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Date: Fri, 8 Nov 2013 16:29:53 +0100
From: Michel Brunel <f5wk@mterrier.net>
Message-ID: <102427694.20131108162953@mterrier.net>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: remote antenna tuning
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Bonjour Rik,

Hi Rik,

I think it's better to bring the antenna to resonance with a phasemeter suc=
h as the M0BMU's one.
This avoids the issue of a reactive load to the transmitter. With an induct=
ive load, power consumption increases, giving
in turn more antenna current. Tuning the antenna to max current is definite=
ly not the way to go.

Michel - F5WK


I monitor everyday the antenna resistance (Rr & Rloss) with a resistive bri=
dge ,  so I can have a good
idea of the VSWR.=20

Le vendredi 8 novembre 2013 =E0 14:03:56, Rik =E9crivait :


Dear all,
=20
I want to share an experience hat might be interesting for others too:
=20
After moving from 501-504kHz to 472-479kHz I noticed that even my lossy ant=
enna needs retuning within the band.
As it is not very convenient to do that at the loading coil (abt 30m from t=
he house) I decided to install a small DC motor for remote tuning the loadi=
ng coil. Tuning can be done both at the TX (in the shack) and at the loadin=
g coil. Between both is about 40m of coax cable.
A first test done at the loading coil showed that it worked fine and I tune=
d the antenna to maximum current (550 mA for 20W TX power) on 475 kHz (+/- =
band mid).
When I went into the shack and from there I tuned the antenna to maximum cu=
rrent at the lower band end (472 kHz) I noticed 2 things:
1. The variation of the loading coil was much more than expected.
2. The maximum current (at the TX output) was 760 mA.
Very strange. So I went back out to the loading coil to measure the antenna=
 current (leaving the remote tuning in the position for maximum current at =
the TX). The current had dropped to 410 mA and I had to do some serious ret=
uning to get it back to maximum (550 mA).
Back in the shack I measured the RF current at the TX: also 550 mA (as it s=
hould be).
So despite the fact that the coax cable is merely 10% of the wavelength it =
seriously affects remote tuning. I did some calculations and even with a sh=
ort coax cable (10 m) this effect should be noticable.
=20
By the way: remote tuning can be done correctly by tuning for best SWR inst=
ead of highest RF current at the TX output.
=20
73, Rik  ON7YD - OR7T
=20
=20


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<html><head><title>Re: LF: remote antenna tuning</title>
<META http-equiv=3DContent-Type content=3D"text/html; charset=3Diso-8859-1">
</head>
<body>
<span style=3D" font-family:'Calibri'; font-size: 12pt;">Bonjour Rik,<br>
<br>
Hi Rik,<br>
<br>
I think it's better to bring the antenna to resonance with a phasemeter suc=
h as the M0BMU's one.<br>
This avoids the issue of a reactive load to the transmitter. With an induct=
ive load, power consumption increases, giving<br>
in turn more antenna current. Tuning the antenna to max current is definite=
ly not the way to go.<br>
<br>
Michel - F5WK<br>
<br>
<br>
I monitor everyday the antenna resistance (Rr &amp; Rloss) with a resistive=
 bridge , &nbsp;so I can have a good<br>
idea of the VSWR.&nbsp;<br>
<br>
Le vendredi 8 novembre 2013 =E0 14:03:56, Rik =E9crivait :<br>
<br>
</span><table>
<tr>
<td width=3D2 bgcolor=3D #0000ff><br>
</td>
<td><span style=3D" font-family:'tahoma'; font-size: 10pt;">Dear all,<br>
&nbsp;<br>
I want to share an experience hat might be interesting for others too:<br>
&nbsp;<br>
After moving from 501-504kHz to 472-479kHz I noticed that even my lossy ant=
enna needs retuning within the band.<br>
As it is not very convenient to do that at the loading coil (abt 30m from t=
he house) I decided to install a small DC motor for remote tuning the loadi=
ng coil. Tuning can be done both at the TX (in the shack) and at the loadin=
g coil. Between both is about 40m of coax cable.<br>
A first test done at the loading coil showed that it worked fine and I tune=
d the antenna to maximum current (550 mA for 20W TX power) on 475 kHz (+/- =
band mid).<br>
When I went into the shack and from there I tuned the antenna to maximum cu=
rrent at the lower band end (472 kHz) I noticed 2 things:<br>
1. The variation of the loading coil was much more than expected.<br>
2. The maximum current (at the TX output) was 760 mA.<br>
Very strange. So I went back out to the loading coil to measure the antenna=
 current (leaving the remote tuning in the position for maximum current at =
the TX). The current had dropped to 410 mA and I had to do some serious ret=
uning to get it back to maximum (550 mA).<br>
Back in the shack I measured the RF current at the TX: also 550 mA (as it s=
hould be).<br>
So despite the fact that the coax cable is merely 10% of the wavelength it =
seriously affects remote tuning. I did some calculations and even with a sh=
ort coax cable (10 m) this effect should be noticable.<br>
&nbsp;<br>
By the way: remote tuning can be done correctly by tuning for best SWR inst=
ead of highest RF current at the TX output.<br>
&nbsp;<br>
73, Rik &nbsp;ON7YD - OR7T<br>
&nbsp;<br>
&nbsp;</td>
</tr>
</table>
<br><br>
<br>
<br>
<span style=3D" font-family:'arial'; color: #c0c0c0;"><i>--&nbsp;</body></h=
tml>
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