Opinions on VNA Purchase

[Cigarsnob]

I'll try to keep this brief and not ramble too much.

EE by day and over the past couple of years, I started my own business as a side gig. Initially purchased Altium to get layout and design jobs and recouped that cost fairly quickly. Now I'm setting new goals for myself and trying to take it to the next level. Which for me, is more design work and more specifically, in the RF world.

Been purchasing ebay items and hustling as much as I can to save on money for these purchases. Recently got a sweet deal on a R&S scope by talking with a local dealer and now I'm in the process of getting a VNA to complete my lab.

Already bought the TTR506 VNA (6GHz) from Tektronix. To save money, I bought a refurbished one and the sales rep added on a slight discount. It should ship shortly. However, on ebay, I just saw an HP 8720B VNA (20GHz). Messaged the seller as he's local and offered him cash at a $2k discount than his asking price. He accepted. Price is about half of what I payed for the TTR506.

Reasoning for VNA: Have some RF side gig opportunities for RF board in the 8-10GHz range. HP VNA opens the door to these jobs. Similar job opportunities for Tek VNA, just much lower frequencies. Planning on also attempting to sell some items on my site. Both VNAs will allow for that (i.e. tools for the job), just limits the frequency range of said items.

Tek is new, warranted, offers some better specs

HP is old, end of life risk (it breaking), offers BW opportunities/a tool to grow into, and is half the cost.

What are your opinions? Like I said, I already bought the Tek VNA so that money is more or less spent mentally. But saving half the cost and taking that money to feed into some projects that I want to attempt to design, package, and sell is inciting.

This is all out of pocket expenses. Basically the jobs I do, I save that cash and reinvest in equipment to grow. 

[DaJMasta]

Tough to say, I think the USB VNA is a much better instrument overall, smaller, simpler, more powerful software, more reliable, faster.... but having the other is nice.  Do you see yourself working in that 6-10GHz band much?  The higher bandwidth does open up some nice potential options, but in addition to the cost of the bench space, the reliability concerns, and the initial cost of the analyzer, you're going to need a full new set of RF plumbing and SOLT calibration kit to really get proper use out of it, so the extra expense can be considerable.


Aside from wanting to have neat equipment and just amassing it (see TEA thread), I see two good reasons to keep the HP for use:
Designing parts above the Tek's 6GHz bandwidth (the obvious one)
Testing high bandwidth rated parts and accessories for potential resale

The extra cost of the cables and calibrators is a two way street, if you can use your new decked out high bandwidth VNA to verify parts for use in those bandwidths, there's probably a good margin available, since few people have equipment with that bandwidth in good nick to actually test them out properly.  You'd need a source (or just a big pile as a one off) of such RF goodies, but if you used your VNA to validate high frequency cables, cal kits, attenuators, filters, etc., you could probably justify keeping it around.  In the same token, you can use a really wide bandwidth VNA that has the proper accessories to validate anything else RF you're working with to a reasonable degree of certainty, which could potentially be useful.

[Cigarsnob]

Thanks for the feedback DaJMasta...Good points you listed and you're right about new RF plumbing. I didn't take that into consideration. At the moment, my SOLT that I bought for the Tek is rated to 13GHz, so I would keep that if I were to return the tek for the HP as that would cover me on my initial projects. I also bought some government own Gore cables on ebay. These two at least covers the basics/everyday needs.

Would I work in the 6-10GHz often? Yes and now. I have some potential customers that would need some boards in that range. And I would obviously seek out more customers needing such services. So I would say the demand now is low based on current customers. With that said, I believe in buying tools that you can grow into as your skills improve. I also have some RF projects in that band for optical purposes that I would like to design and sell. 

I like your idea of utilizing the bandwidth to test RF components for resale. I'm all about getting my hustle on and hadn't thought of that. I may have some contacts in which I can offer such a service to.

I did visit the VNA today. Physically, it looks good. Screen is nice and bright. Didn't bring any components to test, but the guy did have a cal kit. So I at least did a 2 port cal that made sense. I'll see if I can't bring some filters to quickly set up and test to better confirm.

[TheSteve]

If properly working you can't go wrong with the old HP gear - where else will you get a 20 GHz 2 port VNA for that kind of money with good performance?
And yes, never forget the cost of a good cal kit.

[Howardlong]

I agree, I love HP gear, but realistically nowadays I only use a VNA sporadically, for intensive periods of a few days during product R&D. It probably only gets turned on ten times a year, and maybe a total of ten hours of use.

While I have it out on the bench permanently, it does take up a lot of space. The UI is pretty good and easy to navigate considering its age, far better than fiddling around with a USB based device where you’ll inevitably spend an hour installing or upgrading the host software to the latest version for little or no benefit.

Nowadays, based on the relapatively low frequency of use and paucity of bench space, I’d probably be better off with a USB based instrument. But I do like knobs and buttons!

[virtualparticles]

I evaluated the Tek VNA. It's measurement accuracy is quite good but the measurement speed.... OMG. I got old just waiting for it. This is the slowest VNA on the market.