Good day all,
Just ordered a SDRPlay and patiently waiting it's arrival. Having read through this thread I though I would post a couple of comments.
Someone said (an earlier post in this thread) that all SMA connectors are 50 ohm. That isn't so, there are also (at least) 75 ohm SMA connectors as there are 75 ohm BNC and Type N connectors. 75 ohm cables and connectors are far more common than many realize.
Someone mentioned the I.PX connectors. IPX connectors are also referred to as uFL or u.FL or IPEX. A search on eBay will find a number of sources of pigtails having just about another other type of connector on the other end. Some sellers will make up custom cables as well. I don't recall seeing an IPX to SO-239 however. Some GPS receivers which have external antennas will frequently have a connector on board which is an IPX.
The coax cable used with these small IPX connectors is typically RG178 and is much smaller than RG174/RG316. You will also find listings and references for these connectors using 1.13 (mm) size cable. I don't know if "fairy's" assemble these things but I manage with my big fat fingers but does require a delicate touch.
A couple of links that might be of interest to others:
https://www.adafruit.com/product/851
https://www.sparkfun.com/pages/RF_Conn_Guide.
I have a preference for F connectors in receive systems. Good quality cable is easily found and usually inexpensive. The screw on no crimp or cheap crimp on type connectors are really not that good (i.e. crap) but the use of properly installed quality compression connectors give you connections which are weather proof, robust and good for several GHz. 75 ohm cable actually has a slight advantage to 50 ohm cable in receive only service - 75 ohm cable is better (less loss) voltage wise than 50 ohm which is better (less loss) for power. Do a search for something like "why 50 ohm" or "50 ohm vs 75 ohm" .
As for SMA connectors, they are a good all round choice and good quality versions of SMA connectors are usable well into the 10's of GHz range. The inexpensive ones commonly available from Asia on eBay are OK but probably only good up to a few GHz's. Oh, and don't get the RP vs non RP mixed up, they are not the same thing. SMA-RP have the pins swapped around - the socket has the pin and the screw on plug has the hole.
BNC connectors as with SMA connectors are available in a wide range of quality or precision. Inexpensive ones will be good up to a GHz or so and the higher quality (i.e. more expensive brand names like Pasternak) can be had for ranges up to several 10's of GHz.
At the end of the day, whether the input socket is 75 ohm with a short piece of 50 ohm cable to 75 ohm or 50 ohm connector, the typical user will likely never notice any difference. As someone already stated, the input impedance to this SDRPlay will not be one or the other over it's full range of operation - could be higher, could be lower or somewhere in between.
I am glad to see that the SDRPlay v2 still have the IPX socket on board and short pigtail to the connector on the case. SMA connectors are OK but mine will have it changed out for a F connector before too long. The flexibility of the design to allow this in such an easy fashion is plus in favour of the SDRPLay.
cheers, Graham ve3gtc