Good observations, Dennis.
The FR4 is 0.8mm, so there's a little standoff with the SMA launcher. No 0.8mm SMA launchers I know of.
The PCB perimeter gap you see is 0.050", not 0.100". Now since the SMA launcher is grounded at all 4 points the net 'inductance' increase derives from 0.0125" ....which is too small for significant phase effects at 1.050 Ghz.
I built another 'experimental' SMA unit. But I couldn't get the performance as good as the first. I got +/- 0.07dB over the range vs +/- 0.05dB. I fab the boards (PCB trace etch tolerance) and then there's component & connector tolerances and soldering thickness variations (which affects inductance a little).
What I am seeing is a little bit of VSWR 'ripple' across the span, equivalent to around one complete sine wave; (+/- .02dB worth.)
But I suppose I am splitting hairs as there's always a bit of performance difference between parts.
The positive outcome though is I reduced the component count by one using PCB capacitance parasitics to do the 'tuning' and got a bit more ground plane % coverage out of it as well as a more solid mechanical assembly.
I'll build one more SMA unit to nail down the dimensions of the parasitic cap, but it's around 0.25pF based on the permittivity of the 0.8mm FR4.
I'll put up the extra SMA units on Ebay, as tuned units. There doesn't seem to be any fundamental performance gains in using the SMA vs the BNC at 1Ghz. There is miniaturization and better build convenience by not converting the BNC connector into a launcher.
As it stands the stock PCB design can use both the BNC launcher mod. and the stock SMA Launcher with no alterations or 'nibbling' etc. Similarly, the latest compact enclosure accommodates both varieties.
I'm taking pics as I go along to do the build blog for the DIY page.
Ancel
