Mike, a couple ideas. Some Ethernet cards can be configured to be manually set for speed and duplex (full or half) or it can be set for auto-negotiation. Chances are, it is set for auto-negotiation and is usually the best setting for most occasions. As a test, you might try setting the Ethernet (if possible) to 100 Megabit and Full Duplex on your PC. The radio will no longer need to try to negotiate the link speed and the link may then "just become reliable".
The reason that you are not having the problem when connected to the switch, each port on the switch is doing its own negotiation with each device. It works out any differences between the connected devices internally.
another adapter setting, a good while back, was to turn off "green ethernet"...not sure why I don't see that any more
73, w5xz, dan
Best possible solution. Do not use direct connection. But rather connect your radio thru a router so that it always gets a routable IP address. This should solve your problem.
When I was yielding to my desire to purchase a 6300 at Dayton, I spent a few minutes talking to Tim about how the radio would be integrated into my household network. As it turns out, the gigabit portion of the network is located adjacent to my shack, so a wired connection to the radio was no problem. The computer already had a wired GB connection. I use a D-Link GB switch which acts as a hub for the GB network. The router is a venerable Linksys WRT54G, which is not a GB rated device, but neither is the "broadband" connection to the outside world. The router provides all DHCP services. Modern router/switches are all GB, so my configuration is unusual these days.
Tim enthusiastically agreed that I should simply "plug the radio into the switch". There would be no bandwidth problems. That's what I did and I've never noticed any. If any problems appeared, I would start by assuming a defective switch, noisy wires, etc. This is common off the shelf tech.
Yes, you can configure Windows or IOS or Linux to supply DHCP and run a two node network without a switch, but why press your luck? These systems all expect to be connected to a high speed router/switch network that provides these services. They are bound to be more stable in this client configuration rather than the DHCP server configuration.
Certainly, it makes sense to spend some time looking at the NIC configurations, but I would expect most out of the box configurations to be pretty good. Might not be quite so good in Linux systems, as they are intended to be closely configured by pro Admins.