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Re: Topband: cutting coax stubs for 80 meter 4-square

To: topband@contesting.com
Subject: Re: Topband: cutting coax stubs for 80 meter 4-square
From: terry burge <ki7m@comcast.net>
Reply-to: terry burge <ki7m@comcast.net>
Date: Sat, 9 Jun 2018 22:42:18 -0700 (PDT)
List-post: <mailto:topband@contesting.com>
Hi guys and gals,


Well, to make a long story short my Rig Experts AA-170 has quite working. Looks 
normal but a 56 ohm resistor at the end of the 75 ohm coax reads infinite. On 
the MFJ-259b it reads 56 ohms. Check SWR and the MFJ reads 7.499.2 Mhz 1.1:1 
SWR R=56/57 ohms X=0. Coax is 55' 4 3/8" long when I got very near 7500 KHz. 
With the shorted coax the MFJ-259b read 7.484.2 to 7.523 Mhz, 20.2 SWR, R=2 
ohms, X=0. Seems like the velocity factor is considerably higher than what was 
stated to me by DX Eng.. The velocity factor is some where around 0.84401... as 
best I can figure it. So I guess that makes it 0.84 VF FWIW.


Anyway, I have it figured that 55' 4 3/8" will do the trick for my 80 meter 
4-Square at 3.750 Mhz. 

But why my RE analyzer went out today I don't have any idea. Back to the MFJ!


Terry

KI7M


> On June 9, 2018 at 6:59 PM terry burge wrote:
> 
> 
>     Good point Wes. I will see if I can find a decent value of resistor. My 
> Rig Experts AA-170 was purchased because I did not trust the readings my 
> MFJ-259b was giving me while working on my hytower. Pretty penny for these 
> antenna analyzers. But I will bet if it won't do the stub frequency checks it 
> won't do the velocity factor and more. Did work pretty good for checking SWR 
> and feedpoint impedance on antennas like the hytower. Really liked it until 
> this.
> 
> 
>     Terry
> 
>     KI7M
> 
>         > > On June 9, 2018 at 5:11 PM Wes Stewart wrote:
> > 
> > 
> >         Since he said the coax was 75-ohm, a 75-ohm termination would be 
> > better.
> > 
> > 
> >         On 6/9/2018 5:07 PM, Richard (Rick) Karlquist wrote:
> >         > > As a sanity check, terminate the coax with a 50 ohm resistor 
> > and verify
> > 
> >             > > > that you have good coax. Flat line at 1:1 SWR, etc.
> > > 
> > >             Rick N6RK
> > > 
> > >             On 6/9/2018 4:57 PM, terry burge wrote:
> > >             > > > I don't know what is wrong here but I keep getting in 
> > > this situation where my
> > > 
> > >                 > > > > typing starts running back over my writing. I 
> > > will try again to reply.
> > > > 
> > > > 
> > > >                 Joel,
> > > > 
> > > >                 I have tried all that the manual says without success. 
> > > > All I see is the
> > > >                 horizontal solid and dashed lines of R and X. No 
> > > > indication of a resonance
> > > >                 point anywhere from 1880 KHz up to 10,500 KHz. Go 
> > > > figure? At least my
> > > >                 mfj-259b is working old as it may be. Rig Experts is 
> > > > going to get a nasty
> > > >                 note I think. Disappointing, huh?
> > > > 
> > > > 
> > > >                 Terry
> > > > 
> > > >                 KI7M
> > > >                 > > > > On June 9, 2018 at 2:54 PM Joel Harrison wrote:
> > > > 
> > > >                     > > > > > Hi Terry,
> > > > > 
> > > > >                     I replaced the 1/4 lines on my 80 meter 4 square 
> > > > > this past fall and used
> > > > >                     my AA-170 to set the length with no problem.
> > > > > 
> > > > >                     Just select "all" for the mode and set the freq 
> > > > > you're aiming for and then
> > > > >                     trim the line until X equals zero with the far 
> > > > > end open. Should work fine.
> > > > >                     I always calculate the length x VF then add a few 
> > > > > feet to start.
> > > > > 
> > > > >                     73 Joel W5ZN > > Hi guys and gals,
> > > > >                     >
> > > > >                     >
> > > > >                     > > > > > I have got DX Engineering 75 ohm foam 
> > > > > coax to make the
> > > > > 
> > > > >                         > > > > > > stubs/feeders for
> > > > > >                         my Comtek 80 meter 4-Square and am finding 
> > > > > > some difficulty.
> > > > > >                         Neither my
> > > > > >                         MFJ-259B nor my Rig Experts AA-170 seem to 
> > > > > > indicate a 1/2 WL at
> > > > > >                         7500 KHz
> > > > > >                         or a 1/4 WL at 3750 KHz? Or any frequency 
> > > > > > up or down from there.
> > > > > >                         Seems to
> > > > > >                         me the last time I did this a few years ago 
> > > > > > I didn't have a problem
> > > > > >                         getting a 1/2 WL dip indicating a resonance 
> > > > > > location. But now I
> > > > > >                         just don't
> > > > > >                         get any indication of a resonance.
> > > > > > 
> > > > > > 
> > > > > >                         DX Engineering said they had got some 75 
> > > > > > ohm foam coax that
> > > > > >                         instead of
> > > > > >                         0.84 VF was more like 0.80 down to 0.76 VF. 
> > > > > > But checking all the
> > > > > >                         way down
> > > > > >                         to 6000 KHz on 40 meters or 2500 KHz on 80 
> > > > > > meters fails.
> > > > > > 
> > > > > > 
> > > > > >                         My test is to use either antenna analyzer 
> > > > > > with a PL-259 installed
> > > > > >                         at one
> > > > > >                         end and an open or a short at the other. I 
> > > > > > started with 57'7" of
> > > > > >                         coax.
> > > > > >                         Tried both with the coax in a roll and 
> > > > > > strung out. What am I doing
> > > > > >                         wrong?
> > > > > > 
> > > > > > 
> > > > > >                         Terry
> > > > > > 
> > > > > >                         KI7M
> > > > > > 
> > > > > >                         😞
> > > > > >                         _________________
> > > > > >                         Topband Reflector Archives - 
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> > > > > > 
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