Message-Id: <7.0.1.0.1.20120114082716.01cb5bf8@xtra.co.nz>
Date: Sat, 14 Jan 2012 09:37:45 +1300
To: rsgb_lf_group@blacksheep.org
From: Brenda Hayes <bjhayes@xtra.co.nz>
In-Reply-To: <593F4C0651144C339855AFC49ED4329E@computereebf79>
References: <593F4C0651144C339855AFC49ED4329E@computereebf79>
Mime-Version: 1.0
Subject: Re: LF: Tuning inductance for 137kHz receive.
Content-Type: text/plain; charset="us-ascii"; format=flowed
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
X-AOL-SCOLL-URL_COUNT: 0  
X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-m020.1 ; domain : yahoo.com DKIM : pass  
x-aol-sid: 3039ac1d404b4f1096f05d4a
X-AOL-IP: 195.171.43.25
X-AOL-SPF: domain : blacksheep.org SPF : none


At 09:44 a.m. 12/01/2012, you wrote:
>I use a decade inductance bridge to series tune my  (approximately) 
>50m end-fed  inverted U wire for 137kHz.
>
>It uses 3mH - 2mH is too little, 4mH is 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.
>
>Anyone know what the "inductance per turn", or total inductance, of 
>such an animal might be?
>
>Any idea if it would work?
>
>Yes, I know I should wind a coil & tap it, but I like to be different!
>
>Martin  GW3UCJ  Swansea, South Wales.

Hello Martin /LF,

Here is one effortless method that I have used for years to tune a 
random wire for LF reception:

First, find an old AM car radio that tunes with three ganged movable 
ferrite slugs and extract the tuning unit.
The three coils are all shielded from each other and can be series 
connected in any order and polarity to maximise the total inductance. 
One unit tested here allows continuous variation from 0.3mH to 2.8mH.
On occasion, I have connected a fixed inductor in series to increase 
the maximum possible inductance.

I guess the major problem is to find a suitable old car radio - not 
variable capacitor tuned.

Kevin    ZL4MD