So... assuming (as someone suggested) that an S-Unit is 3dB... can you hear
the difference between S9+40 and S9+41? S9 & S10? S7 & s8?
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Stan Stockton
Sent: Thursday, February 11, 2010 8:17 PM
To: Tower and HF antenna construction topics.
Subject: Re: [TowerTalk] Measuring Coax Loss
dB's.....They are really easy to get in the beginning and become VERY
difficult to get once you have about a dozen. They are also extremely
addictive. The more of them you have the more of them you want. At
some point in time you think about them constantly and buy lotto
tickets hoping to win so you can get (please give me!) just three more.
3 dB is very large regardless of how many you are starting with.
73...Stan, K5GO
Sent from Stan's IPhone
On Feb 11, 2010, at 6:34 PM, "Jim Brown" <jim@audiosystemsgroup.com>
wrote:
> On Thu, 11 Feb 2010 19:03:51 -0500, Mike Besemer \(WM4B\) wrote:
>
>> 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.
>
> Only by someone's definition, not in reality. If you actually
> MEASURE the
> response of the S-meters in REAL radios, you find that an S-unit may
> be close
> to 6dB near S9, but is usually closer to 3dB at S5 and below.
>
> As to a hill of beans -- many hams have long runs of coax to their
> antennas,
> so loss can be a BIG deal, not a hill of beans. The loss in dB of
> verious RG8
> style coaxes ranges by a factor of about 2:1 from the lowest to the
> highest.
> Over the past several years, I've been doing a lot of little things to
> improve my station. A dB here, a dB there, they all add up. Smart
> operators
> know that. The difference between a 3-el yagi and a 4-el yagi of
> comparable
> design is only 1-2 dB, and often double the cost. That doesn't stop
> a lot of
> guys who have the space from putting up 4-el yagis!
>
> Somehow, the scientific method seems to be lost on some of those
> commenting
> on my post. How do you know that the MFJ (or any piece of test gear)
> is
> accurate if you don't compare it to another measurement or test
> method of
> known accuracy? I'll bet a six pack of your favorite 807s that if I
> had
> posted loss measuerements made ONLY with an MFJ, someone would have
> pooh-
> poohed them because I didn't use equipment traceable to a
> calibration lab.
>
>> Forgot to mention... unless I actually SAW the 10' piece being cut
>> off the
>> longer roll I was considering buying from, I wouldn't trust the
>> measurements
>> anyway.
>
> Did it ever occur to you that sometimes ham stores, even the best
> known, with
> the biggest ads in QST, may not have good data on what they're
> selling? I
> don't trust some of them any more than an anonymous vendor in a flea
> market.
> But there ARE some good deals out there, IF you have an open mind
> and know
> how to evaluate them. The point of my post was to show that you CAN
> get
> decent data from an MFJ259B that has been calibrated if you're
> measuring a
> sample that is long enough.
>
> How many measurements of coax loas have you actually made? How did
> you do it?
> How did you know that you had good data? At some point, you've got
> to know
> exactly how long that piece of coax is. RG8 is big and heavy, so
> unspooling
> enough of it to get a good measurement isn't always easy. You've got
> to deal
> with the length of cable sample you can get.
>
> 73,
>
> Jim K9YC
>
>
> _______________________________________________
>
>
>
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