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Date: Sat, 09 Nov 2013 10:19:59 +0100
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: remote antenna tuning
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Status: O

Hi Clemens,

Yes, and that's why i was asking how the coax is connected to the coil.=20
With an isolating ferrite transformer, these currents are unlikely, at=20
least on 475 kHz.

73, Stefan

Am 09.11.2013 09:59, schrieb Clemens Paul:
> Hi Alan,
>
>   =20
>> 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?
>>     =20
> 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 g=
one.
>
> 73
> Clemens
> DL4RAJ
>
>   =20
>> -----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.
>> =09
>> 	73, Stefan
>> =09
>> 	Am 08.11.2013 19:40, schrieb pat:
>>
>> 		Hi All,
>> 	=09
>> 		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).
>> 	=09
>> 		73
>> 	=09
>> 	=09
>> 	=09
>> 	=09
>> 	=09
>> 	=09
>> 		On 08/11/13 16:09, Stefan Sch=E4fer wrote:
>> 	=09
>>
>> 			Hi Rik,
>> 		=09
>> 			Am 08.11.2013 16:06, schrieb Rik Strobbe:
>>
>> 				Hi Stefan,
>>
>> 			=09
>>
>> 				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).
>> 		=09
>> 		=09
>>
>> 				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..
>> 		=09
>> 			73, Stefan
>> 		=09
>> 		=09
>>
>>
>>
>> 		--
>> 		73 de pat g4gvw
>> 		es gd dx
>> 		qth nr Felixstowe
>> 		East Coast UK
>>
>>
>>     =20
>
>   =20