HF Preselector revised


Chris Moulding
 

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.

It now has a 2.1mm DC socket on the rear so that 12 -15 V DC can be applied. It takes 1.2 mA.

One interesting possibility is that if the tuning control (variable resistor) is set fully clockwise the DC input could be a variable voltage between 15V and zero allowing the Preselector tuning to be remotely controlled.

The text on the web page has been updated, I'll add a revised photograph of the rear of the Preselector soon.

The web page is:

http://www.crosscountrywireless.net/preselector.htm

Regards,

Chris


Nicolas Kulaga
 

Hi Chris.

I just ordered a preselector some days ago. 

Will I get the revised version ?



Le dim. 29 sept. 2019 à 21:40, Chris Moulding <chrism@...> a écrit :
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.

It now has a 2.1mm DC socket on the rear so that 12 -15 V DC can be applied. It takes 1.2 mA.

One interesting possibility is that if the tuning control (variable resistor) is set fully clockwise the DC input could be a variable voltage between 15V and zero allowing the Preselector tuning to be remotely controlled.

The text on the web page has been updated, I'll add a revised photograph of the rear of the Preselector soon.

The web page is:

http://www.crosscountrywireless.net/preselector.htm

Regards,

Chris


Chris Moulding
 

Hi Nicolas,

Yes you will get the revised version.

Regards,

Chris

--
Chris Moulding
Cross Country Wireless
Unit 24562, PO Box 4336, Manchester, M61 0BW, UK
Cell/Workshop: +44(0)7752 391908
Fax: +44(0)1204 410626
Secure email: g4hyg@protonmail.com
Website: http://www.crosscountrywireless.net
Groups.io: https://groups.io/g/CrossCountryWireless

On 29/09/2019 20:46, Nicolas Kulaga wrote:
Hi Chris.
I just ordered a preselector some days ago.
Will I get the revised version ?
Le dim. 29 sept. 2019 à 21:40, Chris Moulding <chrism@crosscountrywireless.net <mailto:chrism@crosscountrywireless.net>> a écrit :
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.
It now has a 2.1mm DC socket on the rear so that 12 -15 V DC can be
applied. It takes 1.2 mA.
One interesting possibility is that if the tuning control (variable
resistor) is set fully clockwise the DC input could be a variable
voltage between 15V and zero allowing the Preselector tuning to be
remotely controlled.
The text on the web page has been updated, I'll add a revised
photograph of the rear of the Preselector soon.
The web page is:
http://www.crosscountrywireless.net/preselector.htm
Regards,
Chris


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?]


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