said by warwick:I presume this upper limit has much to do with the actual length of wavelength itself?
Correct.
If you still want to use heliax in the future for the 5.8 GHz, the 5/8" foam LDF4.5-50 looks like it would work good for you. The attenuation is 4.765 dB/100 ft. per the Andrews spec sheet. The list price is ~$6 per foot...trade pricing less.
