[TowerTalk] Coax loss. Has anybody measured it ?

[Jim Thomson]

Has anybody actually measured the loss on their coax from back of amp to top of tower,  for various freqs if a multiband yagi used..... or what ever band your monobander is?     I mean using accurate watt meters at both ends?   That above data could then be compared to the online loss calculators..like the times microwave one  in the below url...... or your favourite method of measuring coax losses. 
http://www.timesmicrowave.com/calculator/?productId=139&frequency=10&runLength=90&mode=calculate#form

The only time I have seen this done was back in the 80s.   A buddy ran 1kw into the long run of 213U coax, 300 feet.... and measured a lousy 350 watts at the top of his 100ft tower.... on 28.6 mhz. Flat swr on his 10m
yagi. 

K9YC sez the losses on HF are all copper dc resistance losses..and nothing to do with the dielectric etc.   I see you can get  Andrew .5 inch heliax that consist of a Cu clad  solid AL wire for the center conductor.   You can also buy .5 inch  heliax  (think it was cablewave)... that consist of a solid cu center conductor.  Andrew  .875 heliax consist of a hollow  .375 OD cu tube for the center conductor. 

What baffles me is that 213 U per times calculator is 1.1 db per 100 feet...at  29 mhz, yet  RG-393 is 1.1 db per hundred ft.    213 has a single copper braid.  393 has TWO silver plated braids.  213 has a 12 ga  CU stranded center conductor.  393 has a silver stranded  center conductor.   VF on 213 is .66    VF on 393 is .69  

I highly suspect if folks actually measured the power at the top of the tower, vs the back of amp..... they would be in for a rude awakening......esp on long runs...and on upper bands like 20-10m.  I might be wrong here, but it would prove to be an interesting exercise.  I mean the difference between a 5-6 el  yagi and a 3 el yagi is typ  2 to 2.5 db.   If you are losing 1-3 db in the coax, that’s a bunch, compared to the gain of the yagi itself. 

Jim  VE7RF