[Lowfer] Finally completed my LOWfer Variometer

[Dave Brown]

----- Original Message ----- 
From: "Peter Barick" <pbarick at wpo.cso.niu.edu>
To: <lowfer at mailman.qth.net>
Sent: Tuesday, September 23, 2008 9:38 AM
Subject: Re: [Lowfer] Finally completed my LOWfer Variometer


Congrats Andy,

Keep up the improvements/experimentation, seems like you're on the 
right track.

I maight add a hint about a LF loading coil. When I first saw your 
post on the vari coil and the main coil having 5.88mH and that the 
vari coil negated a chunk of that to an effective value of 3.28, I 
guessed you had too much to start with. While the negative brings it 
in tune, it does so and adds an unnecessary amount of resistance, R. A 
better approach would reduce the main coil turns to a value that 
supports a small amount in the vari coil to tune, say 184-190. That 
keeps the coil as small as possible, reducing R.

My case is a little different as my setup is rx only. When using the 
vertical T, the loading was brought to res. by trial to peak at 185. 
No further tuning. I did measure the L of the two coils I used, one 
high, the other lower and it was about 2.6mH.

Carrry on the good works -- Peter
2008 16:08

 Worth repeating an old trick-for receive only.
 Find an old AM auto radio and use the variable inductance tuning unit 
with all sections in series- it's often easier to extract it from the 
radio and put it in a new case, but YMMV. Depending on your antenna, 
some extra fixed L in series may be necessary.

 73, Dave, ZL3FJ