[Lowfer] AMRAD Converter and Lowpass Filter

[Zack Widup]

Hi Ben,

Where can I find this design (The AMRAD design as modified by Todd Roberts)?

73, Zack W9SZ

On Sat, Jan 31, 2015 at 6:24 PM, Ben Hall <kd5byb at gmail.com> wrote:

> Good evening all,
>
> Today I assembled my versions of the AMRAD LF Converter and Lowpass filter.
>
> The converter is the AMRAD design as modified by Todd Roberts to accept a
> 3 MHz OCXO input for high stability.
>
> My modifications consisted of:
>
> 1) replacing the thru-hole parts for surface-mount
> 2) the inclusion of a 24VDC to 12VDC regulator stage for the output
> amplifier
> 3) a 12VDC to 5VDC regulator stage for the remaining circuitry
> 4) plus instead of the 74HC4053, I'm giving the 74LVX4053 a try instead of
> the 74HC4053.  The LVX has the same pinout and much lower switch
> on-resistance.  We'll see how well this works.  I do have a supply of
> HC4053's so I can always pull the LVX and replace it.
>
> The OCXO runs off of 24VDC, which is why I added the regulators so I can
> use one power supply.
>
> I have yet to test the converter on the air, as I wanted to get the
> lowpass filter built first.
>
> The lowpass filter mostly follows the AMRAD design.  The Toko slug-tuned
> coils are no longer available, so they were replaced with Coilcraft Slot-10
> units.  The Coilcraft units have a lower Q than the original Toko
> parts...but seem to work just fine (more later).  Instead of thru-hole
> capacitors which are hard to find in 2% or better values, I again used
> surface-mount poly-film devices.
>
> I did omit several parallel capacitors to get the trap tuning frequencies
> up a bit.  The article mentions:
>
> "With the values shown, all three circuits tune from about 530 kHz to 700
> kHz.  To reject stations above 700 kHz, use capacitors of lower value..."
>
> Being that I have a really strong station nearby on both 730 kHz and 770
> kHz, I needed to move the tuning range up.  So C1A, C2A, and C3A were
> omitted.
>
> Using my trusty URM-25D signal generator and 'scope, I was able to easily
> adjust the traps to put a very healthy dent at 730 and 770 kHz.  :)
>
> Tomorrow I'll get the lowpass filter mounted in a box, get the converter,
> lowpass filter, OCXO, and 24VDC linear mounted on some sort of plate (so
> they are not banging around) and will get them on the air.  :)
>
> thanks much and 73,
> ben, kd5byb
>
>
>
>
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