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Old 13th Apr 2021, 8:29 pm   #21
Skywave
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Arrow Re: Which signal generator?

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Originally Posted by G0HZU_JMR View Post
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.
As for maintenance on a TF2022, bear in mind that you can't swop boards around between different TF2022s.

Al. / Apr. 13.
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Old 13th Apr 2021, 9:35 pm   #22
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Default 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The classic 203x/204x models superseded these and were amongst the best, bust still probably a bit pricey - 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.
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Old 13th Apr 2021, 9:58 pm   #23
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Default 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.
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Old 14th Apr 2021, 1:01 am   #24
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Default 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!
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Old 14th Apr 2021, 2:17 pm   #25
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Default 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?
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Old 14th Apr 2021, 3:43 pm   #26
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Default Re: Which signal generator?

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Originally Posted by Steve Gibson View Post
>>
>>

Does anyone have any BNC DC blockers spare?
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.
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Old 14th Apr 2021, 3:47 pm   #27
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Default Re: Which signal generator?

Quote:
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Quote:
Originally Posted by Steve Gibson View Post
>>
>>

Does anyone have any BNC DC blockers spare?
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.
Good info

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
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Old 14th Apr 2021, 4:04 pm   #28
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Default 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.

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Old 14th Apr 2021, 4:15 pm   #29
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Default 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.
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Old 14th Apr 2021, 4:16 pm   #30
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Default 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?
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Old 15th Apr 2021, 1:39 pm   #31
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Default 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
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Old 15th Apr 2021, 2:59 pm   #32
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Default 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.
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Old 15th Apr 2021, 3:27 pm   #33
Steve Gibson
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Default Re: Which signal generator?

Quote:
Originally Posted by loulou31 View Post
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

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?
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Old 15th Apr 2021, 3:39 pm   #34
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Default 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
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Old 16th Apr 2021, 9:51 am   #35
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Default 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


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Old 16th Apr 2021, 7:16 pm   #36
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Default Re: Which signal generator?

Quote:
Originally Posted by loulou31 View Post
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.

Jean-Louis
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
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Old 16th Apr 2021, 7:22 pm   #37
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Default 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]
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Old 16th Apr 2021, 8:26 pm   #38
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Default 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
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Old 16th Apr 2021, 10:51 pm   #39
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Default Re: Which signal generator?

Quote:
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!
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.
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Old 17th Apr 2021, 8:49 am   #40
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Default 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.
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