[TowerTalk] Measuring coax loss with MFJ-259B

[jeremy-ca]

I got so disgusted with the uselessness of my 259B that I dumped it on Ebay.
Back to the old faithful Birds with my son in the shack driving a cable with 
an exact 10W on 440 MHz when I signal him. The Birds are as close to a 
perfect match as I could get and I can refer to the recorded as installed 
loss for any cable. With cable runs up to 450' I like to keep an eye on 
losses.

Carl
KM1H


----- Original Message ----- 
From: "Pete Smith" <n4zr at contesting.com>
To: "TowerTalk" <towertalk at contesting.com>
Sent: Friday, October 05, 2007 5:43 PM
Subject: [TowerTalk] Measuring coax loss with MFJ-259B


>I recently replaced my two main 190-foot feedlines to the tower with
> LDF4-50A hardline.  On the shack end, there is about 50 feet of fairly old
> RG-213 (12 years or so).  Today I used my 259B to measure the combined 
> loss
> at 30 MHz, with the far end open-circuited.  I got 1.3 dB on one cable and
> 1.4 on the other, which correlates very nicely with the rated attenuation
> of the cables.  However, there was one strange thing - strange to me,
> anyway.  with the 259B in coax loss mode, I found that relatively small
> frequency excursions would cause a relatively large change in the reported
> loss - going, for example, from 1.3 dB at 30 MHz to 1.6 at 29.6 MHz - and
> of course, if anything, you'd expect the attenuation to go down with
> decreasiong frequency.  The variation in reported loss is also cyclical as
> I tune further down.
>
> The manual for the 259B doesn't say anything about this sort of frequency
> sensitivity, but I remember that with my old Autek it was necessary to 
> tune
> for minimum R and then apply a formula to determine loss.  Is this just an
> omission in the MFJ manual, or something I don't understand, or maybe a
> problem with the unit itself?
>
> 73, Pete N4ZR
> The World HF Contest Station Database
> Full details on 3300 contest stations
> Updated 5/5/07 http://www.pvrc.org/WCSD/WCSDsearch.htm
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