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Arduino-based amateur radio antenna tuner [Project]
posted February 3 2014 4:03.27 by spic0m

Jean-Jacques De Rey, made an excellent project that finds synergy between the Arduino development platform and the world of amateur radio. In this example he has designed and build an antenna tuner for his 20/40m end-fed half-wave antenna, that can be interfaced for control by and used with his Icom IC7000 transceiver.

"This project describes an ARDUINO based automatic antenna tuner, for an end fed half wave (EFHW) antenna, dual band for 20 & 40m.

This project realization is for 'advanced' OM's ... I am hereby publishing all information I have on hand, so what is missing must be experimentally defined in your setup ! My intention is not to withhold any information whatsoever and feel free to ask if you are missing something.

Why an EFHW antenna ? The big advantage of this type antenna is that (1) it is end fed, thus very easily set up (horizontally, slant, vertically on a fishing pole ... (2) it is fed with high impedance, thus requiring only a minimum of grounding (counterpoise) - so this antenna is very 'portable' and ideal for a temporary or portable setup.

The fact that this antenna has an end impedance which is very high - measured in practice to be around 3.000 Ohm (up to 5.000 max, in theory when radiating in 'free space' ) makes it necessary to feed it in an appropriate manner. One of the methods was invented by FUCHS, who used a resonating L/C circuit to step-up the impedance from 50 Ohm to the required 3k. The advantage of this method is that, by tuning the L/C circuit, a good match can be obtained under various conditions - so the system not only transforms the impedance, but matches as well to some extent.

On basis of this principle, the idea was to have:

ARDUINO tune the L/C circuit automatically, acting as a matching unit. (with manual operation as backup)

have the system/antenna operating dual band, on 20 & 40m !

the ATU working in a seamless manner with my Icom IC-7000 (but other Icom TRX should be compatible), by depressing the 'TUNE' button on the front panel

with a minimum external components & wiring required

Note : instead of an EFHW antenna, a magnetic loop antenna could in principle be tuned in same manner....
The first idea ... leading to a 'dead end' !

The IC-7000 has an integrated SWR bridge and the possibility to read it's the value by a CAT command ... GREAT ! I lost hours trying to get this running, looking into my code .... searching for mistakes, debugging ... before realizing that the SWR reading is available through CAT EXCEPT DURING 'TUNE' PROCEDURE ! So, as soon as the 'TUNE' button is depressed, no more information can be retrieved through CAT about SWR .... this is a pity and forces to use an external SWR bridge / directional coupler."

[Link: QSL.net]

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