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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