[Elecraft] Re: MFJ259

[Don Wilhelm]

Yes, that is true - the laws of reciprocity apply, and a conjugate match is
indicated here - but OTOH, the MFJ259 does not display the sign of the
reactance directly, one must check above and below the frequency of interest
to determine the sign - some other analyzers do display the sign of the
reactance..

73,
Don W3FPR

> -----Original Message-----
>
> If the L-net brings the system to resonance (X=0) then whatever reactance
> the L-net introduces must be equal to the reactance present at the antenna
> but opposite in sign!
>
> For example, if the antenna shows j-500 ohms, the L-net must show j+500
> ohms. So if you want to know what the antenna shows based on measuring the
> L-net, you must reverse the sign!
>
> Ron AC7AC
>
> -----Original Message-----
>
> Don Wilhelm wrote:
> > Jack,
> >
> > Yes, connecting a measureing instrument directly to an antenna can be
> > troublesome if there are strong broadcast stations in the area or
> > other sources of signals that can fool the instrument.
> >
> > Zack Lau addressed that situation in a Technical Correspondence
> > article in QST a while ago - his answer was to measure the antenna
> > indirectly with an L network - the L network provides selectivity -
> > adjust the L network to provide a 50 ohm match, then remove it from
> > the antenna, terminate what was the measurement side with 50 ohms and
> > measure the side previously connected to the antenna.
> >
> > Sounds like a sane way to approach it to me.
>
> I'm not sure of the reasoning, but he also said that if you do this, you
> need to reverse the sign of the reactance that you get when you measure
> the network.
> --
> 73,
> Vic, K2VCO
> Fresno CA
>
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