On 12/30/2015 6:48 AM, Roger Hayter wrote:
gareth wrote:

What is interesting is the simplicity of the approach (ignoring the hidden
cost of the ubiquitous PC), but it ignores the multiple harmonics that
come out of DDS chips.

Up to about 600MHz I think the DDSen are pure enough, but above that the
VNWA deliberately uses mixer products of some kind. As to how, without
losing all accuracy, I afraid is beyond my understanding. And down to
the genius of the inventor.



So, if you were to working at, say, 3MHz, how would youknow that you were
not actually analysing responses at 6, 9, 12, 15, etc MHz?

The multiple spurious products around are many more than simply
harmonics. But in some way the phase of the desired product is
tracked(?).




http://sdr-kits.net/DG8SAQ/VNWA/Baier_VNWA2_QEX.pdf

But it does raise one question, and that is, who is fooling who about
its purchase price of ooo £450, for there cannot be more than about £40
in its component costs?

That is simply not true. In small quantities they would cost a great
deal more than 450GBP, and the VNWA is not produced in very large
quantities. Consider the costs of quite a complicated PCB in relatively
small quantities, the USB chip is quite expensive to pay for so-called
intellectual property, and requires individual licensing. The DDSs are
not cheap, neither is the hardware.

I think the price is a bit high for a PCB, but 450GBP is for a tested
unit in the "presention case". The driver is not just the parts cost at
low volume, as that only goes up some. I estimate total parts cost of ~
$100. The problem is just as much the labor involved in turning the
parts into a final product. This type of assembly is done on machines
and at low volume the set up costs become a significant portion of the
total costs. Then adding profit easily brings this up to 450GBP.

I don't know how many of these units have been sold, but the Yahoo group
has 2830 members. If only half the owners are members that is still
less than 6000 units. Spread over a few years that is only 150 a month
or so. Not really high volume, but a nice workable volume.

--

Rick