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Date: Thu, 12 Jan 2012 10:52:04 +0000 (GMT)
From: M0FMT <m0fmt@yahoo.co.uk>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
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Subject: Re: LF: Tuning inductance for 137kHz receive.
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Hi Martin=0A=A0=0AJust make a variometer two inductors one inside the other=
 like piston and cylinder and adjust in and out to resonance (I think this =
design is the simplest form of variometer mechanically). I use a couple of =
plastic paint buckets, mine are 200mm diameter. 3mH looks about right for t=
he antenna described but fine=A0inductance=A0adjustment is necessary and it=
 is best to get as high a 'Q' as you can. The band is very narrow and 'Q' h=
elps reduce out of band high power signals. I am in fact describing my TX s=
etup the primary inductor is a large 600mm diameter coil tapped. All my ind=
uctors are air cored.=0A=A0=0AFor RX you can tune the inductor with a large=
 variable capacitor strapped across because there are no flash over issues.=
 It is quite simple to make these tuning coils from scratch a lot of wire t=
hough, but I would recommend it.=0A=A0=0ATry Rick Strobbe ON7YD's site high=
ly recommended=A0=A0=A0 http://www.strobbe.eu/on7yd/136ant/#Introduction=0A=
=A0=0AHope this helps.=0A=A0=0A=A073 es GL Pete M0FMT IO91UX=0A=0AFrom: Mar=
tin Evans <books@mollies.freeserve.co.uk>=0ATo: rsgb_lf_group@blacksheep.or=
g =0ASent: Wednesday, 11 January 2012, 20:44=0ASubject: LF: Tuning inductan=
ce for 137kHz receive.=0A=0AI use a decade inductance bridge to series tune=
 my=A0 (approximately) 50m end-fed=A0 inverted U wire for 137kHz.=0A=0AIt u=
ses 3mH - 2mH is too little, 4mH is too much. Obviously I need to be able t=
o vary this inductance rather more finely and I thought of using a small va=
riac (don't laugh!) as a variable inductance, connecting one end, and the t=
ap, in series with the wire.=0A=0AAnyone know what the "inductance per turn=
", or total inductance, of such an animal might be?=0A=0AAny idea if it wou=
ld work?=0A=0AYes, I know I should wind a coil & tap it, but I like to be d=
ifferent!=0A=0AMartin=A0 GW3UCJ=A0 Swansea, South Wales. 
--1325147710-104640475-1326365524=:91314
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<html><body><div style=3D"color:#000; background-color:#fff; font-family:ta=
homa, new york, times, serif;font-size:12pt"><div style=3D"RIGHT: auto"><SP=
AN style=3D"RIGHT: auto">Hi Martin</SPAN></div>
<div style=3D"RIGHT: auto"><SPAN style=3D"RIGHT: auto"></SPAN>&nbsp;</div>
<div style=3D"RIGHT: auto"><SPAN style=3D"RIGHT: auto">Just make a variomet=
er two inductors one inside the other like piston and <SPAN style=3D"RIGHT:=
 auto" id=3Dmisspell-1>cylinder</SPAN> and adjust in and out to resonance (=
I think this design is the simplest form of variometer mechanically). I use=
 a couple of plastic paint buckets, mine are 200mm diameter. 3mH looks abou=
t right for the antenna described but fine&nbsp;inductance&nbsp;adjustment =
is necessary and it is best to get as high a 'Q' as you can. The band is ve=
ry narrow and 'Q' helps reduce out of band high power signals. I am <SPAN s=
tyle=3D"RIGHT: auto" id=3Dmisspell-4>in fact</SPAN> describing my TX setup =
the primary inductor is a large 600mm diameter coil tapped. All my inductor=
s are air cored.</SPAN></div>
<div style=3D"RIGHT: auto"><SPAN style=3D"RIGHT: auto"></SPAN>&nbsp;</div>
<div style=3D"RIGHT: auto"><SPAN style=3D"RIGHT: auto">For RX you can tune =
the inductor with a large variable capacitor strapped across because there =
are no <SPAN style=3D"RIGHT: auto" id=3Dmisspell-5>flash over</SPAN> issues=
. It is quite simple to make these tuning coils from scratch a lot of wire =
though, but I would recommend it.</SPAN></div>
<div style=3D"RIGHT: auto"><SPAN style=3D"RIGHT: auto"></SPAN>&nbsp;</div>
<div style=3D"RIGHT: auto"><SPAN style=3D"RIGHT: auto">Try Rick<VAR id=3Dyu=
i-ie-cursor></VAR> Strobbe ON7YD's site highly recommended&nbsp;&nbsp;&nbsp=
; <A href=3D"http://www.strobbe.eu/on7yd/136ant/#Introduction">http://www.s=
trobbe.eu/on7yd/136ant/#Introduction</A></SPAN></div>
<div style=3D"RIGHT: auto"><SPAN style=3D"RIGHT: auto"></SPAN>&nbsp;</div>
<div style=3D"RIGHT: auto"><SPAN style=3D"RIGHT: auto">Hope this helps.</SP=
AN></div>
<div style=3D"RIGHT: auto"><SPAN style=3D"RIGHT: auto"></SPAN>&nbsp;</div>
<DIV></DIV>
<DIV style=3D"RIGHT: auto">&nbsp;73 es GL Pete M0FMT IO91UX<BR></DIV>
<DIV>
<DIV style=3D"FONT-FAMILY: tahoma, new york, times, serif; FONT-SIZE: 12pt"=
>
<DIV style=3D"FONT-FAMILY: times new roman, new york, times, serif; FONT-SI=
ZE: 12pt">
<DIV dir=3Dltr><FONT size=3D2 face=3DArial>
<DIV style=3D"BORDER-BOTTOM: #ccc 1px solid; BORDER-LEFT: #ccc 1px solid; P=
ADDING-BOTTOM: 0px; LINE-HEIGHT: 0; MARGIN: 5px 0px; PADDING-LEFT: 0px; PAD=
DING-RIGHT: 0px; HEIGHT: 0px; FONT-SIZE: 0px; BORDER-TOP: #ccc 1px solid; B=
ORDER-RIGHT: #ccc 1px solid; PADDING-TOP: 0px" class=3Dhr contentEditable=
=3Dfalse readonly=3D"true"></DIV><B><SPAN style=3D"FONT-WEIGHT: bold">From:=
</SPAN></B> Martin Evans &lt;books@mollies.freeserve.co.uk&gt;<BR><B><SPAN =
style=3D"FONT-WEIGHT: bold">To:</SPAN></B> rsgb_lf_group@blacksheep.org <BR=
><B><SPAN style=3D"FONT-WEIGHT: bold">Sent:</SPAN></B> Wednesday, 11 Januar=
y 2012, 20:44<BR><B><SPAN style=3D"FONT-WEIGHT: bold">Subject:</SPAN></B> L=
F: Tuning inductance for 137kHz receive.<BR></FONT></DIV><BR>I use a decade=
 inductance bridge to series tune my&nbsp; (approximately) 50m end-fed&nbsp=
; inverted U wire for 137kHz.<BR><BR>It uses 3mH - 2mH is too little, 4mH i=
s too much. Obviously I need to be able to vary this inductance rather more=
 finely and
 I thought of using a small variac (don't laugh!) as a variable inductance,=
 connecting one end, and the tap, in series with the wire.<BR><BR>Anyone kn=
ow what the "inductance per turn", or total inductance, of such an animal m=
ight be?<BR><BR>Any idea if it would work?<BR><BR>Yes, I know I should wind=
 a coil &amp; tap it, but I like to be different!<BR><BR>Martin&nbsp; GW3UC=
J&nbsp; Swansea, South Wales. <BR><BR><BR><BR></DIV></DIV></DIV></div></bod=
y></html>
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