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From: Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Thread-Topic: LF: remote antenna tuning
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Date: Sat, 9 Nov 2013 10:30:07 +0000
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Subject: RE: LF: remote antenna tuning
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Hi Stefan, Clemens, Alan,

the coax is directly connected to the loading coil, no isolating transforme=
r.
About induced currents, that is an option but I have some contra indication=
s:

1. I do measure the same current with a current transformer meter and with =
a thermal ampmeter.

2. At resonance I do measure (almost) the same current at both ends of the =
coax. The small difference can be explained by the fact that Rant (=3D Rrad=
+Rloss) is 60 Ohm, so a slight mismatch.
Only off resonance the measured currents are different.
After tuning the antenna to resonance (max. current at the antenna base) at=
 475 kHz I did measure the current at resonance frequency and at the band e=
nds:
- at 475 kHz: 550 mA at both ends of the coax cable
- at 472 kHz: 530 mA at the antenna base / 580 mA at the TX
- at 479 kHz: 530 mA at the antenna base / 520 mA at the TX

73, Rik  ON7YD - OR7T

________________________________________
Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org=
] namens Stefan Sch=E4fer [Stefan.Schaefer@iup.uni-heidelberg.de]
Verzonden: zaterdag 9 november 2013 10:19
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: Re: LF: remote antenna tuning

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 gon=
e.
>
> 73
> Clemens
> DL4RAJ
>
>
>> -----Original Message-----
>> From: owner-rsgb_lf_group@blacksheep.org
>> [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Alan Melia
>> Sent: Friday, November 08, 2013 8:35 PM
>> To: rsgb_lf_group@blacksheep.org
>> 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 Sch=E4fer
>> <mailto:Stefan.Schaefer@iup.uni-heidelberg.de>
>>      To: rsgb_lf_group@blacksheep.org
>>      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 Sch=E4fer 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
>>
>>
>>
>
>=