Author Topic: RF Signal Generator purchase - Advice sought  (Read 10482 times)

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Offline LaurenceW

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RF Signal Generator purchase - Advice sought
« on: August 12, 2014, 10:17:08 am »
Hello All. I have been extending my electronics lab of late, but still have a slot on my shelf where an RF signal generator should go! I already have a capable low speed (up to 20 MHz) Rigol function generator, so have that end of the spectrum covered.   Also a fine condition HP 8594E Spectrum Analyser, which has piqued my interest in things that wiggle back and forth faster than a few million times a second....

I am now looking for an RF SigGen up to around 1GHz, that will take FM and AM modulation (most do, I realise). I am looking at the second hand market, and want something that is reliable and, in the event of a fault, at least reasonably repairable and not full of too much Unobtainium (there is always some, I realise!).

My need is not yet well defined! Hobby/experimental/personal education, and moving into the radio sphere. Can't think I need networking/GPIB connections.

My budget is up to about  GBP £400 or USD $550, and I am looking to buy in the UK.  So far, my shortlist has Marconi 2022x and HP 8656B (not 8656A, I read) on it, but I am open to others, too.

Any thoughts?
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Offline idpromnut

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Re: RF Signal Generator purchase - Advice sought
« Reply #1 on: August 12, 2014, 11:30:31 am »
Last year I picked up an HP 8642B. There be a lot of dark RF magic in this unit, and it weighs a ton. The output is rather good however, and I am very happy with it. I ended up building a rack for it out of angle steel. Picked it up locally for ~200$ and it works perfectly :)
 

Offline Richard Head

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Re: RF Signal Generator purchase - Advice sought
« Reply #2 on: August 12, 2014, 12:13:57 pm »
I've got an HP8656B, 8657A and 8657B and HP8640B. The HP8657 range are relatively cheap at around $600-$1000 and seems to be within your budget.
They have very low phase noise down to -136dBm/Hz and are really well made, but weigh a ton.
The newer generation of vector signal generators are MUCH more expensive and I can't yet justify one.
If your budget doesn't stretch that far then look at a good quality HP8640B. It's ancient but has a cavity oscillator so has a very low phase noise, even lower than the HP8657B. It only goes to 500Mhz though (some to 1Ghz). The Marconi 2022x sounds interesting. An excellent instrument, no doubt.
Try to get it in your country to avoid the huge courier cost from overseas.
Remember, sig gens are like power supplies, you generally need more than one. A two-tone test requires two, a blocking test requires two etc etc. 
Next it'll be directional couplers, tracking generator, VNA, power meter etc etc.
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Offline G0HZU

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Re: RF Signal Generator purchase - Advice sought
« Reply #3 on: August 12, 2014, 08:44:03 pm »
A lot depends on what you want to do in terms of accuracy and quality.

However, of all the sig gens mentioned on here the little Marconi 2022 is likely to be the best choice for most people for small business/hobby use. However, they are not always that reliable because they have a known weakness in the (many) OM345 modules inside the unit. But these are relatively easy to repair/replace and there is very little else in the way of unobtanium inside the generator.

The Mi2022 is small, easy to use and has reasonable phase noise performance. We have loads and loads of them at work (at least 10) and I don't think any have had an OM345 failure in the many years we have had them.

The main problem with the HP sig gens mentioned on here is the size and weight. I don't rate the HP8657 series as worth the bench space because the size/cost/performance/'ease of repair' ratio doesn't add up for me. The performance is fairly average but the generator is big and heavy.

The HP8640 is a classic signal generator with fantastic spectral purity but for most modern users it will be too big, way too heavy and old and slow/clunky and fragile. The Marconi 2017 is a decent competitor/alternative to the HP8640 with a much, MUCH better user interface but it is incredibly heavy and I wouldn't recommend it unless you want diehard spectral purity and you can live with the size/weight/power requirements.

The Marconi 2019(A) is fairly common as a used buy in the UK for maybe  £150 -£300 but I would advise against these unless you are prepared to put up with lots of niggly/intermittent reliability. This is fine if you like taking things apart and fixing minor faults but not good if you want decent long term reliability. They are much bigger/heavier than the 2022. I have two of them here and they are nice to use but they are big and heavy and the attenuators can stick/misbehave if the instrument does not see regular use. But most of the modules inside use discrete, easy to find components so repairs can often be very cheap and quick.
The other bonus with the 2019 is that it is totally SILENT in operation because there are no fans anywhere. So if you like to work in silence and hate fan noise then the 2019 can become top choice if you have the necessary bench space and get one that is reliable. The phase noise performance of the 2019 is fairly poor above about 300MHz but it gets better at lower frequencies because of the way it uses dividers for the lower bands. So it is quite respectable for close to carrier phase noise across 2-30MHz.
This makes it a good (but not spectacular) choice for use in this range of frequencies.

There's a very good reason why the little 2022 holds its (£200-£400) price so well. It is in a class of its own in terms of size/weight/performance/ease of repair and this makes it a very popular choice for hobby users :)

Ebay has its fair share of sellers trying to get very high prices for the 2022 (eg >£800) but I think you can often get them for under £300.

If you do go for a 2022 then it's worth asking the seller if the generator works on all its sub ranges. Even though it appears to be a seamless interface to 1GHz the generator can have known dead 'gaps' in this frequency range if it is faulty. eg it can work perfectly well in parts of its range but be dead on others. Usually it means a dead OM345 module somewhere.

There are various options if an OM345 fails. You can try and buy an OEM version (£30 each?) or buy a dodgy 'equivalent' on ebay for about half this amount or you can try and repair the OM345 yourself (at zero cost)


 
« Last Edit: August 12, 2014, 10:25:40 pm by G0HZU »
 

Offline LaurenceW

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Re: RF Signal Generator purchase - Advice sought
« Reply #4 on: August 13, 2014, 05:21:46 pm »
G0HZU, that is a fullsome response - many thanks. Yes the HP devices certainly seem to put the "anchor" in "boat anchor" and seem to come at a much higher weight/bench space premium than the Marconi 2022 series, that has caught my eye.

So, another couple of questions, then.

What is the difference between a 2022 no-suffix, and the 2022A to 2022E variants that I see?
Does the modulation (not carrier) frequency go down to DC? I've read the specs, but can't make it out.

Ive read about this little OM345, and have seen replacement devices. If it comes to it, I'll whip out my ESD-safe, temperature controlled iron, and swap any duds out.

Looks like I might have a bit of a wait for a bargain one, tho.
If you don't measure, you don't get.
 

Offline G0HZU

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Re: RF Signal Generator purchase - Advice sought
« Reply #5 on: August 13, 2014, 07:44:04 pm »
I'm not an expert on the 2022 versions but the early ones only go up to +7dBm for cw signals.

I think the C version goes up to +13dBm and the later ones +10dBm. I think the later ones go to 1.010GHz rather than 1.000GHz. There will be other differences but I really don't bother looking at the version letter of the ones at work. I just grab the nearest one although the white/blue ones look much fresher than the traditional chocolate coloured ones so these catch my eye first. Note: GPIB is an option and it would help with resale value even if you don't want to use this feature yourself.

In external modulation they work down to a few Hz eg 10Hz. If you explore below this I would expect the performance to fall off.
If you need to use DC coupled modulation with reasonable precision/drift then maybe you can look at the Marconi/IFR 2023/4/5 although you will need to at least double your budget.

These do external DC coupled modulation. Also the quality of the modulation is far superior to the 2022 as the 2024 uses DSP for the AF source and has much better modulator hardware. The 2022 is really aimed at testing basic comms gear and the accuracy/distortion levels for the modulation modes is 'adequate'.

I have a 2024 here in front of me and I like it a lot. However, the prices have crept up recently. I bought three of them a few years ago for £800 each with options 4 and 11 (high stability OCXO and +25dBm RF o/p level) but you are looking at >£1200 today unless you buy a scruffy one.

I guess the other option for external DC modulation is the HP/Agilent ESG series. These are economy class generators  in terms of phase noise performance but are otherwise surprisingly good. Prices vary a LOT for these and there are lots of versions (1GHz to 4GHz)(analogue/digital) covering up to 4GHz.

But they are outside your price range unless you are very patient. Prices usually start at about £600 for a basic analogue generator but the most popular versions are the 3GHz analogue version and these are usually about £850.
 
« Last Edit: August 13, 2014, 08:02:09 pm by G0HZU »
 

Offline G0HZU

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Re: RF Signal Generator purchase - Advice sought
« Reply #6 on: August 13, 2014, 08:21:24 pm »
One thing to watch out for on the 2023/4 series is that the front panel buttons on the user interface can become a bit 'deaf' if it has seen a hard life. I think the membrane behind the switches can get worn/damaged and the button can become deaf/intermittent.

When this happens it makes the generator a real chore to use. So be wary of scruffy 'bargains' unless you get to try out all the buttons yourself!

This can also affect the 2022.

Also, be wary of a 2023/4 with a less than perfect LCD display. The 2023/4 often gets dropped on the floor because it has very weak plastic handles at the front corners. Lazy people use these mini handles to pick up the generator by one corner and the plastic handles can break like this because they become weak with age.

So never pick up a 2024 like this! The LCD display can get damaged if it gets dropped. The usual clues are obvious impact damage, missing front handles/ears, damaged front panel rotary knob or BNC connectors and maybe issues with the LCD display.
« Last Edit: August 13, 2014, 08:35:18 pm by G0HZU »
 

Offline LaurenceW

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Re: RF Signal Generator purchase - Advice sought
« Reply #7 on: August 13, 2014, 09:41:59 pm »
Yes, based on the fact that there seems very little information about to differentiate the various 2022 models, I conclude that they are all very similar bar the output levels and top frequencies. Looks like the same firmware and basic design, throughout.

<Scope creep alert!> Of course, stepping up to a 2023/2024 is going to yield better performance and an appropriatley higher price, but I don't think my knowledge/budget stretches to that - yet.

These RF sig gens seem to hold their price well enough - I will maybe contend myslef with a good example 2022 for now, and consider a trade up when funds/knowledge allows!

I don't know that I need DC performance, but it seemed kinda neat for Phase-Lock loop applications. Maybe getting ahead of myself <again>

Thanks again for your wise words, G0HZU.

Let me know if you see a Marconi 2022 looking for a good home at a good price!! :)
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Offline G0HZU

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Re: RF Signal Generator purchase - Advice sought
« Reply #8 on: August 13, 2014, 10:11:28 pm »
Quote
<Scope creep alert!>

 ;D

Yes, that can happen very easily... :)

However, decades of experience has taught me that 'signal generators' are the items that will reward you the most the more you spend although I have never spent more than about £1k on one for home use.

I can live with fairly basic and old scopes, very basic and cheap DMMs, cheap/old counters, and basic old school PSUs but I hate poor quality sig gens or generators that have a poor user interface.

If I have to fault the 2022 it is that it doesn't have a whirly wheel on the front panel to allow user rotary control of power or frequency or modulation etc. That's partly why I would recommend you buy one with GPIB because you can control it remotely with an analogue control on a PC screen if you write a simple program for it.

Otherwise you have to do things like press this button sequence to tune up/down:

DELTA
FREQUENCY
1
kHz

and then use the up/down keys to tune it 'manually' in 1kHz chunks per keypress.

On a PC screen you can have 'almost' real time control via GPIB with software sliders  set up for several adjusters at once. But I guess few people bother with this and they just use the front panel controls.



 

Offline LaurenceW

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Re: RF Signal Generator purchase - Advice sought
« Reply #9 on: August 14, 2014, 08:42:11 am »
Wise words, sir. I totally undersand your useability arguemnt. My head is turned by the Mi 2023/4 and HP8647/8, but there goes my budget, again. I will keep looking, though.

There are a couple of amateur radio rallies in the UK Midland this/next weekend, so I think I will mosey over to those and see if there are any bargains to be had.

At least, now I know better what I am looking for :)
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Offline Andy Watson

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Re: RF Signal Generator purchase - Advice sought
« Reply #10 on: August 14, 2014, 10:16:55 am »
I have a 2022E and I agree with everything G0HUZ says about them. It's my go-to generator for higher frequencies, but, one thing to be aware of is that the carrier spurs can be quite high. Also, there is some leakage from the internal 10 MHz clock - can make life interesting when tuning radios and other sensitive equipment.
 

Offline HighVoltage

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Re: RF Signal Generator purchase - Advice sought
« Reply #11 on: August 14, 2014, 08:50:41 pm »
I am also looking for a used RF generator and I came across this Marconi IFR 2030
http://www.ebay.de/itm/Signal-Generator-Marconi-IFR-2030-10-kHz-Zu-1-35-GHz-Mit-GPIB-I-/231304274658?pt=Mess_Pr%C3%BCftechnik&hash=item35dacf22e2
The price seems reasonable
Located in the UK

Does anyone of you have experience with this model Marconi?


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Offline G0HZU

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Re: RF Signal Generator purchase - Advice sought
« Reply #12 on: August 14, 2014, 09:51:37 pm »
I've only used the 2031 and the 5.4GHz 2032.

We have several of the 2032 generators at work and they have some very versatile modulation modes.

I can't comment on the 2030 phase noise performance other than I think the 2030 generators use division to get the lower frequencies. However, I don't think the phase noise performance will be quite as good as a 2023/4. (but that's just a guess)

Apart from this, the 2030 is very big. The display on this series seems quite rugged because we have a 2032 that has been dropped and the LCD glass is badly cracked (spider web cracks) but the display still works!

The 2030 is a decent generator but my best advice would be to be patient, spend just a little more and get a tidy looking 2024 (or haggle a LOT and see how cheap you can get that 2030 for)  :)

« Last Edit: August 14, 2014, 09:53:13 pm by G0HZU »
 

Offline LaurenceW

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Re: RF Signal Generator purchase - Advice sought
« Reply #13 on: August 15, 2014, 06:34:59 pm »
G0HZU, I think you should write the book about this stuff!

"Big Dummies Guide to RF Sig Gens"  :-DD
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Offline grumpydoc

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Re: RF Signal Generator purchase - Advice sought
« Reply #14 on: August 15, 2014, 07:53:39 pm »
The 2024 display can be replaced with this one with a little work - see https://www.eevblog.com/forum/repair/quick-repair-project-marconi-2024/

The various 2022's are very similar, the later models do offer more output - +13dBm on the "C" (although the "E" was +10dBm), very slightly higher frequency range (1.01GHz vs 1GHz) and more internal modulation frequencies (400Hz, 1kHz and 5kHz rather than just 1kHz).

The service manual for the "C" and "E" are on the k04bb site, the service manual for the "plain" 2022 is available in the files section of the Yahoo Marconi group or here
 

Offline Radio Tech

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Re: RF Signal Generator purchase - Advice sought
« Reply #15 on: August 15, 2014, 09:42:39 pm »
I have a 2022E and I agree with everything G0HUZ says about them. It's my go-to generator for higher frequencies, but, one thing to be aware of is that the carrier spurs can be quite high. Also, there is some leakage from the internal 10 MHz clock - can make life interesting when tuning radios and other sensitive equipment.

This is a statement that should not be over looked when it comes to radio or any rf producing repairs.
One reason why Ham operators like the HP and IFR gear. Trying to get a receiver right with a big fat "birdy" sitting in the middle of it can be a pain in the rear.

Offline avvidclif

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Re: RF Signal Generator purchase - Advice sought
« Reply #16 on: August 16, 2014, 01:16:18 pm »
I have an HP 8656B that I have been using since 1987, it's a few years older than that. It has never failed and is used daily. Once a year I take it apart and blow out the dust. Yep, it's big and heavy but like a Timex it just keeps on ticking. I've seen them as low as $300 USD, most around $500 for a working/guaranteed unit.

I would also suggest to keep your eyes open for an HP Service Monitor (8921 etc) I've seen those for under $1k USD. The telco's have been dumping them. That gives you a signal generator, spectrum analyzer, tracking generator, audio oscillators(2), hi-stab osc, etc. If you are doing 2 way stuff they are the cats meow.

I don't know anything about the Marconi line so can't comment.
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Offline Chris Jones

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Re: RF Signal Generator purchase - Advice sought
« Reply #17 on: August 18, 2014, 12:52:33 pm »
If you're in the UK and happen to be going close to Reading, then a visit to Stewart of Reading http://www.stewart-of-reading.co.uk may be worthwhile. You can haggle with them. I have to admit that most of my purchases from there have developed minor faults sooner or later, but that is more due to the age of equipment that I tend to buy, and I am not disappointed with anything I bought there. It's worth going through the specials page of their website as I have found some real bargains there, mostly unusual stuff that they have trouble selling. Also e-mail ahead with a list of stuff that interests you because sometimes it takes them a few days to find stuff and drag it out for you to inspect.
 

Offline LaurenceW

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Re: RF Signal Generator purchase - Advice sought
« Reply #18 on: August 18, 2014, 04:23:57 pm »
Chris, that's a good call, thanks. I was aware of Stewarts, and they are not 90 minutes from me. But their list prices seem a little high to me (as a private buyer). Genuinely hadn't occured to me to haggle, tho! Worth a try ...
If you don't measure, you don't get.
 

Offline grumpydoc

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Re: RF Signal Generator purchase - Advice sought
« Reply #19 on: August 19, 2014, 03:59:42 pm »
I got them (Stewart of Reading) down on one item but not by much - although I was negotiating by email rather than in person. They seem to discourage popping in though.

Actually I bought my first oscilloscope from them in about 1980, old even then but worked fine until stolen in about 1989.
 


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