Miniature SMA Step Attenuator

QEX September/October  2021 pp 9-21 by Tom Alldred VA7TA.

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page last updated 12/19/2021

This page is for additional information about the QEX Step Attenuator

I have placed three orders for boards from JLCPCB for the
QEX September/October  2021 “Miniature SMA Step Attenuator”
pp 9-21 by Tom Alldred VA7TA.  I had no idea of the popularity of this project.
The first batch, of 10, was sold out very quickly.

All available boards from the second order have been requested and reshipped.
Over 80 boards now have been requested and the interest still continues.

NOTE:  As of 10/12/2021 I have placed another (3rd) buy of 50 pieces.
Will continue to fill order requests until
my inventory has been completely depleted.
[12/19/2021] I inventory is 10 boards remaining

Contact me if you are interested in a board
1 @ $3.00, 2 @ $4.50 ppd CONUS
Now have info for international shipments
1@ $3.75 USD and 2@ $5.25 USD

Original Docs rev1

Some additional information about the QEX article
 BOM Plus_60dBStepAtten_with Mouser.pdf

An ebay source for SMA connectors that include the hardware
10X SMA female jack with nut connector end launch
PCB mount straight goldplated $5.80 + $1.50 shipping
Ebay - 10 SMA with hardware

If you have a need for 3 or more 1590A boxes
3 X New 1590A Aluminum Metal Stomp Box Case
Enclosure Guitar Effect Pedal $10.99 + $4.50 shipping
Ebay - 3 1590A Boxes

Some Notes on my observations:

 The original template in the QEX download
[SMA_StepAttenDrillTemplateRev1.jpg] is not at 1:1 scale.
It appears, on my system, to be at approximately 1.535:1 so be careful !
Tom VA7TA sent me a pdf of the cover at 1:1 scale. 
Be sure to print at full size and check the 100mm lines.
Found some minor dimensional discrepancies on the paper drill template above.
Perhaps I am just too fussy about accurate dimensions, but I created an
alternate template from openSCAD and the excel spreadsheet
 noted in the section below.  Alt_Paper_Template.pdf 
Do not forget to print at 1:1 scale

Also note for the cover and PCB that:
Spacing between J1 & SW1 center lines is 10.5mm
Spacing between J2 & SW6 center lines is 9.5mm
Spacing between all SW center lines is 10mm
Spacing between J1 & J2 center lines is 70mm

Note the proper mounting locations of the SMA jacks and the 6 switches.
Hole and position information from my excel file for the top cover
drill pos n Top Cover hole locations.pdf

The whole excel file: drill pos.xlsx  [I needed this for the 3D template design]

Construction NOTE:
On page 5 of the article Tom mentions in the second column
to mount the SMA connectors to the top cover before soldering to the PCB.
Please observe this advice as assembly will be much easier !

I am planning to make a 3D printed pilot hole template for the cover,
along with a modification to the 3D printed 1590A cover mentioned at

Decided that I preferred my design for the box & Drill Template.

  3D Printed Cover                           Drill Template
The 3D-Box if you want to see it Atten_Box.png [uses #4 or M3 pan head screws]

The Drill Template uses 1/8 " drill and is mounted on top of the metal 1590A cover with
4, 6-32 machine screws inserted from the bottom side of the 1590A cover and secured with nuts.
After the bigger holes have been drilled place the template on the 1590A cover from the bottom
to check spacing, before final assembly.
There is also a second template with 1/16" holes and no posts.

Design is verified [10/10/21]. Files posted below
QEX Step
Note, haven't drilled the metal cover yet, but the template and the board fits in the 3D-cover.

contact info ok on QRZ