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Re: [TowerTalk] [Bulk] Coax loss. Has anybody measured it ?

To: Jim Thomson <jim.thom@telus.net>, towertalk@contesting.com
Subject: Re: [TowerTalk] [Bulk] Coax loss. Has anybody measured it ?
From: Grant Saviers <grants2@pacbell.net>
Date: Mon, 24 Nov 2014 09:55:02 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
I've measured losses on many lengths, primarily to see if they aged, using the same Bird wattmeter at both ends into a dummy load. Conclusions: losses as predicted by the manufacturers and little change with age upwards of 20 years in some cases, all Belden or MIL-SPEC surplus in RG8/213/214 and some new RG8X LL. While the old stuff is old, it didn't have heavy sun exposure of more than 8 years or so. These are now Field Day etc. cables. It's all LDF4 and LDF5 from now on to and up my new tower. LDF4 for 80 & 40 and LDF5 for 20 > 10, with 7/16 DINs and Buryflex from the shack bulkhead to the rigs. The goal (met it) is less than 1.0db loss in the coax for each antenna/stack from amp out to driven element feed point.

Grant KZ1W


On 11/24/2014 7:56 AM, Jim Thomson wrote:
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
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