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-   -   Which signal generator? (https://www.vintage-radio.net/forum/showthread.php?t=178824)

Steve Gibson 11th Apr 2021 10:59 pm

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

Cruisin Marine 11th Apr 2021 11:30 pm

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.

Radio Wrangler 12th Apr 2021 12:08 am

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

Steve Gibson 12th Apr 2021 8:27 am

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!

loulou31 12th Apr 2021 10:23 am

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

Radio Wrangler 12th Apr 2021 10:57 am

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

dave cox 12th Apr 2021 1:18 pm

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

Radio Wrangler 12th Apr 2021 1:28 pm

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

Steve Gibson 12th Apr 2021 3:19 pm

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

Steve Gibson 13th Apr 2021 10:09 am

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?

loulou31 13th Apr 2021 11:00 am

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

Radio Wrangler 13th Apr 2021 11:38 am

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

Steve Gibson 13th Apr 2021 12:06 pm

Re: Which signal generator?
 
Quote:

Originally Posted by Radio Wrangler (Post 1363840)
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

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

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

Steve Gibson 13th Apr 2021 12:42 pm

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?

Radio Wrangler 13th Apr 2021 1:33 pm

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

G0HZU_JMR 13th Apr 2021 1:59 pm

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.

ms660 13th Apr 2021 2:12 pm

Re: Which signal generator?
 
Quote:

Originally Posted by Steve Gibson (Post 1363865)
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?

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

Lawrence.

Steve Gibson 13th Apr 2021 2:18 pm

Re: Which signal generator?
 
Quote:

Originally Posted by G0HZU_JMR (Post 1363900)
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.

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

Steve Gibson 13th Apr 2021 3:14 pm

Re: Which signal generator?
 
Quote:

Originally Posted by G0HZU_JMR (Post 1363900)
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.

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

G0HZU_JMR 13th Apr 2021 7:49 pm

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.


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