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Re: [TowerTalk] Measuring Coax Loss

To: "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] Measuring Coax Loss
From: jimlux <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Thu, 11 Feb 2010 21:30:47 -0800
List-post: <">>
Mike Besemer (WM4B) wrote:
>> -----Original Message-----
>> From: [mailto:towertalk-
>>] On Behalf Of Jim Brown
>> Sent: Thursday, February 11, 2010 6:49 PM
>> To: Tower and HF antenna construction topics.
>> Subject: Re: [TowerTalk] Measuring Coax Loss
>> Todd asked:
>>> Tell me again how I can productively use the more precise information
>> [0.6
>>> versus 0.62 dB loss in 208 feet at 3 MHz.] in constructing my antenna
>> feed
>>> line system.
>> That's my point. If you're measuring a long piece of cable at a
>> hamfest, the
>> MFJ is plenty good enough. If you're measuring a 10 ft piece of cable
>> but
>> want to know how it would work on a very long run, especially at low
>> frequencies, you need the greater precision of the HP setup.
>> 73,
>> Jim K9YC
> Still... a dB or so (or even 3) on a long run of coax isn't going to make a
> hill of beans difference for most applications... an S-Unit is ~ 6dB.  For
> microwave and weak signal... sure, but you probably shouldn't be buying your
> coax at a hamfest if that's what your interests and concerns are. 
> Mike
> WM4B

True, one needs to look at your overall goals.

3dB is the difference between 500 and 1000W..but for skywave paths, 
typically, you've either got propagation or you don't. If you do, 10W 
will work, if you don't nothing helps.

But those extra 1dB bumps make the band open slightly earlier and close 
slightly later, when you're on the transition between closed and open. 
For some folks, that's important.

Not for me,  but, on the other hand, I do precision measurements of RF 
things at work, so the topic is generically interesting.. The QuikScat 
satellite which measured ocean winds for more than 10 years until it 
recently died did so by measuring the difference in the 13.4GHz radar 
signal reflected from the ocean's surface to an accuracy of better than 
0.1dB.  A change of a few dB corresponds to a wind speed change of tens 
of m/sec.

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