VNA advice

[TerraHertz]

I'm still not seeing a compelling reason to justify the need for a very expensive piece of test gear.

Given that decent old VNAs seem to be available in the 1 to 3 thousand $ range, isn't simply wanting to learn the techniques, using professional test gear, reason enough? Working applications come later. Also some of us simply don't care about 'return on capital' since our objectives are not economically motivated.

I don't have a VNA, and know I don't yet know enough to usefully apply one. However a decent VNA and associated S/T-R and cal sets is on my 'eventually' list. In the meantime I'm still trying to learn RF basics.  This thread has been an interesting read, with lots of useful references. Thanks.

Incidentally, for Smith chart historical reference there's this 1969 book "Electronic Applications of the Smith Chart" by the developer of the chart, Phillip H. Smith. Pic at ebay 231328916531.

Several posters have very briefly referred to network analysis software they use. For those of us with no working experience in this field, could people familiar with such utilities please post some details? Like package names, sources, freeware/cost, and comments on the intended purpose and quality of the software?
Notes like "It's a pain in the butt because it doesn't do ...." can save an awful lot of time for beginners.

[vk6zgo]

"Then, in the 70’s, it was shown that the relationship between the frequency domain and the time domain could be described using the Fourier Transform"
1970s, my bum!!

FFT (Fast Fourier Transform) algorithm was popularized in 1965 according to Wikipedia. I believe that application of FFT became feasible in around 1970 when algorithm and computing power were at  levels when such application became practical. I don't think they were referring to Fourier transform itself.

But that is not what they said-----if they meant solving Fourier Transforms with a computer,they should have said just that!

Stuff published by Agilent/Keysight has become increasingly lightweight over the years,with Marketing taking precedence over Engineering.

[Howardlong]

BTW the 8753A have an infamous CRT that more than often fails. HP did trade in our A for an E, as they really wanted the A to disappear, and not show up as 2:d hand, I kept the s-parameter test set but this did not affect the trade-in Now what to do with that box??

You can buy color LCD kit for it on Ebay.

Yip, I already ordered one a few days ago as this thread prompted me to do something about mine. Considering it's 30 years old, it's astonishing that the market value of these things continues to be maintained, goes to show what good engineering is all about, except for that pesky CRT that is!

[KJDS]

Several posters have very briefly referred to network analysis software they use. For those of us with no working experience in this field, could people familiar with such utilities please post some details? Like package names, sources, freeware/cost, and comments on the intended purpose and quality of the software?
Notes like "It's a pain in the butt because it doesn't do ...." can save an awful lot of time for beginners.

I've started a new topic rather than further derail this one.

https://www.eevblog.com/forum/testgear/rf-design-software-a-follow-up-from-vna-advice/

[coppice]

They don't teach young EEs much history,though!---

"Then, in the 70’s, it was shown that the relationship between the frequency domain and the time domain could be described using the Fourier Transform"

1970s, my bum!!

Where is that quote come from? I think the timing is a little off. From memory I think it was the 1790s rather than the 1770s. Laplace was active in the 1770s, but Fourier was a bit younger.

[coppice]

"Then, in the 70’s, it was shown that the relationship between the frequency domain and the time domain could be described using the Fourier Transform"
1970s, my bum!!

FFT (Fast Fourier Transform) algorithm was popularized in 1965 according to Wikipedia. I believe that application of FFT became feasible in around 1970 when algorithm and computing power were at  levels when such application became practical. I don't think they were referring to Fourier transform itself.

The quote is about the Fourier transform, not the FFT. Fourier transforms can be performed in several ways in practical engineering systems. Before it was practical to build an FFT in software or digital hardware a lot of systems used optical Fourier transforms. Some advanced radar systems were doing this in the 60s. Fourier transforms in optics are still a big deal.

As someone else commented, it appears Gauss was the first to formulate the FFT, but it was forgotten and rediscovered multiple times. Without automated ways of calculating a numerical Fourier transform there wasn't a lot of interest in them until the 1950s, when computers first became available, and people started performing DFTs in software. The slowness of the DFT made people search for shortcuts. Cooley and Tukey rediscovered the FFT thinking there were the first, but it soon became obvious they were not.

A lot of stuff gets lost if people don't use it. LDPC was first described in the early 60s, before digital comms took off. We went through years of poorer coding schemes before that one was rediscovered.

[XFDDesign]

Given that decent old VNAs seem to be available in the 1 to 3 thousand $ range, isn't simply wanting to learn the techniques, using professional test gear, reason enough? Working applications come later. Also some of us simply don't care about 'return on capital' since our objectives are not economically motivated.

I don't think there is a particularly right or wrong answer to this question, because it is a philosophical one.

In my opinion, just buying a piece of gear every time you want to "learn" something is something of a lie. One isn't wanting to learn something, but pay for what others have learned as a kind of short-cut. Consider, what piece of test gear do those who are learning (i.e. researching) in the domain of 220GHz+? Repeat this kind of thought experiment rolling back to the developments in Radar in WW2.  In essence, it really isn't learning, but "buying" your way to knowledge without a lot of the core supports. You can see this with a lot of spaghetti-against-the-wall spice designs, where people have the tool that "tells" them whether something works or it doesn't. They then throw parts at spice until it spits out a desirable answer - one which might not actually work in the real world.

When I read the comments in this thread, almost everyone has the fundamentals. They "get it" and are using the tool as an expression of those fundamentals. It's how some people say they don't bother with the smith chart, or leverage some tools in particular ways - each have their methods of using the basics to get to their end result. If their instrument is giving them a bogus result, they have a reasonable expectation of what they should be getting instead of what they are. Someone who just picks up a VNA, turns it on and starts "collecting data" to "learn" with, doesn't have that.

[eurofox]

Given that decent old VNAs seem to be available in the 1 to 3 thousand $ range, isn't simply wanting to learn the techniques, using professional test gear, reason enough? Working applications come later. Also some of us simply don't care about 'return on capital' since our objectives are not economically motivated.

I don't think there is a particularly right or wrong answer to this question, because it is a philosophical one.

In my opinion, just buying a piece of gear every time you want to "learn" something is something of a lie. One isn't wanting to learn something, but pay for what others have learned as a kind of short-cut. Consider, what piece of test gear do those who are learning (i.e. researching) in the domain of 220GHz+? Repeat this kind of thought experiment rolling back to the developments in Radar in WW2.  In essence, it really isn't learning, but "buying" your way to knowledge without a lot of the core supports. You can see this with a lot of spaghetti-against-the-wall spice designs, where people have the tool that "tells" them whether something works or it doesn't. They then throw parts at spice until it spits out a desirable answer - one which might not actually work in the real world.

When I read the comments in this thread, almost everyone has the fundamentals. They "get it" and are using the tool as an expression of those fundamentals. It's how some people say they don't bother with the smith chart, or leverage some tools in particular ways - each have their methods of using the basics to get to their end result. If their instrument is giving them a bogus result, they have a reasonable expectation of what they should be getting instead of what they are. Someone who just picks up a VNA, turns it on and starts "collecting data" to "learn" with, doesn't have that.

Disagree with you, I spend my career mainly in automation, electronic and mechanics as an engineer but most of the time in middle management and executive management having a bunch of engineer working for me. I speak 7 foreign languages and was active in many country's.

I'm retired now and was never involved in RF, you are telling me that I have to go back to school or read 200 book about RF technology 

I have NO INTEREST in RF in general, I don't care about RF amplifier and antennas, I'm interested in ultra fast rising pulses and therefore to improve my design need to understand some aspect of RF technology, that is the only reason why I'm interested in a VNA to improve my cables, connectors, splitters ...
I'm able to design pulses with rising edges below 30ps, you can compute the RF frequency for this yourself.

[G0HZU]

Have you considered spending some time with an RF simulator?

The good ones can mimic an 'n port' VNA and you could mess about with simulated splitter designs and transmission lines up into the GHz region and you can also model the circuit in the time domain on the very best simulators. eg you can inject simulated pulses of your own spec to the simulated circuit. This could prove a useful learning curve and it may help you choose the spec of your 'real' VNA

For example: It's very easy to make a precision wideband resistive splitter up into the GHz region if you follow a few basic RF design rules. The last one I did, I designed on a simulator (Genesys + Sonnet EM) and the measured results were pretty much bang on with the simulator up to several GHz. So it was arguable that the 'real' VNA wasn't needed. However, if I wanted to make a splitter that worked well up beyond 10GHz then I would need to use a real VNA to verify my various component models. But up to 6GHz, say, its fairly easy to produce a decent model of a tiny SMD resistor and a decent RF simulator and a decent RF layout can do the rest.

I still think you will find out that you will need a very fast VNA for your project. But if this is the case you will also need some very expensive test fixtures and cal kits and a fair bit of RF experience to get the best from it and to avoid falling into a few traps. However, you could probably learn enough to get good results with just a few days' decent study time, especially if you can find an experienced tutor to sit with you as well

[XFDDesign]

Disagree with you, I spend my career mainly in automation, electronic and mechanics as an engineer but most of the time in middle management and executive management having a bunch of engineer working for me. I speak 7 foreign languages and was active in many country's.

I'm retired now and was never involved in RF, you are telling me that I have to go back to school or read 200 book about RF technology 

I have NO INTEREST in RF in general, I don't care about RF amplifier and antennas, I'm interested in ultra fast rising pulses and therefore to improve my design need to understand some aspect of RF technology, that is the only reason why I'm interested in a VNA to improve my cables, connectors, splitters ...
I'm able to design pulses with rising edges below 30ps, you can compute the RF frequency for this yourself.

It's perfectly find to disagree with me. Your long list of achievements are commendable (I can barely do 4 languages), but not really important or relevant to this particular topic at hand though. There was a guy at Tektronix, an MIT graduate who was the expert in superconducting something or other. Ask this guy anything about superconductors, inside or out, and he could give you answers. One day, this guy frantically waffled around to all of the surrounding labs, and told everyone to shut down,  because their labs emitted too much noise for his sensitive measurements. So everyone complied, albeit grudgingly. The guy never came back, so after a while everyone went back up. A bit later, he comes back and barks the same orders. Finally someone decided to go see what the hell it was he was trying to do. The guy went on, in great detail about his experiment, but in the end, what was it that originated all of the commotion? He was trying to measure a 4GHz signal, of anticipated 500uV amplitude.

On a 200MHz scope.

On 50mV/division with full power bandwidth.

There are many disciplines, and being a master of one does not automatically make one a master of all others. 

If your purpose is to buy a VNA, for the sake of it, go for it. Apparently you'll need one that's capable of doing the inversion back to time domain, and even still if you're on that blisteringly fast edge of speed (supposing 30ps rise time), a cheap 3GHz VNA is unlikely to be a benefit.

[ivaylo]

In my opinion, just buying a piece of gear every time you want to "learn" something is something of a lie.

People learn differently, man... If you tell me one way of learning is better than another, I'll have to disagree too. Call me an idiot, but I remember for the first time I got what a current source was when I laid my hands on a PSU with a CC mode. Yet on paper I cuold solve the craziest circuit with Kirchoff, Thevenin and what not...

[eurofox]

In my opinion, just buying a piece of gear every time you want to "learn" something is something of a lie.

People learn differently, man... If you tell me one way of learning is better than another, I'll have to disagree too. Call me an idiot, but I remember for the first time I got what a current source was when I laid my hands on a PSU with a CC mode. Yet on paper I cuold solve the craziest circuit with Kirchoff, Thevenin and what not...

+1 

[XFDDesign]

In my opinion, just buying a piece of gear every time you want to "learn" something is something of a lie.

People learn differently, man... If you tell me one way of learning is better than another, I'll have to disagree too. Call me an idiot, but I remember for the first time I got what a current source was when I laid my hands on a PSU with a CC mode. Yet on paper I cuold solve the craziest circuit with Kirchoff, Thevenin and what not...

I don't think there is a particularly right or wrong answer to this question, because it is a philosophical one.

In my opinion, just buying a piece of gear every time you want to "learn" something is something of a lie.

Learning itself, is an integration of concepts. You had the math to "solve" a few styles of problems. You had a piece of gear which took the practical component and combined it with the math component, and then you "got it." You learned the concept of a current source and could then have that tool in your tool box.

What would that experience have been like, without the basics of understanding KCL and KVL? What if you only had a power supply that had both CV and CC mode, but none of the fundamentals behind it?

[eurofox]

What would that experience have been like, without the basics of understanding KCL and KVL? What if you only had a power supply that had both CV and CC mode, but none of the fundamentals behind it?

If you think you have the exclusivity to have "maybe" the knowledge of RF technology you are really an idiot. 

This forum aim is to share experience an not to waste time arguing with pretentious people.

I learn what I want the way I want and your comments here are simply ridiculous, most people here try to help but obviously you are an idiot thinking that you are smarter than others.

[XFDDesign]

If you think you have the exclusivity to have "maybe" the knowledge of RF technology you are really an idiot. 

This forum aim is to share experience an not to waste time arguing with pretentious people.

I learn what I want the way I want and your comments here are simply ridiculous, most people here try to help but obviously you are an idiot thinking that you are smarter than others.

"When the debate is lost, slander becomes the tool of the loser."

Perhaps you wish to quote me where I stated that I have an exclusive ownership of knowledge in RF? Or perhaps you wish to quote exactly where I said I am smarter than others, for surely you observed the point where I was informed about VNAs being used for TD measurements. No, what you're shopping for is not "help" but an excuse to buy something. Don't ask for advice, if you don't want to listen to what you're given. Fundamentally, you've presented no actual argument, either in calling me an idiot, or your "disagreement."

Cheers.

[eurofox]

If you think you have the exclusivity to have "maybe" the knowledge of RF technology you are really an idiot. 

This forum aim is to share experience an not to waste time arguing with pretentious people.

I learn what I want the way I want and your comments here are simply ridiculous, most people here try to help but obviously you are an idiot thinking that you are smarter than others.

"When the debate is lost, slander becomes the tool of the loser."

Perhaps you wish to quote me where I stated that I have an exclusive ownership of knowledge in RF? Or perhaps you wish to quote exactly where I said I am smarter than others, for surely you observed the point where I was informed about VNAs being used for TD measurements. No, what you're shopping for is not "help" but an excuse to buy something. Don't ask for advice, if you don't want to listen to what you're given. Fundamentally, you've presented no actual argument, either in calling me an idiot, or your "disagreement."

Cheers.

I'm retired after a full career, what I do I do it for pleasure, on this forum people are usually friendly.
I have no need to get very deep into RF technology but I do have a SA up to 21Ghz, a microwave counter/counter meter, an RF generator and I build myself a microwave generator and I can use and fully understand all those instruments.

I don't cry for help, just share people experience in some specific area is that all and many people kindly answer , only one was playing the smart-ass.

I never touch a VNA in my life like most of EE engineers and I was just asking some advice but in the mean time I order an new VNA this way I will be able to learn without asking advice an get unpleasant reaction 

[Alexei.Polkhanov]

Eurofox you live in the middle of Europe - everything is around you. When I needed VNA to debug my RF project I just went and rented one from local cal lab for $350/week. Better than buying one for  $38K and not using it. Vancouver is not that big on electronics, so cal lab that used to rent equipment got new owner and they don't rent anymore. 6 pack of beer and trip to a buddy with VNA works as fine 

Good way to meet new people that have interesting projects is to join local hackers club and then you meet people that have something you don't and in reverse. I found that what works better than beer is an interesting project - if you have something built already like wide band antenna, microwave filter, ...  or anything and then you need equipment to test/tune it almost certainly there will be people more than wiling to help you.

World is an interesting place - I have seen people with $5M worth of equipment in a lab that does nothing ... errr humidity sensors, and then I see dudes that have bunch of super exciting projects like air pollution radars, 3D scanners, amateur radio telescope receivers which they finish with 30 y old analog scopes and always looking for test equipment to debug their stuff.

[eurofox]

Eurofox you live in the middle of Europe - everything is around you. When I needed VNA to debug my RF project I just went and rented one from local cal lab for $350/week. Better than buying one for  $38K and not using it. Vancouver is not that big on electronics, so cal lab that used to rent equipment got new owner and they don't rent anymore. 6 pack of beer and trip to a buddy with VNA works as fine 

Good way to meet new people that have interesting projects is to join local hackers club and then you meet people that have something you don't and in reverse. I found that what works better than beer is an interesting project - if you have something built already like wide band antenna, microwave filter, ...  or anything and then you need equipment to test/tune it almost certainly there will be people more than wiling to help you.

World is an interesting place - I have seen people with $5M worth of equipment in a lab that does nothing ... errr humidity sensors, and then I see dudes that have bunch of super exciting projects like air pollution radars, 3D scanners, amateur radio telescope receivers which they finish with 30 y old analog scopes and always looking for test equipment to debug their stuff.

You know some people spend 500 thousand Euros for a stupid super exclusive watch or 100 thousand for a special stamp, my lab is my way to keep myself busy en enjoy what I'm doing, I'm retired and have a lot of time.

 

[Howardlong]

So my experience may go against the grain of some of the "professional" EEs on here.

I've been fiddling with electronics since about 1973 when I made a crystal set with my old man. To be honest I think he enjoyed doing it as much as I did. I was eight years old. At eleven, I wrote my first program in Algol 60 on paper tape. At twelve, I'd designed and built a digital clock out of 74 series TTL ICs. I used to tell my mum off for using the washing machine because my clock's time base ran off the mains 50Hz, so it skipped many seconds while the washing machine relays etc clicked through. That was 20 odd ICs all hand wired, and I designed the whole thing myself. When I was 13 I built my first computer, again hand wired, based on an older school friend's design. I still have it, although I doubt it works any more. At 15, I was designing my own computers. I then did a EE degree, worked in ATE (automatic test equipment) for a while, and then sold myself to the devil and did software professionally almost exclusively for 25 years.

Back in the 70s, having a scope was sheer luxury (Monty Python fans please note). The holy grail (oops) was a scope, and if really lucky it was dual trace, but the nerdgasm of the day was a scope with a dual trigger, not that I had much clue what to do with that at 12 unless I was tutored by my older peers. I didn't own a scope myself until I was in my mid-twenties. My debugging tools were a 1k ohm per volt analogue multimeter and an LED with a resistor. Plus, the nose to "smell" the heat, and the back of the finger to do a similar thing, both techniques I still use to this day.

I am absolutely certain that having the right tools, particularly a scope, back in the day it would have speeded up debugging of problems, but you can get away with an awful lot with a crappy meter and an LED, and a good degree of healthy persistence.

More recently, about 1999, I got back into RF, and was doing a lot of work on antennas at VHF and above, but particularly in the 2.4GHz band. After messing about with SWR bridges in 2000/2001 for some time I bought that 8753A VNA with a T/R test set. I'd spent some months investigating and gritting my teeth about blowing £3k on such a thing. At that time I wasn't making a living from electronics either, this was an academic pursuit. It was an eureka moment. Pretty much my understanding of impedance matching and how antennas and transmission lines work suddenly clicked into place. Yes, I knew about phase, Smith Charts, return loss etc. But I'd never had a way of applying it so directly and seeing it so interactively.

Since then, I've gone on to many other things, all with RF connections, including designing and troubleshooting several items of space hardware that are orbiting the planet right now. I rarely take those old software contracts anymore. These days I get asked to universities to teach postgraduate students. I'm still astounded at how little real applied knowledge there is out there.

Of course, the well-paid bean counters still think they are saving everyone a buck by offering crap wages to inexperienced workers and bugger all equipment. Yes, you can do an awful lot when you don't have the best test equipment, but it takes a lot of patience and analytical skills. That means time, and as any well-paid bean counter should know, time is money.

[eurofox]

I build on the age of 13 my first oscilloscope with valves and continue to be passionate by electronics until I got graduated as an engineer and PhD.

I start building my first computer in fact a PCB with ram, prom and display and HEX keyboard with I/O's on the very beginning when µprocessors became available.

I wrote code in hex, when computers became available I start to use assembler.
I got my first real oscilloscope when I was 23, it was an HP that I could buy second hand.

I work several year in automation on many project, design during the CP/M time a SCADA system and start to develop protocols to communicate with PLC's, this was in the beginning of the 80's.

Shortly after this period I moved to middle management and up to executive management. I was plant manager for many year with different divisions, the biggest one was electronics assembly with up to 300 people only in this department. I learn everything about pick-place machines and production.

The last 5 year of my career I was involved in photovoltaics from physic up to participate on getting a complete production plan ready.

Most of my professional live I got my lab at home and from time to time did some freelance projects. After the Apple II appear on the market I designed a compatible system with 80 column instead of 40 original from the AppleII, the guy for whom I designed never got the money to put it on the market. 

I still program for the fun micro controllers in C and assembly.

Now I 'm retired and catch up again with electronics, I do it as a pleasure and learn new things the way i want it.

[G0HZU]

Pretty much my understanding of impedance matching and how antennas and transmission lines work suddenly clicked into place. Yes, I knew about phase, Smith Charts, return loss etc. But I'd never had a way of applying it so directly and seeing it so interactively.

I think you could also have done the same with a decent simulator and a decent smith chart program

I would argue that you can learn more and learn it quicker with access to a decent simulator. Obviously there is a bit of a learning curve with the simulator but a modern simulator is usually the most powerful tool in the box. Usually way ahead of a VNA if you want to explore new concepts and do research work.

When I started doing RF design professionally 25yrs ago we had a HP8753A T/R VNA and it was a fabulous bit of kit. But what I really wanted to have at home was the CAD software we were using. Back then it was DOS based stuff  called star/sstar/pro from Circuitbuster (later to become eagleware).

Today, the modern CAD tools take you to learning levels way beyond having a 'real' VNA on the bench.

[eurofox]

Today, the modern CAD tools take you to learning levels way beyond having a 'real' VNA on the bench.

I can agree but what is the cost of such a simulator ?
What could you advice that is affordable?

[G0HZU]

It would be very expensive to buy AWR or Genesys products as a private individual. It could easily end up costing $20k or more if you want to add a few options. If you search online you will see that some hobbyists choose to hack the SW and run it for free at home. I'm not sure anyone really minds if this happens at the hobby level but it becomes much more serious if a company tries the same.

RFSIM99 is quite good as freeware though. However, I don't think it would be what you need.

[Bud]

Today, the modern CAD tools take you to learning levels way beyond having a 'real' VNA on the bench.

Way beyond that is true because the firmware in the bench devices is limited in its math and presentation capabilities.

However, there is a magic in a real VNA on the bench. You touch it, you connect real circuits, you learn how strays, parasitics and different setup can affect real measurements.

[TerraHertz]

Given that decent old VNAs seem to be available in the 1 to 3 thousand $ range, isn't simply wanting to learn the techniques, using professional test gear, reason enough? Working applications come later. Also some of us simply don't care about 'return on capital' since our objectives are not economically motivated.

I don't think there is a particularly right or wrong answer to this question, because it is a philosophical one.

Actually I meant it as a rhetorical question, to illustrate a point. So you're right.

In my opinion, just buying a piece of gear every time you want to "learn" something is something of a lie. One isn't wanting to learn something, but pay for what others have learned as a kind of short-cut.

Well now, that very much depends on the details. For instance, as someone with no RF experience and little theory, but a need/desire to know, I decided my best path was to start with very basic gear. So I bought some slotted lines, SWR meters, power meters, vector voltmeter, and so on. Because I'm well aware that trying to use more complicated gear before I understand the principles is a trap waiting to be sprung.

Consider, what piece of test gear do those who are learning (i.e. researching) in the domain of 220GHz+? Repeat this kind of thought experiment rolling back to the developments in Radar in WW2.  In essence, it really isn't learning, but "buying" your way to knowledge without a lot of the core supports. You can see this with a lot of spaghetti-against-the-wall spice designs, where people have the tool that "tells" them whether something works or it doesn't. They then throw parts at spice until it spits out a desirable answer - one which might not actually work in the real world.

I don't think your point here is very logical. Yes, some people with fundamentally broken learning abilities will take silly paths, and produce rubbish. That isn't a basis for never buying expensive equipment as a learning aid.

When I read the comments in this thread, almost everyone has the fundamentals. They "get it" and are using the tool as an expression of those fundamentals. It's how some people say they don't bother with the smith chart, or leverage some tools in particular ways - each have their methods of using the basics to get to their end result. If their instrument is giving them a bogus result, they have a reasonable expectation of what they should be getting instead of what they are. Someone who just picks up a VNA, turns it on and starts "collecting data" to "learn" with, doesn't have that.

Agreed. having some idea of what results should be, is very important. That's why learning is a process. However there's still nothing wrong with buying test gear appropriate to one's present position on the curve. Whether economics factors are important to someone or not, is an entirely separate matter, and depends on their circumstances and objectives. Some people may make silly choices in their circumstances; that doesn't mean the same choices by other people are necessarily silly.

As for using simulator software packages - in many cases buying these can cost more than 2nd hand test gear providing similar abilities. Also personally I prefer hands-on learning. Simulators have their place, but I'm not a fan of paying lots of money for software, especially since experience has taught me that compatibility lifetimes can be quite short. How many old CAD tools do I have that won't run (or just aren't installed) on my current machines? I hate to think. I'm developing a bit of a PC phobia actually.