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" <[email protected]>
To: <[email protected]>
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
|
