On 7/20/22 10:12 AM, W0LEV wrote:
SMA connectors are for good two reasons: 1) Small size and 2)
Frequency response.
SMA connectors are bad for one reasonable consideration: Limited service
lifetime for mates/demates.
500 mate/demate cycles is typical spec sheet number, but I'd say that there are plenty of SMAs that have seen a lot more cycles and are just fine, as long as they're not bent or damaged.
There's a paper out there by some folks at Maury Microwave, where they mated/demated an SMA thousands of times with the intent of understanding the degradation in repeatability.
The reason a spec sheet calls out a number like 50 or 500 cycles is because that's a "testing" number that is bigger than the customer is likely to use, but which is small enough that the price is reasonable.
Typically it would derived from some MIL-STD and is basically a statement that the connector will meet the requirements after that many cycles.
Another thing to watch out for is a loss or mismatch spec. Most connectors do NOT have anywhere near the loss in the data sheet, it's more driven by the lowest number that is practical to measure in a manufacturing environment.
So an SMA (Amphenol M39012) at 1 GHz is 0.06 dB max loss - that's pretty close to the minimum measurable loss at 1GHz without going to a lot of trouble.
Likewise, the mismatch (VSWR) is given as 1.05 to 1.20 plus some frequency dependent factor. It would be hard to measure a VSWR of 1.01 (46 dB RL), even if that is what the connector usually is.
Banana jacks/plugs work fine at HF but not at or above 50 MHz. BNCs and
Type-N connectors are appropriate at and above 50 MHz. Top "careless" use
of BNCs is around 1 GHz. From there on upward in frequency, either SMA or
Type-N connectors should be used.
Well, I'd say that banana jacks and similar single pin connectors are something that you need be aware of the non-ideal nature. Fortunately, with a NanoVNA, one can actually measure that non-ideal.
If you must, SO-239 / PL-259 connectors are *only* for HF use. Their
impedance is NOT controlled as are the other referenced RF connectors.
True, the UHF connector isn't constant impedance, however, if you have a set of calibration standards in UHF, then that is managed in the calibration.
