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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