Or, you have something outside rectifying the 40m tx signal to make
harmonics not related to the transmitter output. Or, you have receiver
overload that is creating harmonics in the receiver... add attenuation to be
sure the receiver isn't the cause of the problem. Harmonics generated
outside are a worse problem.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Felipe Ceglia - PY1NB
> Sent: Wednesday, August 20, 2008 19:03
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] stubs for the SO2R setup
>
> Hi again... some updates on my issue.
>
> First of all, thanks for the replies concerning my first problem, which
> actually wasn't a problem, but some misunderstanding about how the subs
> actually work.
>
> Now I have a second issue to deal with.
>
> I have trimmed the stubs separately, using the X reading on my MFJ259.
>
> I followed the example from W2VJN book, for 40m band:
>
> 1/4 wave coupling cable (between TX and "stub pack")
> 1/4 wave shorted (nulls 20 & 10m)
> 1/16 wave coupling cable
> 1/4 wave shorted (nulls 20 & 10m)
> 1/12 wave open (nulls 15m)
> 1/6 wave short (nulls 15m)
>
> After I assembled that, I used the MFJ259 as a signal generator, and
> radio B listening, I see that I have quite a big difference, with stubs
> inline and out. S9+60 vs S9 on 20m, S9+60 vs S9+20 on 15m. )
>
> When I plug radio A, on its minimum power level, to the stubs, and my
> 40m antenna, and listen with radio B on the tribander, there is no
> significant difference when I put the stub online or offline.
>
> For the sake of simplicity, I removed amplifier and the sixpak. Just
> radioA-stub-antenna and radioB-antenna.
>
> Seems now that I have some RF leakage between my radio's output and the
> stubs input, right?
>
> 73,
>
> Felipe
>
>
>
> David Robbins K1TTT wrote:
> > With the mfj meter you should plug the stub straight into the meter and
> just
> > read the max or min impedance points for the pass and stop bands. Cut
> the
> > stub to tune the If you add a piece of cable and try to measure the
> dips
> > at the reject points, that is where the stub looks like a short circuit,
> you
> > are measuring the very low impedance transformed by the length of cable,
> > which will be different than the real impedance. You should be able to
> read
> > the pass band ok, but there you are going to see a very wide peak
> because of
> > the high impedance presented by the stub in parallel with the dummy
> load.
> >
> >
> > David Robbins K1TTT
> > e-mail: mailto:k1ttt@arrl.net
> > web: http://www.k1ttt.net
> > AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> >
> >
> >> -----Original Message-----
> >> From: towertalk-bounces@contesting.com [mailto:towertalk-
> >> bounces@contesting.com] On Behalf Of Felipe Ceglia - PY1NB
> >> Sent: Tuesday, August 19, 2008 01:30
> >> To: towertalk@contesting.com
> >> Subject: [TowerTalk] stubs for the SO2R setup
> >>
> >> Hello,
> >>
> >> I am trying to make a set of stubs to be used on my SO2R station setup.
> >>
> >> Those stubs should be plugged to a six pak box.
> >>
> >> When I measure the 1/4 wave shorted 40m stub, plugged directly on the
> >> MFJ-259, with a dummy load paralelled by a tee connector, I can see the
> >> nulls on 14 and 28mhz.
> >>
> >> When I plug that stub and that very dummy load on the six pak 40m port,
> >> things change. Nulls go to 12.9mhz and 24.9mhz.
> >>
> >> The obvious explanation is that the length of cable between the amp
> >> output and the six pak input is being added to the stub, right?
> >>
> >> If so, also seem obvious that I should have the same length of cable
> >> between both of the amps and the six pak, right?
> >>
> >> If so, I should take this length into account, and things will change
> if
> >> I turn the amplifier online, offline, right?
> >>
> >> If so, how can I deal with it in situations where I have multiple
> stubs?
> >> For example: on 40m, I plan to have 2 1/4 wave shorted stubs nulling 14
> >> and 28mhz, and the 1/6 + 1/12 wave for nulling 21mhz
> >>
> >> If so, I have quite a terrible problem in hands.
> >>
> >> 73 and thanks in advance for your advice,
> >>
> >> Felipe - PY1NB
> >>
> >> _______________________________________________
> >>
> >>
> >>
> >> _______________________________________________
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> >> TowerTalk@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
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> >
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>
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