[TowerTalk] Measuring Coax Loss

Thu Feb 11 17:13:16 PST 2010

Think what you want, Dan... I stand by my argument that 99% of the time 3dB
is inaudible.

I love the sanctimonious attitude on this list.  If somebody disagrees,
they're automatically unqualified or stupid.  

That's why I left last time.

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Dan Schaaf
Sent: Thursday, February 11, 2010 8:07 PM
To: Tower and HF antenna construction topics.
Subject: Re: [TowerTalk] Measuring Coax Loss

A really serious DXer is concerned about these losses.
Someone who casually operates may not care too much.
The  point is that all losses add up.
I CAN hear the difference.
For example.  +/- 3 db is either 1/2 or 2 x the power whether transmitted or

received. I can clearly hear the difference in a weak signal if  itdrops3 db

or raises 3 db.
I think that you are just repeating something that you heard and have not 
actually experienced these differences on the  air.

Best Regards
Dan Schaaf
K3ZXL   www.k3zxl.com   "In the Beginning, there was Spark Gap"
===============================
NOBSKA
www.nobska.net
===============================
Cape Cod Instruments
www.oceanbiz.net
===============================
----- Original Message ----- 
From: "Mike Besemer (WM4B)" <mwbesemer at cox.net>
To: "'Tower and HF antenna construction topics.'" <towertalk at contesting.com>
Sent: Thursday, February 11, 2010 8:01 PM
Subject: Re: [TowerTalk] Measuring Coax Loss

>I qualified my comments to exclude microwave/weak signal work.
>
> If you have that many connectors in-line, how concerned are you REALLY 
> about
> loss?
>
> C'mon guys... for HF and probably VHF, it isn't that critical.
>
> WM4B
>
> -----Original Message-----
> From: towertalk-bounces at contesting.com
> [mailto:towertalk-bounces at contesting.com] On Behalf Of Dan Schaaf
> Sent: Thursday, February 11, 2010 7:45 PM
> To: Tower and HF antenna construction topics.
> Subject: Re: [TowerTalk] Measuring Coax Loss
>
> Having been a calibration Engineer in my early days, I concur with Jim.
> In addition, each coax connector inline introduces losses. They all add 
> up.
> Definitely worse in VHF/UHF. Some folks say you can't hear the difference,
> but when you are trying to hear and work a weak signal in/above the noise,
> every db counts.
>
> Dan Schaaf
> K3ZXL
> "In the Beginning there was Spark Gap"
> www.k3zxl.com
> ----- Original Message ----- 
> From: "Jim Brown" <jim at audiosystemsgroup.com>
> To: "Tower and HF antenna construction topics." <towertalk at contesting.com>
> Sent: Thursday, February 11, 2010 7:34 PM
> Subject: Re: [TowerTalk] Measuring Coax Loss
>
>
>> 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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>
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