[time-nuts] VNA design

Don Latham djl at montana.com
Mon Jun 2 17:49:58 UTC 2014


Those interested might look at RedPitaya.com for a new piece of hardware that
might be used. Less than $500 without a "box"
Don

Dr. David Kirkby
> On 2 Jun 2014 15:50, "Attila Kinali" <attila at kinali.ch> wrote:
>>
>> I recently got introduced into the usefullness of a VNA. But these
>> things are horribly expensive for home use, even if bought from ebay
>> (before you say anything, remember i live in europe, where every
>> boat anchor hast to travel a long way). But given that most of the
>> designs that are on ebay are from the 80s and early 90s, i thought that
>> with todays ICs it should be easy to come up with a design that does
>> the same thing but can be build on a kitchen table.
>
> There are a few designs around.  The early version of the VNWA was
> described in QEX. There is the N2PK design too. The latter has a limited
> frequency range, but a high dynamic range.
>
> All modern professional systems with two ports use 4 receivers.  Earlier
> designs use 3 receivers which is not good for TRL calibration.
>
> I think it would be a huge task. I think that the main issue would be the
> software.
> I have been considering adding the "unknown thru" calibration method to my
> HP 8720D. That in itself would be quite a task, but writing all the
> software for a VNA would be a huge task.
>
> I thought TAPR had a similar project but I don't recall it producing
> anything close to workable.
>
> BTW the software options for the HP 8753's are now easily available,  so if
> you do buy an 8753 (probably the best choice), don't worry about what
> software options it has.
>
> I would really like to see an open hardware and software VNA,  but it would
> be a lot of work.
>
> If you do it, think about having 3 or 4 ports with independent sources for
> optimal balanced measurements.
>
> I don't think that there's much point producing a design with just a TR
> test set.
>
> Dave.
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-- 
"The power of accurate observation is commonly called cynicism by those who
have not got it."
 -George Bernard Shaw

Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
Huson, MT, 59846
mail:  POBox 404
Frenchtown MT 59834-0404
VOX 406-626-4304
Skype: buffler2
www.lightningforensics.com
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