Automatic SWR meter and semi-automatic tuning unit

1st edition : May 2004

Revision 6, added peak power meter : May 2013

By Dominique F1FRV

Tous droits réservés (Copyright) F1FRV

First circuit: Automatic direct reading SWR meter and Wattmeter

Only improvement, since first edition in 2004, is the addition of the possibility to measure peak envelope power (PEP).

New layout, still in "SCHUBERT" tiny boxes, but easier for cabling flat in a larger box, instead of stacked PCBs when semi-auto tuner is used.

With supply 13.8 V, if your SWR bridge detectors output exceeds 11 volts, you will have to increase the auto SWR board supply voltage (up to 28 volts) in order to have at least about 3 volts more in supply than detectors voltage. You can also change the bridge design (with EXCEL sheet) to reduce maximum output voltages.


Second circuit, If you want to make a "Semi-auto Antenna Tuning Unit"

This is NOT A TRUE automatic antenna tuner, but this can be useful for adjustement of long wire or vertical antenna in portable operations on low bands, or for magnetic loop automatic tuning. Motor is ~ 3 rpm low voltage DC, and CV1 , air variable, with no ends of strokes.

NOTA: To use a DC motor with magnetic loop antennas, it can be necessary to reduce motor speed for precise tuning. To do this, either you decrease motor voltage (with torque loss, but generaly acceptable) , or you use a "PWM" without torque loss. PWM to be built by yourselves, or, purchased at very low cost via E-PAY, in searching "DC Motor Speed Control". Results examples: TCHONG2, or other similars , or BAKATRONICS.

NOTA: Pour utiliser le moteur sur des antennes "boucle magnétique" il peut être nécéssaire de diminuer la vitesse de rotation pour avoir un accord fin. Pour ce faire, soit vous réduisez la tension d'alimentation du moteur (avec perte de couple, mais généralement acceptable), soit vous utilisez un "PWM" sans perte de couple. PWM à réaliser par vous même, ou, à acheter pour quelques Euro, port inclus, sur E-PAY, en cherchant "DC Motor Speed Control". Exemples de résultats: TCHONG2, ou autres similaires, ou BAKATRONICS.

Semi automatic antenna tuner with PIC ( Not very useful, only if you write code yourselves )

Description de la logique de réglage

 Shielding of electronic circuits is mandatory.

SWR bridge picture

Front plate & meter scale

Download files for PCB and documentation:  SIMPLE semi-auto ATU.zip

Download files for PCB and documentation:  SWR + PEAK POWER METER.zip

Download files for PCB and documentation:  Semi-auto antenna tuner WITH PIC.zip

Link to SWR modified Bruene bridges, calculations and EXCEL design sheet

Meters scales can be made with F5BU’s POSTCARDware “GALVA” available here.

That’s All Fox ! ! ! !

Dominique - f1frv@sfr.fr OR

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