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Re: Oops - variable bandwidth IF

 

One could try 2n7000, source grounded and the drain connected to a 470pf which is in turn connected as a tuning cap of the filter. Changing gaye voltage will change the effective reactance of the circuit.
- f

On Mon, 14 May 2018, 01:10 Arv Evans, <arvid.evans@...> wrote:
Once the proper capacitance has been determined for 2800 Hz and 500 Hz
bandwidth, it should be possible to use fixed capacitors with diode, transistor,
MOSFET, or relay switching to select bandwidth.

Arv? K7HKL
_._

On Sun, May 13, 2018 at 1:34 PM, ajparent1/KB1GMX <kb1gmx@...> wrote:
The hyperabrupt diodes can easily go from a 400pf down to 50 and there are smaller value diodes
for the 40- 250pf range.? They are not all that cheap.

The alternate is switching between two filters each tuned as desired.? Diodes or relays can do
the switching.? The advantage of doing that is the end transformers can be optimized for the filter
in question as the terminating impedance changes with bandwidth.

Allison


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