Simplified Patterson Coupler

1. Introduction
   1. The Patterson match
2. Building
   1. First Generation
   2. Second generation
   3. Third generation
   4. Fourth generation
   5. Fifth generation
3. References

Introduction

The Patterson coupler or Patterson match is very useful for trying out small transmitting loop antennas. It was described in a paper 1967 , ref [6].

Original drawing – I suspect it is a little wrong, match capacitor shouldn’t be grounded…

In experiments below we try to evolve it into a low cost device that can be built in kitchen with few parts.

For lower power QRP at 10W the C4 and C6 can be removed, because we do not need to handle very high voltages.

The Patterson match

From ref [6]. Simplified schematic. I suspect that C3 is wrong and should be connected as in third generation below.

If your are not transmitting high power C2 can be omitted further simplifying.

Building

First Generation

First build was with capacitors and electromechanical components. It is a variant with common stator for C1/C2 that is grounded and C3 feeds to antenna.

Good performance but very expensive and complicated.

Second generation

Then we designed capacitors as part of antenna

The antenna was used as stator with rotor for C1 and C2 inside as cylinders inserted inside antenna :

It works fine, but is not durable, rotors not sliding well inside, C3 is difficult to control.

Third generation

Thinking a lot since last experiment and try to evolve the coupler into something that may be 3D printed.

We call the fixed part of capacitor stator and moving part rotor below.

Imagining first implementing coupler using two tubes

One tube could share stator and C2 be removed (QRP)

Now C3 rotor could be put inside pipe:

By turning two rotor/stators C1 and C3 we can tune for a match. The rotor of C1 is now stator for C3. Need to make prototype to test this. Tried capacitors of tomato can 🥫 produce 150-200 pF, but are hard to work with – maybe good choice for higher power.

This should be possible to push further with 3D printer and also including mechanical solution for tuning in same design.

Instead of the can I tested with my tube. It did not work well until I changed into the modified Patterson

Modified Patterson omitting C2

It was easy to tune 5357 kHz, 60m with VSWR 1.07:1 you can see the “calibration” capacitance in pF on the tubes.

Outer tube stator made of steel with two inner rotors are cardboard with copper tape. Indicator lines in pF

<<< paused here >>> will try the cans again with same coupling.

Fourth generation

The 40m version of spiral loop worked well with 1st generation coupler, I checked the capacitance in coupler for C1||C2=101pF and C3=83pF for resonance at 7074 kHz.

Now we can implement this capacitance by applying copper foil on opposite side of cardboard as indicated below and make the antenna 50 ohm for 7074 kHz.

Two pieces of copper foil implements C1 and C3

The Cu foil is 50mm wide and cardboard is 2mm. Paper has dielectric constant of 3.7.

Now we have to check with measurement how long piece of Cu foil to achieve wanted capacitance. Also the breakdown voltage is good to know.

Length and max voltage

I put some packing tape as isolation and then carefully put each capacitor while checking tuning. First I tried some bigger pieces that I moved around to get idea of sizes. When applying with glue the fit is much more narrow and pieces can be smaller.

“Pettersson patch” 🙂

Because this is spiral loop I put test result in that article – works as well as the complicated first generation. Takes a while to tune but, I plan to make a couple maybe add simple fine tuning to move around in each band.

Later we found that small capacitors are hard to tune so we put them on opposite site, because cardboard is thicker capacitor need more area.

On opposite side we implement capacitive coupler using two pieces of copper. See measurements in NVIS build description.

Fifth generation

The 3D printed hexagon coupler

Before adding cables and cover.

Hexagon coupler is available here:

• https://www.printables.com/model/617620-hexagon-coupler-v1

References

1. Brad D Moore (N7RF) presentation: PDF from Kendal Amateur Radio Society KB5TX.
2. Cavattoni Andrea (IN3ECI) list of antenna designs: Page
3. Dr. Carol F. Milazzo, (KP4MD) A Universal HF Magnetic Loop Antenna NEC Model
4. Parallel circuit https://eng.libretexts.org/Bookshelves/Electrical_Engineering/Electronics/Book:_AC_Electrical_Circuit_Analysis:_A_Practical_Approach_(Fiore)/08:_Resonance/8.3:_Parallel_Resonance
5. Small transmitting loops STL: 80-20m Mag Loop STL
6. Patterson, K. Aug 1967. Down to earth army antenna. In Electronics Aug 1967
7. The Army Loop (Patterson match) , openduffy