Although APC-7 connectors from China are now available, they still aren't
cheap. One connector from China costs about as much as the entire NanoVNA;
the US-made ones from Amphenol are double that. And you need two of them
for each NanoVNA, not to mention the connecting cables.
On Sun, Aug 16, 2020 at 10:28 AM biastee via groups.io <biastee=
[email protected]> wrote:
Two opposite camps have emerged in the connector debate. I suspect the
preference for either N or SMA is dictated by the application. The 1st camp
consists of those whose primary application is evaluating HF/VHF aerials
and so they chose N connector because it is more congruent with the thick
coax, e.g. RG-213, which they use to minimize loss. On the other hand, the
2nd camp comprises those who evaluate RF circuits - of course, they will
vote for SMA because of the near universal adoption of edge-mounted SMA
females in evaluation boards (one example:
).
In contrast, the N connector cannot be mounted on either 0.8mm or 1.5mm
thick PCB without some form of mechanical backing. Moreover, the size of an
N connector relative the PCB is akin to the proverbial tail wagging the
dog.
I am somewhat surprised and even dismayed that nobody has agitated for the
APC7 which I believe is the default connector on HP/Agilent/Keysight's sub
6 GHz VNAs. For those unfamiliar with VNAs, calibration is typically NOT
done using APC7 standards but with either N or 3.5 mm standards via
adapters. In VNA applications, this sex-less APC7 has two technical
advantages over either N or SMA:
1. Ordinarily, the THRU calibration results in one reference plane at a
male connector and the second reference plane at a female connector. So a
two port DUT will require the odd combination of one male connector and a
female one. Using APC-7 phase matched adapter, the "Swap equal adapters"
method enables a two port device with all female connectors to be
measured.
2. APC7 has lower reflection coefficient than either N or SMA in the sub 6
GHz range. Eg. APC-7 to SMA (m) adapter has a worse case SWR of 1.06. In
comparison, a N (m) to SMA (m) adapter has a worse case SWR of 1.25.
APC7's biggest setback is cost. However, China made APC7s are now
available. :-) Technical merits aside, by adopting APC7, Hugen / Gabriel
can demonstrate their impartiality and that they not siding with either N
or SMA camp.
Shirley Dulcey KE1L