Jim and the group,
I may have improperly used my power ratio to decibels calculator. :)
With exactly 10 W going into the cables, I measured
8 W out (RG-11); 7.2 W (RG-213); and 7 W (RG-6) at 30 MHz.
Upon reflection (pun intended), my 2.8 dB figure can't be correct...
Thanks,
Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from www.stealthamateur.com
and on the Amazon Kindle (soon)
On Sunday, November 29, 2020, 11:59:15 AM CST, Jim Thomson
<jim.thom@telus.net> wrote:
Date: Sat, 28 Nov 2020 11:43:28 +0000 (UTC)
From: Kirk Kleinschmidt <sohosources@yahoo.com>
To: Towertalk Reflector <towertalk@contesting.com>
Subject: [TowerTalk] Understanding Coax Loss Measurements
<Method 2: RF Power meter and TX. Calibrate: Connect TX output to RF power
meter, then through the test length of coaxial cable, then to dummy load.
Carefully set TX output to to 10 W. Swap test cable and power meter, so TX
output now goes to test <length of cable, then to power meter, then to dummy
load. Record power levels of between 7 and 9.1 W with TX power set to same
level as "calibration " run, but with meter now placed after test cable length.
<Testing 100-foot lengths of RG-6, RG-11 and RG-213.
<With the power meter, loss values are RG-6, 3 dB; RG-11, 1.9 dB; RG-213, 2.8 dB
<As you can see, these methods don't line up well.
<Help?
<--Kirk, NT0Z
## How did you manage to arrive at a whopping 2.8 db loss , at 30 mhz,
with 100 feet of RG-213 U ?
The bird wattmeter method at each end of the coax has worked flawlessly for
years. DL at far end of feedline, or ant with 1:1 swr.
## Try it again, but use exactly 100 watts at the near end. You should
measure aprx 77 watts at the far end... at 30 mhz.
Jim VE7RF
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