage stuff before you can use it!

[Alas, l having stopped working some years back I no longer have access to my beloved Anritsu]

Re: Which signal generator?
 

All far too modern! I use a Marconi TF995A/2M which still works a treat! Otherwise a Pongrance kit DDS with an HP 355D attenuator.

https://www.pongrance.com/DDS2018.html

Re: Which signal generator?
 

Sadly, I have found that test gear doesn't have to be that old before this gradual decline into unreliability starts to happen... I think I've had to repair all but two of my RF sig gens at some point and I have a lot of fairly modern sig gens here.

Re: Which signal generator?
 

Indeed. I often find myself having to fix the test equipment again before I can use it to test a radio.

Re: Which signal generator?
 

A lot of test equipment is simply weighed down by the sheer number of parts involved. Even if the parts were reliable examples of their type, the final calculation of mean time between failures would not come out well.

We have far better parts nowadays and that helps.

Back in the 80's I had a spell in the 'manufacturing engineering' department at HP. During that time I got the task of deciding what changes we needed to make to reduce the measured failure rate (we only got data for the warranty period) across all our products. The aim was a 'decade in a decade' the clever sounding words chosen to appeal to top management. Well we did it. We got much better than a tenfold reduction in failures in the field and we did it in well under ten years.

The most powerful tool was a database.

Each failure was broken down into the parts that got replaced in the repair. Repairers in the field weren't really up to the task of always investigating a root cause, they had the next box to fix, waiting. The database could be searched by part, PCB assembly, instrument or groups of instruments.

Each part had a preference code, used by the materials department to flag preferable parts and rogue parts. I could scan an instrument looking for low preference parts, for parts that just failed. I found patterns. Ostensibly good parts with a good fail rate across the whole corporation showed up bad in some instruments. The database gave component designators as well. I could dive into that assembly and go looking for under-rated components and plain design errors.

Several years later, those top managers decided the database IT costs were too high, so they shut it down.... oh, well.

So yes, test gear is unreliable. The reasons are understood and real action has been taken to improve it.

At the same time I also had the responsibility across the division's product line to do what changes were necessary to get it all through the new EMC regulations.

I stayed in manufacturing for about 7 years and learned a lot I'd never have come across if I'd stayed in R&D. Having someone with a design viewpoint and the depth to understand it all, made quite a difference to manufacturing engineering, and then I moved into R&D at the new RF/microwave instruments division being set up.

David

Re: Which signal generator?
 

Hi David,

Yes I know that there is a D/C for the HP8554. It includes a 50MHz LO, mixer, and filters. Not easy to find a used 11710B. May be possible to built it with a 50MHz Xtal oscillator, a passive mixer, some filters, plus one amplifier go get 0dB gain...

Jean-Louis

Re: Which signal generator?
 

I don't know of anyone who used the downconverter accessory, most people screwed a few minicircuits bits together and used a spare sig gen as the LO.... A spare sig gen? Ooops, I think we just went recursive!

David

Re: Which signal generator?
 

Yes, but problem with modern test equipement is that when fails it is often not possible to repair it : no service manual nor schematics, spare component not available ( specific, SW embedded...), component difficult to remove/resolder with active SMT, more expensive to repair througth pro company that buy a new one.
However most of us uses both new and old test equipments....


Jean-Louis

Re: Which signal generator?
 

Just a heads-up.

In the small adverts of the latest Radcom (big photo pf the Duke of Edinburgh on the cover)

There's a marconi 2022 sig gen in the small adverts. No mention of price.

David