Re: HF Preselector revised


WA8LMF
 

On 9/29/2019 3:40 PM, Chris Moulding wrote:
We have recently been building a small batch of HF Preselectors and found that the variable capacitor we use in them is no longer available. I couldn't source an alternative.

As a result it has now been redesigned to use varactor diodes for tuning. It now uses an array of four diodes that cancel out any IP3 and IP2 effects from high RF voltages on the DC tuning voltage applied to the varactors.

 

What effect has the varactor diodes had on the selectivity/bandwith of the preselector?    Are the pics on the web page of the selectivity sweeps of the old air variable version, or the new varicap version?      [I would assume the varactor caps are lower-Q  than traditional air variables -- or am I wrong?]


Stephen H. Smith    wa8lmf (at) aol.com
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