Topband: cutting coax stubs for 80 meter 4-square

[terry burge]

Hi Ed,

Unfortunately I don't get any indication per the Rig Experts manual with an open. The R/X just does not get any indication from 1982Khz all the way to 10,500+ KHz. On my MFJ-259B (old one) with a short I get at 7.234 Mhz (or about) R=1 and X=0. Suspect the R indicates the short of course but the X=0 is what I am looking for. I'm going to start cutting a little bit at a time and see what happens. I have already verified the coax is not shorted with my ohm meter till I put the gator on it so the coax appears alright. 

I am wondering just how 'critical' is getting the lengths exact? One thing I did not quite understand was why the RE said to cut for 20% lower?

Terry
KI7M

> On June 9, 2018 at 2:09 PM Ed Hughes <kg4w at comcast.net> wrote:
> 
> 
> Hi Terry, see page 16 of this site
> https://www.rigexpert.com/files/manuals/aa170/aa-170-manual.pdf
> 
> when looking for a 1/4 wave, leave the far end of the coax under test open.
> when looking for a 1/2 wave, short the far end of the coax under test.
> 
> Your 57'7" pc of  would be 1/4 wave at 3750 if the vf is 87.77
> at vf .76 = 49.85 ft
> at vf .80 = 52.48 ft
> at vf .84 = 55.10 ft
> 
> Set your rig expert on freq 3750 and have it in the RX mode and you 
> should see something that makes sense.
> 
> Good Luck
> Ed
> KG4W
> On 6/9/2018 3:55 PM, terry burge wrote:
> > 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 - http://www.contesting.com/_topband
> 
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband