Gained some....power/knowledge

Rerouted the coax lines. The PL259 in front is a
spare coax to the garage. 

Approx 2 years ago I wrote something about coax loss. I just discovered I had some coax routed the wrong way (read previous post). So, time to measure the actual loss in my coax to the tower and reroute the coax. Basically I use 2 coax lines to the tower, at the tower I got some lightning protection devices and a good quality coaxrelay which I can control remote from the shack. One coax line is made from 3 lengths of H2007 (similair to Aircell7) the other one is made from 2 lengths of H2007 and 1 large length of LMR400. Of course the line with LMR400 has less loss and therefore I use this exclusively for the highest frequencies I transmit on, at least I thought so....but after the reroute I do. But how much power have I gained by this action? And how much stronger will you see you meter swing when you hear me on air? Read and shiver...










Before I changed the cables I took the opportunity to measure the loss in the lines on 70MHz, 50MHz and 28MHz, the highest frequencies I'm using.

Loss in line 1: approx 35m H2007 coax

28MHz - 1,4dB
50Mhz - 2 dB
70Mhz - 2,5dB

Loss in line 2: approx 30m LMR400 + 5m H2007

28MHz - 1 dB
50MHz - 1,4dB
70MHz - 1,6dB




I use this site; http://www.sengpielaudio.com/calculator-amplification.htm for calculations.

I had the 10m LFA beam connected to line 1 which had a loss of 1,4dB. 100W in gave me 85W at the junction cabinet below the tower. Estimated loss in the coax from the cabinet to the beam including the 0,1dB loss from the lightning protection and coaxrelay is a additional 0,5dB. So in the end only 80W is arriving at the antenna.

Now I connected the HF vertical to line 1 and moved line 2 from the vertical to the 10m LFA beam. 1dB loss calculated 100W in gave me 89W at the junction cabinet. With a additional 0,5dB loss to the antenna I have 84W at the antenna.

Yes, by switching the cables I have 4W more power at the antenna. Will anyone notice??
I could have told you that before I did this experiment, but just to show that it doesn't matter much what coax you use on HF. I wrote about that before

On the other hand. Line 1 would be almost cut my power in half on 70Mhz! Coax is a whole different story on VHF. I have the 50MHz/70MHz yagi connected to line 2. Based on earlier measurements and calculations the coax from junction box to the antenna including loss from lightning protector and antennarelay for VHF will be 0,7dB.

50MHz total loss over coax 2,1dB. 100W in will give 78W at the antenna.
70MHz total loss over coax 2,3dB. 50W in will give 38W at the antenna.
(Why not 100W at 70MHz? We are only allowed 50W at that frequency...)

Well you see that the worst effect is on 70MHz. But would a coax upgrade make a huge difference?

Very expensive coax cable like M&P hyperflex13 or Ecoflex15 have a loss of about 0,6dB for 30m length. Even more expensive would be hardline like cellflex have 0,2dB loss for a cheap one and 0,15dB loss for a expensive one. (all on 50MHz). Would it be worth the expense to invest in such cables?

Let's asume I change the entire cable from shack to antenna for Ecoflex15. It is about 40m of coax and leave the relay and lighning protectors outside this. Loss would be 0,7dB in total including the connectors (N-type). 100W in will give 92W at the antenna. I think you will hardly notice the difference between 78W and 92W. But you will notice that your wallet is empty! (it would cost me €300 including quality connectors!)

Overall I won't change my coax. It is still good enough for me. If I want to gain something I better invest in a bigger antenna on 50MHz/70MHz. You can easily compensate your coax loss with a few extra directors on the beam and it could be cheaper as well.

Compensation for coax loss!!