[Lowfer] Motor Driven VC

[Jay Rusgrove]

Bill

No, I didn't catch your earlier post. Makes for an easy way to change Q.

Probably won't need a preamplifier tonight,  anyway. According to the step
attenuator the noise floor at the moment is about 10 dB above the winter night
level. Big rain on the way for tomorrow.

Jay

Bill Ashlock wrote:

> Jay,
>
> >Don't write off all preamplifiers too quick. The preamplifier that I'm
> > >using (and JA has been using this season) is a 50 ohm in/out (with
> > >excellent return loss) 2.5 dB noise figure, 20 dB gain with a  1 dB
> > >compression of +22 dBm, 3rd order intercept of +38 dBm and 2nd order
> > >intercept of +55 dBm. It draws 40 mA at 12VDC. See attached .pdf. A
> > >robust amplifier like this does not suffer overload like those whimpy,
> > >high-impedance input JFETs do.
>
> You must have forgotten that you sent me a copy of your spiffy looking
> amplifier about 6 months ago. Good specs! I'll add a wallmount power supply
> check it out. But remember I always strive for the simplest configuration
> and I can't really see a need for an amp at this time except for the
> possibility that the remote loop tuning is too critical.
>
> >A separate ferrite transformer is used between the well defined 50 ohm
> >preamplifier input and the loop. The turns ratio determines the >reflected
> >resistance into the loop and therefore controls the Q.
>
> Right. Voltage in this case is inversely proportional to Q. The transformer
> is already in there and the ratio is easy to modify. In case you missed my
> original post, this is a J core with a single pass on the loop side and
> something like 6 turns on the output side to match the 75 ohm line.
>
> Bill
>
> _________________________________________________________________
> The new MSN 8: advanced junk mail protection and 2 months FREE*
> http://join.msn.com/?page=features/junkmail
>
> _______________________________________________
> >From the Lowfer mailing list
> Send messages to: Lowfer@mailman.qth.net
> To sub/unsub visit: http://mailman.qth.net/mailman/listinfo/lowfer