Topband: cutting coax stubs for 80 meter 4-square
terry burge
ki7m at comcast.net
Sun Jun 10 23:01:12 EDT 2018
All's well that ends well I'm happy to report. K2AV, Guy suggested I check the SO-239 on the Rig Experts AA-170 and I found an open solder joint between the back of the connector and the circuit board. Even with my close in glasses and a magnifying glass it was hard to be certain. So a little solder and 'hop-a-long' rides again! It's working. Will check out the coax stub again to see what the RE reads now.
Thanks Guy!
Terry
KI7M
> On June 9, 2018 at 10:42 PM terry burge <ki7m at comcast.net> wrote:
>
>
> 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
> > > > > > >
> > > > > > > 😞
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