Two further questions if I may.

1)  Does it harm the receiver or transmitter if I power it on and have not screwed in any antennas.
Will it overheat etc.?
 
2)  My goggles have a mushroom antenna and a panel antenna, if I cover the mushroom antenna with a large chunk of tin foil to temporarily negate its power, will the unit be harmed?
I am trying to gauge the effectiveness of the panel antenna.

Thanks

Yes! A VTx powered on without an antenna will burn up quickly!

As far as I know you should be ok to "shield" your mushroom (also refered to as "circularly polarized") antenna for your testing

You should definitely not power your video transmitter on without antenna but AFAIK there's no such problem on the receiver side so you could just remove the mushroom antenna to test the patch.

Check the manual for your goggles. With diversity receiver which uses 2 antennae, you may have the option of switching between the 2. I know on my Aomway, I have the option of setting it as 1, 2 or auto (which automatically selects which one is more appropriate for the location of the quad)

You should never power up any radio transmitter, be it a 5.8GHz FPV transmitter or a 2.4GHz RC control transmitter, without an antenna or a dummy load attached.

If there is no antenna, all the power that the output stage of the transmitter is generating gets reflected back from the open end of the transmission line into the output circuitry. Unless there have been specific steps taken in the design to deal with the reflected signal, it will damage the output transistor.

If you power up a receiver without an antenna, it simply does not receive a signal.

However, one word of warning. Both the inputs and outputs of microwave transmitters and receivers are extremely sensitive to static electricity. For this reason, you should keep the antenna attached as much as possible. If an antenna has exposed metal elements, you should avoid touching them as much as possible.