Roger roger...50 ohm coax. Some co-phase harnesses actually use 75 ohm coax for the y-splitter.

got her working now! thank goodness!!

If I can find a jumper, I will experiment this afternoon. How much dB loss does this cause?

It's not so much the loss, Matt, as the "foldback" it causes in your transmitter. Most modern rigs detect mismatch and reduce output power accordingly. Most impedance mismatches (particularly when purely "resistive") cause their loss in two ways then:

1) Reflected power is wasted, disappated in the final of your rig.
2) The reflected power is used by the rig to determine final drive and most rigs reduce final drive in direct proportion to detected reflective power.

Even a 3:1 SWR actually represents rather small power loss in terms of how much is wasted in reflection -- but the rig will see it and to "save the finals" will reduce the drive.

Does it cause any measurable loss on RX?

Not so much. I remember a discussion about this and that was supposed to be one of the weird things: it was hard to measure the receiving loss. It should because some of the power from the antenna on receive is reflecting back from the receiver -- but I really can't say how much. Almost all discussions I've seen focus on transmit.

If you read that article I linked, you see that in some cases a transmission line might IMPROVE the match by being deliberately cut off-length. Often, when we mount antenna's close to reflective surfaces (like cabs in our truck) we make the antenna "reactive". It's actually possible to cut the feedline to make it reactive in the opposite direction (like, if the antenna has capacitive reactance, make the feedline inductively reactive) to acheive a better match.