[TowerTalk] Understanding Coax Loss Measurements DAVIS RF Re: TowerTalk Digest, Vol 215, Issue 36

[Steve Davis | Davis RF]

Hi Kirk,

I could perhaps shed more light on this but I need to know
what freqcy are you using to test, and what is your VSWR.

Jim mentions 30 MHz, and he is correct as to what the avg. loss ( 1.0 dB )is with various quality 213 cables @ 30 MHz, but I didn't see where you mention testing at that freqcy. So my question is where would you like to test it, what freqcy?

However, at the freq. range of HF for 213, the loss curve is linear, 1 - 30 MHz for good quality cables.

Lets start with those questions and I can shed some light
on the matter.

Regards, Steve  K1PEK   DAVIS RF Co.  (and DavisRope LLC, a separate entity for all kinds/sizes of rope, Made in USA... DavisRopeAndCable.com   ( the "cable" of this co. is metallic cable, not RF cable. for RF items, see DAVISRF.com  )

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Sent: Monday, November 30, 2020 12:00 PM
To: towertalk at contesting.com <towertalk at contesting.com>
Subject: TowerTalk Digest, Vol 215, Issue 36

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Message: 1
Date: Sun, 29 Nov 2020 09:58:52 -0800
From: "Jim Thomson" <jim.thom at telus.net>
To: "kj6y--- via TowerTalk" <towertalk at contesting.com>
Subject: [TowerTalk] Understanding Coax Loss Measurements
Message-ID: <887BA95DE5C849978032714E2E54CD0D at DESKTOPSV54DBH>
Content-Type: text/plain;       charset="iso-8859-1"

Date: Sat, 28 Nov 2020 11:43:28 +0000 (UTC)
From: Kirk Kleinschmidt <sohosources at yahoo.com>
To: Towertalk Reflector <towertalk at 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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End of TowerTalk Digest, Vol 215, Issue 36
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