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@contesting.com>
To: "TowerTalk" <towertalk@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
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|