SWR control of loop capacitor for tx using Tayloe swr bridge HELP

hello i am totally new to arduino but have 40 years in mechanic engineering have been radio ham since 1992 this question may well have been asked before but here goes

1 a low variable DC voltage into arduino read system to turn stepper motor to obtain minimum voltage should correspond with lowest swr for tuned frequency i.e. MAG loop antenna

the voltage would be derived from the Tayloe QPR swr bridge using 3 50 ohm resistors small wound toroid an in4148 or similar diode led is normally used for best swr led goes out as antenna should be resonant 50 ohm best description i can write
i want to tune the loop using stepper motor under automatic control any transmit would tune for minimum swr has anybody tried this and do they have code to share
possible prog would be

read voltage =v on input pin?

turn stepper speed varies cw c cw while reading v
if increase in v
turn stepper c cw cw to read Min v on input pin?

as always there is never a stupid question


Agh SWR circuits are so easy to upset. Rather than connect anything directly to the circuit, I'd be inclined to replace the LED with the LED of an opto issolator. This would leave the original circuit, in essence exactly the same.

In the meantime the opto issolator would be able to provide a signal to your IO pin on the arduino (via another LED to replace the functionality of the one you removed).

yes I was going to remove led from circuit very much a novice on electronics an op-to isolator to isolate feed into arduino sounds good have ordered copy from china [bad me] will experiment with that before committing funds I need to build two loops as cheap as possible one for me one for my son a 2w0 licence but want to auto tune loop from micro controller it also leaves room to expand onto system i am not as dull as i sound but a novice on control systems thanks for the reply steve

This is the kind of mod I was thinking.


yes that's the circuit and what I was thinking of was using accellstepper to slow ramp speed on 28byj-48 motor got a few here to read input should be same as potentiometer control or similar the choice of motor was price and its already geared down it has been tested using remote control unit feeding uln2003 driver fwd. / reverse turns capacitor ok

I favor this style of resistive QRP SWR meter because it gives you a Forward power value, and therefore something to scale the Reflected power reading:

your second swr bridge is correct but requires manual input to set fwd. power I was looking at using proportional control using no manual input I have to measure volts on input pin to determine safe input for the stepper control to work
if the tayloe unit requires tweaking it would be at small toroid transformer output I am only using TX 5w to setup but want to TX 100 ft950 its a lot to ask for full automation from such a simple circuit but I am a KISS type of person [keep it simple stupid ref to me always] by the way I have several swr meters on hand to play with will post findings when I can
what I want is ANY maximum reflected voltage being read on input turns stepper motor to find lowest voltage read that on the same pin a magnetic loop should be at resonance at that point

The tayloe unit is so simple using the high swr to generate dc volts to led as resonance approaches voltage decreases led goes out or dims to minimum I have 50w thick film carbon resistors on hand its the toroid windings will require playing with using 50watt resistors just in case I forget to drop power on tune up we don't want SMOKE lol

Hi, google this arduino ham radio auto tuner

A score of amateurs have done this before, the trick is to detect inductive or capacitive mismatch from what I can see.

Tom....... :slight_smile:
This looks a bit too much, but might give you some ideas.

your second swr bridge is correct but requires manual input to set fwd. power

No, you just read it with the Arduino and compare against the reflected power voltage. No need to physically adjust it.

I was thinking it gives you more of a quantitative number of SWR. If you are always using the same power, no problem. But if you sometimes transmit 50W, and other times use only 0.5W, a given voltage from reflected power on 50W that indicates a low SWR, would indicate a very high SWR with only 0.5W from the transmitter.

Just a suggestion.