The bits to make up the adapter between the the SDR dongle and the external antennas here were all in place by Friday evening, so I did a hasty bit of construction on Saturday morning. Tested the adapter and it was fine. Unfortunately though, hooking up the SDR to the external antenna revealed very little activity. I have a feeling that in some of my tests, transmitting physically close to the dongle, I've blown the front end up! Ooops!
However, great to hear from David G4ASR who has been getting on really well with his. He hooked the SDR up during yesterday's excellent Es opening on 70MHz and was hearing a number of stations including an Estonian on FM. It's working well on 144MHz too and Dave was getting good results from the GB3VHF beacon. Sean, G4UCJ was also doing well with his and receiving stations on 70MHz - including the wideband FM which was very strong yesterday. Dave reckoned that his dongle was about 7KHz off 'calibration' on 70MHz. I found mine was about 20KHz off at 145MHz. You can cope with this using the 'shift' feature in SDRSharp.
Given that it's only £11, I've ordered another dongle and hopefully that will behave better if I don't transmit close by!