Message-ID: <15000DFE778F4A17BC1E9784B7B3F837@GaryAsus>
From: "Gary - G4WGT" <g4wgt@tiscali.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <50F1BC6E.9090405@iup.uni-heidelberg.de> <427C8E7C302341129739C903AAC04464@GaryAsus> <50F28C3F.3060405@xs4all.nl> <50F2D0A5.4070806@iup.uni-heidelberg.de> <A693692C3A8947C998D5745A69A266BF@GaryAsus> <50F2DE2D.20904@iup.uni-heidelberg.de>
In-Reply-To: <50F2DE2D.20904@iup.uni-heidelberg.de>
Date: Sun, 13 Jan 2013 16:57:38 -0000
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Subject: Re: LF: Re: MF variometer
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Hi Stefan,

I think that due to the difficulties in switching the 2 bands I will change 
the connectors over to 4mm banana plugs/sockets. I will still have to go 
outside & physically change them over but it will be much easier & quicker.

I was hoping some like yourself may have used then with no problems, so it 
is worth a try. I have a large number of the solder bucket variety so that 
will be more permanent than the screw type.

Thanks for your comments.

Cheers, Gary - G4WGT.


----- Original Message ----- 
From: "Stefan Schäfer" <Stefan.Schaefer@iup.uni-heidelberg.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Sunday, January 13, 2013 4:17 PM
Subject: Re: LF: Re: MF variometer


> Hi Gary,
>
> Am 13.01.2013 16:51, schrieb Gary - G4WGT:
>> Hi Stefan,
>>
>> I have thought about LF & MF antenna coil switching but I am very wary 
>> about the very high voltages on the LF coil due to my short vertical 
>> antenna. At the moment I have 3 screw connectors to change over :-
>>
>> 1 - Main coil inductance
>> 2 - Matching transformer input
>> 3 - Matching transformer output
>>
>> I have also thought about using 4mm banana plugs to make the change over 
>> easier & quicker.
>> But not sure about using banana plugs, are they suitable ?
> ...at least i'm using one for LF and it still isn't molten or evaporated 
> ;-) Since i have to manually change the coil to the antenna wire i would 
> notice when the contact becomes loose, so i see no problem, so far.
> But for a remote antenna switch i would have to use something special. Not 
> an ordinary relay of course.. The distance between the contacts should be 
> at least 20 cm.
>
> One idea would be a use a motor that turns an arm (isolated between motor 
> and arm). The arm is stiff and there is a thin wire connected to it, 
> coming from the coil. The arm turns until it touches the electrode of the 
> antenna (here it is the upper part of the HV isolator, see 
> https://dl.dropbox.com/u/19882028/MF/MF_vs_LF.JPG). The force to get a 
> goot contact could be achieved by using a magnet, maybe from an old HDD. 
> Of course the force must be lower than the force the motor torque can be, 
> so the ferromagnetic element which touches the HDD magnet must be quite 
> small because these magnets are strong! If the length of the arm is 30 cm 
> and the force is say 2 N than the drive motor must generate at least 0.6 
> Nm, of course ;-)
> As i was young i built a similar arrangement to discharge a 5 uF / 30 kV 
> capacitor via remote. The arrangement was floating (on a few cassette 
> boxes), including a small battery. The motor was activated by a transistor 
> and a light dependent resistor (LDR) and a hand lamp :-)
>
> 73, Stefan/DK7FC
>