Dear all,
I have already noticed on 160 m that such an isolating transformer was
necessary. Without it the SWR changed when connecting or disconnecting
other electric equipment in the shack to/from the mains. These problems
had disappeared on LF after using an isolation transformer below the
loading coil of the aerial, which was also used for matching the
resonant aerial to 50 ohms. On MF I am not yet qrv for transmitting (I
had been on this band professionally for two years around 1957 so in
general I know how it works) but the aim is also to use such a
transformer on this band.
73 Ha-Jo, DJ1ZB
"Stefan Schäfer" <[email protected]> schrieb:
> Hi Clemens,
>
> Yes, and that's why i was asking how the coax is connected to the coil.
> With an isolating ferrite transformer, these currents are unlikely, at
> least on 475 kHz.
>
> 73, Stefan
>
> Am 09.11.2013 09:59, schrieb Clemens Paul:
> > Hi Alan,
> >
> >
> >> I would be inclined to suspect currents induced in the
> >> coax braid. SWR indicators can easily be confused by induced
> >> braid currents......could this be the cause of Riks strange
> >> effects?
> >>
> > That's exactly what happened to a fellow ham on SW.
> > When he had tuned the vertical antenna at the feedpoint to SWR 1 (ref. to
> > 50 Ohm)
> > he observed a different SWR in the shack.
> > I suggested to insert a common mode chocke and the strange effect was gone.
> >
> > 73
> > Clemens
> > DL4RAJ
> >
> >
> >> -----Original Message-----
> >> From: [email protected]
> >> [mailto:[email protected]] On Behalf Of Alan Melia
> >> Sent: Friday, November 08, 2013 8:35 PM
> >> To: [email protected]
> >> Subject: Re: LF: remote antenna tuning
> >>
> >> Rik, Stefan, I follow your points but there would seem to be
> >> something strange in Rik's antenna or his appreciation of
> >> what/how its working.
> >>
> >> Contrary to an earlier assertion, the antenna current flowing
> >> through Rrad generates the radiated power, so lower current,
> >> if Rrad doesnt change, MUST mean lower tranmitted power. It
> >> matters not that the SWR is unity. A unity SWR indication at
> >> the transmitter says that the impedance at the end of the coax
> >> is 50ohms, but it does not necessarily indicate the the the
> >> antenna is resonant i.e the inherent capacitance of a short
> >> antenna totally compensated by the loading inductance. If we
> >> assume that Rrad+Rloss does not change across the band the
> >> matching transformer should transform the value of Rrad+Rloss
> >> to 50 ohms across all the band. The coax will now be matched
> >> and will present 50ohms at the shack end. If this does not
> >> happen I would be inclined to suspect currents induced in the
> >> coax braid. SWR indicators can easily be confused by induced
> >> braid currents......could this be the cause of Riks strange
> >> effects? This might be a function of having a "better" ground
> >> in the shack than at the base of the antenna.
> >>
> >> Alan
> >> G3NYK
> >>
> >>
> >> ----- Original Message -----
> >> From: Stefan Schäfer
> >> <mailto:[email protected]>
> >> To: [email protected]
> >> Sent: Friday, November 08, 2013 6:53 PM
> >> Subject: Re: LF: remote antenna tuning
> >>
> >> Oh yes, or, a phase meter (M0BMU) and a battery
> >> operated variometer motor. Without an additional cable to the
> >> shack. Then the SWR meter in the shack confirms that
> >> everything is fine.
> >>
> >> 73, Stefan
> >>
> >> Am 08.11.2013 19:40, schrieb pat:
> >>
> >> Hi All,
> >>
> >> A suggestion: battery operated tuning device at
> >> antenna end and "wireless" link back to shack. Wireless can
> >> operate at a non-interfering frequncy (HF/VHF/UHF/Optical).
> >>
> >> 73
> >>
> >>
> >>
> >>
> >>
> >>
> >> On 08/11/13 16:09, Stefan Schäfer wrote:
> >>
> >>
> >> Hi Rik,
> >>
> >> Am 08.11.2013 16:06, schrieb Rik Strobbe:
> >>
> >> Hi Stefan,
> >>
> >>
> >>
> >> remote tuning of the loading
> >> should be done by optimizing SWR (at the TX), not for maximum
> >> RF current.
> >>
> >> If one keeps that in mind there
> >> is no problem.
> >>
> >> ...which is in agreement with what i said.
> >> But once you have matched your antenna
> >> to 50 Ohm on resonance and you can only vary the reactive part
> >> of the antennas impedance (after doing QSY), then you will get
> >> the maximum antenna current at best SWR (assuming that
> >> Rrad+Rloss is constant which is not to far from reality).
> >>
> >>
> >>
> >> I am not sure if I will keep
> >> the remote variometer tuning. It needs some extra wires to the
> >> loading coil and I am not sure how long the small DC motor
> >> will function properly with all the rain and frost coming up.
> >>
> >> Here it holds since more than 2 years
> >> for LF now..
> >>
> >> 73, Stefan
> >>
> >>
> >>
> >>
> >>
> >> --
> >> 73 de pat g4gvw
> >> es gd dx
> >> qth nr Felixstowe
> >> East Coast UK
> >>
> >>
> >>
> >
> >
>
>
>
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