I am building an Ozark Patrol regen. The stock tuning range is very large and I would like to limit it. By default, there is a SPDT switch that adds a parallel capacitance for a second range. My goal is to align the two ranges with the 20 and 40 m bands.

Math shows that I need two fixed capacitors (one in series with the tuning, one in parallel with that) for each band. My thought is to replace the SPDT with a DPDT. I would build the circuit for 20 m and the switch poles would select in the appropriate differences to each fixed capacitor.

Does this seem reasonable? Is this how it's done?

Thanks for the feedback! Also, btw: the schematic says L1 is 1.5 uH but 20 turns on a T50-2 is supposed to be 1.96 uH. Any thoughts on that?

On Sat, Apr 5, 2025 at 11:30 Steve Ratzlaff via <ratzlaffsteve=[email protected]> wrote:

Hi Ross,

On mine, the Low band tunes 3.90-5.24 MHz; High band tunes 5.46-- ~19
MHz, as you note at least the High band is very wide tuning. Your scheme
would probably work but I predict it will take a lot of experimentation
to achieve it. Good luck and please let us know how it all turns out.

73,

Steve AA7U

On 4/5/2025 8:10 AM, Ross Tucker (NS7F) via wrote:
> I am building an Ozark Patrol regen. The stock tuning range is very large and I would like to limit it. By default, there is a SPDT switch that adds a parallel capacitance for a second range. My goal is to align the two ranges with the 20 and 40 m bands.
>
> Math shows that I need two fixed capacitors (one in series with the tuning, one in parallel with that) for each band. My thought is to replace the SPDT with a DPDT. I would build the circuit for 20 m and the switch poles would select in the appropriate differences to each fixed capacitor.
>
> Does this seem reasonable? Is this how it's done?
>
>
>
>
>

Hi Ross,

My experience with all iron powder toroids is there are always variations from toroid batch to batch, and actual? inductance can vary quite a bit--one measures the final inductance and adjusts turns and spacing to give the desired inductance.

73,

Steve AA7U

On 4/5/2025 1:49 PM, Ross Tucker (NS7F) via groups.io wrote:

Thanks for the feedback! Also, btw: the schematic says L1 is 1.5 uH but 20 turns on a T50-2 is supposed to be 1.96 uH. Any thoughts on that?

On Sat, Apr 5, 2025 at 11:30 Steve Ratzlaff via <ratzlaffsteve=[email protected]> wrote:

Hi Ross,

On mine, the Low band tunes 3.90-5.24 MHz; High band tunes 5.46-- ~19
MHz, as you note at least the High band is very wide tuning. Your scheme
would probably work but I predict it will take a lot of experimentation
to achieve it. Good luck and please let us know how it all turns out.

73,

Steve AA7U

On 4/5/2025 8:10 AM, Ross Tucker (NS7F) via wrote:
> I am building an Ozark Patrol regen. The stock tuning range is very large and I would like to limit it. By default, there is a SPDT switch that adds a parallel capacitance for a second range. My goal is to align the two ranges with the 20 and 40 m bands.
>
> Math shows that I need two fixed capacitors (one in series with the tuning, one in parallel with that) for each band. My thought is to replace the SPDT with a DPDT. I would build the circuit for 20 m and the switch poles would select in the appropriate differences to each fixed capacitor.
>
> Does this seem reasonable? Is this how it's done?
>
>
>
>
>

Are you sure the 5.24 and 5.46 aren't swapped? I calculated that the minimum capacitance of the circuit is -78 pF...

On Sat, Apr 5, 2025 at 11:30 Steve Ratzlaff via <ratzlaffsteve=[email protected]> wrote:

Hi Ross,

On mine, the Low band tunes 3.90-5.24 MHz; High band tunes 5.46-- ~19
MHz, as you note at least the High band is very wide tuning. Your scheme
would probably work but I predict it will take a lot of experimentation
to achieve it. Good luck and please let us know how it all turns out.

73,

Steve AA7U

On 4/5/2025 8:10 AM, Ross Tucker (NS7F) via wrote:
> I am building an Ozark Patrol regen. The stock tuning range is very large and I would like to limit it. By default, there is a SPDT switch that adds a parallel capacitance for a second range. My goal is to align the two ranges with the 20 and 40 m bands.
>
> Math shows that I need two fixed capacitors (one in series with the tuning, one in parallel with that) for each band. My thought is to replace the SPDT with a DPDT. I would build the circuit for 20 m and the switch poles would select in the appropriate differences to each fixed capacitor.
>
> Does this seem reasonable? Is this how it's done?
>
>
>
>
>